Geography 1000 Ch 14
adobe
sun-dried mud brick
factor that influences the amount or pattern of weathering
the relative resistance of different kinds of rock at an outcrop. Some rocks are simply harder than others and are thus more resistant to weathering and erosion.
chemical weathering processes
(oxidation, carbonation, hydrolysis) The decomposition and alteration of rocks due to chemical actions of natural physical and biological processes. This decomposition occurs through the interaction of air, water, biological processes, and rock minerals in various ways. The decomposition and alteration of rocks due to chemical actions of natural physical and biological processes.
Earthflow
A slow‐to‐rapid type of mass movement that involves soil and other loose sediments, some of which may be coarse.
Clean Air Act of 1970
Before the first federal regulatory controls on air quality were passed in 1970, the amount of pollutants emitted into the air had risen steadily since the onset of the Industrial Revolution in the 19th century. These emissions peaked at 28.8 million tons in 1973 in the United States alone. Given growing concerns about acid rain in the 1970s and 1980s, the Clean Air Act was amended in 1990 to give industries more pollution control options such as switching to low‐sulfur coal or adding scrubbers to control acid emissions. In more extreme cases, plants were ordered closed because they could not comply. The 1990 amendments clearly had a positive effect on acid emissions, with a 32% decrease to about 18 million tons in 1995. By 2010 the amount had dropped to about 11 million tons.
calcite
Calcium Carbonate (CaCO3)
(limestone) chalk
Composed mostly of calcium carbonate with minor amounts of silt and clay. Chalky, white.
Colluvium
Unconsolidated sediment that accumulates at the base of a slope.
Limestone - Sedimentary
Forms in warm, shallow seas. May be composed of the remains of sea creatures. Calcium carbonate is the main mineral. Fizzes in the presence of Hydrochloric Acid. With these rock masses, the dolomite units are typically more resistant than chalky rocks, which sometimes dissolve easily due to the chemical interactions discussed in
Quartz
Silicate
acid rain cntd
Subsequently, they are deposited on the surface of Earth through precipitation or within fog. In these downwind areas the pH of rainfall is about 4, whereas it is generally above 5 in the western half of the country. Similar patterns have been identified in other parts of the world, particularly eastern Europe. The impact of acid rain on the landscape and as a weathering agent has been significant. With respect to chemical weathering, acid rain dramatically accelerates the weathering process. Although some of this weathering would have naturally occurred by carbonation, it has been enhanced by acid rain. In addition to the acceleration of chemical weathering, acid rain is also associated with several negative environmental impacts especially on forests and lakes.
Shearing strength
The ability to resist applied parallel or tangential to a face of a material, as opposed to a normal stress which is applied perpendicularly, e.g. scissors.
soil creep
The gradual downhill movement of soil, trees, and rocks due to the force of gravity. The slowest mass‐wasting process is appropriately called this. This occurs on virtually every soil‐covered slope, as the persistent force of gravity slowly pulls surface particles downhill. In this fashion, the soil behaves as a plastic substance that is gradually molded over time. This process is enhanced by cycles of wetting, drying, freezing, and thawing in the soil, as well as by disturbances caused by burrowing animals and even people. The net result of soil creep is that the angles of hillslopes and the elevation of hilltops slowly decrease over time.
Regolith
The layer of unconsolidated rocky material covering bedrock.
Kiva
a round room used by the Pueblo peoples for religious ceremonies
Kaolinite
a white to cream-colored clay produced by the weathering of feldspar
Humans have increased the amount of chemical weathering downwind of industrial cities through the process of? And that is composed of what (x 2)?
acid rain. Most of these acids come in the form of sulfur dioxide and nitrogen oxides derived from coal‐burning power plants.
differential weathering
is the pattern that results with long-term weathering of rock outcrops with variability. Important factor influencing the amount or pattern of weathering is the relative resistance of different kinds of rock at an outcrop Some rock types are harder and more resistant Some rocks have more resistant or less resistant parts due to variations in firmness of cementing materials, known as differential cementation
Half Dome -granite monoliths
large exfoliation dome The most famous of these landforms which towers over the adjacent Yosemite Valley (Figure 14.9b).
Hydrolysis
A chemical weathering process that results in the decomposition of silicate molecules within rock through the reaction of hydrogen and hydroxyl ions in water. Water is very important as a weathering agent because of its ability to dissolve minerals. As a result, chemical weathering is typically more active in warm, humid environments. a weathering process that decomposes silicate minerals within rocks. This form of weathering occurs when silicate molecules are split after the addition of hydrogen and hydroxyl ions derived from water. In granitic rocks, for example, hydrolysis causes feldspars to weather into clays, such as kaolinite and silica, which may be subsequently washed or blown away and deposited somewhere in a soil or stream system. If a sufficient amount of clay is removed in this fashion, more resistant quartz grains are exposed and, with further weathering, liberated from the host rock, to be transported by a stream or perhaps blown into sand dunes.
Joint
A crack or fissure along horizontal or vertical planes in a rock mass that divides the rock into large blocks. can form when rock repeatedly expands and contracts with heating and cooling, respectively, causing fractures to develop along horizontal and vertical planes that essentially break the rock into large blocks. can also form due to regional tectonic forces that produce stress within the rock mass. Although they're features may look like faults, they are not because no relative vertical or horizontal movement is occurring on either side of the fracture.
Madison Slide
A debris slide which occurred in Montana near Yellowstone National Park on August 17, 1959 when a magnitude 7.1 earthquake rocked the region late in the evening for about 30 sec. This earthquake initiated a massive landslide (Figure 14.20) on a mountain that borders the Madison River, which flows through the area. Approximately 28 million m3 (37 million yd3) of rock was instantly detached from the mountain in an area that measured about 600 m (about 2000 ft) in length and 300 m (about 980 ft) in thickness. During the ensuing landslide, the rock mass slid down the mountain slope, crossed the Madison River, and, in the process, killed 28 people who had been camping in the vicinity. The landslide was so large that it dammed the Madison River, creating a new lake, now known as Earthquake Lake, which is nearly 100 m (330 ft) deep.
Oxidation
A form of chemical weathering in which oxygen chemically combines with metallic iron to form iron oxides, resulting in the loss of electrons. A chemical change in which a substance combines with oxygen, as when iron oxidizes, forming rust
Solifluction
A form of soil creep that occurs in arctic environments where freeze‐thaw processes result in lobes of soil moving gradually downslope.. the slow, downslope flow of soil saturated with water in areas surrounding glaciers at high elevations. (meaning "soil flowage"), which occurs above the tree line in tundra landscapes. This process is very straightforward and involves the impact of seasonal temperature changes on the landscape. Most of the year, the soil is frozen from the surface to some depth. During the short summer months, the upper part of the soil thaws. Water within this part of the soil (the active layer) cannot percolate very deeply, however, because the sediment beneath it is continuously frozen as permafrost. As a result, the overlying (unfrozen) soil becomes saturated and slowly sags downhill in a very uneven way, producing distinct lobes that overlap one another
avalanche
A large mass of snow or rock that suddenly slides down a mountainside. These steep‐angled snow deposits can become unstable when a subsequent large storm produces another layer of snow of lighter density than the snow it buries. Under these conditions, an avalanche will occur because the two layers of snow are not firmly bound together to form a uniform mass. When the uppermost layer is somehow destabilized, a section will break free as a slab avalanche. Such an avalanche may release over 225 million m3 (~300 million yd3) of snow, which is equivalent to about 20 football fields covered with about 3 m (10 ft) of snow.
Slump
A mass‐wasting process in which rock and sediment rotate and move down the slope along a concave plane relative to the surface. In contrast to debris slides, which flow parallel to the surface, these occur when rock and sediment rotate and move down the slope along a concave plane relative to the surface. They typically occur when impermeable clay‐rich deposits such as shale underlie more porous rock or sediment. Under such circumstances, water will flow through the upper deposits and then parallel to the clay surface upon encountering it. This water lubricates the contact between the rock layers and thus reduces frictional force, causing the rock and sediment mass to rotate as it slides down the hill.
Rockfall
A mass‐wasting process in which rocks break free from cliff faces and rapidly tumble into the valley below.. occurs when rocks or rock fragments fall freely through the air; common on steep slopes. most common in places where extensive rock outcrops occur on steep hillslopes or canyon walls. Frost wedging and large temperature changes contribute significantly to this because these processes gradually split outcropping rocks apart from one another. Eventually, the gravity threshold is passed and stones and boulders break free to fall onto the lower part of the hillslope. This also occurs in association with differential weathering in places where relatively resistant rocks such as limestone and sandstone overlie softer rocks like shale. In these situations, the shale surfaces gradually retreat into the cliff through a combination of weathering and erosion, leaving the resistant rock as a ledge that juts out over the shale. Sooner or later the force of gravity exceeds the strength of the rock and it collapses. This process is very common in places like the Grand Canyon.
debris slide
A mass‐wasting process in which slope failure occurs along a plane that is roughly parallel to the surface. occurs when slope failure occurs along a plane that is roughly parallel to the surface.
talus slope
A pile of rock fragments and boulders that accumulates below a cliff due to rockfall. formed by angular rock fragments that cascade down a slope along the base of a mountain; poorly sorted, cone-shaped deposits
debris flow
A rapidly flowing and extremely powerful mass of water, rocks, sediment, boulders, and trees. are very serious natural hazards that can impact people catastrophically. An unfortunate example was a massive one swept down a steep hillslope into the coastal community of La Conchita, California, in January 2005 (Figure 14.23). This one was triggered by a three‐day storm that produced nearly 25 cm (10 in.) of rain in the region. The slopes above La Conchita consist of ancient ones and landslide deposits that had failed to a smaller extent in 1995 when a large slump destroyed nine homes and blocked a county road. When these deposits became saturated again in early 2005, they failed on a much larger scale, releasing approximately 14,000 m3 (18,311 yd3) of material that flowed more than 100 m (330 ft) into the community. This one destroyed 13 homes and killed ten people. Given that slope failures frequently occur in California during winter.
Carbonation weathering
A type of chemical weathering caused by rainwater that has absorbed atmospheric carbon dioxide and formed a weak carbonic acid that slowly dissolves rock. (because carbon is reacting with minerals) and occurs because carbon dioxide is easily dissolved by atmospheric water vapor, forming carbonic acid. Weathering of limestone and chalk by acidic rainwater (NOT acid rain). As a result, precipitation contains this carbonic acid, which is sufficiently acidic to dissolve many minerals, especially limestone (calcium carbonate). When rainfall collects on the rock surface, it dissolves the limestone and forms pits and rounded surfaces (Figure 14.12). If you are interested in your local weathering rates, visit a cemetery and compare the decomposition in limestone versus marble or slate tombstones. Because marble and slate are much more resistant than limestone to weathering, the difference can be dramatic.
Caprock
A unit of relatively resistant rock that caps the top of a landform and thus protects underlying rocks from erosion. A more resistant rock layer overlies a less resistant layer, it protects the underlying rock somewhat from erosion.
Mudflow
A well‐saturated and highly fluid mass of fine‐textured sediment. is very similar to an earthflow, it differs because it consists of fine‐textured sediments and is extremely fluid; thus, it moves more quickly. These are most frequently associated with steep canyons in mountainous regions and are initiated in humid zones when heavy rains fall on already saturated slopes. In arid zones, they occur when heavy rains fall on hillslopes that are unprotected by vegetation. Regardless of the environment, these start when large volumes of water begin to run directly off the surface down the canyon. As the water flows, it picks up increasing amounts of mud from the underlying soil, resulting in a thick, viscous flow of water‐laden sediment that has tremendous power. In large their power is so great that large boulders are frequently transported great distances and human structures such as homes and bridges can be destroyed. Once they reach the valley, it often spreads out across the landscape.
Mancos Shale
Although the history of the Pueblo extends back several thousand years, perhaps the most distinctive period occurred between about a.d. 1100 and 1300 when they built elaborate villages in canyon walls throughout much of the region. The niches in which the dwellings were constructed occur within the thick sandstones of the Mesa Verde Group, which overlies the relatively impermeable . This rock sequence is very much like the one shown in Figure 14.8 and is the perfect setup for salt-crystal growth and niche formation.
Dolomite
An anhydrous carbonate mineral composed of calcium magnesium carbonate, ideally CaMg(CO₃)₂. The term is also used for a sedimentary carbonate rock composed mostly of the mineral dolomite. An alternative name sometimes used for the dolomitic rock type is dolostone. (Wikipedia)
landslide
An instantaneous movement of soil and bedrock down a steep slope in response to gravity, triggered by an event such as an earthquake. or period of heavy rain causes the downward force of gravity to overcome the sediment's cohesiveness and internal friction. Slope shear strength depends on the frictional resistance and overall cohesion of the underlying sediment. When slope shear strength is reduced for some reason, a portion of a hillslope can move downhill at a rapid rate, either as a debris slide or a slump.
salt‐crystal growth
Another kind of physical weathering process, which involves the buildup of salts on rock surfaces. Salt is a dispersing agent, and its concentration subsequently causes the minerals that cement the sediment grains within the rock to weaken their bonds; this, in turn, loosens sediment so that it can then be eroded. This process is similar to frost action in that it requires the presence of water moving within rock. A weathering process involving the buildup of salts on rock surfaces through evaporation. These salts weaken the cement that bonds rock particles, allowing them later to be washed or blown away.
Unloading
Another way in which rock physically weathers. occurs when deep rocks are slowly uncovered because overlying rock gradually erodes off of them.
salt‐crystal growth cntd
As a result of this evaporation, salts build up on the rock surface at the contact between the sandstone and shale. This high concentration of salts dissolves the cementing mineral bonds, which, in turn, causes the sand grains within the rock to separate slowly from one another. These loosened grains are then washed or blown away by the water or wind, forming a niche at the contact between the two rock types. Although salt‐crystal growth is a small‐scale process, it has contributed greatly to the evolution of landscapes in the canyons of the desert Southwest by creating large niches and cave‐like recesses in cliff walls.
acid rain's effect on forests and lakes
Forests that lie within the belt of acid precipitation are often stressed (Figure 14.13). This stress occurs in part because supporting soils are acidified, which accelerates the leaching of nutrient cations before the trees absorb them. Evidence also exists that acid deposition on the needle leaves of conifers reduces their tolerance to cold. Similarly, the pH of lakes and ponds can be lowered due to acid rain, causing stress to the plants and animals that live within those water bodies. Many lakes in New England, for example, do not support fish because they contain toxic levels of inorganic acids.
Exfoliation
Form of physical weathering in which sheets of rock flake away due to seasonal temperature changes or by the expansion of the rock due to unloading. Although unloading may be the dominant cause of exfoliation, the process is probably enhanced by daily and seasonal temperature cycles that cause the rock to expand and contract. pg 328 is most active in igneous and metamorphic rocks, but also occurs in some sedimentary rocks. A great place to see exfoliation on a large scale is Yosemite National Park in California, where several large exfoliation domes occur in granite monoliths.
Local relief (hot/humid)
In relatively humid areas, the solid core is mantled by regolith, which, if you recall, is formed when rock is weathered.
mass wasting (mass movement)
Movement of rock, sediment, and soil downslope due to the force of gravity. The effect of gravity and the role it plays in landscape evolution by moving large volumes of sediment through the process. when the downward force of gravity overcomes the resisting force of the slope material's shearing strength—in other words, its cohesiveness and internal friction. The point at which sediment becomes unstable is called the threshold point and depends a great deal on the material's angle of repose. This angle is the natural maximum slope that any deposit of a particular kind of sediment—for example, sand—can achieve without moving under the force of gravity. The angle of repose ranges between about 25° for fine sands and approximately 40° for angular pebbles and cobbles. You can see these relationships when you see piles of sediment deposited at construction sites or sand and gravel quarries. After the sediment is dumped, its slope naturally moves to the angle of repose (Figure 14.14).
Felsenmeer
Once joints develop, they allow water to flow deeper into the rock mass at different points. If the rock body lies in a region that has distinct winter and summer seasons, the water will tend to go through numerous freeze and thaw cycles during the transitional months. When water freezes, it expands its volume as much as 9%. You can see this in the way that water in an ice cube tray freezes into cubes that are slightly larger than the liquid water level. If water subsequently thaws back to liquid form, it then contracts. (By the way, water is one of the very few substances that act this way; most materials are larger in volume as a liquid than as a solid.) Over the course of time, the stress produced by this freeze‐thaw cycle causes the joints progressively to enlarge so that boulders slowly break away from each other (Figure 14.4). In places where frost action is most active, such as high mountain peaks or arctic environments, large fields of fractured boulders form (Figure 14.5); they are called _________ (German for "rock sea").
Weathering
Physical or chemical modification of rock or sediment that occurs over time. Its' the process by which rocks break down or decay into smaller fragments. Two primary kinds of these types of processes that occur on Earth: mechanical (also called physical) and chemical. Although they can operate alone, they often work together to break rocks apart. Physical weathering is more pronounced in colder/drier environments, whereas chemical weathering is related more to warmer/wetter climates.
acid rain
Rain containing acids that form in the atmosphere when industrial gas emissions (especially sulfur dioxide and nitrogen oxides) combine with water. According to the U.S. Environmental Protection Agency, about two‐thirds of all sulfur dioxide and one‐fourth of all nitrogen oxides in the atmosphere come from electric power generation plants that rely on burning fossil fuels such as coal. After these acids are emitted from factories in the industrial Midwest, they are carried aloft and eastward by the prevailing westerly winds(in NE states and Canada).
Mechanical weathering (physical weathering)
Reduces solid rock to smaller fragments but does not alter the chemical composition of the rocks and minerals. also called physical weathering, involves the destruction of rocks through physical stresses. they simply break into progressively smaller pieces of the same kind of rock. As they do so, the overall surface area of the rock progressively increases, which facilitates even more weathering because more area within the rock mass is available for additional weathering to occur.
Exfoliation
Rock expands through the process of unloading, which occurs when deep rocks are slowly uncovered by erosion of overlying rock and compression pressure lessens The flaking of loosened rock from the main rock along curved joints is the specific exfoliation process Enhanced by daily and seasonal temperature cycles causing rock to expand and contract Most active in igneous or metamorphic rock
differential cementation
Rock units weather at different rates, and it is possible that certain parts of an individual rock unit are more resistant to weathering and erosion than others within the same unit due to variations in the strength of the cementing materials. This kind of happening is particularly common in sandstone. In places where this kind of variability exists within a rock outcrop or within an individual rock unit, long‐term weathering can have a noticeable impact and can even result in very unusual landforms
How mass wasting is subdivided.
The kinds of Earth materials being moved, such as rock or regolith, and their association with the presence of water. Their physical properties, including whether they are hard, plastic, or fluid. The kind of motion; for example, whether the material is falling or flowing. How quickly the process occurs. The following discussion focuses on the processes outlined in Figure 14.16.
frost wedging
The mechanical breakup of rock caused by the expansion and contraction of water in rock cracks due to freezing and thawing.
spheroidal weathering
The most prominent impact of hydrolysis on the landscape is that the sharp edges and corners of rocks become rounded. Any weathering process that tends to produce a spherical shape from an initially blocky shape.
The 4 corners region today and speculations on the Pueblos of the past.
What prompted the ancestral Pueblo to leave their elaborate cliff dwellings? No one knows for sure. The best scientific guess is that the Pueblo were influenced by a variety of factors, including climate change, drought, deforestation, and competition from other cultural groups. Regardless, their descendants live on in the modern Tanoan and Hopi peoples who live in the region today.
Feldspar
any of a group of hard crystalline minerals that consist of aluminum silicates of potassium or sodium or calcium or barium
Pueblo peoples' history
archaeological perspective, niches within cliffs of the southwestern United States are interesting because many contain the remains of ancient villages. These settlements were constructed by Native Americans, the ancestors of the modern-day __________ people who still inhabit the region. Fantastic cliff dwellings can be seen in a variety of places in the southwestern United States, such as Canyon de Chelly in Arizona, Bandalier National Monument in New Mexico, and Mesa Verde in Colorado. Although these sites are 700 to 800 years old, they clearly were built by people living in a complex culture, with villages occupied by hundreds to thousands of people. The structures ranged in size from one-room storage units to large, multipurposed buildings with more than 150 rooms. Ceremonial rooms (called kivas), which were used for religious ceremonies, are present at many sites, as are open plazas where cultural and civic events took place.
Gypsum
calcium sulfate. Mineral used in the formation of plaster of Paris and stone
local relief
change in elevation between two specified points. that is, the vertical distance between the top of the hills and the stream downslope—may have been created either through uplift of the landscape or through downcutting by the stream. In some cases, both processes occur. Regardless of how the relief was created, the resulting hillslopes contain many distinctive components. In all probability, the core of the slope is some form of bedrock that dates to either an igneous or sedimentary process that occurred tens of millions or hundreds of millions of years ago.
The three major kinds of mechanical weathering are?
frost wedging, salt‐crystal growth, and exfoliation. Frost wedging involves water that expands and contracts upon freezing and thawing in joints and cracks in rock. Salt‐crystal growth occurs when water seeps out of rock in arid environments. Exfoliation happens when rock expands because of unloading and temperature changes.
The three major kinds of chemical weathering are?
hydrolysis, oxidation, and carbonation. Hydrolysis occurs when water interacts with rocks, causing chemical reactions to occur. Oxidation occurs when oxygen combines with metals to form oxides. Carbonation takes place when carbonic acid in precipitation accumulates on rocks and causes them slowly to dissolve.
sheeting structure
rock joints in layers parallel to surface, forming exfoliation domes. As the overlying rock mass is gradually removed, the amount of compression on the deeper rocks progressively lessens. If unloading progresses to the point where the formerly deep rocks become surface rocks, they may expand so much that curved joints develop parallel to the surface. These joints are called this, and results in the flaking of loosened rock from the main rock mass in a process called exfoliation
root wedging
roots growing under rocks causing it to break
Halite
sodium chloride as a mineral, typically occurring as colorless cubic crystals; rock salt. An excellent place to see the effects of salt‐crystal growth is in the steep cliffs of the southwestern United States, where permeable sandstones often overlie relatively impermeable shales. Water stored within the sandstones tends to move downward fairly easily because these rocks have large pore spaces. This moving water easily dissolves salts such as halite (sodium chloride), calcite (calcium carbonate), or gypsum (calcium sulfate). When this downward‐moving water meets the shale, it can no longer move vertically and thus flows horizontally toward the cliff wall, where it seeps out and rapidly evaporates.
Temperature Weathering
temperature changes that occur over the course of seasons, between day and night, or due to changes in the direction in which the Sun faces a rock over the course of the day. These temperature fluctuations can cause rock to expand and contract when heated and cooled, respectively. Over the course of countless such cycles, the rock will gradually break into progressively smaller pieces. This kind of mechanical weathering is very common in arid regions (Figure 14.7) or at high elevations where intense solar radiation occurs during the day and radiational cooling prevails at night.
Frost line
the boundary in the solar nebula beyond which ices could condense; only metals and rocks could condense within the frost line. The depth of this line is progressively greater with higher latitude or altitude.
Mass wasting refers to?
the downslope movement of sediment, soil, and rock under the force of gravity. processes are differentiated on the basis of how quickly they move and the relative saturation of sediments. Rockfall, creep, solifluction, and landslides are these processes that occur under the force of gravity. Rockfall and landslides occur when rocks and sediments break free for some reason, such as lubrication of underlying clays or earthquakes. Flows occur when sediments become saturated and then move under the force of gravity. Flow processes include earthflows, mudflows, and debris flows. Avalanches occur in mountainous areas when steep snow packs break free.
Frost Heaving and Wedging
the freezing and thawing of water can also cause modifications in soil. Upthrust of sediment or soil due to the freezing of wet soil beneath. These modifications are most pronounced where soils are fine‐textured with horizontal planes between silt and clay particles. Under these conditions, water collects in the planes and then expands upward upon freezing, causing the soil to rise upward in a process called this. If you happen to live in the northern part of the United States or in Canada, you can often see evidence of this in farm fields. In these areas, individual stones and cobbles (large, rounded rock fragments) can be slowly brought to the surface over time when water collects beneath them and freezes. After each winter, farmers pull any freshly surfaced rocks out of their fields to make plowing easier and stack them in a pile at the edge of the lot. You can also see the effects of this on northern paved roads when cracks develop in them because they are upliterm-19fted somewhat during the winter. Building contractors are acutely aware of the frost‐heaving process. To avoid problems with structures such as decks settling in uneven ways, builders are required to install support footings below the depth of the frost line. The depth of this line is progressively greater with higher latitude or altitude.
pedogenic processes
the natural processes of soil formation that involve additions, translocations, transformations, and losses. Depending on the steepness of the hillslope and the regional environmental conditions, the soil will be either well developed and thick, or poorly developed and thin. Most mass‐wasting processes occur within the mantling regolith and soil, although where relief is particularly steep, they may also impact outcropping bedrock.
angle of repose
the steepest angle at which loose material remains stationary without sliding downslope
