physical geography 3

delta

where river flows into large body of water into deposition

water shed

where water comes from

watersheds

where water is gathered (collection point of where water is

divides

where water is going to flow

35 percent of land area is semi

area

great basin

area of internal storage

natural

by tectonic

geologic cycle

c, and geochemical cycles

The term river is applied to a trunk, or main stream; a network of tributaries forms a river system

s

local base level

the level of a lake, resistant rock layer, or any other base level that stands above sea level

meander

(v.) to wander about, wind about; (n.) a sharp turn or twist

1/5 of all fresh water is discharged by this river

( i think amazon)

drainage basin:

(every stream has a drainage basin)spatial geomorphic unit occupied by a river system

a major drainage basin system is made up of any

(many) smaller drainage basin systems which in trun compromise even more smaller ones, each divided into specific watersheds

how much water flows through earths waterways?

.1250km (300mi) (represents 0.003% of all freshwater) (dominant natural agent of landmass denudation)

colorado river has blank dams

9

dominates beach sands because it resists weathering and therefore remains after other minerals are removed. In volcanic areas, beaches are derived from wave-processed lava. Hawai'i and Iceland, for example, feature some blacksand beaches. Many beaches, such as those in southern France and western Italy, lack sand and are composed of pebbles and cobbles—a type of shingle beach. Some shores have no beaches at all; scrambling across boulders and rocks may be the only way to move along the coast. The coasts of Maine and portions of Canada's Atlantic Provinces are classic examples. These coasts, composed of resistant granite rock, are scenically rugged and have few beaches.

A beach acts to stabilize a shoreline by absorbing wave energy, as is evident by the amount of material that is in almost constant motion (see "Sand movement" in Figure 12.10a). Some beaches are stable. Others cycle seasonally: They accumulate during the summer; are moved offshore by winter storm waves, forming a submerged bar; and are redeposited onshore the following summer. Protected areas along a coastline tend to accumulate sediment, which can lead to large coastal sand dunes. Prevailing winds often drag such coastal dunes inland, sometimes burying trees and highways.

In arid and semiarid climates, a prominent fluvial landform is an alluvial fan, which occurs at the mouth of a canyon where an ephemeral stream channel exits into a valley (Figure 11.25). Alluvial fans are produced when flowing water (such as a flash flood) abruptly loses velocity as it leaves the constricted channel of a canyon, or whenever the stream gradient suddenly decreases, and therefore drops layer upon layer of sediment along the base of the mountain block. Water then flows over the surface of the fan and produces a braided drainage pattern, sometimes shifting from channel to channel

A continuous apron, or bajada (Spanish for "slope"), may form if individual alluvial fans coalesce into one sloping surface (see Figure 9.14b). Alluvial fans also can occur in humid climates along mountain fronts

barrier spit

A depositional landform that develops when transported sand or gravel in a barrier beach or island is deposited in long ridges that are attached at one end to the mainland and partially cross the mouth of a bay.

An ice field is not extensive enough to form the characteristic dome of an ice cap; instead, it extends in a characteristic elongated pattern in a mountainous region. A fine example is the Patagonian ice field of Argentina and Chile, one of Earth's largest. It is only 90 km (56 mi) wide, but stretches 360 km (224 mi), from 46° to 51° S latitude. (Figure 13.4b)

A glacier is a dynamic body, moving relentlessly downslope at rates that vary within its mass, excavating the landscape through which it flows. The mass is dense ice that is formed from snow and water through a process of compaction, recrystallization, and growth. A glacier's mass budget consists of net gains or losses of this glacial ice, which determine whether the glacier expands or retreats.

About 77% of Earth's freshwater is frozen, with the bulk of that ice sitting restlessly in just two places—Greenland and Antarctica. The remaining ice covers various mountains and fills some alpine valleys. A volume of more than 32.7 million km3 (7.8 million mi3) of water is tied up as ice: in Greenland (2.38 million km3), Antarctica (30.1 million km3), and ice caps and mountain glaciers worldwide (180,000 km3). These deposits provide an extensive frozen record of Earth's climatic history over the past several million years and perhaps some clues to its climatic future. This is Earth's cryosphere, the portion of the hydrosphere and groundwater that is perennially frozen, generally at high latitudes and elevations. The cryosphere is in a state of dramatic change as worldwide glacial and polar ice inventories melt. In 2007, Arctic Ocean sea ice decreased to its smallest areal extent in the past century as regional temperatures set records of more than 5 C° (9 F°) above normal. The surface ice loss in 2008 was second to this record, with 2009 and 2010 tying for third.

A glacier is a large mass of ice resting on land or floating as an ice shelf in the sea adjacent to land. Glaciers are not frozen lakes or groundwater ice. Instead, they form by the continual accumulation of snow that recrystallizes under its own weight into an ice mass. Glaciers are not stationary; they move slowly under the pressure of their own great weight and the pull of gravity. In fact, they move slowly in streamlike patterns, merging as tributaries into large rivers of ice, as you can see in the satellite image and aerial photos in Figure 13.1. In Greenland and Antarctica, vast sheets of ice dominate, slowly flowing outward toward the ocean. Today, these slowly flowing rivers and sheets of ice dominate about 11% of Earth's land area. Glacial ice covered as much as 30% of continental land during colder episodes in the past. Through these "ice ages," below-freezing temperatures prevailed at lower latitudes more than they do today, allowing snow to accumulate year after year. Glaciers form in areas of permanent snow, both at high latitudes and at high elevations at any latitude. A snowline is the lowest elevation where snow can survive year-round; CHAPTER 13 GLACIAL AND PERIGLACIAL LANDSCAPES 411 Glaciers are as varied as the landscape itself. They fall within two general groups, based on their form, size, and flow characteristics: alpine glaciers and continental glaciers.

continental glacier

A glacier that covers much of a continent or large island

desert pavement

A layer of coarse pebbles and gravel created when wind removed the finer material.

local base level

A local base level, or temporary one, may control the lower limit of local streams for a region. The local base level may be a river, a lake, hard and resistant rock, or the reservoir formed by a human-made dam (Figure 11.7b). In arid landscapes, with their intermittent precipitation, valleys, plains, or other low points determine local base level.

braided stream

A stream or river that is composed of multiple channels that divide and rejoin around sediment bars

Rills

A tiny groove in soil made by flowing water

Coral reefs may experience a phenomenon known as bleaching, which occurs as normally colorful corals turn stark white by expelling their own nutrient-supplying algae. Exactly why the corals eject their symbiotic partner is unknown, for without algae the corals die. Scientists are currently tracking this worldwide phenomenon, which is occurring in the Caribbean Sea and the Indian Ocean as well as off the shores of Australia, Indonesia, Japan, Kenya, Florida, Texas, and Hawai'i. Possible causes include local pollution, disease, sedimentation, changes in ocean salinity, and increasing oceanic acidity. One acknowledged cause is the warming of sea-surface temperatures, linked to greenhouse warming of the atmosphere. In Status of Coral Reefs of the World: 2000, a report from the Global Coral Reef Monitoring Network, warmer water was found to be a greater threat to corals than local pollution or other environmental problems

Although a natural process, coral bleaching is now occurring at an unprecedented rate as average ocean temperatures climb higher, thus linking the issue of climate change to the health of all living coral formations. By the end of 2000, approximately 30% of reefs were lost, with much of the die-off related to the record El Niño event of 1998. In 2010, scientists reported one of the most rapid and severe coral bleaching and mortality events on record near Aceh, Indonesia, on the northern tip of the island of Sumatra. Some species declined 80% in just a few months, in response to sea-surface temperature anomalies across the region. Many of these corals previously were resilient to other ecosystem disruptions, such as the Sumatra-Andaman tsunami in 2004.

Unevenness in the landscape beneath the ice may cause the pressure to vary, melting some of the basal ice by compression at one moment, only to have it refreeze later. This process is ice regelation, meaning to refreeze, or re-gel. Such melting/refreezing action incorporates rock debris into the glacier. Consequently, the basal ice layer, which can extend tens of meters above the base of the glacier, has a much higher debris content than the ice above. A flowing alpine glacier or ice stream in a continental glacier can develop vertical cracks known as crevasses (Figure 13.7a and b). Crevasses result from friction with valley walls, or from tension due to stretching as the glacier passes over convex slopes, or from compression as the glacier passes over concave slopes. Traversing a glacier, whether an alpine glacier or an ice sheet, is dangerous because a thin veneer of snow sometimes masks the presence of a crevasse.

Although glaciers flow plastically and predictably most of the time, some will lurch forward with little or no warning in a glacier surge. A surge is not quite as abrupt as it sounds; in glacial terms, a surge can be tens of meters per day. The Jakobshavn Glacier on the western Greenland coast, for example, is one of the fastest moving at between 7 and 12 km (4.3 and 7.5 mi) a year. The doubling of ice-mass loss from Greenland between 1996 and 2005 means that glaciers are surging overall. In southern Greenland in 2007, outlet glaciers were averaging a speed of 22.8 m (75 ft) per year, a significant increase from the 1999 average flow rate of 1.8 m (6 ft) per year. Scientists determined that Greenland experienced more days of melting snow at higher elevations than average in 2006-2007, thereby contributing to the glacial surges. The meltwater works its way to the basal layer, lubricating underlying soft beds of clay. In addition, the warmer surface waters draining beneath the glacier deliver heat that increases basal melt rates. These trends are continuing

worlds rivers with the greatest discharge (Stream flow rate)

Amazon, congo (zaire), chang jiang (yangtze), and orinoco of south america

discharge

An outflow of water from a stream, pipe, groundwater aquifer, or watershed; the opposite of recharge.

Rocks exposed to eolian abrasion appear pitted, fluted (grooved), or polished. They usually are aerodynamically shaped in a specific direction, according to the consistent flow of airborne particles carried by prevailing winds. Rocks that have such evidence of eolian erosion are ventifacts (literally, "artifacts of the wind"). On a larger scale, deflation and abrasion are capable of streamlining rock structures that are aligned parallel to the most effective wind direction, leaving behind distinctive, elongated ridges or formations called yardangs. These wind-sculpted features can range from meters to kilometers in length and up to many meters in height. On Earth, some yardangs are large enough to be detected on satellite imagery. The Ica Valley of southern Peru contains yardangs reaching 100 m (330 ft) in height and several kilometers in length. Abrasion is concentrated on the windward end of each yardang, with deflation operating on the leeward portions (Figure 12.24). The Sphinx in Egypt was perhaps partially formed as a yardang, suggesting a head and body. Some scientists think this shape led the ancients to complete the bulk of the sculpture artificially with masonry.

Atmospheric circulation can transport fine material, such as volcanic debris, fire soot and smoke, and dust, worldwide within days. Wind exerts a drag, or frictional pull, on surface particles until they become airborne, just as water in a stream picks up sediment (again, think of air as a fluid). The distance that wind is capable of transporting particles in suspension varies greatly with particle size. Only the finest dust particles travel significant distances, so the finer material suspended in a dust storm is lifted much higher than are the coarser particles of a sandstorm. People living in areas of frequent dust storms are faced with infiltration of very fine particles into their homes and businesses through even the smallest cracks. Figure 2.22 illustrates such dust storms. People living in desert regions and along sandy beaches, where frequent sandstorms occur, contend with the sandblasting of painted surfaces and etched window glass.

Two principal wind-erosion processes are deflation, the removal and lifting of individual loose particles, and abrasion, the grinding of rock surfaces by the "sandblasting" action of particles captured in the air. Deflation and abrasion produce a variety of distinctive landforms and landscapes. Deflation Deflation literally blows away loose or noncohesive sediment and works with rainwater to form a surface resembling a cobblestone street: a desert pavement that protects underlying sediment from further deflation and water erosion. Traditionally, deflation was regarded as a key formative process, eroding fine dust, clay, and sand and leaving behind a concentration of pebbles and gravel as desert pavement

Another hypothesis that better explains some desert pavement surfaces states that deposition of windblown sediments, not removal, is the formative agent. Windblown particles settle between and below coarse rocks and pebbles that are gradually displaced upward. Rainwater is involved as wetting and drying episodes swell and shrink clay-sized particles. The gravel fragments are gradually lifted to surface positions to form the pavement (Figure 12.23b). Desert pavements are so common that many provincial names are used for them—for example, gibber plain in Australia; gobi in China; and in Africa, lag gravels or serir, or reg desert if some fine particles remain. Heavy recreational activity damages fragile desert landscapes, especially in the United States, where more than 15 million off-road vehicles are now in use. Such vehicles crush plants and animals; disrupt desert pavement, leading to greater deflation; and create ruts that easily concentrate sheetwash to form gullies.

You have just seen how glaciers excavate tremendous amounts of material and create fascinating landforms in the process. Glaciers produce a different set of distinctive landforms when they melt and deposit their debris cargo at the glacier's terminus. As shown in Figure 13.5a, e, and f, after the glacier melts, accumulated debris marks the former margins of the glacier, both its end and its sides. The general term for all glacial deposits, both unsorted and sorted, is glacial drift. Sediments deposited by glacial meltwater are sorted by size and are stratified drift.

As a glacier flows to a lower elevation, a wide assortment of rock fragments becomes entrained (carried along) on its surface or embedded within its mass or in its base. As the glacier melts, this unsorted debris is deposited on the ground surface as till. Retreating glaciers leave behind large rocks (sometimes house-sized), boulders, and cobbles that are "foreign" in composition and origin from the ground on which they were deposited. These glacial erratics, lying in strange locations with no obvious means of transport, were an early clue that blankets of ice once had covered the land (pictured in Figure 13.10).

With few exceptions, a glacier in a mountain range is an alpine glacier, or mountain glacier. The name comes from the Alps of central Europe, where such glaciers abound. Alpine glaciers form in several subtypes. One prominent type is a valley glacier, literally a river of ice confined within a valley that originally was formed by stream action. Such glaciers range in length from only 100 m (325 ft) to more than 100 km (60 mi). In Figure 13.2, at least a half dozen valley glaciers are identifiable in the high-altitude photograph of the Alaska Range. Several are named on the map—specifically, the Eldridge and Ruth Glaciers, which fill valleys as they flow from source areas near Mount McKinley

As a valley glacier flows slowly downhill, the mountains, canyons, and river valleys beneath its mass are profoundly altered by its erosive passage. Some of the debris created by the glacier's excavation is transported on the ice, visible as dark streaks and bands being transported for deposition elsewhere; other portions of its debris load are carried within or along its base (see Figure 13.1b). Most alpine glaciers originate in a mountain snowfield that is confined in a bowl-shaped recess. This scooped-out erosional landform at the head of a valley is a cirque. A glacier that forms in a cirque is a cirque glacier. Several cirque glaciers may jointly feed a valley glacier, a

After weathering, mass movement, erosion, and transportation, deposition is the next logical event in a sequence.In deposition, a stream deposits alluvium, or unconsolidated sediment, thereby creating depositional landforms, such as bars, floodplains, terraces, or deltas.

As discussed earlier, stream meanders tend to migrate downstream through the landscape. Over time, the landscape near a meandering river comes to bear meander scars of residual deposits from abandoned channels. Former point bar deposits leave low-lying ridges, creating a barand-swale relief (a swale is a gentle low area), forming a scroll topography. T

) Paleoclimatic indicators, such as ice cores and deep-sea cores, are providing detailed records of weather and climate patterns, volcanic eruptions, and trends in the biosphere (discussed in Focus Study 13.1); (2) to understand present and future climate change and to refine general circulation models, we must understand the natural variability of the atmosphere and climate; and (3) anthropogenic global warming, and its relation to background climatic rhythms, is a major concern. Because past occurrences of low temperature appear to have followed a pattern, researchers have looked for causes that also are cyclic in nature. They have identified a complicated mix of interacting variables that appear to influence long-term climatic trends. Let us take a look at several of them.

As our Solar System revolves around the distant center of the Milky Way, it crosses the plane of the galaxy approximately every 32 million years. At that time, Earth's plane of the ecliptic is parallel to the galaxy's plane, and we pass through regions in space of increased interstellar dust and gas, which may have some climatic effect. Milutin Milankovitch (1879-1954), a Yugoslavian astronomer who studied Earth-Sun orbital relations, proposed other possible causes of climate variation. Milankovitch wondered whether the development of an ice age relates to seasonal astronomical factors—Earth's revolution around the Sun, rotation, and tilt—extended over a longer time span (Figure 13.28 on page 434). In summary: ■ Earth's elliptical orbit about the Sun is not constant. The shape of the ellipse varies by more than 17.7 million kilometers (11 million miles) during a 100,000-year cycle, from nearly circular to an extreme ellipse (Figure 13.28a). ■ Earth's axis "wobbles" through a 26,000-year cycle, in a movement much like that of a spinning top winding down. Earth's wobble is precession. As you can see in Figure 13.28b, precession changes the orientation of hemispheres and landmasses to the Sun. ■ Earth's present axial tilt of about 23.5° varies from 21.5° to 24.5° during a 41,000-year period (Figure 13.28c). ■ During MIS 11 (Figure 13.24, page 428), these three astronomical factors were the same as today

Changes in coastal sediment transport can disrupt human activities—beaches are lost, harbors are closed, and coastal highways and beach houses can be inundated with sediment. Thus, people use various strategies to interrupt littoral drift and beach drift. The goal is either to halt sand accumulation or to force accumulation in a desired way through construction of engineered structures, or "hard" shoreline protection. Figure 12.14 illustrates common approaches: a groin to slow drift action along the coast, a jetty to block material from harbor entrances, and a breakwater to create a zone of still water near the coastline. However, interrupting the littoral drift that is the natural replenishment for beaches may lead to unwanted changes in sediment distribution downcurrent. Careful planning and impact assessment should be part of any strategy for preserving or altering a beach. In contrast to the term hard structures, the hauling of sand to replenish a beach is considered "soft" shoreline protection. Beach nourishment refers to the artificial replacement of sand along a beach. Through such efforts, a beach that normally experiences a net loss of sediment will be "nourished" with new sand. Years of human effort and expense to build beaches can be erased by a single storm, however.

Barrier chains are long, narrow, depositional features, generally of sand, that form offshore roughly parallel to the coast. Common forms are barrier beaches and the broader, more extensive landforms called barrier islands. Tidal variation in the area usually is moderate to low, with adequate sediment supplies coming from nearby coastal plains. Figure 12.15 illustrates the many features of barrier chains, using North Carolina's famed Outer Banks as an example, including Cape Hatteras, across Pamlico Sound from the mainland. The area presently is designated as one of 10 national seashore reserves supervised by the National Park Service.

The suspended load consists of fine-grained, clastic particles (bits and pieces of rock). They are held aloft in the stream, with the finest particles not deposited until the stream velocity slows nearly to zero. Turbulence in the water, with random upward motion, is an important mechanical factor in holding a load of sediment in suspension.

Bed load refers to coarser materials that are dragged, rolled, or pushed along the streambed by traction or by saltation, a term referring to the way particles bounce along in short hops and jumps (from the Latin saltim, which means "by leaps or jumps"). Particles transported by saltation are too large to remain in suspension, but are not limited to the sliding and rolling motion of traction. These processes relate directly to a stream's velocity and its ability to retain particles in suspension. With increased kinetic energy, parts of the bed load are rafted upward and become suspended load.

Many people know arid landscapes only from the movies, which leave the impression that most deserts are covered by sand. Instead, desert pavements predominate across most subtropical arid landscapes; only about 10% of desert areas are covered with sand. Sand grains generally are deposited as transient ridges or hills called dunes. A dune is a wind-sculpted accumulation of sand. An extensive area of dunes, such as that found in North Africa, is characteristic of an erg desert, or sand sea. The Grand Erg Oriental in the central Sahara exceeds 1200 m (4000 ft) in depth and covers 192,000 km2 (75,000 mi2), comparable to the area of Nebraska. This sand sea has been active for more than 1.3 million years. Similar sand seas, such as the Grand Ar Rub'al Kha-lı- Erg, are active in Saudi Arabia. Dune fields, whether in arid regions or along coastlines, tend to migrate in the direction of effective, sandtransporting winds. In this regard, stronger seasonal winds or winds from a passing storm may prove more effective than average prevailing winds. When saltating sand grains encounter small patches of sand, their kinetic energy (motion) is dissipated and they accumulate. As height increases above 30 cm (12 in.), a slipface and characteristic dune features form.

By studying the dune model in Figure 12.28, you can see that winds characteristically create a gently sloping windward side (stoss side), with a more steeply sloped slipface on the leeward side. A dune usually is asymmetrical in one or more directions. The angle of a slipface is the steepest angle at which loose material is stable— its angle of repose. Thus, the constant flow of new material makes a slipface, a type of avalanche slope. Sand builds up as it moves over the crest of the dune to the brink; then it avalanches, falling and cascading as the slipface continually adjusts, seeking its angle of repose (usually 30° to 34°). In this way, a dune migrates

North American Great Plains, the Palouse of Washington State, the Pampas of Argentina, and the region from Manchuria in China through to Europe—belong to this group. Agriculture in these areas ranges from large-scale commercial grain farming to grazing along the drier portions. With fertilization or soil-building practices, high crop yields are common. The "fertile triangle" of Ukraine, Russia, and western portions of the former Soviet Union is of this soil type. In North America, the Great Plains straddle the 98th meridian, which is coincident with the 51-cm (20-in.) isohyet of annual precipitation—wetter to the east and drier to the west. The Mollisols here mark the historic division between the short- and tall-grass prairies (Figure 14.14).

Calcification is a soil process characteristic of some Mollisols and adjoining marginal areas of Aridisols. Calcification is the accumulation of calcium carbonate or magnesium carbonate in the B and C horizons. Calcification by calcium carbonate (CaCO3) forms a diagnostic sub surface horizon that is thickest along the boundary between dry and humid climates (Figure 14.15 on page 463). Alfisols Spatially, Alfisols (moderately weathered forest soils) are the most widespread of the soil orders, extending in five suborders from near the equator to high latitudes. Representative Alfisol areas include Boromo and Burkina Faso (interior western Africa); Fort Nelson, British Columbia; the states near the Great Lakes; and the valleys of central California. Most Alfisols are grayish brown to reddish and are considered moist versions of the Mollisol soil group. Moderate eluviation is present as well as a subsurface horizon of illuviated clays and clay formation because of a pattern of increased precipitation (Figure 14.16 on page 463).

Port and dock facilities were built, as were river bridges. Because water is a basic industrial raw material used for cooling and for diluting and removing wastes, waterside industrial sites became desirable. These competing human activities on vulnerable flood-prone lands place lives and property at risk during floods. Nationally, floods average about $6 billion in annual losses. The catastrophic floods along the Mississippi River and its tributaries in 1993 and again in 2011 produced damage that exceeded $30 billion in each occurence. In 2001, tropical storm Allison alone left $6 billion in damage in its wandering visit to Texas in June.

Catastrophic floods continue to be a threat, especially in less-developed regions of the world. Bangladesh is perhaps the most persistent example: It is one of the most densely populated countries on Earth, and more than three-fourths of its land area is a floodplain. The country's vast alluvial plain sprawls over an area the size of Alabama (130,000 km2, or 50,000 mi2). The flooding severity in Bangladesh is a consequence of human economic activities, along with heavy precipitation episodes. Excessive forest harvesting in the upstream portions of the Ganges-Brahmaputra River watersheds increased runoff. Over time, the increased sediment load

Recent compilations of data from around the world show that soil erosion under conventional ag ri cul ture exceeds both rates of soil production and geo log i - cal erosion rates by several orders of magnitude Consequently, modern agriculture—and therefore global society—faces a fundamental question over the upcoming centuries. Can an agricultural system capable of feeding a growing population safeguard both soil fertility and the soil itself?*

Classification of soils is complicated by the variety of interactions that create thousands of distinct soils—well over 15,000 soil types in the United States and Canada alone. Not surprisingly, a number of different classification systems are in use worldwide, including those from the United States, Canada, the United Kingdom, Germany, Australia, Russia, and the United Nations Food and Agricultural Organization (FAO). Each system reflects the environment of its country

shows the distribution of living coral formations. Corals mostly thrive in warm tropical oceans, so the difference in ocean temperature between the western coasts and eastern coasts of continents is critical to their distribution. Western coastal waters tend to be cooler, thereby discouraging coral activity, whereas eastern coastal currents are warmer and thus enhance coral growth. Living colonial corals range in distribution from about 30° N to 30° S. Corals occupy a very specific ecological zone: 10- to 55-m (30- to 180-ft) depth, 27‰-40‰ salinity, and 18°C to 29°C (64°F to 85°F) water temperature. Their upper threshold is 30°C (86°F); above that temperature, the corals begin to bleach and die. Corals require clear, sediment-free water and consequently do not locate near the mouths of sediment-charged freshwater streams. For example, note the lack of these structures along the U.S. Gulf Coast. Corals have low genetic diversity worldwide and long generation times, which together mean that corals are slow to adapt and vulnerable to changing conditions.

Corals exist as both solitary and colonial formations. The colonial corals produce enormous structures. Their skeletons accumulate, forming coral rock. Through many generations, live corals near the ocean's surface build on the foundation of older coral skeletons, which, in turn, may rest upon a volcanic seamount or some other submarine feature built up from the ocean floor. Coral reefs form by this process. Thus, a coral reef is a biologically derived sedimentary rock. It can assume one of several distinctive shapes. In 1842, Charles Darwin hypothesized an evolution of reef formation. He suggested that, as reefs develop around a volcanic island and the island itself gradually subsides, equilibrium is maintained between the subsidence of the island and the upward growth of the corals. This idea, generally accepted today, is portrayed in Figure 12.19. Note the specific examples of each reef stage: fringing reefs (platforms of surrounding coral rock), barrier reefs (reefs that enclose lagoons), and atolls (circular, ring-shaped reefs). Earth's most extensive fringing reef is the Bahamian platform in the western Atlantic (Figure 12.19c), covering some 96,000 km2 (37,000 mi2). Look at the composite Terra and GOES image of the Western Hemisphere on the half-title page of Elemental Geosystems. Can you spot the Bahama coral platform? The largest barrier reef, the Great Barrier Reef along the shore of the state of Queensland, Australia, exceeds 2025 km (1260 mi) in length, is 16-145 km (10-90 mi) wide, and includes at least 700 coral-formed islands and keys (coral islets or barrier islands).

distinct dry season following a wet season. Although widespread, individual Vertisol units are limited in extent. Vertisol clays are black when wet, but not because of organics; rather, the blackness is due to specific mineral content. They range from brown to dark gray. These deep clays swell when moistened and shrink when dried. In the drying process, they may form vertical cracks as wide as 2-3 cm (0.8-1.2 in.) and up to 40 cm (16 in.) deep. Loose material falls into these cracks, only to disappear when the soil again expands and the cracks close. After many such cycles, soil contents tend to invert or mix vertically, bringing lower horizons to the surface

Despite the fact that clay soils are plastic and heavy when wet, with little available soil moisture for plants, Vertisols are high in bases and nutrients and thus are some of the better farming soils where they occur. For example, they occur in a narrow zone along the coastal plain of Texas (Figure 14.23c) and in a section along the Deccan region of India. Vertisols often are planted with grain sorghums, corn, and cotton. Histosols Accumulations of thick organic matter can form Histosols (organic soils). In the midlatitudes, when conditions are right, beds of former lakes may turn into Histosols, with water gradually replaced by organic material to form a bog and layers of peat (Figure 14.24). (Lake succession and bog or marsh formation are discussed in Chapter 15.) Histosols also form in small, poorly drained depressions, with conditions ideal for significant deposits of sphagnum peat to form. This material can be cut, baled, and sold as a soil amendment. Peat is cut by hand with a spade into blocks, which are then set out to dry. In Figure 14.24c, note the fibrous texture of the sphagnum moss growing on the surface and the darkening layers with depth in the soil profile as the peat is compressed and chemically altered. Such beds can be more than 2 m thick. Once dried, the peat blocks burn hot and smoky. Peat is the first stage in the natural formation of lignite, an intermediate step toward coal. Imagine such soils forming in plant-lush swamp environments in the Carboniferous Period (359 to 299 million years ago), only to go through coalification to become coal deposits.

As a book cannot be judged by its cover, so soils cannot be evaluated at the surface only. Instead, a soil profile should be studied from the surface to the deepest extent of plant roots or to the point where regolith or bedrock is encountered. Such a profile is a pedon, a hexagonal column measuring 1 to 10 m2 in top surface area (Figure 14.1). At the sides of the pedon, the various layers of the soil profile are visible in cross section and are labeled with letters. A pedon is the basic sampling unit used in soil surveys. Many pedons together in one area make up a polypedon, which has distinctive characteristics differentiating it from surrounding polypedons. A polypedon is an essential soil "individual," comprising an identifiable series of soils in an area. The polypedon is the basic mapping unit used in preparing local soil maps

Each distinct layer exposed in a pedon is a soil horizon. A horizon is roughly parallel to the pedon's surface and has characteristics distinctly different from horizons directly above and/or below. The boundary between horizons usually is distinguishable when viewed in profile, such as along a road cut, using the properties of color, texture, structure, consistence (meaning soil consistency or cohesiveness), porosity, the presence or absence of certain minerals, moisture, and chemical processes (Figure 14.2). Soil horizons are the building blocks of soil classification.

s The mouth of a river is where it reaches a base level. The river's velocity rapidly decelerates as it enters a larger, standing body of water. The reduced stream energy causes deposition of the sediment load. Coarse sediment such as sand and gravel drops out first and is deposited closest to the river's mouth. Finer clays are carried farther and form the extreme end of the deposit, which may be subaqueous, or underwater, even at low tide. The level or nearly level depositional plain that forms at the mouth of a river is a delta for its characteristic triangular shape, after the Greek letter delta

Each flood stage deposits a new layer of alluvium over portions of the delta, growing the delta outward. As in braided rivers, channels divide into smaller courses known as distributaries, which appear as a reverse of the dendritic drainage pattern of tributary streams discussed earlier. Here are a few examples: ■ The Ganges River delta in south Asia features an extensive lower delta plain formed in relation to high tidal ranges in an arcuate (arc-shaped) pattern. It is covered by an intricate maze of distributaries. Bountiful alluvium carried from deforested slopes upstream is deposited to form many deltaic islands (Figure 11.26). The combined delta complex of the Ganges and Brahmaputra Rivers is the largest in the world at some 60,000 km2 (23,165 mi2). ■ The Nile River delta is an arcuate delta (Figure 11.27), as is the Danube River delta in Romania, where it enters the Black Sea, and the Indus River delta in south Asia (see Figure 11.29). ■ The Tiber River in Italy has an estuarine delta, one that is in the process of filling an estuary, the body of water at a river's mouth where freshwater flow encounters seawater.

utes are blended rapidly in a mixing zone that represents only 2% of the oceanic mass. Below the mixing zone is the thermocline transition zone, a region more than 1 km deep of decreasing temperature gradient that lacks the motion of the surface. Friction at these depths dampens the effect of surface currents. In addition, colder water temperatures at the lower margin tend to inhibit any convective movements.

Earth's surface features, such as mountains and crustal plates, were formed over millions of years. However, most of Earth's coastlines are relatively new, existing in their present state as the setting for continuous change. The land, ocean, atmosphere, Sun, and Moon interact to produce tides, currents, waves, erosional features, and depositional features along the continental margins. Inputs to the coastal environment include many elements we have already discussed:

Alfisols have moderate to high reserves of basic cations and are fertile. However, productivity depends on moisture and temperature. Alfisols usually are supplemented by a moderate application of lime and fertilizer in areas of active agriculture. Some of the best U.S. farmland occurs in the humid continental hot summer climates surrounding the Great Lakes. These Alfisols produce grains, hay, and dairy products. The moist winter, dry summer pattern of the Mediterranean climate also produces Alfisols. These naturally productive soils are farmed intensively for subtropical fruits, nuts, and special crops that grow in only a few locales worldwide—for example, California olives, grapes, citrus, artichokes, almonds, and figs (Figure 14.16c).

Farther south in the United States are the Ultisols, highly weathered forest soils. An Alfisol might degenerate into an Ultisol, given time and exposure to increased weathering under moist conditions. These soils tend to be reddish because of residual iron and aluminum oxides in the A horizon (Figure 14.17 on page 464). The relatively high precipitation in Ultisol regions causes greater mineral alteration and more eluvial leaching than in other soils. Therefore, the level of basic cations is lower, and the soil fertility is lower. Fertility is further reduced by certain agricultural practices and the effect of soil-damaging crops such as cotton and tobacco, which deplete nitrogen and expose soil to erosion. These soils respond well if subjected to good management—for example, crop rotation restores nitrogen, and certain cultivation practices prevent sheetwash and soil erosion. Peanut plantings assist in nitrogen restoration. Much needs to be done to achieve sustainable management of these soils.

The continental ice sheets that covered portions of Canada, the United States, Europe, and Asia about 18,000 years ago are illustrated on the maps in Figure 13.25. Ice sheets ranged in thickness to more than 2 km (1.2 mi). In North America, the Ohio and Missouri River systems mark the southern terminus of continuous ice at its greatest extent during the Pleistocene Epoch. The ice sheet disappeared by 7000 years ago. As both alpine and continental glaciers retreated, they exposed a drastically altered landscape: the rocky soils of New England, the polished and scarred surfaces of Canada's Atlantic Provinces, the sharp crests of the Sawtooth Range and Tetons of Idaho and Wyoming, the scenery of the Canadian Rockies and the Sierra Nevada, the Great Lakes of the United States and Canada, the Matterhorn of Switzerland, and much more. In the Southern Hemisphere, there is evidence of this ice age in the form of fjords and sculpted mountains in New Zealand and Chile.

Figure 13.26 on page 430 portrays the American West dotted with large lakes 12,000-30,000 years ago. Except for the Great Salt Lake in Utah (a remnant of the former Lake Bonneville noted on the map) and a few smaller lakes, only dry basins, ancient shorelines, and lake sediments remain today. These ancient lakes are paleolakes, or pluvial lakes. The term pluvial (from the Latin word for "rain") describes any period of wet conditions, such as occurred during the Pleistocene Epoch. During pluvial periods, lake levels increase in arid regions. The drier periods between pluvials, called interpluvials, are often marked by lacustrine deposits, the name for lake sediments that form terraces, or benches, along former shorelines. Scientists have attempted to correlate pluvial and glacial ages, given their coincidence during the Pleistocene. However, few sites actually demonstrate such a simple relation. For example, in the western United States, the estimated volume of melted ice from glaciers is only a small portion of the actual water volume that was in the paleolakes. Also, these lakes tend to predate glacial times and are correlated instead with periods of wetter climate or periods thought to have had lower evaporation rates.

laminar flow

Flows in parallel lines in a smooth progression

At the top of the soil profile is the O (organic) horizon, named for its organic composition, derived from plant and animal litter that was deposited on the surface and transformed into humus. Humus is not just a single material; it is a mixture of decomposed and synthesized organic materials, usually dark in color. Microorganisms work busily on this organic debris, performing a portion of the humification (humus-making) process. The O horizon is 20%-30% or more organic matter, which is important because of its ability to retain water and nutrients and because of the way it acts in a complementary manner to clay minerals. At the bottom of the soil profile is the R (rock) horizon, consisting of either unconsolidated (loose) material or consolidated bedrock. When bedrock physically and chemically weathers into regolith, it may or may not contribute to overlying soil horizons. The A, E, B, and C horizons mark differing mineral strata between O and R. These middle layers are composed of sand, silt, clay, and other weathered by-products. In the A horizon, humus and clay particles are particularly important, for they provide essential chemical links between soil nutrients and plants. This horizon usually is richer in organic content, and hence darker, than are lower horizons. Here is where human disruption through plowing, pasturing, and other uses takes place. The A horizon grades into the E horizon, made up of coarse sand, silt, and resistant minerals.

From the lighter-colored E horizon, silicate clays and oxides of aluminum and iron are leached (removed by water) and carried to lower horizons with the water as it percolates through the soil. This process of removing fine particles and minerals by water, leaving behind sand and silt, is eluviation—thus, the E designation for this horizon. As precipitation increases, so does the rate of eluviation. In contrast to the A and E horizons, B horizons accumulate clays, aluminum, and iron. B horizons are dominated by illuviation, a depositional process (in contrast, eluviation is an erosional process). B horizons may exhibit reddish or yellowish hues because of the presence of illuviated minerals (silicate clays, iron and aluminum, carbonates, gypsum) and organic oxides. Some materials occurring in the B horizon may have formed in place from weathering processes rather than arriving there by translocation, or migration. In the humid tropics, these layers often develop to some depth. Likewise, clay losses in an A horizon may be caused by destructive processes in place and not eluviation. Research to better understand the erosion and deposition of clays between soil horizons is one of the challenges in modern soil science.

A horizon is sandy and bleached in color and is eluviated, leached of clays and iron; the B horizon is composed of illuviated organic matter and iron and aluminum oxides (Figure 14.18c). The surface horizon receives organic litter from base-poor, acid-rich evergreen trees, which contribute to acid accumulations in the soil. The solution in acidic soils effectively leaches clays, iron, and aluminum, which are passed to the upper diagnostic horizon. An ashen-gray color is common in these subarctic forest soils and is characteristic of podzolization (Figure 14.19). When agriculture is attempted, the low basic cation content of Spodosols requires the addition of nitrogen, phosphate, and potash (potassium carbonate)—and perhaps crop rotation as well. A soil amendment such as limestone can significantly increase crop production by raising the pH of these acidic soils. For example, the yields of several crops (corn, oats, wheat, and hay) grown in specific Spodosols in New York State were increased up to a third with the application of 1.8 metric tons (2 tons) of limestone per 0.4 hectare (1.0 acre) during each 6-year rotation. Entisols The Entisols (recent, undeveloped soils) lack vertical development of their horizons. The presence of Entisols is not climate-dependent, for they occur in many climates worldwide. Entisols are true soils, but they have not had sufficient time to generate the usual horizons.

Gelisols contain about half of the pool of global carbon. The latest estimate of the carbon contained in these periglacial soils is 1.7 trillion tons. When permafrost thaws, substantial amounts of greenhouse gases are released into the atmosphere. The process begins as warming occurs in the higher latitudes. Gelisols can quickly become wet and soggy with only a slight shift in their thermal balance. As this thaw happens, the poorly decomposed organic content begins to decay, with decomposition releasing enormous quantities of carbon dioxide into the atmosphere through increased respiration. Another greenhouse gas, methane, is released as well. Researchers stated the linkage in these systems in 2009: We show that approximately 1 C° warming accelerated total ecosystem respiration rates from carbon in peat . . . . Our findings suggest a large, long-lasting, positive feedback of carbon stored in northern peatlands to the global climate system.* In 2010, the Joint Research Center of the European Commission published the Soil Atlas of the Northern Circumpolar Region, an excellent reference for periglacial environments and permafrost-affected soils. It is available for download from http://eusoils.jrc.ec.europa.eu/library/ maps/Circumpolar/. Gelisols are subject to cryoturbation (frost churning and mixing) in the freeze-thaw cycle in the active layer (see Chapter 13). This process disrupts soil horizons, pulling organic material to lower layers and rocky C-horizon material to the surface. Patterned-ground phenomena are possible under such conditions.

). Recent data show a 4.5-cm (1.7-in.) rise in global MSL from 1993 to 2008. About 50% is attributed to thermal expansion produced by higher water temperatures. The balance of sea-level rise is from worldwide losses in glacial ice and losses from the Greenland and West Antarctic Ice Sheets. The 2007 Intergovernmental Panel on Climate Change (IPCC) forecast for global MSL rise this century, given regional variations, is a range from 0.18 to 0.59 m (7.1 to 23.2 in.). However, the 2006-2009 measurements of Greenland's ice loss were not included in the forecasts, and data suggest an acceleration of ice melt. Scientists are carefully monitoring the growing instability in the West Antarctic Ice Sheet as well. A fair working estimate for sea-level rise this century now stands at 1.0 to 1.4 m (3.28 to 4.6 ft); the state of California is using a rise of 1.4 m in its planning models.

Given these trends and the predicted climatic changes ahead, sea level will continue to rise and be potentially devastating for many coastal locations. A rise of only 0.3 m (1 ft) would cause shorelines worldwide to move inland an average of 30 m (100 ft). This elevated sea level would inundate valuable real estate along coastlines all over the world. Some 20,000 km2 (7800 mi2) of land along North American shores alone would be drowned, at a staggering loss of trillions of dollars. A 95-cm (3.1-ft) sea-level rise could inundate 15% of Egypt's arable land, 17% of

Sometimes an isolated block of ice, perhaps more than a kilometer across, remains in a ground moraine, on an outwash plain, or on a valley floor after a glacier has retreated. As much as 20 to 30 years is required for it to melt. In the interim, material continues to accumulate around the melting ice block. When the block finally melts, it leaves behind a steep-sided hole. Such a feature then frequently fills with water. This feature is a kettle. Thoreau's famous Walden Pond in Massachusetts is such a glacial kettle. Another feature of outwash plains is a kame, a small hill, knob, or mound of poorly sorted sand and gravel that is deposited directly by water or by ice in crevasses or in ice-caused indentations in the surface. Kames also can be found in deltaic forms and in terraces along valley walls.

Glacial action also forms two types of streamlined hills. One is erosional, a roche moutonnée, and the other is depositional, a drumlin. A roche moutonnée ("sheep rock" in French) is an asymmetrical hill of exposed bedrock. Its gently sloping upstream side (stoss side) has been polished smooth by glacial action, whereas its downstream side (lee side) is abrupt and steep where the glacier plucked rock pieces (Figure 13.16). A drumlin is deposited till that was streamlined in the direction of continental ice movement, blunt end upstream and tapered end downstream. Multiple drumlins (drumlin swarms) occur across the landscape in portions of New York and Wisconsin, among other areas. Sometimes their shape is that of an elongated teaspoon bowl, lying face down. Drumlins may attain lengths of 100-5000 m (330 ft-3.1 mi) and heights up to 200 m (650 ft). Figure 13.17 shows a portion of a topographic map for the area south of Williamson, New York, which experienced continental glaciation

Glacial erosion and deposition produce distinctive landforms that differ greatly from the way the land looked before the ice came and went. You might expect all glaciers to create the same landforms, but alpine and continental glaciers each generate their own characteristic landscapes. We look first at erosional landforms created by alpine glaciers and then at their depositional landforms. Finally, we examine the landscape that results from continental glaciation. Erosion by Alpine Glaciation Alpine glaciers create spectacular, dramatic landforms that bring to mind the Canadian Rockies, the Swiss Alps, or vaulted Himalayan peaks. Geomorphologist William Morris Davis depicted the stages of a valley glacier in drawings published in 1906

Glacial erosion and transport actively remove much of the regolith (weathered bedrock) and the soils that covered the stream-valley landscape. As the cirque walls erode away, sharp ridges form, dividing adjacent cirque basins. These arêtes ("knife-edge" in French) become the sawtooth, serrated ridges in glaciated mountains. Two eroding cirques may reduce an arête to a saddlelike depression or pass, forming a col. A horn, or pyramidal peak, results when several cirque glaciers gouge an individual mountain summit from all sides. Most famous is the Matterhorn in the Swiss Alps, but many others occur worldwide. A bergschrund forms when a crevasse or wide crack opens along the headwall of a glacier and is most visible in summer when covering snow is gone. Figure 13.10 shows the same landscape at a time of warmer climate when the ice retreated. The glaciated valleys now are U-shaped, greatly changed from their previous stream-cut V form. You can see the steep sides and the straightened course of the valleys. Physical weathering from the freeze-thaw cycle has loosened rock along the steep cliffs, where it has fallen to form talus slopes along the valley sides. Retreating ice leaves behind transported rocks as erratics

In fact, glacial ice behaves in a plastic (pliable) manner, for it distorts and flows in its lower portions in response to weight and pressure from above and the degree of slope below. In contrast, the glacier's upper portions are quite brittle. Rates of flow range from almost nothing to a kilometer or two per year on a steep slope. The rate of accumulation of snow in the formation area is critical to the speed.

Glaciers are not rigid blocks that simply slide downhill. The greatest movement within a valley glacier occurs internally, below the rigid surface layer, which fractures as the underlying zone moves forward (Figure 13.7a). At the same time, the base creeps and slides along, varying its speed with temperature and the presence of any lubricating water beneath the ice. This basal slip usually is much less rapid than the internal plastic flow of the glacier, so the upper portion of the glacier flows ahead of the lower portion.

Areas of volcanic activity feature Andisols (soils with volcanic parent materials). Andisols are derived from volcanic ash and glass. Previous soil horizons frequently are found buried by ejecta from repeated eruptions. Volcanic soils are unique in their mineral content because they are recharged by eruptions. Weathering and mineral transformations are important in this soil order. Volcanic glass weathers readily into a clay colloid and oxides of aluminum and iron. Andisols feature a high CEC and high water-holding ability and develop moderate fertility, although phosphorus availability is an occasional problem. In Hawai'i, the fertile Andisol fields produce coffee, pineapples, macadamia nuts, and some sugar cane as important cash crops (Figure 14.22a). Andisol distribution is small in areal extent; however, such soils are locally important in the volcanic ring of fire surrounding the Pacific Rim. In the Atlantic region, feed crops and pastureland of fertile Andisols sustain a large sheep industry in Iceland. Another example of Andisol fertility occurs on Fogo Island in the central Atlantic off the African coast, where the early stages of local wine production are supplied by grapes planted in fresh volcanic soils (

Heavy clay soils are the Vertisols (expandable clay soils). They contain more than 30% swelling clays (clays that swell significantly when they absorb water), such as montmorillonite. They are located in regions experiencing highly variable soil-moisture balances through the seasons. These soils occur in areas of subhumid to semiarid moisture and moderate to high temperature. Vertisols frequently form under savanna and grassland vegetation in tropical and subtropical climates and are sometimes associated with a

The active layer is the zone of seasonally frozen ground that exists between the subsurface permafrost layer and the ground surface. The active layer is subjected to consistent daily and seasonal freeze-thaw cycles. This cyclic melting of the active layer affects as little as 10 cm (4 in.) of depth in the north (Ellesmere Island, 78° N), up to 2 m (6.6 ft) in the southern margins (55° N) of the periglacial region, and 15 m (50 ft) in the alpine permafrost of the Colorado Rockies (40° N).

Higher temperatures degrade (reduce) permafrost and increase the thickness of the active layer; lower temperatures gradually aggrade (increase) permafrost depth and reduce active-layer thickness. Although somewhat sluggish in response, the active layer is a dynamic, open system driven by energy gains and losses in the subsurface environment. As you might expect, most permafrost exists in disequilibrium with environmental conditions and therefore actively adjusts to changing climatic conditions. With the incredibly warm temperatures recorded in the Canadian and Siberian Arctic since 1990, more disruption of permafrost surfaces is occurring— leading to highway, railway, and building damage. In Siberia, many lakes have disappeared in the discontinuous permafrost region as subsurface drainage opens; yet new lakes have formed in the continuous region as thawed soils become waterlogged. In Canada, hundreds of lakes have disappeared simply from excessive evaporation into the warming air. These trends are measurable from satellite imagery

An uplifting of the landscape or a lowering of base level may rejuvenate stream energy so that a stream again scours downward with increased erosion. The resulting entrenchment of the river into its own floodplain produces alluvial terraces on both sides of the valley, which look like topographic steps above the river. Alluvial terraces generally appear paired at similar elevations on the sides of the valley (Figure 11.24). If more than one set of paired terraces is present, the valley probably has undergone more than one episode of rejuvenation

If the terraces on the sides of the valley do not match in elevation, then entrenchment actions must have been continuous as the river meandered from side to side, with each meander cutting a terrace slightly lower in elevation. Thus, alluvial terraces represent an original depositional feature, a floodplain, that is subsequently eroded by a stream that has experienced a change in gradient and is downcutting.

turbulent flow

Irregular flow with random variations in pressure.

Soil drainage is poor in areas of permafrost and ground ice. The active layer of soil and regolith is saturated with soil moisture during the thaw cycle (summer), and the whole layer commences to flow from higher to lower elevation if the landscape is even slightly inclined. This flow of soil is generally called solifluction and may occur in all climate conditions. In the presence of ground ice or permafrost, the more specific term gelifluction is applied. In this icebound type of soil flow, movement up to 5 cm (2 in.) per year can occur on slopes as gentle as a degree or two. The cumulative effect of this landflow can be an overall flattening of a rolling landscape, with identifiable sagging surfaces and scalloped and lobed patterns in the downslope soil movements. Other types of periglacial mass-movement include failure in the active layer, producing translational and rotational slides and rapid flows associated with melting ground ice. Periglacial mass movement processes are related to slope dynamics and processes

In areas of permafrost and frozen-ground phenomena, people face several related problems. Because thawed ground above the permafrost zone frequently shifts, highways and rail lines may warp or twist, and utility lines are disrupted. In addition, any building placed directly on frozen ground will "melt" into the defrosting soil, creating subsidence in structures (Figure 13.22). In periglacial regions, structures must be constructed above the ground to allow air circulation beneath. This airflow allows the ground to cycle through its normal annual temperature pattern. Utilities such as water and sewer lines must be built aboveground in "utilidors" to protect them from freezing and thawing ground (Figure 13.23). Likewise, the trans-Alaska oil pipeline was constructed aboveground on racks for 675 km of its 1285-km length (420 mi of its 800-mi length) to avoid melting the frozen ground, causing shifting that could rupture the line. The pipeline that is underground uses a cooling system to keep the permafrost around the pipeline stable.

Waterfalls are interesting and beautiful gradient breaks. At the edge of a fall, a stream is free-falling, moving at high velocity under the acceleration of gravity, causing increased abrasion and hydraulic action in the channel below. The increased action generally undercuts the waterfall. Eventually, the excavation will cause the rock ledge at the lip of the fall to collapse, and the waterfall will shift a bit farther upstream. The height of the waterfall is gradually reduced as debris accumulates at its base (see Figure 11.21b). Thus, a nickpoint migrates upstream, sometimes for kilometers, until it becomes a series of rapids and is eventually eliminated.

In doing so, they exposed resistant rock strata that are underlain by less-resistant shales. This tilted formation is a cuesta, which is a ridge with a steep slope on one side and beds gently sloping away on the other side (Figure 11.21a). This Niagara escarpment actually stretches across more than 700 km (435 mi); from east of the falls, it extends northward through Ontario, Canada, and the Upper Peninsula of Michigan and then curves south through Wisconsin along the western shore of Lake Michigan and the Door Peninsula. As this less-resistant material continues to weather away, the overlying rock strata collapse, allowing Niagara Falls to erode farther upstream toward Lake Erie. Niagara Falls is a place where natural processes labor to eliminate a nickpoint and reduce this portion of the river to a series of mere rapids. In fact, the falls have retreated more than 11 km (6.8 mi) from the steep face of the Niagara escarpment. A nickpoint is a relatively temporary and mobile feature on the landscape. In the past, engineers have used control facilities upstream to reduce flows over the American Falls at Niagara in order to inspect cliff erosion; compare this reduced flow (Figure 11.21c) to the normal discharge

When the backwash of water flows to the ocean from the beach in a concentrated column, usually at a right angle to the line of breakers, it is a rip current. A person caught in one of these can be swept offshore, but usually only a short distance. These brief, short torrents of water can be dangerous (Figure 12.8c). As various wave trains move along in the open sea, they interact by interference. These interfering waves sometimes align, so that the wave crests and troughs from one wave train are in phase with those of another. When this inphase condition occurs, the height of the waves is amplified, sometimes dramatically. The resulting "killer waves" or "sleeper waves" can sweep in unannounced and overtake unsuspecting victims. Signs along portions of the California, Oregon, Washington, and British Columbia coastline

In general, wave action tends to straighten a coastline. Where waves approach an irregular coast, they bend around headlands, which are protruding landforms generally composed of resistant rocks (Figure 12.9). The submarine topography refracts, or bends, approaching waves. The refracted energy is focused around headlands and dissipates energy in coves, bays, and the submerged coastal valleys between headlands. Thus, headlands receive the brunt of wave attack along a coastline. This wave refraction redistributes wave energy, so that different sections of the coastline vary in erosion potential, with the long-term effect of straightening the coast.

A talik is unfrozen ground that may occur above, below, or within a body of discontinuous permafrost or beneath a water body in the continuous region. Taliks occur beneath deep lakes and may extend to bedrock and noncryotic soil beneath large, deep lakes (see Figure 13.19). Taliks form connections between the active layer and groundwater, whereas in continuous permafrost, groundwater is essentially cut off from surface water. In this way, permafrost disrupts aquifers and taliks, leading to water-supply problems.

In regions of permafrost, frozen subsurface water is ground ice. The moisture content of areas with ground ice varies from nearly none in drier regions to almost 100% in saturated soils. From the area of maximum energy loss, freezing progresses through the ground along a freezing front, or boundary between frozen and unfrozen soil. The presence of frozen water in the soil initiates geomorphic processes associated with frost action and the expansion of water as it freezes.

The combined gravitational effect of the Sun and Moon is strongest in the conjunction alignment and results in the greatest tidal range between high and low tides, known as spring tides

In this arrangement, the Moon and Sun cause separate tidal bulges, affecting the water nearest to each of them. In addition, the left-behind water resulting from the pull of the body on the opposite side augments each bulge. When the Moon and Sun are neither in conjunction nor in opposition, but are more or less in the positions shown in Figure 12.6c and d, their gravitational influences are offset and counteract each other, producing a lesser tidal range known as neap tide. (Neap means "without the power of advancing.")

what are the driving sources of fluvial systems?

Insolation and gravity because they power the hydrologic cycle

Recall that soil pores may be filled with air, water, or a mixture of the two. Consequently, soil chemistry involves both air and water. The atmosphere within soil pores is mostly nitrogen, oxygen, and carbon dioxide. Nitrogen concentrations are about the same as in the atmosphere, but oxygen is less and carbon dioxide is greater because of ongoing respiration processes. Water present in soil pores is the soil solution. It is the medium for chemical reactions in soil. This solution is critical to plants as their source of nutrients, and it is the foundation of soil fertility. Carbon dioxide combines with the water to produce carbonic acid, and various organic materials combine with the water to produce organic acids. These acids are then active participants in soil processes, as are dissolved alkalies and salts. To understand how the soil solution behaves, let us go through a quick chemistry review. An ion is an atom, or group of atoms, that carries an electrical charge (examples: Na1, Cl2, HCO3 2). An ion has either a positive charge or a negative charge. For example, when NaCl (sodium chloride) dissolves in solution, it separates into two ions: Na1, a cation (positively charged ion), and Cl2, an anion (negatively charged ion). Some ions in soil carry single charges, whereas others carry double or even triple charges (e.g., sulfate, SO4 22; and aluminum, Al31).

Ions in soil are retained by soil colloids. These tiny particles of clay and organic material (humus) carry a negative electrical charge and consequently attract any positively charged ions in the soil (Figure 14.5). The positive ions, many metallic, are critical to plant growth. If it were not for the negatively charged soil colloids, the positive ions would be leached away in the soil solution and thus would be unavailable to plant roots. Individual clay colloids are thin and platelike, with parallel surfaces that are negatively charged. They are more chemically active than silt and sand particles, but less active than organic colloids. Metallic cations attach to the surfaces of the colloids by adsorption (not absorption, which means "to enter"). Colloids can exchange cations between their surfaces and the soil solution, an ability called cation-exchange capacity (CEC), which is the measure of soil fertility. A high CEC means that the soil colloids can store or exchange more cations from the soil solution, an indication of good soil fertility (unless a complicating factor exists, such as a soil that is too acid). Therefore, soil fertility is the ability of soil to sustain plants. Soil is fertile when it contains organic substances and clay minerals that absorb water and adsorb certain elements needed by plants. Billions of dollars are expended to create fertile soil conditions, yet the future of Earth's most fertile soils is threatened because soil erosion is on the increase worldwide.

Over the long term, sea-level fluctuations expose a range of coastal landforms to tidal and wave processes. As average global temperatures cycle through cold or warm climatic spells, the quantity of ice locked up in the ice sheets of Antarctica and Greenland and in hundreds of mountain glaciers can increase or decrease and result in sea-level changes accordingly. At the peak of the most recent Pleistocene glaciation, about 18,000 b.p. (years before the present), sea level was about 130 m (430 ft) lower than it is today. On the other hand, if Antarctica and Greenland ever became ice-free (if their ice sheets fully melted), sea level would rise at least 65 m (215 ft) worldwide.

Just 100 years ago sea level was 38 cm (15 in.) lower along the coast of southern Florida. Venice, Italy, has experienced a rise of 25 cm (10 in.) since 1890. During the last century, average sea level rose 10-20 cm (4- 8 in.), a rate 10 times higher than the average rate during the last 3000 years. Since 1930, sea-level rise has continued at an increasing rate, with some variability explained by global dam construction and artificial reservoir impoundments of water. The present sea-level rise is spatially uneven, as is MSL; for instance, the rate along the coast of Argentina is nearly 10 times the rate along the coast of France.

local base level or a temporary one:

May control the lower limit of local streams

Sea level is an important concept. Every elevation you see in an atlas or on a map is referenced to mean sea level. Yet this average sea level changes daily with the tides and over the long term with changes in climate, tectonic plate movements, and glaciation. Thus, sea level is a relative term. At present, no international system exists to determine exact sea level over time. The Global Sea Level Observing System (GLOSS) is an international group actively working on sea-level issues and is part of the larger Permanent Service for Mean Sea Level

Mean sea level (MSL) is a value based on average tidal levels recorded hourly at a given site over many years. MSL varies spatially because of ocean currents and waves, tidal variations, air temperature, pressure differences and wind patterns, ocean temperature variations, slight variations in Earth's gravity, and changes in oceanic volume. At present, the overall U.S. MSL is calculated at approximately 40 locations along the coastal margins of the continent. These sites are being upgraded with new equipment in the Next Generation Water Level Measurement System, using next-generation tide gauges, specifically along the U.S. and Canadian Atlantic Coast, Bermuda, and the Hawaiian Islands. The NAVSTAR satellites of the Global Positioning System (GPS) make possible the correlation of data within a network of ground- and ocean-based measurements.

greatest discharges (Stream flow rate) in north america is from

Mississipi-missouri-ohio, saint lawrence, and mackenzie river systems.

When the longitudinal profile of a stream shows an abrupt change in gradient, such as at a waterfall or an area of rapids, the point of interruption is a nickpoint (also spelled knickpoint). At a nickpoint, the conversion of potential energy in the water at the lip of the falls to concentrated kinetic energy at the base works to eliminate the nickpoint interruption and smooth out the gradient. Figure 11.20 includes an illustration of a stream in South Dakota with two such interruptions as well as actual nickpoints

Nickpoints can result when a stream flows across a zone of hard, resistant rock or from various tectonic uplift episodes, such as might occur along a fault line. Temporary blockage in a channel, caused by a landslide or a logjam, also could be considered a nickpoint; when the logjam breaks, the stream quickly readjusts its channel to its former grade.

A reasonable conclusion seems to be that the key to protective environmental planning and zoning is to allocate responsibility and cost in the event of a disaster. An ideal system places a hazard tax on land, based on assessed risk, and restricts the government's responsibility to fund reconstruction or an individual's right to reconstruct on frequently damaged sites. Comprehensive mapping of erosion-hazard areas would help avoid the ever-increasing costs from recurring disasters.

Not all coastlines form by purely physical processes. Some form as the result of biological processes, such as coral growth. A coral is a simple marine animal with a small, cylindrical, saclike body called a polyp; it is related to other marine invertebrates, such as anemones and jellyfish. Corals secrete calcium carbonate (CaCO3) from the lower half of their bodies, forming a hard, calcified external skeleton. Corals live in a symbiotic relationship with algae: They live together in a mutually helpful arrangement, each dependent on the other for survival. Corals cannot photosynthesize, but they do obtain some of their own nourishment. Algae perform photosynthesis and convert solar energy to chemical energy in the system, providing the coral with about 60% of its nutrition and assisting the coral with the calcification process. In return, corals provide the algae with nutrients. Coral reefs are the most diverse marine ecosystems. Preliminary estimates of coral species place the number at a million worldwide, yet, as in most ecosystems in water or on land, biodiversity is declining in these communities.

Permanent tracts of cleared land, taken out of the former rotation mode, brought disastrous consequences regarding soil erosion. When Oxisols are disturbed, soil loss can exceed 1000 tons per square kilometer per year, not to mention the greatly increased extinction rates of plant and animal species that accompany such soil depletion and rain forest destruction. The regions dominated by the Oxisols and rain forests are rightfully the focus of much worldwide environmental attention. Aridisols The largest single soil order occurs in the world's dry regions. Aridisols (desert soils) occupy approximately 19% of Earth's land surface (see Figure 14.9). A pale, light soil color near the surface is diagnostic

Not surprisingly, the water balance in Aridisol regions is characterized by periods of soil-moisture deficit and generally inadequate soil moisture for plant growth. High potential evapotranspiration and low precipitation produce very shallow soil horizons. Usually, there is no period greater than 3 months when the soils have adequate moisture. Lacking water and therefore lacking vegetation, Aridisols also lack organic matter of any consequence. Low precipitation means infrequent leaching, yet Aridisols are leached easily when exposed to excessive water, for they lack a significant colloidal structure. Representing about 16% of Earth's agricultural land, irrigated land accounts for nearly 36% of the harvest. Two related problems common in irrigated lands are salinization and water logging, especially in arid lands that are poorly drained. Salinization is common in Aridisols, resulting from excessive potential evapotranspiration rates in deserts and semiarid regions. Salts dissolved in soil water migrate to surface horizons and are deposited as the water evaporates. These deposits appear as subsurface salty horizons, which will damage or kill plants when the horizons occur near the root zone. The introduction of irrigation water for farming may either waterlog poorly drained soils or lead to salinization.

Water is the "universal solvent," dissolving at least 57 of the 92 elements found in nature. In fact, most natural elements and the compounds they form are found in the seas as dissolved solids, or solutes. Thus, seawater is a solution, and the concentration of dissolved solids is salinity. The ocean remains a remarkably homogeneous mixture. The ratio of individual salts does not change, despite minor fluctuations in overall salinity. In 1874, the British HMS Challenger sailed around the world taking surface and depth measurements and collecting samples of seawater. Analyses of those samples first demonstrated the uniform composition of seawater

Ocean chemistry is a result of complex exchanges among seawater, the atmosphere, minerals, bottom sediments, and living organisms. In addition, significant flows of mineral-rich water enter the ocean through hydrothermal (hot water) vents in the ocean floor. These vents are the "black smokers," noted for the dense, black, mineral-laden water that spews from them (Figure 8.10b). The uniformity of seawater results from complementary chemical reactions and continuous mixing—after all, the ocean basins interconnect, and water circulates among them.

.1a and b? Wherever several valley glaciers pour out of their confining valleys and coalesce at the base of a mountain range, a piedmont glacier is formed and spreads freely over the lowlands, such as the remnants of the Malaspina Glacier, which flows into Yakutat Bay, Alaska. A tidewater glacier, or tidal glacier, ends in the sea, calving to form floating pieces of ice known as icebergs (Figure 13.3a). Icebergs usually form wherever glaciers meet an ocean, bay, or fjord. Icebergs are inherently unstable, as their center of gravity shifts with melting and further breaking. Figure 13.3b shows a tabular iceberg that broke away from ice shelves near the Weddell Sea, Antarctica. The annual layers of ice are clearly visible in the tabular berg. In Figure 13.3c, a magnificent ice tower berg brings to mind the ratio of 1/7 (14%) exposed and 6/7 (86%) submerged—these proportions vary, depending on the age of the ice and air content.

On a much larger scale than individual alpine glaciers, a continuous mass of ice is a continental glacier. In its most extensive form, it is an ice sheet. Most of Earth's glacial ice exists in the ice sheets that blanket 81% of Greenland—1,756,000 km2 (678,000 mi2) of ice—and 90% of Antarctica—14.2 million km2 (5.48 million mi2) of ice. Antarctica alone has 92% of all the glacial ice on the planet. The ice sheets of Antarctica and Greenland have such enormous mass that large portions of each landmass beneath the ice are isostatically depressed (pressed down by weight) below sea level. Each ice sheet reaches depths of more than 3000 m (9800 ft), with average depths around 2000 m (6500 ft), burying all but the highest peaks. Two additional types of continuous ice cover associated with mountain locations are ice caps and ice fields. An ice cap is roughly circular and, by definition, covers an area of less than 50,000 km2 (19,300 mi2). An ice cap completely buries the underlying landscape. The volcanic island of Iceland features several ice caps, such as the Vatnajökull Ice Cap in southeastern Iceland (outlined in Figure 13.4a). Volcanoes lie beneath these icy surfaces. Iceland's Grímsvötn Volcano erupted in 1996 and again in 2004, producing large quantities of melted glacial water and floods, a flow Icelanders call a jökulhlaup. To the southwest in the image is the Eyjafjallajökull Volcano, which began erupting in 2010.

The flat, low-lying area flanking many stream channels that is subjected to recurrent flooding is a floodplain. It is formed when the river overflows its channel during times of high flow. Thus, when floods occur, the floodplain is inundated. When the water recedes, it leaves behind alluvial deposits that generally mask the underlying rock with their accumulating thickness. The present river channel is embedded in these alluvial deposits

On either bank of some streams, low depositional ridges form natural levees as by-products of flooding. When floodwaters rise, the river overflows its banks, loses stream competence and capacity as it spreads out, and drops a portion of its sediment load to form the levees. Larger, sand-sized particles drop out first, forming the principal component of the levees, with finer silts and clays deposited farther from the river. Successive floods increase the height of the levees (levée is French for " raising"). The levees may grow in height until the river channel becomes elevated, or perched, above the surrounding floodplain.

Grain size is important in wind erosion. Intermediatesized grains move most easily—it is the largest and the smallest sand particles that require the strongest winds to move. The large particles are heavier and thus require stronger winds. The small particles are difficult to move because they exhibit a mutual cohesiveness and because they usually present a smooth (aerodynamic) surface to the wind. The term saltation was used in Chapter 11 to describe movement of particles by water. The term also describes the wind transport of grains, usually larger than 0.2 mm (0.008 in.), along the ground. About 80% of wind transport of particles is accomplished by this skipping and bouncing action (Figure 12.25). Compared with fluvial transport, in which saltation is accomplished by hydraulic lift, eolian saltation is executed by aerodynamic lift, elastic bounce, and impact

On impact, grains hit other grains and knock them into the air. Saltating particles crash into other particles, knocking them both loose and forward. This type of movement is surface creep, which slides and rolls particles too large for saltation and affects about 20% of the material transported by wind. Once in motion, particles continue to be transported by lower wind velocities. In a desert or along a beach, sometimes you can hear a slight hissing sound, almost like steam escaping, produced by the myriad saltating grains of sand as they bounce along and collide with surface particles. Both human and natural sand erosion and transport from a beach are slowed by conservation measures such as the introduction of stabilizing native plants, the use of fences, and the restriction of pedestrian traffic to walkways (Figure 12.26). As human settlement encroaches on coastal dunes, sand transport becomes problematic.

The term ice age, or glacial age, is applied to any extended period of cold (not a single brief cold spell), which may last several million years. An ice age is a time of generally cold climate that includes one or more glacials, interrupted by brief warm spells known as interglacials. Each glacial and interglacial is given a name that is usually based on the location where evidence of the episode is prominent—for example, the Wisconsinan glacial.

One method for determining Pleistocene temperatures is by evidence from deep-sea cores—specifically, from the oxygen isotope fluctuations in fossil plankton, tiny marine organisms with a calcareous shell. Glaciologists currently recognize the Illinoian glacial and Wisconsinan glacial intervals, with the Sangamon interglacial between them. These events span the 300,000-year interval prior to our present Holocene Epoch.

Wave action can cut a horizontal bench in the tidal zone, extending from a sea cliff out into the sea. Such a structure is a wave-cut platform, or wave-cut terrace. If the relation between the land and sea level has changed over time, multiple platforms or terraces may rise like stair steps back from the coast. These marine terraces are remarkable indicators of a changing relation between the land and sea, with some terraces more than 370 m (1200 ft) above sea level. A tectonically active region, such as the California coast, has many examples of multiple wave-cut platforms, which at times can be unstable and vulnerable to failure

One notable depositional landform is the barrier spit, which consists of material deposited in a long ridge extending out from a coast. It partially crosses and blocks the mouth of a bay. A classic barrier spit is Sandy Hook, New Jersey (south of New York City). Such barrier spit formations are also found at Point Reyes (Figure 12.13c) and Morro Bay

Tides also are influenced by other factors, including ocean-basin characteristics (size, depth, and topography), latitude, and shoreline shape. These factors cause a great variety of tidal ranges. For example, some locations may experience almost no difference between high and low tides. The highest tides occur when open water is forced into partially enclosed gulfs or bays. The Bay of Fundy in Nova Scotia records the greatest tidal range on Earth, a difference of 16 m (52.5 ft)

Only 30 locations in the world are suited for tidal power generation. At present, only 3 are producing electricity. Two are outside North America—a 4-megawattcapacity station in Russia in operation since 1968 (at Kislaya-Guba Bay on the White Sea) and a facility in France operating since 1967 (on the Rance River estuary on the Brittany coast). The tides in the Rance estuary fluctuate up to 13 m (43 ft), and power production has been almost continuous there, providing an electricalgenerating capacity of a moderate 240 megawatts (about 20% of the capacity of Hoover Dam).

s Earth's highest-discharge river is the Amazon, which has an average flow greater than 175,000 m3/s (6.2 million cfs) and carries sediment far into the deep Atlantic offshore. Yet the Amazon lacks a true delta. Its mouth, 160 km (100 mi) wide, has formed a subaqueous deposit on a sloping continental shelf. As a result, the Amazon's mouth is braided into a broad maze of islands and channels (see Figure 11.1)

Other rivers that lack deltas include the Rio de la Plata, Argentina and the Sepik River of Papua New Guinea. On some rivers, deltaic formations are absent if they do not produce significant sediment or if they discharge into strong erosive currents. The Columbia River of the U.S. Northwest lacks a delta because offshore currents remove sediment as it is deposited.

Dunes have many wind-shaped styles that make classification difficult. We simplify dune forms into three classes—crescentic (crescent, curved shape), linear (straight form), and massive star dunes. Examples of each are in Figure 12.29 and detailed on the MasteringGeography web site. Active sand dunes cover about 10% of Earth's deserts. Dune fields are also present in humid climates, such as along coastal Oregon, the south shore of Lake Michigan, and the U.S. Gulf and Atlantic coastlines; in Europe; and elsewhere. These same dune-forming principles and terms (for example, dune and slipface) apply to snow-covered landscapes. Snow dunes are formed as wind deposits snow in drifts. In semiarid farming areas, capturing drifting snow with fences and tall stubble left in fields contributes significantly to soil moisture when the snow melts

Patterns of cross bedding, or cross stratification, are sometimes present in desert sandstone, formed by lithification of ancient sand dunes. When such a dune was accumulating, sand cascaded down its slipface and distinct bedding planes (layers) were established that remained after the dune lithified (Figure 12.30). Ripple marks, animal tracks, and fossils also are found preserved in these sandstones.

Color is important, for it sometimes suggests composition and chemical makeup. If you look at exposed soil, color may be the most obvious trait. Among the many possible hues are the reds and yellows found in soils of the southeastern United States (high in iron oxides), the blacks of prairie soils in portions of the U.S. grain-growing regions and in Ukraine (richly organic), and the white to pale hues found in soils containing silicates and aluminum oxides. However, color can be deceptive: Soils with high humus content are often dark, yet clays of warm temperate and tropical regions with less than 3% organic content are some of the world's blackest soils

Perhaps a soil's most permanent attribute is soil texture, which refers to the mixture of sizes of its particles and the proportion of different sizes. Individual mineral particles are soil separates. All particles smaller in diameter than 2 mm (0.08 in.), such as very coarse sand, are considered part of the soil. Larger particles, such as pebbles, gravel, or cobbles, are not part of the soil. (Sands are graded from coarse, to medium, to fine, down to 0.05 mm; silt to 0.002 mm; and clay at less than 0.002 mm.) Figure 14.3 is a soil texture triangle showing the relation of sand, silt, and clay concentrations in soil. Each corner of the triangle represents a soil consisting solely of the particle size noted (although rarely are true soils composed of a single separate). Every soil on Earth is defined somewhere in this triangle.

Friction between moving air (wind) and the ocean surface generates undulations of water in waves. Waves travel in groups of wave trains. Waves vary widely in scale: On a small scale, a moving boat creates a wake of small waves; at a larger scale, storms generate large groups of wave trains. At the extreme is the wind wake produced by the presence of the Hawaiian Islands, traceable westward across the Pacific Ocean surface for 3000 km (1865 mi). The islands disrupt the steady trade winds and produce related surface temperature and wind changes. A stormy area at sea is a generating region for large wave trains, which radiate outward in all directions. The ocean is crisscrossed with intricate patterns of these multidirectional waves. The waves seen along a coast may be the product of a storm center thousands of kilometers away.

Regular patterns of smooth, rounded waves, the mature undulations of the open ocean, are swells. As waves leave the generating region, wave energy continues to run in these swells, which can range from small ripples to very large flat-crested waves. A wave leaving a deep-water generating region tends to extend its wavelength horizontally for many meters. Tremendous energy occasionally accumulates to form unusually large waves

ultimate base level

Sea level; the lowest level to which stream erosion could lower the land.

Four levee breaks and at least four dozen levee breaches, in which water flows over the embankment, permitted the inundation of a major city (Figure 11.30). The polluted water remained for weeks. Figure 11.31 from Landsat-7 presents matching images of New Orleans along the shore of Lake Pontchartrain on (a) April 24 and (b) August 30, 2005. The map helps you locate the areas that are below sea level, the levees and floodwalls, and the four major breaches. The darker areas in Figure 11.31b indicate flooding; at the time, some neighborhoods were submerged up to 6.1 m (20 ft), and approximately 80% of New Orleans was under water.

Several of the floodwalls and pilings were not anchored to the design depth. This inadequate anchoring made parts of the system inherently weak. In 2007, inspections by civil engineers found that the composition of levee

s The Spodosols (northern coniferous forest soils) occur generally to the north and east of the Alfisols. They are in cold and forested moist regimes (humid continental mild-summer climates) in northern North America and Eurasia, Denmark, The Netherlands, and southern England. Because no comparable climates exist in the Southern Hemisphere, this soil type is not identified there. Spodosols form from sandy parent materials, shaded under evergreen forests of spruce, fir, and pine. Spodosols with more moderate properties form under mixed or deciduous forests (Figure 14.18). Spodosols lack humus and clay in the A horizon. Characteristics of the podzolization process are present: The Entisols generally are poor agricultural soils, although those formed from river silt deposits are quite fertile. The same conditions that inhibit complete development also prevent adequate fertility—too much or too little water, poor structure, and insufficient accumulation of weathered nutrients. Active slopes, alluvium-filled floodplains, poorly drained tundra, tidal mudflats, dune sands and erg (sandy) deserts, and plains of glacial outwash all are characteristic regions that have these soils. Figure 14.20 shows an Entisol in a desert climate where shales formed the parent material.

Since they have not reached a mature condition, Inceptisols (weakly developed soils) are inherently infertile. They are young soils, although they are more developed than the Entisols. Inceptisols include a wide variety of different soils, all having in common a lack of maturity, with evidence of weathering just beginning. Inceptisols are associated with moist soil regimes and are regarded as eluvial because they demonstrate a loss of soil constituents throughout their profile, but retain some weatherable minerals. This soil group has no distinct illuvial horizons. Inceptisols include most of the glacially derived till and outwash materials from New York down through the Appalachians and alluvium on the Mekong and Ganges floodplains. Gelisols The Gelisols are cold and frozen soils, including high-latitude (Canada, Alaska, Russia, Arctic Ocean islands, and the Antarctic Peninsula) and high-elevation (mountain) soil conditions. Temperatures in these regions are at or below 0°C (32°F), making soil development a slow process and disturbances of the soil long-lasting. Gelisols can develop organic diagnostic horizons because cold temperatures slow decomposition of materials (Figure 14.21). These are permafrost-affected soils

Fluvial:

Stream-related processes; from the Latin fluvius for "river" or "running water." geographers seek to describe recognizable stream patterns and the fluvial proccesses and produce predictable landforms yet a stream system can behave with randomness, unpredictability, and disorder

A soil solution may contain significant hydrogen ions (H1), the cations that stimulate acid formation. The result is a soil rich in hydrogen ions, or an acid soil. On the other hand, a soil high in base cations (calcium, magnesium, potassium, sodium) is a basic or alkaline soil. Such acidity or alkalinity is expressed on the pH scale (Figure 14.6). Pure water is nearly neutral, with a pH of 7.0. Readings below 7.0 represent increasing acidity. Readings above 7.0 indicate increasing alkalinity. Acidity usually is regarded as strong at 5.0 or lower on the pH scale, whereas 10.0 or above is considered strongly alkaline. The major contributor to soil acidity in this modern era is acid precipitation (rain, snow, fog, or dry deposition). Acid rain actually has been measured below pH 2.0—an incredibly low value for natural precipitation, as acid as lemon juice. Increased acidity in the soil solution accelerates the chemical weathering of mineral nutrients and increases their depletion rates. Because most crops are sensitive to specific pH levels, acid soils below pH 6.0 require treatment to raise the pH. This soil treatment is accomplished by the addition of bases in the form of minerals that are rich in base cations, usually lime (calcium carbonate, CaCO3).

Soil is an open system involving physical inputs and outputs. Soil scientists recognize five primary natural soilforming factors: parent material, climate, organisms, topography and relief, and time. Human activities, especially those related to agriculture and livestock grazing, also affect soil development and cause soil erosion. The roles of these factors are considered here and in the soilorder discussions that follow.

Earth's landscape generally is covered with soil. Soil is a dynamic natural material composed of fine particles in which plants grow, and it contains both mineral fragments and organic matter. The soil system includes human interactions and supports all human, other animal, and plant life. If you have ever planted a garden, tended a houseplant, or been concerned about famine and soil loss, this chapter will interest you. A knowledge of soil is at the heart of agriculture and food production. You kneel and scoop up a handful of prairie soil, compressing it and breaking it apart with your fingers. You are holding a historical object, one that bears the legacy of the last 15,000 years or more. This lump of soil contains information about the last ice age and intervening warm intervals, about distinct and distant source materials, about several physical processes. We are using and abusing this legacy at rates much faster than it was formed. Soils do not reproduce, nor can they be re-created.

Soil science is interdisciplinary, involving physics, chemistry, biology, mineralogy, hydrology, taxonomy, climatology, and cartography. Physical geographers are interested in the spatial patterns that are formed by soil types and the physical factors that interact to produce them. As an integrative science, physical geography is well suited for the task of understanding soils. Pedology deals with the origin, classification, distribution, and description of soils (ped is from the Greek pedon, meaning "soil" or "earth"). Edaphology specifically focuses on the study of soil as a medium for sustaining the growth of higher plants (edaphos means "soil" or "ground"). Soil science deals with a complex substance whose characteristics vary from kilometer to kilometer—and even centimeter to centimeter. In many locales, an agricultural extension service can provide specific information and perform a detailed analysis of local soils.

common designation loam, which is a balanced mixture of sand, silt, and clay that is beneficial to plant growth. Farmers consider ideal a sandy loam with clay content below 30% (lower left) because of its water-holding characteristics and ease of cultivation. Soil texture is important in determining water-retention and water-transmission traits. To see how the soil texture triangle works, consider a Miami silt loam soil type from Indiana. Samples from this soil type are plotted on the soil texture triangle as points 1, 2, and 3. A sample taken near the surface in the A horizon is recorded at point 1, in the B horizon at point 2, and in the C horizon at point 3. Textural analyses of these samples are summarized in the table and in the three pie diagrams to the right of the triangle. Note that silt dominates the surface, clay the B horizon, and sand the C horizon. The Soil Survey Manual presents guidelines for estimating soil texture by feel, a relatively accurate method when used by an experienced person. However, laboratory methods using graduated sieves and separation by mechanical analysis in water allow more precise measurements

Soil texture describes the size of soil particles, but soil structure refers to their arrangement. Structure can partially modify the effects of soil texture. The smallest natural lump or cluster of particles is a ped. The shape of soil peds determines which of the structural types the soil exhibits: crumb or granular, platy, blocky, prismatic, or columnar (Figure 14.4). Peds separate from each other along zones of weakness, creating voids, or pores, that are important for moisture storage and drainage. Rounded peds have more pore space between them and greater permeability than do other shapes. They are therefore better for plant growth than are blocky, prismatic, or platy peds, despite comparable fertility. Terms used to describe soil structure include fine, medium, and coarse. Adhesion among peds ranges from weak to strong.

The combination of the A and E horizons and the B horizon is designated the solum, considered the true definable soil of the pedon. The A, E, and B horizons experience active soil processes (labeled in Figure 14.1). Below the solum is the C horizon of weathered bedrock or weathered parent material. This zone is identified as regolith (although the term sometimes is used to include the solum as well). The C horizon is not much affected by soil operations in the solum and lies outside the biological influences experienced in the shallower horizons. Plant roots and soil microorganisms are rare in the C horizon. It lacks clay concentrations and generally is made up of carbonates, gypsum, or soluble salts of iron and silica, which form cemented soil structures. In dry climates, calcium carbonate commonly forms the cementing material of these hardened layers. Soil scientists using the U.S. classification system employ letter suffixes to further designate special conditions within each soil horizon, including anthropogenic influences.

Soils are complex and varied, as this section reveals. Observing a real soil profile will help you identify color, texture, structure, and other soil properties. A good location to observe soil profiles is a construction site or excavation, perhaps on your campus, or a road cut along a highway. The NRCS Soil Survey Manual (U.S. Department of Agriculture Handbook No. 18, October 1993) presents information on all soil properties. The NRCS Soil Survey Laboratory Methods Manual (U.S. Department of Agriculture Soil Survey Investigations Report No. 42, v. 4.0, November 2004) details specific methods and practices used to conduct soil analysis. Both documents are available for download at the NRCS web site.

Major glaciations are associated with plate tectonics because some landmasses migrated to higher, cooler latitudes. Chapters 8 and 9 explained that the shape and orientation of landmasses and ocean basins changed greatly during Earth's history. Continental plates drifted from equatorial locations to polar regions, and vice versa, thus exposing the land to a gradual change in climate. Gondwana (the southern half of Pangaea) experienced extensive glaciation that left its mark on the rocks of parts of present-day Africa, South America, India, Antarctica, and Australia. Landforms in the Sahara, for example, bear the markings of even earlier glacial activity. These markings are partly explained by the fact that portions of Africa were centered near the South Pole during the Ordovician Period, 465 million years ago (see Figure 8.15a). Episodes of mountain building over the past billion years affected climate change as mountain summits rose above the snowline, where snow remains after the summer melt. Mountain chains influence downwind weather patterns and jet-stream circulation, which, in turn, guides weather systems. More dust was present during glacial periods, suggesting drier weather and more extensive deserts beyond the frozen regions.

Some events alter the atmosphere and produce climate change. A volcanic eruption might produce lower temperatures for a year or two. The lower temperatures could initiate a buildup of long-term snow cover at high latitudes. These high-albedo snow surfaces then would reflect more insolation away from Earth to further enhance cooling in a positive feedback system. The fluctuation of atmospheric greenhouse gases could trigger higher or lower temperatures. Ice cores from Greenland and Antarctica contain trapped air samples that show carbon dioxide levels varying from 180 ppm to 290 ppm. Higher levels of carbon dioxide generally correlate with each interglacial, or warmer, period. Over the past four decades, atmospheric carbon dioxide increased dramatically, principally a result of anthropogenic (human-caused) forcing. Refer to the carbon dioxide records in Figures 7.23 (1000-year record), 7.25 (1880 to 2010), and 7.27 (10,000-year record), and Figure 2.18 for the past 60 years. Climate and Oceanic Circulation Finally, changes in oceanic circulation patterns may affect climate. For example, the Isthmus of Panama formed about 3 million years ago and effectively separated the circulation of the Atlantic and Pacific Oceans. Changes in ocean basin configuration, surface temperatures, salinity, and rates of upwelling and downwelling affect air mass formation and air temperature. Our understanding of Earth's climate—past, present, and future—is unfolding. We are learning that climate is a multicyclic system controlled by an interacting set of cooling and warming processes, all founded on celestial relations, tectonic factors, atmospheric variables, changes in oceanic circulation, and human impacts.

irrigated worldwide. Today, approximately 255 million hectares (about 630 million acres) are irrigated, and this figure is on the increase in some parts of the world (Figure 14.12c). However, in many areas, production has decreased and even ended because of salt buildup in the soils. Examples include areas along the Tigris and Euphrates Rivers in Iraq, the Indus River Valley in Pakistan, sections of South America and Africa, and the western United States. In California, the former Kesterson Wildlife Refuge was reduced to a toxic waste dump in the early 1980s by contaminated agricultural drainage. Focus Study 14.1 elaborates on the Kesterson tragedy

Some of Earth's most significant agricultural soils are Mollisols (grassland soils). This group includes seven recognized suborders, which vary in fertility. The dominant diagnostic horizon is a dark, organic surface layer some 25 cm (10 in.) thick (Figure 14.13 on page 461). As the Latin name implies (words using the same root, mollis, are mollify and emollient, meaning "soft"), Mollisols are soft, even when dry. They have granular or crumbly peds, loosely arranged when dry. These humus-rich soils are high in basic cations (calcium, magnesium, and potassium) and have a high CEC and therefore high fertility. In soil moisture, these soils are intermediate between humid and arid.

When the former meander becomes isolated from the rest of the river, the resulting oxbow lake (4) may gradually fill with organic debris and silt or may again become part of the river when it floods. The Mississippi River is many miles shorter today than it was in the 1830s because of artificial cutoffs that were dredged across meander necks to improve navigation and safety.

Streams often form natural political boundaries, as we saw with the Danube River earlier. Yet problems may arise when boundaries are based on river channels that change course. For example, the Ohio, Missouri, and Mississippi Rivers can shift their positions quite rapidly during times of flood and therefore make confusing the boundaries based on them. Carter Lake, Iowa, provides us with a case in point (Figure 11.17). The Nebraska- Iowa border was originally placed mid-channel in the Missouri River. In 1877, the river cut off the meander loop around the town of Carter Lake, leaving the town "captured" by Nebraska. The new oxbow lake was called Carter Lake and still is the state boundary. In order to avoid boundary disputes along the Rio Grande near El Paso, Texas, and the Colorado River between Arizona and California, surveys have permanently established political boundaries separate from changing river locations.

water freezes, the saturated soil and rocks are subjected to frost heaving (vertical movement) and frost thrusting (horizontal movement). Boulders and rock slabs may be thrust to the surface. Soil horizons (layers) may be disrupted by frost action and appear to be stirred or churned. Frost action also can produce contractions in soil and rock, opening up cracks for ice wedges to form. An ice wedge develops when water enters a crack in the permafrost and freezes (Figure 13.20). Thermal contraction in ice-rich soil forms a tapered crack—wider at the top, narrowing toward the bottom. Repeated seasonal freezing and thawing progressively enlarge the wedge, which may widen from a few millimeters to 5-6 m (16-20 ft) and deepen up to 30 m (100 ft). Widening may be small each year, but after many years, the wedge can become significant, as in Figure 13.20c. Fascinating research identified unique synergies at work to form patterned ground. The expansion and contraction of frost action result in the movement of soil particles, stones, and small boulders. During this freeze-thaw process is when self-organization begins. Imagine a process where stones move toward stone domains (stone-rich areas) and soil particles move toward soil domains (soilrich areas). The stone-centered polygons in Figure 13.21b indicate higher stone concentrations, and the soil-centered polygons in Figure 13.21c indicate higher soil particle concentrations with lesser availability of stones. Patterned ground emerges that may take centuries to form. Added to this is the role of slope angles—greater slopes produce striped patterns, whereas lesser slopes result in sorted polygons.

Such polygon nets in patterned ground provide vivid evidence of frozen subsurface water on Mars (Figure 13.21d). In this 1999 image, the Mars Global Surveyor captured a region of these features on the Martian northern plains. To date, some 600 different sites on Mars demonstrate such patterned ground, and in 2008, the Phoenix lander set down in the middle of a Martian arctic plain covered with polygonal forms. The craft dug into the Martian surface and verified the presence of ground (water) ice.

The Nile River, one of Earth's longest rivers, drains much of northeastern Africa. But as it courses through the deserts of Sudan and Egypt, it loses water, instead of gaining it, because of evaporation and withdrawal for agriculture. By the time it empties into the Mediterranean Sea, the Nile's flow has dwindled so much that it ranks only 36th in discharge

The Colorado River in the United States is also an exotic stream. Discharge decreases with distance from its source; in fact, the river no longer produces enough natural discharge to reach its mouth in the Gulf of California—only some agricultural runoff remains at its delta. The river is depleted by passage across desert lands and by upstream removal of water for agriculture and municipal uses as well as by decreasing precipitation because of shifting pressure systems with climate change;

If a spit grows to completely cut off the bay from the ocean and form an inland lagoon, it becomes a bay barrier, or baymouth bar. Spits and barriers are made up of materials that have been eroded and transported by littoral drift (considered beach drift and longshore drift combined). For much sediment to accumulate, offshore currents must be weak, since strong currents carry material away before it can be deposited. Tidal flats and salt marshes are characteristic low-relief features wherever tidal influence is greater than wave action. As noted earlier, if these deposits completely cut off the bay from the ocean, an inland lagoon forms. A tombolo occurs when sediment deposits connect the shoreline with an offshore island or sea stack by accumulating on an underwater wave-built terrace (Figure 12.13a). Not all the beaches of the world are composed of sand, for they can be made up of shingles (beach gravel) and shells, among other materials (Figure 12.13b). Let us examine these transient coastal deposits in more detail— let's go to the beach.

Technically, a beach is that place along a coast where sediment is in motion, deposited by waves and currents. Material from the land temporarily resides on the beach while it is in active transit along the shore. You probably have experienced a beach at some time, along a seacoast, a lakeshore, or even a stream. Perhaps you have even built your own "landforms" in the sand, only to see them washed away by the waves: a lesson in erosion. On average, the beach zone spans the area from about 5 m (16 ft) above high tide to 10 m (33 ft) below low tide (see Figure 12.3). However, the specific definition varies greatly along individual shorelines. Worldwide, quartz

Climatologists use environmental criteria to define the Arctic and the Antarctic regions. The 10°C (50°F) isotherm for July defines the Arctic region (green line on the map in Figure 13.29a). This line coincides with the visible tree line—the boundary between the northern forests and tundra. The Arctic Ocean is covered by two kinds of ice: floating sea ice (frozen seawater) and glacier ice (frozen freshwater). This pack ice thins in the summer months and sometimes breaks up (Figure 13.29b). As mentioned elsewhere, almost half of the Arctic ice pack by volume has disappeared since 1970 due to regional-scale warming. The year 2007 broke the record for lowest sea-ice extent, falling below the previous record low in 2005 by 24%. The fabled Northwest Passage across the Arctic from the Atlantic to the Pacific was ice-free in September 2007, as the Arctic ice continues to melt. The Northeast Passage, north of Russia, has been ice-free for the past several years. Please review Geosystems Now in Chapter 3, which outlines the problems this presents. The Antarctic convergence defines the Antarctic region in a narrow zone that extends around the continent as a boundary between colder Antarctic water and warmer water at lower latitudes. This boundary follows roughly the 10°C (50°F) isotherm for February, the Southern Hemisphere summer, and is located near 60° S latitude

The Antarctic landmass is surrounded by ocean and is much colder overall than the Arctic, which is an ocean surrounded by land. In simplest terms, Antarctica can be thought of as a continent covered by a single enormous glacier, although it contains distinct regions such as the East Antarctic and West Antarctic Ice Sheets, which respond differently to slight climatic variations. These ice sheets are in constant motion, as indicated by the arrows in Figure 13.29c. The fact that Antarctica is so remote from civilization makes it an excellent laboratory for sampling past and present evidence of human and natural variables that are transported by atmospheric and oceanic circulation to this pristine environment. High elevation, winter cold and darkness, and distance from pollution sources make this polar region an ideal location for certain astronomical and atmospheric observations (Figure 13.30). At the South Pole, 50 scientists and support people work through the winter work season (February to October), and 130 persons, or more, research and work there during the brief summer

A large undersea disturbance usually generates a solitary wave of great wavelength. Tsunami generally exceed 100 km (60 mi) in wavelength (crest to crest) but are only a meter (3 ft) or so in height. They travel at great speeds in deep-ocean water—velocities of 600-800 kmph (375- 500 mph) are not uncommon—but often pass unnoticed on the open sea because their great wavelength makes the rise and fall of water hard to observe. As a tsunami approaches a coast, however, the shallow water forces the wavelength to shorten. As a result, the wave height may increase up to 15 m (50 ft) or more. Such a wave has the potential to devastate a coastal area, causing property damage and death. For example, in 1992 the citizens of Casares, Nicaragua, were surprised by a 12-m (39-ft) tsunami that took 270 lives. A 1998 Papua New Guinea tsunami, launched by a massive undersea landslide of some 4 km3 (1 mi3), killed 2000. During the 20th century, records show 141 damaging tsunami and perhaps 900 smaller ones, with a total death toll of about 70,000.

The active margin of the Pacific Ocean along North and South America is a typical erosional coastline. Erosional coastlines tend to be rugged, of high relief, and tectonically active, as expected from their association with the leading edge of drifting lithospheric plates (review the plate tectonics discussion in Chapter 8). Figure 12.12 presents features commonly observed along an erosional coast. Within this erosional setting, depositional processes can occur, producing depositional landforms. Sea cliffs are formed by the undercutting action of the sea. As indentations slowly grow at water level, a sea cliff becomes notched and eventually will collapse and retreat (Figure 12.12e). Other erosional forms evolve along cliffdominated coastlines, including sea caves, sea arches, and sea stacks. As erosion continues, arches may collapse, leaving isolated stacks in the water

great basin

The area between the Rocky Mountains and the Sierra Nevadas. Dry desert, mostly.

On the landward side of a barrier formation are tidal flats, marshes, swamps, lagoons, coastal dunes, and beaches, visible in Figure 12.15. Barrier beaches appear to adjust to sea level and may naturally shift position from time to time in response to wave action and longshore currents. A break in a barrier forms an inlet that connects a bay with the ocean. The name barrier is appropriate, for these formations take the brunt of storm energy and actually shield the mainland. Various hypotheses exist to explain the formation of barrier islands. They may begin as offshore bars or low ridges of submerged sediment near shore and then gradually migrate toward shore as sea level rises. Barrier beaches and islands are quite common worldwide, lying offshore of nearly 10% of Earth's coastlines. Examples are found off Africa, India's eastern coast, Sri Lanka, Australia, and Alaska's northern slope as well as offshore in the Baltic and Mediterranean Seas. Earth's most extensive chain of barrier islands is along the U.S. Atlantic and Gulf Coasts, extending some 5000 km (3100 mi) from Long Island to Texas and Mexico.

The barrier islands off the Louisiana shore are disappearing. They are affected by subsidence resulting from the compaction of Mississippi delta sediments, deflation from the pumping of oil and gas reserves, a changing sea level that is rising at 1 cm (0.4 in.) per year in the region, and an increase in tropical storm intensity. In 1998, Hurricane Georges destroyed large tracts of the Chandeleur Islands, located 30 to 40 km (19 to 25 mi) from the Louisiana-Mississippi Gulf Coast, leaving the mainland with reduced protection (Figure 12.16). Louisiana's increasingly exposed wetlands are disappearing at the rate of 65 km2 (25 mi2) per year. Hurricane Katrina (2005) alone removed this amount of wetlands and swept away most of the remaining Chandeleur Islands. The regional office of the U.S. Geological Survey predicts that in a few decades the barrier islands may be gone.

■ Solar energy input drives the atmosphere and the hydrosphere. A conversion of insolation to kinetic energy produces prevailing winds, weather systems, and climate. ■ Atmospheric winds, in turn, generate ocean currents and waves, key inputs to the coastal environment. ■ Climatic regimes, which result from insolation and moisture, strongly influence coastal geomorphic processes. ■ The nature of coastal rock and coastal geomorphology are important in determining rates of erosion and sediment production. ■ Human activities are an increasingly significant input to coastal change. All these inputs occur within the ever-present influence of gravity's pull—not only from Earth, but also from the Moon and the Sun. Gravity provides the potential energy of position for materials in motion and produces the tides. A dynamic equilibrium among all these components produces coastline features of infinite variety and beauty.

The coastal environment is the littoral zone, from the Latin word, litoris, for "shore." Figure 12.3 illustrates the littoral zone and includes specific components discussed later in the chapter. The littoral zone spans some land as well as water. Landward, it extends to the highest waterline that occurs on shore during a storm. Seaward, it extends to where water is too deep for storm waves to move sediments on the seafloor—usually around 60 m, or 200 ft, in depth. The specific contact line between the sea and the land is the shoreline, although this line shifts with tides, storms, and sea-level adjustments. The coast continues inland from high tide to the first major landform change and may include areas considered to be part of the coast in local usage. Because the level of the ocean varies, the littoral zone naturally shifts position from time to time. A rise in sea level causes submergence of land, whereas a drop in sea level exposes new coastal areas. In addition, uplift and subsidence of the land itself initiate changes in the littoral zone

suspended load

The load contains small rocks and soil in suspension, which can make the river look muddy.

Wind is an agent of geomorphic change along coastlines as well as in other environments. Although wind's ability to erode, transport, and deposit materials is small compared to that of water and ice, wind processes can move significant quantities of sand and shape landforms.

The ocean is one of Earth's last great scientific frontiers and is of great interest to geographers. Remote sensing from orbiting spacecraft and satellites, aircraft, surface vessels, and submersibles is providing a wealth of data and a new capability to understand the oceanic system.

Approximately 15,000 years ago, in several episodes, Pleistocene glaciers retreated in many parts of the world, leaving behind large glacial outwash deposits of fine-grained clays and silts. These materials were blown great distances by the wind and redeposited in unstratified, homogeneous (evenly mixed) deposits. Peasants working along the Rhine River Valley in Germany gave these deposits the name loess (pronounced "luss"). No specific landforms were created; instead, loess covered existing landforms with a thick blanket of material that assumed the general topography of the existing landscape. Figure 14.7a shows the worldwide distribution of loess deposits. Significant accumulations throughout the Mississippi and Missouri River Valleys form continuous deposits 15-30 m (50-100 ft) thick. Loess deposits also occur in eastern Washington State and Idaho. The hills and gullies in the Loess Hills of Iowa in Figure 14.7b reach heights of about 61 m (200 ft) above the nearby prairie farmlands and Missouri River and run north and south more than 322 km (200 mi). Only China has deposits that exceed these dimensions. This silt explains the fertility of the soils in these regions, for loess deposits are well drained and deep and have excellent moisture retention. Loess deposits also cover much of Ukraine, central Europe, China, the Pampas-Patagonia regions of Argentina, and lowland New Zealand. The soils derived from loess help form some of Earth's "breadbasket" farming regions.

The loess deposits in Europe and North America are thought to be derived mainly from glacial and periglacial sources. The vast deposits of loess in China, covering more than 300,000 km2 (116,000 mi2), are derived from windblown desert sediment rather than glacial sources. Accumulations in the Loess Plateau of China are more than 300 m (1000 ft) thick, forming complex weathered badlands and some good agricultural land. These windblown deposits are interwoven with much of Chinese history and society. Because of its own binding strength and its internal coherence, loess weathers and erodes into steep bluffs, or vertical faces. When a bank is cut into a loess deposit, it generally will stand vertically, although it can fail if saturated (Figure 14.7c). According to historical accounts, Civil War soldiers in the Vicksburg, Mississippi, area excavated places to live in loess banks; in areas of China, dwellings are carved from the loess.

. A scientific assessment estimates that about 40% of Earth's population lives within 100 km (62 mi) of coastlines. In the United States, about 50% of the people live in areas designated as coastal (this includes the Great Lakes). Therefore, an understanding of coastal processes and landforms is important to nearly half the world's population. And because these processes along coastlines often produce dramatic change, they are essential to consider in planning and development. A World Resources Institute study found as much as 50% of the world's coastlines at some risk of loss through erosion and rising sea level or disruption from pollution

The ocean is a vast ecosystem, intricately linked to life on the planet and to life-sustaining systems in the atmosphere, the hydrosphere, and the lithosphere. Oceans act as a vast buffering system, absorbing excess atmospheric carbon dioxide and thermal energy; yet the system is overwhelmed with the rate of change over the past several decades. The first meeting of the Conference on the Ocean Observing System for Climate took place in St. Raphael, France, in 1999; the second meeting occurred 10 years later in Venice, Italy. The program noted the profound changes that had transpired in the ocean system over those 10 years and set a goal for a new physical and carbon ocean-observing system by 2015

In contrast, the Sargasso Sea, within the North Atlantic subtropical gyre, averages 38‰. The Persian Gulf has a salinity of 40‰ as a result of high evaporation rates in a nearly enclosed basin. Deep pockets, or "brine lakes," along the floor of the Red Sea and the Mediterranean Sea register up to a salty 225‰

The ocean reflects conditions in Earth's environment. As an example, the high-latitude oceans have been freshening over the past decade, as mentioned earlier in this chapter and Chapter 13. Another change under way is oceanic acidification, taking place as the ocean absorbs excess carbon dioxide from the atmosphere—acidity is increasing rapidly.

Hydrolysis forms carbonic acid in the seawater, resulting in a lowering of the ocean pH—an acidification. A more acid ocean will cause certain marine organisms such as corals and some plankton to have difficulty maintaining external calcium carbonate structures. pH could decrease by 20.4 to 20.5 units this century; the ocean's average pH today is 8.2. The scale is logarithmic, so a decrease of 0.1 equals a 30% increase in acidity. Oceanic biodiversity and food webs will respond to this change in unknown ways. The dissolved solids remain in the ocean, but the water recycles endlessly through the hydrologic cycle, driven by energy from the Sun. The water you drink today may have water molecules in it that not long ago were in the Pacific Ocean, in the Yangtze River, in groundwater in Sweden, or airborne in the clouds over Peru.

The ocean's surface layer is warmed by the Sun and is wind-driven. Variations in water temperature and sol

Where channel slope is gradual, streams develop a sinuous (snakelike) form, weaving across the landscape. This action produces a meandering stream pattern, with distinct flow and channel characteristics. The tendency to meander is evidence of a river system's struggle to operate with least effort between self-organizing order (equilibrium) and chaotic disorder in nature. Flow characteristics of a meandering stream are best seen in a cross-sectional view. The greatest velocities are near the surface at center channel (Figure 11.15), corresponding to the deepest part of the stream channel. Velocities decrease closer to the sides and bottom of the channel because of the frictional drag on the water flow. The portion of the stream flowing at maximum velocity moves diagonally across the stream from bend to bend in a meandering stream.

The outer portion of each meandering curve is subject to the fastest water velocity and therefore the greatest scouring erosive action; it can be the site of a steep bank called the undercut bank, or cutbank (Figures 11.15 and 11.16). In contrast, the inner portion of a meander experiences the slowest water velocity and thus receives sediment fill, forming a point bar deposit. As meanders develop, these scour-and-fill features gradually work at stream banks. As a result, the landscape near a meandering river bears meander scars of residual deposits from previous river channels

solution load

The process of dissolved pieces of material being transported in a solution.

An important indicator of changing surface conditions is an increase in meltponds across the polar regions, as these meltponds represent positive feedback— meltponds are darker, absorb more insolation, and become warmer, which melts more ice, making more meltponds, and so forth. The Landsat-7 satellite, in tandem with aircraft equipped with video cameras, spotted this increase in meltpond occurrence on glaciers, icebergs, ice shelves, and the Greenland Ice Sheet. Figure 13.31a is a scene from western Greenland in June 2003 made by the Terra satellite. Examine the bare rock indicating that the snow line has retreated to higher elevations. The image shows rapidly increasing numbers of meltponds and areas of water-saturated ice in the melt zone, which advanced 400% from 2001 to 2003. The meltponds look like small blue dots across the ice. In Figure 13.31b and c, you can see the meltponds and melt streams in southwest Greenland as of June 2008.

The streams sometimes melt through the ice sheet, forming a moulin, or drainage channel, that works its way to the base of the glacier (Figure 13.31c). The glacial water can flow through the basal layers of fine clays, thus lubricating and causing acceleration of glacial flow rates; even hydrostatically lifting the ice is possible. Surrounding the margins of Antarctica, and constituting about 11% of its surface area, are numerous ice shelves (Figure 13.32). Although ice shelves constantly break up to produce icebergs, more large sections are breaking free than expected. You read about a recent breakup of the Wilkins Ice Shelf in Geosystems Now for this chapter. In 1998, an iceberg the size of Delaware broke off the Ronne Ice Shelf, southeast of the Antarctic Peninsula. In March 2000, an iceberg tagged B-15, measuring twice the area of Delaware (300 km by 40 km, or 190 mi by 25 mi), broke off the Ross Ice Shelf (some 3027 km, or 1900 mi, west of the Antarctic Peninsula).

Paleolakes existed in North and South America, Africa, Asia, and Australia. In North America, the two largest late Pleistocene paleolakes were Lake Bonneville and Lake Lahontan, located in the Basin and Range Province in the western United States. These two lakes were much larger than their present-day remnants. Figure 13.26 shows these and other paleolakes at their highest level and the few remaining modern lakes in light blue. The Great Salt Lake, near Salt Lake City, Utah, and the Bonneville Salt Flats in western Utah are remnants of Lake Bonneville; today, the Great Salt Lake is the fourth largest saline lake in the world. At its greatest extent, this paleolake covered more than 50,000 km2 (19,500 mi2) and reached depths of 300 m (1000 ft), spilling over into the Snake River drainage to the north. Now, it is a closed-basin terminal lake with no drainage except an artificial outlet to the west, where excess water from the Great Salt Lake can be pumped during rare floods. Lake levels continue to decline in response to climate change to drier conditions. New evidence reveals that the occurrence of these lakes in North America was related to specific changes in the polar jet stream that steered storm tracks across the region, creating pluvial conditions. The continental ice sheet evidently influenced changes in jet-stream position.

The study of Earth's past climates is the science of paleoclimatology. Glacials and interglacials occur because Earth's climate has fluctuated in and out of warm and cold ages. Evidence for this fluctuation now is traced in ice cores from Greenland and Antarctica (Focus Study 13.1), in layered ocean deposits of silts and clays, in the extensive pollen record from ancient plants, and in the relation of past coral productivity to sea level. This evidence is analyzed with radioactive dating methods and other techniques. One especially interesting fact is emerging from these studies: We humans (Homo erectus and Homo sapiens of the last 1.9 million years) have never experienced Earth's normal (more moderate, less extreme) climate, most characteristic of Earth's entire 4.6-billion-year span. Apparently, Earth's climates slowly fluctuated until the past 1.2 billion years, when temperature patterns with cycles of 200-300 million years became more pronounced.

Salinity worldwide normally varies between 34‰ and 37‰; variations are attributable to atmospheric conditions above the water and to the volume of freshwater inflows. In equatorial water, precipitation is great throughout the year, diluting salinity values to 34.5‰ (slightly lower than average). In subtropical oceans—where evaporation rates are greatest because of the influence of hot, dry, subtropical high-pressure cells—salinity is more concentrated, increasing to 36‰. In these regions, salinity is rising as increased evaporation rates rise with temperature.

The term brine is applied to water that exceeds the average of 35‰ salinity. Brackish applies to water that is less than 35‰ salts. In general, oceans are lower in salinity near landmasses because of freshwater runoff and river discharges. Extreme examples include the Baltic Sea (north of Poland and Germany) and the Gulf of Bothnia (between Sweden and Finland), which average 10‰ or less salinity because of heavy freshwater runoff and low evaporation rates.

high tide (flood tide)

The time at which the tide reaches its highest level

The seven most common drainage patterns are shown in Figure 11.6. A most familiar pattern is dendritic drainage (Figure 11.6a). This treelike pattern (from the Greek word dendron, meaning "tree") is similar to that of many natural systems, such as capillaries in the human circulatory system, or the vein patterns in leaves, or tree roots. Energy expended by this drainage system is efficient because the overall length of the branches is minimized.

The trellis drainage pattern (Figure 11.6b) is characteristic of dipping or folded topography. Such drainage exists in the nearly parallel mountain folds of the Ridge and Valley Province in the eastern United States. Refer to Figure 9.18, where a satellite image of this region shows its distinctive drainage pattern. Here drainage patterns are influenced by rock structures of variable resistance and folded strata. Parallel folded structures direct the principal streams, whereas smaller dendritic tributary streams are at work on nearby slopes, joining the main streams at right angles, like a plant trellis. The inset sketch in Figure 11.6b suggests that a headward-eroding part of one stream (to the lower right of the inset) could break through a drainage divide and capture the headwaters of another stream in the next valley—and, indeed, this does happen. The dotted line is the abandoned former channel. The sharp bends in two of the streams in the illustration are elbows of capture and are evidence that one stream has breached a drainage divide. This type of capture, or stream piracy, can also occur in other drainage patterns. The remaining drainage patterns in Figure 11.6c-g are responses to other specific structural conditions: A radial drainage pattern (c) results when streams flow off a central peak or dome, such as occurs on a volcanic mountain. ■ Parallel drainage (d) is associated with steep slopes. ■ A rectangular pattern (e) is formed by a faulted and jointed landscape, which directs stream courses in patterns of right-angle turns. ■ Annular patterns (f) are produced by structural domes, with concentric patterns of rock strata guiding stream courses. Figure 9.10c provides an example of annular drainage on a dome structure.

The exact cause of such a glacier surge is being studied. Some surge events result from a buildup of water pressure under the glacier—sometimes enough to actually float the glacier slightly, detaching it from its bed during the surge. As a surge begins, ice quakes are detectable, and ice faults are visible. Surges can occur in dry conditions as well, as the glacier plucks (picks up) rock from its bed and moves forward. Another cause of glacier surges is the presence of a water-saturated layer of sediment, a soft bed, beneath the glacier, as discussed for Greenland. This is a deformable layer that cannot resist the tremendous sheer stress produced by the moving ice of the glacier. Scientists examining cores taken from several ice streams now accelerating through the West Antarctic Ice Sheet think they have identified this cause of glacial surges—although water pressure is still important.

The way in which a glacier erodes the land is similar to a large excavation project, with the glacier hauling debris from one site to another for deposition. The passing glacier mechanically plucks rock material and carries it away. Debris is carried on its surface and is also transported internally, or englacially, embedded within the glacier itself. Evidence indicates that rock pieces actually freeze to the basal layers of the glacier in a glacial plucking, or a picking-up process, and once embedded, they enable the glacier to scour and sandpaper the landscape as it moves—a process of abrasion. This abrasion and gouging produce a smooth surface on exposed rock, which shines with glacial polish when the glacier retreats. Larger rocks in the glacier act much like chisels, gouging the underlying surface and producing glacial striations parallel to the flow direction

A glacier is an open system, with inputs of snow and outputs of ice, meltwater, and water vapor. Snowfall and other moisture in the accumulation zone feed the glacier's upper reaches (Figure 13.5b). This area ends at the firn line, indicating where the winter snow and ice accumulation survived the summer melting season. Toward a glacier's lower end, it is wasted (reduced) through several processes: melting on the surface, internally, and at its base; ice removal by deflation (wind); the calving of ice blocks; and sublimation (recall from Chapter 5 that this is the direct evaporation of ice). Collectively, these losses are ablation.

The zone where accumulation gain balances ablation loss is the equilibrium line (Figure 13.5a and b). This area of a glacier generally coincides with the firn line. A glacier achieves a positive net balance of mass—grows larger—during cold periods with adequate precipitation. In warmer times, the equilibrium line migrates up-glacier, and the glacier retreats—grows smaller—because of its negative net balance. Internally, gravity continues to move a glacier forward even though its lower terminus might be in retreat owing to ablation. As part of a global trend, the net mass balance of the South Cascade Glacier in Washington State demonstrated significant losses between 1955 and 2010. As a result of this negative mass balance, sometimes the terminus retreated tens of meters a year. The glacier has retreated every year in the record except 1972. Figure 13.6 is a photo comparison of the South Cascade Glacier between 1979 and 2003. A comparison of the trend of this glacier's mass balance with that of others in the world shows that temperature changes apparently are causing widespread reductions in middle- and lower-elevation glacial ice. The present wastage (ice loss) from alpine glaciers worldwide is thought to contribute over 25% to the measured rise in sea level.

Seven elements account for more than 99% of the dissolved solids in seawater. They are (with their ionic form) chlorine (as chloride, Cl2), sodium (as Na1), magnesium (as Mg 21), sulfur (as sulfate, SO4 22), calcium (as Ca21), potassium (as K1), and bromine (as bromide, Br2). Seawater also contains dissolved gases (such as carbon dioxide, nitrogen, and oxygen), suspended and dissolved organic matter, and a multitude of trace elements. Commercially, only sodium chloride (common table salt), magnesium, and bromine are extracted in any significant amount from the ocean. Future mining of minerals from the seafloor is technically feasible, although it remains uneconomical. Average Salinity: 35‰

There are several ways to express salinity (dissolved solids by volume) in seawater, using the worldwide average value: ■ 3.5% (% parts per hundred) ■ 35,000 ppm (parts per million)■ 35,000 mg/l ■ 35 g/kg ■ 35‰ (‰ parts per thousand), the most common notation

Permafrost regions are divided into two general categories, continuous and discontinuous, which merge along a general transition zone. Continuous permafrost is the region of severest cold and is perennial, roughly poleward of the 27°C (19°F) mean annual temperature isotherm (purple area in Figure 13.18). Continuous permafrost affects all surfaces except those beneath deep lakes or rivers. The depth of continuous permafrost may exceed 1000 m (3300 ft), averaging approximately 400 m (1300 ft). Unconnected patches of discontinuous permafrost gradually coalesce poleward toward the continuous zone. Permafrost becomes scattered or sporadic until it gradually disappears equatorward of the -1°C (30.2°F) mean annual temperature isotherm (dark blue area in Figure 13.18). In the discontinuous zone, permafrost is absent on sunexposed south-facing slopes, areas of warm soil, and areas insulated by snow. In the Southern Hemisphere, northfacing slopes experience increased warmth.

These discontinuous zones are most susceptible to thawing with climate change. Affected peat-rich soils (Gelisols, Histosols—Chapter 14) contain twice the amount of carbon that is in the atmosphere, making a powerful positive feedback as soils thaw and oxidation releases more carbon dioxide to the atmosphere. Additionally, the losses of carbon in thawing exceed any increases in carbon uptake that the warmer conditions and higher carbon dioxide levels create, making permafrost thaw an important source of greenhouse gases—a real-time positive feedback mechanism.

The gravitational pull of the Moon tugs on Earth's atmosphere, oceans, and lithosphere. The same is true for the Sun, to a lesser extent. Earth's solid and fluid surfaces all experience some stretching as a result of this gravitational pull. The stretching raises large tidal bulges in the atmosphere (which we can't see), smaller tidal bulges in the ocean, and very slight bulges in Earth's rigid crust. Our concern here is the tidal bulges in the ocean. Gravity and inertia are essential elements in understanding tides. Gravity is the force of attraction between two bodies. Inertia is the tendency of objects to stay still if motionless or to keep moving in the same direction if in motion. The gravitational effect on the side of Earth facing the Moon or Sun is greater than that experienced by the far side, where inertial forces are slightly greater. In effect, from this inertial point of view, as the nearside water and Earth are drawn toward the Moon and Sun, the farside water is left behind because of the slightly weaker gravitational pull. This arrangement produces the two opposing tidal bulges on opposite sides of Earth.

Tides appear to move in and out along the shoreline, but they do not actually do so. Instead, Earth's surface rotates into and out of the relatively "fixed" tidal bulges as Earth changes its position in relation to the Moon and Sun. Every 24 hours and 50 minutes, any given point on Earth rotates through two bulges as a direct result of this rotational positioning. Thus, every day, most coastal locations experience two high (rising) tides, known as flood tides, and two low (falling) tides, known as ebb tides. The difference between consecutive high and low tides is considered the tidal range.

The coastal system is the scene of complex tidal fluctuation, winds, waves, ocean currents, and the occasional impact of storms. These forces shape landforms ranging from gentle beaches to steep cliffs, and they sustain delicate ecosystems.

Tides are complex twice-daily oscillations in sea level, ranging worldwide from barely noticeable to several meters. They are experienced to varying degrees along every ocean shore around the world. Tidal action is a relentless energy agent for geomorphic change. As tides flood (rise) and ebb (fall), the daily migration of the shoreline landward and seaward causes significant changes that affect sediment erosion and transportation

Tides are important in human activities, including navigation, fishing, and recreation. Tides are especially important to ships because the entrance to many ports is limited by shallow water, and thus high tide is required for passage. Tall-masted ships may need a low tide to clear overhead bridges. Tides also exist in large lakes, but because the tidal range is small, tides are difficult to distinguish from changes caused by wind. Lake Superior, for instance, has a tidal variation of only about 5 cm (2 in.).

Tides are produced by the gravitational pull of both the Sun and the Moon. Chapter 2 discusses Earth's relation to the Sun and Moon and the reasons for the seasons. The Sun's influence is only about half that of the Moon's because of the Sun's greater distance from Earth, although it is a significant force. Figure 12.6 illustrates the relation among the Moon, the Sun, and Earth and the generation of variable tidal bulges on opposite sides of the planet

Prior to the Soil Taxonomy system, pedogenic regimes were used to describe soils. These regimes keyed specific soil-forming processes to climatic regions. Although each pedogenic process may be active in several soil orders and in different climates, we discuss them within the soil order where they commonly occur. Such climate-based regimes are convenient for relating climate and soil processes. However, the Soil Taxonomy system recognizes the great uncertainty and inconsistency in basing soil classification on such climatic variables. Aspects of several pedogenic processes are discussed with appropriate soil orders: ■ Laterization: a leaching process in humid and warm climates, discussed with Oxisols and shown in Figure 14.11; ■ Salinization: a process that concentrates salts in soils in climates with excessive potential evapotranspiration (POTET) rates, discussed with Aridisols; ■ Calcification: a process that produces an illuviated accumulation of calcium carbonates in continental climates, discussed with Mollisols and Aridisols and shown in Figure 14.15; ■ Podzolization: a process of soil acidification associated with forest soils in cool climates, discussed with Spodosols and shown in Figure 14.19; and ■ Gleization: a process that includes an accumulation of humus and a thick, water-saturated gray layer of clay beneath, usually in cold, wet climates and poor drainage conditions.

To identify a specific soil series within the Soil Taxonomy, the NRCS describes diagnostic horizons in a pedon. A diagnostic horizon reflects a distinctive physical property (color, texture, structure, consistence, porosity, moisture) or a dominant soil process (discussed with the soil types). In the solum (A, E, and B horizons), two diagnostic horizons may be identified: the epipedon and the diagnostic subsurface. The presence or absence of either of these horizons usually distinguishes a soil for classification. The epipedon (literally, "over the soil") is the diagnostic horizon at the surface, where most of the rock structure has been destroyed. It may extend downward through the A horizon, even including all or part of an illuviated B horizon. It is visibly darkened by organic matter and sometimes is leached of minerals. Excluded from the epipedon are alluvial deposits, eolian deposits, and cultivated areas because soil-forming processes have lacked the time to erase these relatively short-lived characteristics. The diagnostic subsurface horizon originates below the surface at varying depths. It may include part of the A or B horizon or both.

Physical and chemical weathering of rocks in the upper lithosphere provides the raw mineral ingredients for soil formation. These rocks supply the parent materials, and their composition, texture, and chemical nature help determine the type of soil that forms. Clay minerals are the principal weathered by-products in soil. Climate types correlate closely with soil types worldwide. The moisture, evaporation, and temperature regimes of climates determine the chemical reactions, organic activity, and eluviation rates of soils. Not only is the present climate important, but also many soils exhibit the imprint of past climates, sometimes over thousands of years. Most notable is the effect of glaciations. Among other contributions, glaciation produced the loess soil materials that were windblown thousands of kilometers to their present locations. Vegetation and the activities of animals and bacteria determine the organic content of soil, along with all that is living in soil—algae, fungi, worms, and insects. The chemical makeup of the vegetation contributes to the acidity or alkalinity of the soil solution. For example, broadleaf trees tend to increase alkalinity, whereas needleleaf trees tend to produce higher acidity. Thus, when civilization moves into new areas and alters the natural vegetation by logging or plowing, the affected soils are likewise altered, often permanently.

Topography also affects soil formation. Slopes that are too steep cannot have full soil development because gravity and erosional processes remove materials. Lands that are nearly level inhibit soil drainage and can become waterlogged. The compass orientation of slopes is important because it controls exposure to sunlight. In the Northern Hemisphere, a south-facing slope is warmer overall through the year because it receives direct sunlight. Water-balance relations are affected because northfacing slopes are colder, causing slower snowmelt and a lower evaporation rate, providing more moisture for plants than is available on south-facing slopes, which tend to dry faster. All of the identified natural factors in soil development (parent material, climate, biological activity, and topography) require time to operate. Over geologic time, plate tectonics has redistributed landscapes and thus subjected soil-forming processes to diverse conditions.

Human intervention has a major impact on soils. Millennia ago, farmers in most cultures learned to plant slopes "on the contour"—to make rows or mounds around a slope at the same elevation, not vertically up and down the slope. Planting on the contour prevents water from flowing straight down the slope and thus reduces soil erosion. Farmers often planted and harvested floodplains, while living on higher ground nearby. Floods were celebrated as blessings that brought water, nutrients, and more soil to the land. Society is drifting away from these commonsense strategies. A few centimeters' thickness of prime farmland soil may require 500 years to mature. Yet this same thickness is being lost annually through soil erosion when the soilholding vegetation is removed and the land is plowed, regardless of topography (Figure 14.8). Flood control structures block sediments and nutrients from replenishing floodplain soils, leading to additional soil losses. Over the same period, exposed soils may be completely leached of needed cations, thereby losing their fertility. The degradation of soils commonly results from poor land use practices. Chemical processes such as salinization and nutrient depletion, physical processes such as soil compaction, and soil erosion caused by wind or water all cause declines in land productivity. In arid and semiarid regions, land degradation causes desertification, the expansion of deserts that results from overgrazing, soil erosion, land mismanagement, and climate change—a phenomenon now affecting over a billion people worldwide. Please revisit this chapter's Geosystems Now feature for more on this topic.

Unlike living species, soils do not reproduce, nor can they be re-created. Some 35% of farmlands are losing soil faster than it can form—a loss exceeding 23 billion metric tons (25 billion tons) per year. Soil depletion and loss are at record levels from Iowa to China, Peru to Ethiopia, and the Middle East to the Americas. The impact on society is potentially disastrous as population and food demands increase. Soil erosion can be compensated for in the short run by using more fertilizer, increasing irrigation, and planting higher-yielding strains. But the potential yield from prime agricultural land will drop by as much as 20% over the next 20 years if only moderate erosion continues. One study tabulated the market value of lost nutrients and other variables in the most comprehensive soil-erosion study to date. The sum of direct damage (to agricultural land) and indirect damage (to streams, society's infrastructure, and human health) was estimated at more than $25 billion a year in the United States and hundreds of billions of dollars worldwide. Of course, this is a controversial assessment in the agricultural industry. The cost to bring erosion under control in the United States is estimated at approximately $8.5 billion, or about 30 cents on every dollar of damage and loss. A recent article by scientist David Montgomery well summarizes our predicament:

ocean bases: pacific, atlantic, indian, and

arctic ocean

An aspect of an alluvial fan is the natural sorting of materials by size. Near the mouth of the canyon at the apex of the fan, coarse materials are deposited, grading slowly to pebbles and finer gravels with distance out from the mouth. Then sands and silts are deposited, with the finest clays and dissolved salts carried in suspension and solution all the way to the valley floor. As runoff water evaporates, salt crusts may be left behind on the desert floor in a playa (see Figure 9.14b). This intermittently wet and dry lowest area of a closed drainage basin is the site of an ephemeral lake when water is present.

Well-developed alluvial fans also can be a major source of groundwater. Some cities—San Bernardino, California, for example—are built on alluvial fans and extract their municipal water supplies from them. In other parts of the world, such water-bearing alluvial fans are known as qanat (Iran), karex (Pakistan), or foggara (western Sahara).

bed load, suspended load, dissolved load

What are the three types of loads carried by streams?

In 1909, Polish geologist Walery von Lozinski coined the term periglacial to describe frost weathering and freeze- thaw rock shattering in the Carpathian Mountains. These periglacial regions occupy over 20% of Earth's land surface (Figure 13.18). Periglacial landscapes either have a near-permanent ice cover or are at a high elevation and are seasonally snow-free. Under these conditions, a unique set of periglacial processes—including permafrost, frost action, and ground ice—operates.

When soil or rock temperatures remain below 0°C (32°F) for at least 2 years, permafrost ("permanent frost") develops. An area of permafrost that is not covered by glaciers is considered periglacial, with the largest extent of such lands in Russia. Approximately 80% of Alaska has permafrost beneath its surface. Canada, China, Scandinavia, Greenland, and Antarctica, in addition to alpine mountain regions of the world, also are affected. Note that this criterion is based solely on temperature and has nothing to do with how much or how little water is present. Two other factors also contribute to permafrost conditions and occurrence: the presence of fossil permafrost from previous ice-age conditions and the insulating effect of snow cover or vegetation that inhibits heat loss.

One cirque contains small, circular, stairstepped lakes, called paternoster ("our father") lakes for their resemblance to rosary (religious) beads. Paternoster lakes may have formed from the differing resistance of rock to glacial processes or from damming by glacial deposits. The valleys carved by tributary glaciers are left stranded high above the valley floor because the primary glacier eroded the valley floor so deeply. These hanging valleys are the sites of spectacular waterfalls. See how many of the erosional forms from Figures 13.9 and 13.10 (arête, col, horn, cirque, cirque glacier, sawtooth ridge, U-shaped valley, erratic, tarn, and truncated spur, among others)

Where a glacial trough intersects the ocean, the glacier can continue to erode the landscape, even below sea level. As the glacier retreats, the trough floods and forms a deep fjord in which the sea extends inland, filling the lower reaches of the steep-sided valley (Figure 13.12). The fjord may be flooded further by rising sea level or by changes in the elevation of the coastal region. All along the glaciated coast of Alaska, glaciers are now in retreat, thus opening many new fjords that previously were blocked by ice. Coastlines with notable fjords include those of Norway, Greenland, Chile, the South Island of New Zealand, Alaska, and British Columbia.

Wind transport of soils including loess produced a catastrophe in the American Great Plains in the 1930s—the Dust Bowl. More than a century of overgrazing and intensive agriculture left soil susceptible to drought and deflation processes. Reduced precipitation amounts and above-normal temperatures triggered the multi-year period of severe dust storms and loss of farmlands. The deflation of many centimeters of soil occurred in southern Nebraska, Kansas, Oklahoma, Texas, and eastern Colorado—and even in southern Canada and northern Mexico. The transported dust darkened the skies of mid300 m (1000 ft) thick, forming complex weathered badlands and some good agricultural land. These windblown deposits are interwoven with much of Chinese history and society. Because of its own binding strength and its internal coherence, loess weathers and erodes into steep bluffs, or vertical faces. When a bank is cut into a loess deposit, it generally will stand vertically, although it can fail if saturated (Figure 14.7c). According to historical accounts, Civil War soldiers in the Vicksburg, Mississippi, area excavated places to live in loess banks; in areas of China, dwellings are carved from the loess. 452 SOILS, ECOSYSTEMS, AND BIOMES CHAPTER 14 THE GEOGRAPHY OF SOILS 453 Unlike living species, soils do not reproduce, nor can they be re-created. Some 35% of farmlands are losing soil faster than it can form—a loss exceeding 23 billion metric tons (25 billion tons) per year. Soil depletion and loss are at record levels from Iowa to China, Peru to Ethiopia, and the Middle East to the Americas. The impact on society is potentially disastrous as population and food demands increase. Soil erosion can be compensated for in the short run by using more fertilizer, increasing irrigation, and planting higher-yielding strains. But the potential yield from prime agricultural land will drop by as much as 20% over the next 20 years if only moderate erosion continues. One study tabulated the market value of lost nutrients and other variables in the most comprehensive soil-erosion study to date. The sum of direct damage (to agricultural land) and indirect damage (to streams, society's infrastructure, and human health) was estimated at more than $25 billion a year in the United States and hundreds of billions of dollars worldwide. Of course, this is a controversial assessment in the agricultural industry. The cost to bring erosion under control in the United States is estimated at approximately $8.5 billion, or about 30 cents on every dollar of damage and loss. A recent article by scientist David Montgomery well summarizes our predicament: Recent compilations of data from around the world show that soil erosion under conventional ag ri cul ture exceeds both rates of soil production and geo log i - cal erosion rates by several orders of magnitude. western cities, which left the streetlights on throughout the day, and drifted over farmland to depths that covered failing crops. The largest migration in American history occurred as 2 million people moved out of the plains states by 1940. The prolonged drought through 2011 in the American Southwest and into west and central Texas and Oklahoma is bringing back Dust Bowl memories

Wind can also contribute to soil formation in distant places. Fallow fields (those not planted) are especially susceptible to wind erosion. Scientists are only now getting an accurate picture of the amount of windblown dust that fills the atmosphere and crosses the oceans between continents. Chemical fingerprints and satellites trace windblown dust from African soils to South America and Asian landscapes to Europe.

The World Resources Institute and the United Nations Environment Programme estimate that from preagricultural times to today, mangrove losses are running between 40% (examples, Cameroon and Indonesia) and nearly 80% (examples, Bangladesh and Philippines). Deliberate removal was a common practice by many governments in the early days of settlement because of a falsely conceived fear of disease or pestilence in these swamplands

Wind is an agent of geomorphic change in coastal and desert environments. Like moving water, moving air causes erosion, transportation, and deposition of materials ranging from sand to snow. Moving air is a fluid and it behaves similarly, although it has a lower viscosity (it is less dense) than water. Although lacking the lifting ability of water, wind processes can modify and move quantities of materials along coastlines, in deserts, and elsewhere. Consistent local wind can prune and shape vegetation and sculpt ice and snow surfaces (Figure 12.22). The work of wind is eolian (also spelled aeolian, for Aeolus, ruler of the winds in Greek mythology). The ability of wind to move materials is actually small compared with that of other transporting agents such as water and ice because air is so much less dense than those other media. Yet, over time, wind accomplishes enormous work. British Army Major Ralph Bagnold, an engineering officer stationed in Egypt in 1925, was a pioneer in eolian research. Bagnold's often-cited work The Physics of Blown Sand and Desert Dunes was published in 1941. Bagnold studied the ability of wind to transport sand over the surface of a dune. He found that a steady wind of 50 kmph (30 mph) can move approximately one-half ton of sand per day over a 1-m-wide section of dune.

Wherever wind encounters loose sediment, deflation may remove enough material to form basins known as blowout depressions. These depressions range from small indentations less than a meter wide up to areas hundreds of meters wide and many meters deep. Chemical weathering, although slow in arid regions owing to the lack of water, is important in the formation of a blowout, for it removes the cementing materials that give particles their cohesiveness. Large depressions in the Sahara Desert are at least partially formed by deflation. The enormous Munkhafad el Qat.t.âra (Qat.t.âra Depression), which covers 18,000 km2 (6950 mi2) just inland from the Mediterranean Sea in the Western Desert of Egypt, is now about 130 m (427 ft) below sea level at its lowest point

You may have seen work crews sandblasting surfaces on buildings, bridges, or streets to clean them or to remove unwanted markings. Sandblasting uses a stream of compressed air filled with sand grains to quickly abrade a surface. Abrasion by windblown particles is nature's slower version of sandblasting, and it is especially effective at polishing exposed rocks when the abrading particles are hard and angular. Variables that affect the rate of abrasion include the hardness of surface rocks, wind velocity, and wind constancy. Abrasive action is restricted to the area immediately above the ground, usually no more than a meter or two in height, because sand grains are lifted only a short distance.

The Danube serves many economic functions: commercial transport, municipal water source, agricultural irrigation, fishing, and hydroelectric power production. An international struggle is under way to save the river from its burden of industrial and mining wastes, sewage, chemical discharge, agricultural runoff, and drainage from ships. The many shipping canals actually spread pollution and worsen biological conditions in the river. All of this pollution passes through Romania and the deltaic ecosystems in the Black Sea. The river is widely regarded as one of the most polluted on Earth.

a

Dynamic equillibrium:

a balance among force form and process-the preferred method used by many contemporary geomorphologists.

point bar

a crescent-shaped accumulation of sand and gravel deposited on the inside of a meander

base level:

a level below which a stream cannot erode its valley. The hypothetical ultimate base level is a sea level. you can imagine base level as a surface extending inland from sea level, inclined gently upward under the continents (Lowest practical level for all denudation processes)

foot delta

a long channel with many distributaries and sediments carried beyond the tip of the delta into the Gulf of Mexico

neep tide

a tide of lesser than average range occurring during first and third quarters of the moon

glacier

accumulation of snow over a long period of time

the general term for the clay, silt, and sand transported by running water.

alluvium

Some coastal areas have great biological productivity (plant growth; spawning grounds for fish, shellfish, and other organisms) stemming from trapped organic matter and sediments. Such a rich coastal marsh environment can greatly outproduce a wheat field in raw vegetation per acre. Thus, coastal marshes can support rich wildlife habitats. Unfortunately, these wetland ecosystems are quite fragile and are threatened by human development. Wetlands are saturated with water enough of the time to support hydrophytic vegetation (plants that grow in water or wet soil). Wetlands usually occur on poorly drained soils. Geographically, they occur not only along coastlines, but

also as northern bogs (peatlands with high water tables), as potholes in prairie lands, as cypress swamps (with standing or gently flowing water), as river bottomlands and floodplains, and as arctic and subarctic environments that experience permafrost during the year. Coastal wetlands are of two general types—salt marshes and mangrove swamps. In the Northern Hemisphere, salt marshes tend to form north of the 30th parallel, whereas mangrove swamps form equatorward from that parallel in the Eastern and Western Hemispheres. This distribution is dictated by the occurrence of freezing conditions, which control the survival of mangrove seedlings. Roughly the same latitudinal limits apply in the Southern Hemisphere. Coastal wetlands have many important functions, one of which is to buffer coastlines from storm surges associated with hurricanes. On the MasteringGeography web site, you will find a discussion of the impacts of wetland removal, storm surge, and rising sea level on Bayou LaFourche in southern Mississippi.

two forms of intermediate retainment

artificial and and natural

three measurements are needed

at a stream cross section to calculate discharge: width, depth, and velocity. Field measurements of these variables may be difficult to obtain, depending on a stream's size and flow. Velocity for different subsections of the stream cross section is most commonly measured using a movable current meter. Width and depth for each subsection are then combined with velocity to compute subsection discharge, and then the subsection discharges across the stream are totaled (see Figure 11.10). Since channel beds are often composed of soft sediments that may change over short time periods, stream depth is measured as the height of the stream surface above a constant reference elevation (a datum) and is called the stage. Scientists may use a staff gage (a pole marked with water levels) or a stilling well on the stream bank with a gage mounted in it to measure stage

drainage basins dont recognize

boundaries

In most river basins in humid regions, discharge increases in a downstream direction. The Mississippi River is typical. It starts as many small brooks and grows to a mighty river pouring into the Gulf of Mexico. However, if a stream originates in a humid region and subsequently flows through an arid region, this relationship may change. High potential evapotranspiration rates in arid regions may cause dis

charge to decrease with distance downstream (Figure 11.9). Such a stream is an exotic stream (exotic means "of foreign origin").

several high drainage divides that are situated in the united states and canada/are extensive mountain and highland regions that separate drainage basins sending flows to the pacific, gulf of mexico, atlantic, hudson bay, or the arctic ocean

continental divides

During a flood, a river may carry an enormous sediment load as larger material is picked up and carried by the flow. As flood flows return to normal, stream energy is reduced and the sediment transport slows or stops. If the load (bed and suspended) exceeds a stream's capacity, sediment accumulates and the stream channel builds up through deposition—this is the process of aggradation. The general term for the clay, silt, sand, gravel, and mineral fragments deposited by running water is alluvium, which may be sorted or semisorted sediment on a floodplain, delta, or streambed.

d

Insolation and gravity power the hydrologic cycle and are the driving forces of fluvial systems. Individual streams vary greatly from one another, depending on the climate in which they operate, the composition of the surface, the topography over which they flow, the nature of vegetation and plant cover, and the length of time they have been operating in a specific setting.

d

Solution refers to the dissolved load of a stream, especially the chemical solution derived from minerals such as limestone or dolomite or from soluble salts. The main contributor of material in solution is chemical weathering. Sometimes the undesirable salt content that hinders human use of some rivers comes from dissolved rock formations and from springs in the stream channel; as an example, the San Juan and Little Colorado Rivers, which flow into the Colorado River near the Utah- Arizona border, add dissolved salts to the system

d

The amount of material carried by a stream depends on topographic relief, the nature of rock and soil through which the stream flows, climate, vegetation, and human activity in a drainage basin. Competence, which is a stream's ability to move particles of a specific size, is a function of stream velocity and the energy available to move materials. Capacity is the total possible load that a stream can transport. Four processes transport eroded materials: solution, suspension, saltation, and traction;

d

dams disrupt natural river discharge and sediment regimes, usually with detrimental effects on river systems. Glen Canyon Dam on the Colorado River near the Utah- Arizona border controls discharge and blocks sediment from flowing into the Grand Canyon downstream (see the map in Focus Study 6.1 and Figure 11.7). Consequently, over the years, the river's sediment supply was cut off, starving the river's beaches for sand, disrupting fisheries, and depleting backwater channels of nutrients.

d

l. Several major conduits export water from the Delaware River. Note the Delaware Aqueduct to New York City (in the north) and the Delaware and Raritan Canal (near Trenton). Several dams control flow releases, as their reservoirs provide storage for dry periods. Clearly, effective planning for this key water resource requires regional cooperation and careful spatial analysis of all variables within the drainage basin.

d

we can find river by length

d

80 percent of water in ocean is

deep zone

basin

defined by the divide

each drainage basin gathers and

delivers its precipitation and sediment to a larger basin

deltas

deposition of material carried by the river

divide

divides where water goes/water sheds

ridges that form drainage divides are the

dividing lines that control into which precipitation drains

This longshore current, or littoral current, depends on wind direction and resultant wave direction. A longshore current is generated only in the surf zone and works in combination with wave action to transport large amounts of sand, gravel, sediment, and debris along the shore as longshore drift, or littoral drift, the more comprehensive term. Particles on the beach also are moved along as beach drift, shifting back and forth between water and land with each swash and backwash of surf. Individual sediment grains trace arched paths along the beach. You have perhaps stood on a beach and heard the sound of myriad sand grains and seawater in the backwash of surf. These dislodged materials are available for transport and eventual deposition in coves and inlets and can represent a significant volume.

e An occasional wave that momentarily, but powerfully influences coastlines is the tsunami. Japanese for "harbor wave," tsunami is named for its devastating effect when its energy is focused in harbors. Revisit this chapter's opening photo and the photos in Figure 9.1 and in Figures 9.1.1 and Figure 9.1.2 in Focus Study 9.1, and this chapter's Geosystems Now, to see tsunami-related damage in Japan and the tsunami as it moves inland. Often, tsunami are reported incorrectly as "tidal waves," but they have no relation to the tides. Sudden, sharp motions in the seafloor, caused by earthquakes, submarine landslides, or eruptions of undersea volcanoes, produce tsunami. Thus, they properly are seismic sea waves

The effects of urbanization are quite dramatic, both increasing and hastening peak flow, as you can see by comparing preurban discharge (purple curve) and urbanized discharge (light blue) in Figure 11.11a. In fact, urban areas produce runoff patterns quite similar to those of deserts. The sealed surfaces of the city drastically reduce infiltration and soil-moisture recharge; their

effect is similar to that of the usually hard surfaces in the desert. A significant part of urban flooding occurs because impermeable surfaces produce shortened concentration times; peak flows may strike with little warning, as does a flash flood on a desert stream. These issues will intensify as urbanization of vulnerable areas continues.

The natural levees and elevated channel of the river prevent this yazoo tributary from joining the main channel, so it flows parallel to the river and through the backswamp area. The name comes from the Yazoo River in the southern part of the Mississippi floodplain. Humans have traditionally settled on floodplains for their flat topography, proximity to a water source, and fertile alluvial deposits for agriculture. Intensive agriculture occurs along the Nile River in Egypt, where annual flooding

enriches the soils with nutrients. However, floodplains that are covered with coarse sediment—sand and gravel—are less suitable for agriculture. As humans have built on floodplains, artificial flood protection and flood disaster assistance have become common. Government assistance may provide for the building of artificial levees on top of natural levees. Artificial levees do increase the capacity in the channel, but they also lead to even greater floods when they are overtopped by floodwaters. Levees can also fail

Dense ice comprises a glacier, formed from snow and water through a process of compaction, recrystallization, and growth. The essential input to a glacier is snow that accumulates in a snowfield, a glacier's accumulation zone (Figure 13.5a and c). Snowfields typically are at the highest elevation of an ice sheet or ice cap or at the head of a valley glacier, usually in a cirque. Avalanches from surrounding mountain slopes can add to the snowfield. As the snow accumulation deepens in sedimentarylike layers, the increasing thickness results in increased weight and pressure on underlying ice. Rain and summer snowmelt then contribute water, which stimulates further melting, and that meltwater seeps down into the snowfield and refreezes. Snow surviving the summer and into the following winter begins a slow transformation into glacial ice. Air spaces among ice crystals are pressed as snow packs to a greater density. The ice recrystallizes and consolidates under pressure. In a transition step to glacial ice, snow becomes firn, which has a compact, granular texture.

ense glacial ice is produced. Formation of glacial ice is analogous to metamorphic processes: Sediments (snow and firn) are pressured and recrystallized into a dense metamorphic rock (glacial ice). In Antarctica, glacial ice formation may take 1000 years because of the dryness of the climate (minimal snow input), whereas in wet climates, the time is reduced to several years because of rapid, constant snow input to the system.

cut bank

eriosional portion that takes place

waves cause force of

erosion

wind water and ice dislodge or dissolving or remove surface material in the process of:

erosion

two processes produce landforms:

erosive action of flowing water and depostion of stream-transported materials

water gets lost from

evaporization

Flood patterns in a drainage basin are as complex as the weather, for floods and weather are equally variable and both include a level of unpredictability. Measuring and analyzing the behavior of large watersheds and individual streams enables engineers and concerned parties to develop the best possible flood-management strategy. Unfortunately, reliable data often are not available for small basins or for the changing landscapes of urban areas. The key to flood avoidance or management is to possess extensive measurements of a stream's discharge and information on how it performs during a precipitation

event. Scientists hope that adequate funding to maintain such hydrologic monitoring by stream gaging networks will continue, for the data are essential to flood hazard assessment and proper planning. A flood is a high water flow that overflows the natural bank along any portion of a stream. Floods are rated statistically for the expected time intervals between them, based on historical data. Thus, you hear about "10-year floods," "50-year floods," and so on. A 10-year flood is likely to occur once every 10 years. This also means that a flood of this size has only a 10% likelihood of occurring in any one year and is likely to occur about 10 times each century. For any given floodplain, such a frequency indicates a moderate threat.

To have the lush rain forests in the same regions as soils poor in inorganic nutrients seems an irony. How ever, this forest system relies on the recycling of nutrients from soil organic matter to sustain fertility, although this nutrient recycling ability is quickly lost when the ecosystem is disturbed. Consequently, Oxisols have a diagnostic subsurface horizon that is highly weathered, contains iron and aluminum oxides, is at least 30 cm (12 in.) thick, and lies within 2 m (6.5 ft) of the surface (see Figure 14.10)

ever, this forest system relies on the recycling of nutrients from soil organic matter to sustain fertility, although this nutrient recycling ability is quickly lost when the ecosystem is disturbed. Consequently, Oxisols have a diagnostic subsurface horizon that is highly weathered, contains iron and aluminum oxides, is at least 30 cm (12 in.) thick, and lies within 2 m (6.5 ft) of the surface (see Figure 14.10) can be quarried in blocks and used as a building material (Figure 14.10c). Simple agricultural activities can be conducted with care in these soils. Early cultivation practices, called slash-and-burn shifting cultivation, were adapted to these soil conditions and formed a unique style of crop rotation. The scenario went like this: People in the tropics cut down (slashed) and burned the rain forest in small tracts and then cultivated the land using stick-and-hoe tools, planting maize, beans, and squash. Mineral nutrients in the organic material and short-lived fertilizer input from the fire ash were quickly exhausted. After several years, the soil lost fertility through leaching by intense rainfall, so the people shifted cultivation to another tract and repeated the process.

colorado river is an

exotic river

sheetflow

in any drainage basin, water moves downslope in sheetflow, or overland flow.

streams produce:

fluvial erosion, which supplies weathered sediment for transport to new locations where its laid down in a deposition process.

talus slope

formed by angular rock fragments that cascade down a slope along the base of a mountain; poorly sorted, cone-shaped deposits

The Pleistocene Epoch began in earnest 1.65 million years ago, and it still may be in progress. The Holocene Epoch began approximately 10,000 years ago, when average temperatures abruptly increased 6 C° (11 F°). The period we live in may represent an end to the Pleistocene, or it may be merely a mild interglacial time. Figure 13.27 details the climatic record of the past 20,000 years. Medieval Warm Period and Little Ice Age In a.d. 1001, Leif Eriksson inadvertently ventured onto the North American continent, perhaps the first European to do so. He and his fellow Vikings were favored by a medieval warming episode as they sailed the less-frozen North Atlantic to settle Iceland and Greenland. The mild climatic episode that lasted from about a.d. 800 to 1200 is known as the Medieval Warm Period. During the warmth, grape vineyards were planted far into England some 500 km (310 mi) north of present-day commercial plantings. Oats and barley were planted in Iceland, and wheat was planted as far north as Trondheim, Norway. The shift to warmer, wetter weather influenced migration and settlement northward in North America, Europe, and Asia.

from approximately 1200 to 1350 through 1800 to 1900, a Little Ice Age took place. Parts of the North Atlantic froze, and expanding glaciers blocked many key mountain passes in Europe. Snowlines in Europe lowered about 200 m (650 ft) in the coldest years. The Greenland colonies were deserted. Cropping patterns changed, and northern forests declined, along with human population in those regions. In the winter of 1779-1780, New York's Hudson and East Rivers and the entire Upper Bay froze over. People walked and hauled heavy loads across the ice between Staten and Manhattan Islands! Ice cores drilled in Greenland have revealed a record of annual snow and ice accumulation that, when correlated with other aspects of the core sample, was indicative of air temperature. In Figure 13.27, the consistent relative warmth of the Medieval Warm Period is evident, as is the Little Ice Age cold period. Reading the record of the Greenland ice cores, scientists have found many mild years among the colder conditions of the 700-year, somewhat inconsistent, Little Ice Age. More accurately, this was a time of rapid, short-term climate fluctuations that lasted only decades.

The U.S. soil classification system, first developed in 1975, is referred to as Soil Taxonomy. In addition to the 1975 Soil Taxonomy, information in this chapter is based on the publication Keys to Soil Taxonomy, now in its 11th edition (2010), available for free download from the NRCS at http://soils.usda.gov/technical/classification/tax_keys/. Soil properties and morphology (appearance, form, and structure) actually seen in the field are key to the Soil Taxonomy system. Thus, it is open to addition, change, and modification as the sampling database grows. For example, the system originally included 10 soil orders; Andisols (volcanic soils) were added in 1990 and Gelisols (cold and frozen soils) in 1998. The Soil Taxonomy recognizes the importance of interactions between humans and soils and the changes that humans have introduced, both purposely and inadvertently. The classification system divides soils into six categories, creating a hierarchical sorting system. Each soil series (the smallest, most detailed category) ideally includes only one polypedon, but may include portions continuous with adjoining polypedons in the field. In sequence

from smallest to largest categories, including the number of occurrences within each, the Soil Taxonomy recognizes soil series (15,000), soil families (6,000), soil subgroups (1,200), soil great groups (230), soil suborders (47), and soil orders (12)

slope and landform stability:

function of resistance of rock materials to the attack of denudation processes

77 percent of water is

glacial ice

The increased velocity often is masked by the apparent smooth, quiet flow of the water. Discharge also changes over time at any specific channel cross section, especially during periods of high flow. Figure 11.8 shows changes in the San Juan River channel in Utah that occurred during a flood. Greater discharge increases the velocity and therefore the capacity of the river to transport sediment as the flood progresses. As a result, the river's ability to scour materials from its bed is enhanced. You can see in Figure 11.8 that the San Juan River's channel was deepest on October 14, when floodwaters were highest (blue line plot). Then, as the discharge returned to normal on October 26, the kinetic energy of the river was reduced, and the bed again filled as sediment redeposited. The flood and scouring process moved a depth of about 3 m (10 ft) of sediment from this channel cross section. This type of channel adjustment occurs as the system continuously works toward equilibrium, in an effort to balance discharge and sediment load with channel form

h

Interfluve

high ground that separates one valley from another and directs sheetflow

tidal range

highest tide and lowest tide in a day

water is part of

hydrolic cycle

glacial

ice

glaciers melt in spring

in cnayons

alpine glacier

in mountain

endogenic processes build up and create:

initial landscapes,whereas exogenic processes work toward low relief, an ultimate condition of low change, and the stability of sequential landscapes.

dissolve load

ions dissolved in a stream's water

When rainfall occurs in some portion of the watershed, the runoff collects and is concentrated in streams and tributaries. The amount, location, and duration of the rainfall episode determine the peak f low. Also important is the nature of the surface in a watershed, whether permeable or impermeable. A hydrograph for a specific portion of a stream changes after disturbance, such as a forest fire or urbanization of the watershed.

k

body of water surrounded by land

lake

nature without humans creates a natural

landscape

tidal wave/tsunami

large destructive wave caused by earthquakes or strong waves

Soil porosity, permeability, and moisture storage were discussed in Chapter 6. Pores in the soil horizon control the movement of water—its intake, flow, and drainage—and air ventilation. Important porosity factors are pore size, pore continuity (whether pores are interconnected), pore shape (whether pores are spherical, irregular, or tubular), pore orientation (whether pore spaces are vertical, horizontal, or random), and pore location (whether pores are within or between soil peds). Porosity is improved by the biotic actions of plant roots, animal activity such as the tunneling of gophers or worms, and human intervention through soil manipulation (plowing, adding humus or sand, or planting soil-building crops). Much of the soil preparation work done before planting by farmers—and by home gardeners as well—is done to improve soil porosity

large pore spaces have drained of gravitational water. Soil type determines field capacity. The depth to which a plant sends its roots determines the amount of soil moisture to which the plant has access. If soil moisture is removed below field capacity, plants must exert increased energy to obtain available water. This moisture removal inefficiency worsens until the plant reaches its wilting point. Beyond this point, plants are unable to extract the water they need, and they die. Soil moisture regimes and their associated climate types shape the biotic and abiotic properties of the soil more than any other factor. The NRCS Keys to Soil Taxonomy, discussed later in this chapter, recognizes five soil moisture regimes based on Thornthwaite's waterbalance principles (Chapter 6), ranging from constantly wet ("Aquic regime") to dry ("Xeric regime").

continental divide

line that separates rivers that flow toward opposite ends of the continent

no solution load in material

load

suspended load

load that tends to float

valleys, plains, or other lowpoints determine the

local base level.

niall river is

longest

alunium

material that is transported away

Discharge varies throughout the year for most streams, depending on precipitation and temperature. Rivers and streams in arid and semiarid regions may have perennial, ephemeral, or intermittent discharge. Perennial streams flow all year, fed by snowmelt, rainfall, or groundwater, often in some combination. Ephemeral streams flow only after precipitation events and are not connected to groundwater systems. Years may pass between flow events in these usually dry stream channels. Intermittent streams flow for several weeks or months each year and may have some groundwater inputs. Fluvial processes in deserts are

most often characterized by such intermittent running water, with hard, poorly vegetated surfaces of thin soils yielding high runoff during rainstorms. A rare or large precipitation event in a desert can fill a stream channel with a torrent known as a flash flood. These channels may fill in a few minutes and surge briefly during and after a storm

Political changes in Europe in 1989 allowed the first scientific analysis of the entire river system. The United Nations Environment Programme (UNEP) and the European Union, along with other organizations, are dedicated to clearing the Danube, saving the deltaic ecosystems, and restoring the environment of this valuable resource; see

n

Salt marshes usually form in estuaries and behind barrier beaches and spits. An accumulation of mud produces a site for the growth of halophytic (salt-tolerant) plants. This vegetation then traps additional alluvial sediments and adds to the salt marsh area. Because salt marshes are in the intertidal zone (between the farthest reaches of high and low tides), sinuous, branching channels are produced as tidal waters flood into and ebb from the marsh (Figure 12.20). Sediment accumulation on tropical coastlines provides the site for mangrove trees, shrubs, and other small trees. The prop roots of the mangrove are constantly finding

new anchorages. The roots are visible above the waterline, but reach below the water surface, providing a habitat for a multitude of specialized life forms (Figure 12.21). Mangrove swamps often secure and fix enough material to form islands

when 2 cut banks come together, they create a

new path

water wants to find its way back to the

ocean

1/5 of all water flowing is in

one river alone

rills

orgiinal collection of water to form gullies

In soil science, the term consistence is used to describe the consistency of a soil or cohesion of its particles. Consistence is a product of texture (particle size) and structure (ped shape). Consistence reflects a soil's resistance to breaking and manipulation under varying moisture conditions: ■ A wet soil is sticky between the thumb and forefinger, ranging from a little adherence to either finger, to sticking to both fingers, to stretching when the fingers are moved apart. Plasticity, the quality of being moldable, is roughly measured by rolling a

piece of soil between your fingers and thumb to see whether it rolls into a thin strand. ■ A moist soil is filled to about half of field capacity (the usable water capacity of soil), and its consistence grades from loose (noncoherent), to friable (easily pulverized), to firm (not crushable between the thumb and forefinger). ■ A dry soil is typically brittle and rigid, with consistence ranging from loose, to soft, to hard, to extremely hard.

100 year storm

preparing for storms to stay safe

river drains 9 different

r

The deposition of glacial sediment produces a specific landform, a moraine. Several types of moraines are associated with alpine glaciation. A lateral moraine forms along each side of a glacier (Figure 13.13). If two glaciers with lateral moraines join, a medial moraine may form (see Figures 13.1 and 13.5e and f ). Other moraines are associated with both alpine and continental glaciation. Eroded debris that is dropped at the glacier's farthest extent is a terminal moraine. End moraines may also be present, formed at other points where a glacier paused after reaching a new equilibrium between accumulation and ablation. In landscapes of continental glaciation, moraines are much larger in scale. A deposition of till that is generally spread across a surface is a ground moraine, or till plain, and may hide the former landscape. Such plains are found in portions of the U.S. Midwest. All of these till types are unsorted and unstratified. In contrast, streams of glacial meltwater can carry and deposit sorted and stratified glacial drift beyond a terminal moraine. Meltwater-deposited material downvalley from a glacier is a valley train deposit. Peyto Glacier in Alberta, Canada, produces such a valley train that continues into Peyto Lake (Figure 13.14). Distributary stream channels appear braided across its surface. The photo also shows the milky meltwater associated with glaciers, laden with finely ground "rock flour." Meltwater comes from glaciers at all times, not just when they are retreating. The Peyto Glacier (far left in photo) has experienced massive ice losses since 1966 and is in retreat due to increased ablation and decreased accumulation related to climate change.

r. A till plain forms behind an end moraine; it features unstratified coarse till, has low and rolling relief, and has a deranged drainage pattern (Figure 13.15b; see also Figure 11.6g). Beyond the morainal deposits lies the outwash plain of stratified drift featuring stream channels that are meltwater-fed, braided, and overloaded with sorted and deposited materials. A sinuously curving, narrow ridge of coarse sand and gravel is an esker. It forms along the channel of a meltwater stream that flows beneath a glacier, in an ice tunnel, or between ice walls. As a glacier retreats, the steep-sided esker is left behind in a pattern roughly parallel to the path of the glacier. The ridge may not be continuous and in places may even appear to be branched, following the path set by the subglacial watercourse. Commercially valuable deposits of sand and gravel are quarried from some eskers.

surface runoffs concentrate in

rills, or small scale downhill grooves. which may develop into gullies

flufial process

running water in streams (dominates where rainfall is prevalent)

Fluvial (water)

running water, erosional forces

A graph of stream discharge over time for a specific location is a hydrograph. The time scale of a hydrograph is key; for example, annual hydrographs often show the highest discharge occurring during the spring snowmelt season. Storm hydrographs may cover only a period of days, often reflecting changes in discharge resulting from precipitation events, such as flash floods. The hydrograph in Figure 11.11a shows the relation between precipitation input (the bar graph) and stream discharge (the curves). During dry periods, the low discharge is described as base f low and is largely maintained by input from local groundwater (dark blue line).

s

A mass of water positioned above base level in a stream has potential energy. As the water flows downslope, or downstream, under the influence of gravity, this energy becomes kinetic energy. The rate of this conversion from potential to kinetic energy determines the ability of a stream to do geomorphic work, and this depends in part on the volume of water involved. Discharge, or the stream's volume of flow per unit of time, is calculated by multiplying three variables for a specific cross section of the channel

s

A primary feature of any drainage basin is its drainage density, determined by dividing the total length of all stream channels in the basin by the area of the basin. The number and length of channels in a given area reflect the landscape's regional geology and topography.

s

Change that occurs in any portion of a drainage basin can affect the entire system. The stream adjusts to carry the appropriate load of sediment relative to its discharge. If a stream is brought to a threshold where it can no longer maintain its present form, the river system may become destabilized, initiating a transition period to a more stable condition. A river system constantly struggles toward equilibrium among the interacting variables of discharge, sediment load, channel shape, and channel steepness, all of which are discussed in the chapter ahead.

s

Earth's rivers and waterways form vast arterial networks that drain the continents. Rivers are Earth's lifeblood, inasmuch as rivers redistribute mineral nutrients important for soil formation and plant growth and serve society in many ways. They also shape the landscape by removing the products of weathering, mass movement, and erosion and transporting them downstream.

s

In fluvial systems, water dislodges, dissolves, or removes surface material in the process of erosion. Streams produce f luvial erosion, in which weathered sediment is picked up for transport to new locations. Materials are laid down by another process, deposition.

s

Occasionally, drainage patterns occur that are discordant with the landscape through which they flow. For example, a drainage system may flow in apparent conflict with older, buried structures that have been uncovered by erosion, so that the streams appear to be superimposed. Where an existing stream flows as rocks are uplifted, the stream keeps its original course, cutting into the rock in a pattern contrary to its structure. Such a stream is a superposed stream (the stream cuts across weak and resistant rocks alike). A few examples include Wills Creek, cutting a water gap through Haystack Mountain at Cumberland, Maryland; the Columbia River through the Cascade Mountains of Washington; and the River Arun, which cuts across the Himalayas.

s

Ridges form drainage divides that define the catchment (water-receiving) area of every drainage basin. That is, the ridges are the dividing lines that control into which basin runoff water from precipitation drains

s

Rivers provide us with essential water supplies; receive, dilute, and transport wastes; provide critical cooling water for industry; and form one of the world's most important transportation networks. Rivers have been significant throughout human history. Each devastating flood event, such as the August 2010 catastrophe that drowned large areas of Pakistan along the Indus River, demonstrates the interrelationship between rivers and society

s

Stream gradient may be affected by tectonic uplift of the landscape, which changes the elevation of the stream relative to its base level. If tectonic forces slowly lift the landscape, the stream gradient will increase, stimulating renewed erosional activity. A meandering stream flowing through the uplifted landscape becomes rejuvenated; that is, the river actively returns to downcutting and can eventually form entrenched meanders in the landscape

s

Streams are a mixture of water and solids. Fluvial landscapes are the result of the ongoing erosion, transport, and deposition of materials in a downstream direction. The energy of a stream to accomplish this geomorphic work depends on a number of factors, including base level and stream discharge

s

The Danube River in Europe, which flows 2850 km (1770 mi) from western Germany's Black Forest to the Black Sea, exemplifies the complexity of an international drainage basin. The river crosses or forms the borders between nine countries (Figure 11.4). A total area of 817,000 km2 (315,000 mi2) falls within the drainage basin, including some 300 tributaries

s

The Delaware River basin, within the Atlantic Ocean drainage region, is a critical water resource for the entire region (Figure 11.5). The Delaware River headwaters are in the Catskill Mountains of New York. This basin encompasses 33,060 km2 (12,890 mi2) and includes parts of five states along the river's length, 595 km (370 mi) from its headwaters to its mouth. The river system ends at Delaware Bay, which eventually enters the Atlantic Ocean. Topography varies from low-relief coastal plains to the Appalachian Mountains in the north

s

The ongoing interaction between erosion and deposition in a river system produces fluvial landscapes. These processes are affected by discharge and channel slope. Running water is an important erosional force; in fact, in desert landscapes it is the most significant agent of erosion, greater than wind, even though precipitation events are infrequent.

s

s Drainage basins such as the Mississippi are open systems. Inputs include precipitation and the minerals and rocks of the regional geology. Energy and materials are redistributed as the stream constantly adjusts to its landscape. System outputs of water and sediment disperse through the mouth of the river, into a lake, another river, or the ocean

s

At the heart of the Soil Taxonomy are 12 general soil orders, listed in Table 14.1 Their worldwide distribution is shown in Figure 14.9 and in individual maps with each description. Please consult this table and these maps as you read the following descriptions. Because the Soil Taxonomy evaluates each soil order on its own characteristics, there is no priority to the classification. However, you will find a progression in this discussion, for the 12 orders are arranged loosely by latitude; we begin, as in Chapters 7 (climates) and 16 (terrestrial biomes), along the equator.

s The intense moisture, high temperature, and uniform daylength of equatorial latitudes profoundly affect soils. These generally old landscapes, exposed to tropical conditions for millennia or hundreds of millennia, are deeply developed. Soil minerals are highly altered (except in certain newer volcanic soils in Indonesia—the Andisols). Oxisols are among the most mature soils on Earth. Distinct horizons usually are lacking where these soils are well drained (Figure 14.10a on page 458). Related vegetation is the luxuriant and diverse tropical and equatorial rain forest. Oxisols (tropical soils) are named because they have a distinctive horizon of iron and aluminum oxides. The concentration of oxides results from heavy precipitation, which leaches soluble minerals and soil constituents from the A horizon. Typical Oxisols are reddish (from the iron oxide) or yellowish (from the aluminum oxides), with a weathered claylike texture, sometimes in a granular soil structure that is easily broken apart. The high degree of eluviation removes basic cations and colloidal material to lower illuviated horizons. Thus, Oxisols are low in CEC and fertility, except in regions augmented by alluvial or volcanic materials.

35 part per blank

salitity of water

97 percent of water is

salt

With excess sediment, a stream might become a maze of interconnected channels that form a braided stream pattern (Figure 11.14). Braiding often occurs when reduced discharge lowers a stream's transporting ability such as after flooding, or when a landslide occurs upstream, or when load increases where weak banks of

sand or gravel exist. Braided rivers commonly occur in glacial environments, which have abundant supplies of sediment and steep channel slopes, as is the case with the Brahmaputra River in Tibet (Figure 11.14). Glacial action and erosion produced the materials that exceed stream capacity in this river channel.

movement in air creates

sanddunes

Hydrology:

science of water and its global circulation, distribution, and properties (specifically water at and below earths surface)

not every landscape degraded down to

sea level/other bases seemed to be in operation.

bed load

sediment that is carried by a stream along the bottom of its channel

pacific ocean (largest), atlantic ocean (2nd), indian ocean (3rd), arctic ocean

size of these oceans (principal oceans)

wave generating region

stormy area at sea of large wave trains

Every stream has a degree of inclination or gradient, which is the decline in elevation from its headwaters to its mouth. A stream's gradient generally forms a concaveshaped slope (Figure 11.18). Characteristically, the longitudinal profile of a stream (a side view) has a steeper slope upstream and a more gradual slope downstream. This curve assumes its shape for complex reasons related to the stream's ability to do enough work to accomplish the transport of the load it receives. Streams tend to adjust their gradient and other channel characteristics so that they can move the sediment

supply. A graded stream condition occurs when channels adjust their slope, size, and shape so that a stream has just enough energy to transport its sediment load. Over a period of years, slope is delicately adjusted to provide, with available discharge and with prevailing channel characteristics, just the velocity required for transportation of the load supplied from the drainage basin.* This condition is a state of dynamic equilibrium among discharge, sediment load, and channel form. The stream, channel, and landscape work together to maintain this balance within a drainage basin. Both high-gradient and low-gradient streams can achieve a graded condition. A stream's profile tells geographers about characteristics of slope, discharge, and load. Attainment of a graded condition does not mean that the stream is at its lowest gradient, but rather that it has reached a balance among erosion, transportation, and deposition over time along a specific portion of the stream. One problem with applying the graded stream concept is that an individual stream can have both graded and ungraded portions. It may have graded sections without having an overall graded slope. In fact, variations and interruptions are the rule rather than the exception.

deflation

taking material up and taking away

Salinity

the amount of salt in water

drainage pattern

the arrangement of channels in an area. Patterns are quite distinctive and are determined by a combination of regional steepness, variable rock resistance, variable climate, variable hydrology, relief of the land, and structural controls imposed by the underlying rocks. Consequently, the drainage pattern of any land area on Earth is a remarkable visual summary of every characteristic—geologic and climatic—of that region.

Approximately 11,000 stream gaging stations are in use in the United States (an average of more than 200 per state). Of these, 7000 are operated by the U.S. Geological Survey and have continuous recorders for stage and discharge (see http://pubs.usgs.gov/circ/circ1123/). Many of

these stations automatically send telemetry data to satellites, from which information is retransmitted to regional centers (Figure 11.10b and c). The historic gaging station on the Colorado River at Lees Ferry, just south of Glen Canyon Dam, was established in 1921 (Figure 11.10d).

water responds to gravitational pool

tides

2 high tides and 2 low tides in

time period

abrasion

to wear down

amazon river is most with

volume

ocean

waves

fluvial processes

water

water sheds collect

water

a stream is a mixture of:

water and solids, which are carried in solution, in suspension, and by mechanical transport

universal solvent

water is

fluvial

water that runs on streams

Exotic water

water which originates in a wet region then flows through a dry region

drainage divides define a

watershed, the catchment area of the drainage basin

artifical

we create them by creating a damn

eiolian

wind

waves are created by

wind

aviolium

wind shaping landscapes (dominates areas where there is not rainfall)

Salitity

word for salty

amazon river is largest in

world

A stream's erosional turbulence and abrasion carve and shape the landscape through which it flows. Hydraulic action is the work of flowing water alone. Running water causes hydraulic squeeze-and-release action that loosens and lifts rocks. As this debris moves along, it mechanically erodes the streambed further through the process of abrasion, with rock particles grinding and carving the streambed like liquid sandpaper

x

Milankovitch calculated, without the aid of today's computers, that the interaction of these Earth-Sun relations creates a 96,000-year climatic cycle. His glaciation model assumes that changes in astronomical relations affect the amounts of insolation received. Milankovitch died in 1954, his ideas still not accepted by a skeptical scientific community. Now, in the era of computers, remote-sensing satellites, and worldwide efforts to decipher past climates, Milankovitch's valuable work has stimulated research to explain climatic cycles and has experienced some confirmation. A roughly 100,000-year climatic cycle is confirmed in such diverse places as ice cores from Greenland and Antarctica and the accumulation of sediment in Lake Baykal, Siberia. Milankovitch cycles appear to be the primary cause of glacial-interglacial cycles, although other factors, such as changes in the North Atlantic Ocean, gains or losses of Arctic sea ice, and variable carbon dioxide levels, cause second-order effects.

y If the Sun significantly varies its output over the years, as some other stars do, that variation would seem a convenient and plausible cause of ice-age timing. However, lack of evidence that the Sun's radiation output varies significantly over long cycles argues against this hypothesis. Nonetheless, inquiry about the Sun's variability continues. As we saw in Chapter 7, in the Intergovernmental Panel on Climate Change Fourth Assessment Report in Figure 7.26, solar variability is not

it appears that water is migrating in the direction of wave travel, but only a slight amount of water is actually advancing. It is the wave energy that is moving through the flexible medium of water. Water within a wave in the open ocean is simply transferring energy from molecule to molecule in simple cyclic undulations; these are waves of transition (Figure 12.8). Individual water particles move forward only slightly, forming a vertically circular pattern.

y slightly, forming a vertically circular pattern. The diameter of the paths formed by the orbiting water particles decreases with depth. As a deep-ocean wave approaches the shoreline and enters shallower water (10-20 m, or 30-65 ft), the orbiting water particles are vertically restricted. This restriction causes more-elliptical, flattened orbits to form near the bottom. This change from circular to elliptical orbits slows the entire wave, although more waves continue arriving. The result is closer-spaced waves, growing in height and steepness, with sharper wave crests. As the crest of each wave rises, a point is reached when its height exceeds its vertical stability, and the wave falls into a characteristic breaker, crashing onto the beach (Figure 12.8b). In a breaker, the orbital motion of transition gives way to elliptical waves of translation, in which both energy and water move toward shore. The slope of the shore determines wave style. Plunging breakers indicate a steep bottom profile, whereas spilling breakers indicate a gentle, shallow bottom profile. In some areas, unexpected high waves can arise suddenly. Learning to recognize severe wave conditions is a good idea before you venture along the shore in these areas.

165-330 feet of soil being lots per

year