geol exam 4

Let's Talk About Subsidence

What is it? Subsurface ground failure through sinking, Occurrs naturally or induced by human activities, and Slow settling or rapid collapse Causes: Withdrawal of fluids or removal of solid materials from the subsurface

Unidirectional Changes: Evolution of the Solid Earth

When the Earth became hot enough to melt, iron sank to the center, accumulating to form the core.

differentiation (of a planet)

a process early in a planet's history during which dense iron alloy melted and sank downward to form the core, leaving less-dense mantle behind

stream piracy

a process that happens when headward erosion by one stream causes the stream to intersect the course of another stream and capture its flow

Laurentide Ice Sheet

An ice sheet that spread over northeastern Canada during the Pleistocene ice age(s).

glacial drift

sediment deposited in glacial environments

Aquitard

sediment or rock that does not transmit water easily and therefore retards the motion of the water

Aquifer

sediment or rock that transmits water easily

surface load (bed load)

sediment that rolls and bounce along the ground (under the air) or along a stream bed (under water)

recurrence interval

the average length of time between events of a given size of magnitude; the term is commonly used to give a sense of the frequency of earthquakes or of flooding

residence time

the average length of time that a substance stays in a particular reservoir

Headwaters

the beginning point of a stream

equilibrium line (of a glacier)

the boundary between the zone of accumulation and the zone of ablation

Energy

the capacity to do work

lag deposit

the coarse sediment left behind in a desert after wind erosion removes the finer sediment

post glacial rebound

the rise of the surface of a continent after an ice sheet has melted away, so that isostasy is reestablished

sea ice

ice formed by the freezing of the surface of the sea

chimney

(1) A conduit in a magma chamber in the shape of a long vertical pipe through which magma rises and erupts at the surface; (2) an isolated column of strata in an arid region.

bar

(1) A sheet or elongate lens or mound of alluvium; (2) a unit of air-pressure measurement approximately equal to 1 atm.

current

(1) a well-defined stream of ocean water; (2) the moving flow of water in a stream

uplift

(n. geology) the upward vertical motion of Earth's surface

Sort the following characteristics based on the type of unconventional hydrocarbon reserve they are associated with.

-tar sand: associated with sandstone, very viscous bitumen, and open pit mines -shale oil: extracted by hydrofracturing, keerogen transformed into oil, impermeable source rock

Viscosity of a hydrocarbon reflects the number of carbon atoms in the hydrocarbon molecules. Hydrocarbons with larger molecules are more viscous. Rank the following compounds from lowest to highest viscosity by dragging the images to the correct positions. The length of the carbon chain is indicated beneath each image.

-lowest viscosity natural gas gasoline kerosene heating oil lubricating oil tar -highest viscosity

Order the steps involved in hydrofracking.

-start (hole drilled) 1. packers are put in place 2. fluids are pumped in at high pressure 3. the pressure in the hole is increased 4. preexisting cracks open up -gas is extracted

Sort the following characteristics of cut banks and point bars.

-cut bank 1. outer bank 2. erosion dominates 3. faster flow velocities -point bar 1. inner bank

Order the steps in secondary enrichment.

-first 1. igneous activity ceases after producing ore-bearing deposits 2. the ore-bearing deposit cools entirely 3. groundwater flows through an ore deposit and leaches out metals 4. new ore minerals are precipitated in a new location -last

Place these events in chronological order based on causality

-first event 1. groundwater is rapidly removed from a system 2. the level of the water table drops 3. pore collapse takes place 4. subsidence occurs over a broad region -last event

Order the steps in the formation of ocean waves from first to last.

-first step 1. wind begins to blow 2. frictional drag on surface of water 3. ripples form 4. waves form -final step

Rank the three types of sediment load in a stream from smallest to largest.

-smallest dissolved load suspended load bed load -largest

Darcy's Law

1. An equation by which the discharge (rate of flow) of groundwater can be calculated. Q[Discharge] = A[Cross-sectional area of flow] ( K[Permeability (hydraulic conductivity)] x S[Slope of water table = h{vertical drop}/l{flow distance}]) 2. The level to which water rises in a drillhole is the hydraulic head (h). The hydraulic gradient (HG) is the difference in head (h1-h2) at two different locations divided by the length of the flow path (j) between them. The hydraulic gradient is indicated by the slope of the water table. Groundwater flow rate is governed by the permeability of the porous material multiplied by the hydraulic gradient. High permeability increases the rate of flow. Low permeability decreases it. A steeper gradient increases the rate of flow; across less steep gradients, flow rate is lower.

Aquifers and Aquitards

1. Aquifer: A geologic unit capable of storing and transmitting water in sufficient quantities to supply wells. It is a high-porosity, high-permeability rock that transmits water easily. 2. Aquitard: A layer or unit restricting and retarding (slowing) groundwater flow. It is a lower-permeability rock. 3. Aquifers and aquitards are commonly interlayered

Measures of a Streams Ability to Transport Sediment Include:

1. Competence: A measure of the maximum size particle a stream can transport under a given set of flow conditions 2. Capacity: A measure of the total volume of sediment stream can transport under a given set of flow conditions

hydrothermal systems

1. Connection between the lithosphere & the hydrosphere. Formation of hot springs & geysers. 2. Hot Springs: form when heated groundwater reaches the surface. Heated water begins to rise

Topographic Maps

1. Definition - maps that use contour lines to show the shape of the Earth's surface. 2. Contour lines - imaginary lines connecting points having the same elevation on the surface of the land above or below a reference surface, which is usually mean sea level. 3. Contour Interval - the vertical distance between the elevations represented by adjacent contour lines on a map 4. Relief - a location's relief is the difference between its highest and lowest elevations.

Sediment Deposition: How Streams Deposit Sediment

1. Gravel in the bed of a mountain stream in Denali National Park, Alaska. The large clasts were carried during floods. This stream has high competence. 2. Competence decreases with velocity. Mud deposited along a gentle, slowly moving stream in Brazil. This stream has low competence.

Movement of Glacial Ice

1. How do glaciers move? Basal sliding. Significant quantities of meltwater forms at base of glacier. Water decreases friction, ice slides along substrate. Plastic deformation. Plastic deformation occurs below about 60 m depth. Grains of ice change shape slowly. New grains form while old grains disappear. Crevasses form at surface—upper zone too brittle to flow. 2. Why do glaciers move? The pull of gravity is strong enough to make ice flow. A glacier moves in the direction of its surface slope. The ice base can flow up a local incline. In continental glaciers, ice spreads away from center of accumulation. The ice sheet is always thicker in the middle, so it spreads toward the edges.

Revisiting Fundamental Concepts

1. Human population growth: More people living on flood plains 2. Sustainability: Planning for sustainable rivers key to human survival 3. Earth as a System: Changes in land use - filling channels with sediment leading to soil depletion; increasing runoff in urban areas. 4. Hazardous earth processes, risk assessment, and perception: Unwise land use leads to losses (convincing people key) 5. Scientific knowledge and values: Values often conflict with science when it comes to reducing flood hazards and Technology fix or floodplain management???

Streams and Rivers

1. Hydrology: study of water transport in natural systems 2. Runoff - quantity of water discharged in surface streams. -Runoff includes not only the waters that travel over the land surface and through channels to reach a stream but also interflow, the water that infiltrates the soil surface and travels by means of gravity toward a stream channel (always above the main groundwater level) and eventually empties into the channel. Runoff also includes groundwater that is discharged into a stream 3. Drainage basin - see next set of slides

Lateral Erosion

1. Initial downcutting 2. Downcutting is slowing being replaced by lateral erosion 3. Lateral erosion well developed widening the valley

Mechanics of Water Flow

1. Laminar flow: Streamlines flow parallel without turbulent mixing 2. Turbulent flow: Streamlines cross causing turbulent mixing

River valleys are built by two processes

1. Lateral accretion: by the lateral migration of bar deposits (mainly sands and gravels). 2. Vertical accretion: by the deposition of natural levee and flood basin deposits on the floodplain during periods of overbank (flood) flow (mainly silts and clays).

The image above shows the global thermohaline circulation. Which of the following events occur due to thermohaline circulation? Choose one or more: 1. Less salty water rises. 2. Water flows around the Earth in about one year. 3. Bottom currents may be either warm or cold. 4. Cold water sinks in polar regions. 5. Heat is moved through the oceans.

1. Less salty water rises. 4. Cold water sinks in polar regions. 5. Heat is moved through the oceans.

The Two Main Types of Channel Patterns on Floodplains are:

1. Meandering Streams: have a single channel with a sinuous pattern and are the most common pattern on floodplains 2. Braided Streams: have an interlacing network of channels and are relatively uncommon

Mountain/Alpine Glaciers

1. Mountain settings include a variety of glacier types that are classified based on shape and position. Cirque glaciers fill mountaintop bowls. Valley glaciers flow like rivers down valleys. Mountain ice caps cover peaks and ridges. Piedmont glaciers spread out at the end of a valley. 2. Flow from high to low elevation in mountain settings. Include a variety of types: Cirque glaciers fill mountain-top bowls, Valley glaciers flow like rivers down valleys, Mountain ice caps cover peaks and ridges, and Piedmont glaciers spread out at the end of a valley.

Hot Springs

1. Mudpots form where boiling water mixes with volcanic ash. The ash changes to clay and forms a hot, muddy soup. 2. Hot springs lose dissolved minerals upon cooling, crystallizing as deposits of travertine.

Landscapes of Mars

1. No plate tectonics. Most features are older than 3.8 Ga. Hot-spot volcanoes. No vegetation or rain, so weathering different from that on Earth. Mars does have ice caps that grow and recede seasonally. 2. Consider the evidence for the presence of surface water on Mars during its history.

Identify the statement that is true about landscapes on Mars. 1. Olympus Mons is an extinct hot-spot volcano on Mars and is the highest mountain in the Solar System. 2. Similar to the Earth, Mars has mountain belts formed by plate tectonics. 3. Because Mars has no atmosphere, wind erosion does not affect the surface of the planet. 4. Mars no longer has a hydrologic cycle because all water and/or ice is now gone from the surface.

1. Olympus Mons is an extinct hot-spot volcano on Mars and is the highest mountain in the Solar System.

Possible Triggers for Mass Movement

1. Over-steepened slope: erosion / lateral erosion, volcanic ash, and excavation (manmade) 2. Increased water content: intense rainfall and rising water table (e.g. behind dam) 3. Cyclic loading: earthquakes and storms

Baselevel

1. The elevation at which a stream ends by entering a large standing body of water, such as a lake or ocean 2. theoretical lowest level to which a river may erode 3. usually sea level 4. base level may be temporary, as with a lake

Planes of Weakness

1. Planes of weakess, such as those listed below, can result in mass movements: Saturated sand or clay layers, Joints parallel to the land surface, Weak sedimentary bedding (shale, evaporites), and Metamorphic foliation

Confined Aquifer

1. Recharge Area: where the confined aquifer is recharged by infiltration 2. Potentiometric Surface: Height to which water will rise if released from the confined aquifer, which equals the height of the water table in the recharge area

Resources & Reserves

1. Resources: total discovered and undiscovered 2. Reserves: discovered, surveyed, and economically recoverable

Slope Stability

1. Safety Factor: SF = Resisting Forces/Driving Forces. If SF > 1, Then safe or stable slope. If SF < 1, Then unsafe or unstable slope. Driving and resisting forces determined by the interrelationships of the following variables: Type of Earth materials, Slope angle and topography, Climate, Time, Vegetation and water 2. Steeper slopes create a larger force imbalance. Downslope forces = gravity: The weight of Earth materials, The weight of added water, and The weight of added structures. Resisting forces = material strength: Cohesion, Chemical bonds, Electrical charges, Surface tension, and Friction

The image above shows a seamount. Which of the following statements about seamounts are true? Choose one or more: 1. Seamounts probably rose above wave base in the past. 2. Seamounts are extinct volcanoes. 3. Seamounts are sedimentary structures and have nothing to do with volcanoes. 4. Seamounts were never active volcanoes. 5. Seamounts are evidence of plate movement over a stationary mantle plume (hot spot).

1. Seamounts probably rose above wave base in the past. 2. Seamounts are extinct volcanoes. 5. Seamounts are evidence of plate movement over a stationary mantle plume (hot spot).

Nonmetallic Mineral Resources

1. Society uses many nonmetallic mineral resources, also known as industrial minerals. Architects and Geologists have a similar, but different language: Architects "Stone" = Geologists "Rock;" Architects Marble: Any polished carbonate rock; Architects Granite: Any rock containing quartz and feldspar regardless of whether it is igneous or metamorphic. Dimension Stone: intact slabs/blocks of rock. A Quarry provides stone, whereas a Mine provides ore. Split vertically with wedges, split horizontally with wireline saw, thermal lance (blow torch), or high pressure water jet. 2. Crushed Stone & Concrete: Crushed Stone: substrate for roads and railways, raw material for manufacturing cement, asphalt, etc. Quarried by blasting and crushing. Mortar: substance that holds bricks together. Concrete: substance used for roads, walls, etc. Both mortar and concrete contain Cement: ~66% lime (CaO); ~25% silica (SiO2), ~9% Al2O3 and Fe2O3 (from clay or shale). The ideal limestone contains these elements in those proportions. This is from the Jurassic Portland Limestone from England. Cement is now predominantly made by mixing limestone, clay, and quartz (sand) in the right proportions. These are then heated in a kiln to ~1,450°C, which releases CO2 and produces "clinker". This is crushed to give cement. 3. Rare Earth elements (REEs) are essential for high-tech applications: e.g., hybrid/electric cars, cell phones, etc.

Surface water

1. Surface runoff, Evapotranspiration, & Groundwater 2. Watersheds/drainage basins store and move rainwater from higher elevations to lower elevations, but also recharge groundwater (refill an aquifer) 3. Water available to recharge groundwater is dependent on the amount of precipitation minus the amount of evapotranspiration. Evapotranspiration - water lost to the atmosphere from plants transpiring and evaporation

Types of Sediment Transport

1. Suspended Load: Fine-grained sediment (typically clay and silt) transported in suspension due to turbulence 2. Bed (or traction) Load: Coarser-grained sediment (typically sand and gravel) transported on the bottom of the stream bed by rolling and sliding 3. Saltation: Sediment (typically sand) transported by intermittent jumps - a transitional state between bedload and suspended load. 4. Dissolved load: Ions in solution 5. The above combined equals Total Load

Environmental Impacts of Mining

1. Tailing piles are often acidic and laden with toxic metals. Mining creates huge volumes of waste tailings. Waste dumps - leaching and landslides. Subsidence/Earthquakes. Acid mine drainage. Pollution (air & water) 2. Ore processing releases toxic chemicals, which are sometimes dispersed by air and rain. Mining also exposes ore-bearing rock to the atmosphere, and since many ore minerals are sulfides, they react with rainwater to produce acid mine runoff, which can severely damage vegetation downstream. Acid Mine Drainage: Sulfides react with water and O2 to form sulfuric acid (H2SO4). Sulfuric acid (H2SO4) is what gives us acid mine drainage.

Creep

1. The downhill movement of soil and other debris, typically at rates of about 1 to 10 mm/year. The downhill movement of regolith is due to seasonal expansion and contraction of regolith. Wetting and drying and freezing and thawing are contributing factors. Creep operates as grains are moved perpendicularly to the slope as regolith expands and vertically downward by gravity as regolith contracts. 2. Creep is evident from tilting of landscape features. You can't see creep by staring at a hillslope because it occurs so slowly, but over a period of years, creep causes trees, fences, gravestones, walls, and foundations built on a hillside to tilt downslope.

Ore Exploration and Production

1. The type of mining depends on the proximity of the ore body to the surface. A shallow ore body is removed by open-pit mining. A deeper ore body necessitates underground mining. 2. Core Drill - a drill that removes a cylindrical core from the drill hole. Core drilling helps determine the depth and horizontal extent of an ore deposit. 3. Surface Mining: Most suitable for large ore bodies and for low grade, disseminated ore bodies. Usually ore bodies are mined by a combination of surface and underground methods. Initial mining is by surface methods, but as mining deepens, the amount of waste to be removed increases - soon economical to go underground. Surface mining requires huge amounts of material to be removed - highly mechanized. 4. Surface Mining: Two Types -Type 1 - Open Pit Mining: Typically associated with massive ore deposits. Waste is removed from surface and berms are created to allow deeper and wider mining of ore. Open-pit mining is less expensive and less dangerous than underground mining. -Type 2 - Strip Mining: Overburden is stripped off (dumped as spoil banks or spoil piles) the ore removed, and waste replaces it in a cyclic manner. 5. Surface mining is less expensive and less dangerous than underground mining but can have a huge environmental impact. 6. Underground mining is more expensive and dangerous, but can get at deeper deposits. Underground mines are expensive and dangerous due to tunnel collapses and the presence of poisonous and explosive gases. Underground Mining: Adit = horizontal entry; Shaft = vertical entry. Deepest mine = 3.5 km; Temp. ~55°C! Columns of material left for roof support. Underground mining is more expensive and dangerous but can get at deeper deposits. Dangerous due to tunnel collapses, rock bursts = rock falls due to pressure, and the presence of poisonous and explosive gases

The dynamic equilibrium of a stream system is controlled by:

1. Topography: including slope 2. Climate 3. Streamflow 4. Resistance of underlying bedrock

Flood insurance

1. U.S. National Flood Insurance Program: Began in 1968 when private companies began to stop offering flood protection policies 2. Special Flood Hazard Areas: Defined areas inundated by 100-year floods, Owners must buy flood insurance, and Current issue in rebuilding since Hurricanes Katrina, Rita, & Sandy affected areas 3. National Flood Insurance Reform Act of 1994: Mitigate flood hazards - Introduced flood proofing, relocations, buy-outs. 4. The program has been updated in 2004, 2012, & 2014

Types of Aquifers

1. Unconfined Aquifer: the permeable layer extends to the surface. It consists of an unsaturated zone separated from the saturated zone by the groundwater table. Therefore, an unconfined aquifer lies at the surface. Because it is in contact with human activities, it is easily contaminated. 2. Confined Aquifer: the permeable layer is overlain and underlain by a less permeable layer (aquitard). Therefore, a confined aquifer lies beneath an aquitard. Being isolated from the surface, it is less susceptible to pollution.

Types of Unconsolidated Mass Movement

1. Unconsolidated Flows (increased velocity): creep to earth flow to debris flow or earth flow 2. Unconsolidated Slides and Falls (increased velocity): slump to debris slide to debris avalanche

Upstream and Downstream Floods

1. Upstream flood: caused by intense rainfall of short duration over relatively small area. Downstream floods: caused by storms of long duration over large area. 2. Comparison between upstream and downstream floods. Upstream flood covers smaller area and caused by intense local storms. Downstream floods cover wide areas and caused by regional storms or spring runoff.

Reasons for erosion or deposition correlated to physical properties of the river

1. change in channel geometry 2. composition of channel bed and banks 3. Vegetation 4. land use

Channel restoration: alternative to channelization

1. cleaning urban waste from channel 2. allowing stream to flow freely 3. protecting existing banks

Mass Movement Depends on Water Content

1. damp sand: Surface tension in damp sand increases cohesion 2. dry sand: Dry sand is bound only by friction 3. water-saturated sand: Saturated sand flows easily because of interstitial water 4. Steep slopes in damp sand maintained by moisture between grains

Whether Flow is Laminar* or Turbulent Depends On:

1. flow velocity 2. Geometry: primarily depth 3. Viscosity: a measure of a fluids resistance to flow 4. note: laminar flow almost never exists in surface water flows

Water as a resource

1. found in liquid, solid, or gaseous state on or near Earth surface 2. residence time varies depending upon location 3. more than 99% of Earth's water unavailable or unsuitable for human use

Variables that Encourage Channel Braiding Include:

1. highly variable water discharge 2. large sediment load 3. easily eroded bank material

Land use change from forest to agriculture

1. increases soil erosion 2. increases sediment load 3. increases channel slope 4. new dynamic equilibrium may be reached

Groundwater zones

1. major source of groundwater is infiltrated precipitation 2. Where does this water go? Porosity, Permeability, Vadose Zone, and Zone of Saturation

Major Categories of Mineral Resources

1. metallic: gold, silver, copper, lead, zinc, iron, and aluminum 2. nonmetallic: dimension stone, halite, gypsum, sand, and gravel

The global water cycle

1. movement or transfer from one of Earth's storage compartments to another 2. major processes are: evaporation, precipitation, transpiration, surface runoff, and groundwater flow

Match the following descriptions with the type of beach protection to which they correspond.

1. nourishment: often used for beaches frequented by tourists, significantly widens a beach but is a short-term solution 2. breakwater: runs parallel to the shore and disrupts the longshore current, beach accretion occurs by blocking erosion by incoming waves 3. groin: sometimes installed by homeowners to improve their beach area, can create a sawtooth beach pattern, runs perpendicular to the shore and increases erosion down current 4. jetties: improves ship navigation by stopping the formation of spits

The structural approach

1. physical barriers, such as levees and floodwalls 2. reservoirs 3. on-site retention basins

Flood Proofing

1. raising building foundations 2. constructing floodwalls or earth berms around buildings 3. waterproofed doors, walls, windows 4. improved drains with pumps

Dam construction

1. water slows at head of reservoir, causing deposition 2. below dam, water released has minimal sediment 3. channel erosion will predominate below dam

The wave shown below has a wavelength of 24 meters, a wave height of 5 meters, and a wave velocity of 4 meters per second. At what depth would the submarine have to travel in order to not experience any influence of the waves above it?

12 meters 24/2=12

Identify the true statement. 1. Climate does not affect the types of landforms created in a region. 2. Water, ice, and/or air are agents of erosion. 3. Strong rocks, counterintuitively, tend to slide and produce gentle slopes. 4. If the rate of uplift exceeds the rate of erosion, the land surface subsides.

2. Water, ice, and/or air are agents of erosion.

Use the image of surface ocean currents above to answer the following question.If you were drifting off the coast of South America in the Atlantic Ocean, on which coast would you eventually wash up? Choose one: 1. west coast of South America 2. coast of southwest Africa 3. west coast of North America 4. coast of northeast Africa

2. coast of southwest Africa

Which of the following regions would have the highest relief? 1. the Nile River Valley 2. the Himalayas 3. the surface of the Antarctic ice sheet 4. the gentle, rolling hills of southern Scotland

2. the Himalayas

A water molecule in the atmospheric reservoir has a residence time of approximately 1. 10,000 years or more. 2. 10 years. 3. 10 days. 4. 4,000 years.

3. 10 days.

Which of the following statements about how humans have influenced erosion and deposition is true? 1. The area of land now covered by pavement and buildings in the United States is less than the area of the state of Delaware. 2. Agriculture significantly decreases erosion rates. 3. Pavement seals the ground surface and causes runoff to spill into streams rather than into the ground. 4. Mining does not alter the Earth's surface landscape because mines only excavate underground.

3. Pavement seals the ground surface and causes runoff to spill into streams rather than into the ground.

Which of the following energy sources drives landscape evolution? 1. the Earth's magnetic field 2. the tidal pull of the Moon 3. the force of gravity 4. the Coriolis force

3. the force of gravity

Identify the statement that is true about the landscape of Venus. 1. The surface of Venus is significantly older than that of Mars or the Moon. 2. Venus has a very thin, low-density atmosphere that allows for numerous meteor impacts. 3. No evidence of tectonic activity (such as volcanoes, faults, or rifts) has been noted on Venus. 4. Liquid water cannot exist on Venus, and therefore it has no hydrologic cycle.

4. Liquid water cannot exist on Venus, and therefore it has no hydrologic cycle.

Evapotranspiration 1. only occurs in the ocean. 2. is a form of precipitation. 3. is when evaporation transpires. 4. describes the release of water to the atmosphere from the surface, plants, or animals.

4. describes the release of water to the atmosphere from the surface, plants, or animals.

While flash floods can take place in any climate, they are especially dramatic in which type of climate? Choose one: 1. polar, tundra 2. tropical, wet 3. mild, humid, subtropical 4. dry, arid

4. dry, arid

The Moon's landscape 1. changes dramatically because there is continuous surface modification by wind erosion. 2. is constantly altered by meteorite impacts. 3. is constantly altered by plate motions. 4. was generated by meteorite impacts and volcanic activity billions of years ago.

4. was generated by meteorite impacts and volcanic activity billions of years ago.

Which region of this topographic map shows the steepest slope?

A

mid-ocean ridge

A 2-km-high submarine mountain belt that forms along a divergent oceanic plate boundary.

cirque

A bowl-shaped depression carved by a glacier on the side of a mountain.

abyssal plain

A broad, relatively flat region of the ocean that lies at least 4.5 km below sea level.

continental shelf

A broad, shallowly submerged fringe of a continent; ocean-water depth over the continental shelf is generally less than 200 meters; the widest continental shelves occur over passive margins.

organic coast

A coast along which living organisms control landforms along the shore.

Drainage Divides

A continental divide separates flow to different oceans. Watersheds are defined on a variety of scales. Tiny tributaries—tiny watersheds; large continental rivers have large watersheds.

desert varnish

A dark, rusty-brown coating of iron oxide and magnesium oxide that accumulates on the surface of the rock.

trench

A deep, elongate trough bordering a volcanic arc; a trench defines the trace of a convergent plate boundary.

fjord

A deep, glacially carved, U-shaped valley flooded by rising sea level

What Is a Desert?

A desert is a region that is so arid that it contains no permanent surface water and supports no more than 15% vegetation cover. Deserts usually have less than ten inches (25 cm) of annual rainfall. Desert types exist in both hot and cold climates. The definition of a desert is based on aridity, not temperature. Deserts may be hot or cold. Hot desert characteristics: Low latitudes, Low elevations, Far from oceans, and High temp exceeds 35 C. Cold desert characteristics: High latitudes, High elevations, Near cold ocean currents, and Temp usually below 20 C.

ventifact (faceted rock)

A desert rock whose surface has been faceted by the wind.

Mudflow (Mudslide)

A downslope movement of mud at slow to moderate speed.

debris flow (debris slide)

A downslope movement of mud mixed with larger rock fragments.

Drainage Networks: Rectangular

A drainage pattern in which the main streams and their tributaries display many right-angle bends; it is indicative of streams following prominent fault or joint systems that break the rocks into rectangular blocks.

Mudflow

A flowing mass of material (mostly finer than sand, along with some rock debris) containing a large amount of water. It may travel large distances and high speeds and carry particles as large as a house! Mudflows are common in tropical settings with deep weathering of soils and abundant rainfall, especially from tropical storms and hurricanes.

Debris flow

A fluid mass movement of rock fragments supported by a muddy matrix. May move a speeds of up to 100 km/hr! Rocks in a debris flow range from pebbles to large boulders

Earthflow

A fluid movement of relatively fine-grained material, e.g. soils, weathered shale, and clay.

speleothem

A formation that grows in a limestone cave by the accumulation of travertine precipitated from water solutions dripping in a cave or flowing down the wall of a cave.

geyser

A fountain of steam and hot water that erupts periodically from a vent in the ground in a geothermal region

roche moutonnee

A glacially eroded hill that becomes elongate in the direction of flow and asymmetric; glacial rasping smoothes the upstream part of the hill into a gentle slope, while glacial plucking erodes the downstream edge into a steep slope.

depositional landform

A landform resulting from the deposition of sediment where the medium carrying the sediment evaporates, slows down, or melts

Headward Erosion

A ledge of resistant rock may define a local base level. Erosive forces act to slowly remove the resistant layer, restoring the longitudinal profile.

Perched Water Table

A perched water table occurs where a mound of groundwater becomes trapped above a discontinuous aquitard that lies above the regional water table.

artificial levee

A man-made retaining wall to hold back a river from flooding.

darcy's (disappearing stream) law

A mathematical equation stating that a volume of water, passing through a specified area of material at a given time, depends on the material's permeability and hydraulic gradient.

coal rank

A measurement of the carbon content of coal; higher-rank coal forms at higher temperatures.

butte

A medium-sized, flat-topped hill in an arid region.

Desert Landscapes: Plateau, Mesa, & Buttes

A mesa is an isolated, flat-topped hill or mountain with steep sides that is smaller in area than a plateau. A butte is also a flat-topped hill with steep sides, though smaller in area than a mesa.

snowball earth

A model proposing that, at times during Earth history, glaciers covered all land, and the entire ocean surface froze.

desert pavement

A mosaic-like stone surface forming the ground in a desert.

yardang

A mushroom-like column with a resistant rock perched on an eroding column of softer rock; created by wind abrasion in deserts where a resistant rock overlies softer layers of rock.

natural hazard

A natural feature of the environment that can cause injury to living organisms and/or damage to buildings and the landscape

varve

A pair of thin layers of glacial lake-bed sediment, one consisting of silt brought in during the spring floods and the other of clay deposited during the winter when the lake's surface freezes over and the water is still.

Drainage Networks: Parallel

A parallel drainage system is a pattern of rivers caused by steep slopes with some relief. Because of the steep slopes, the streams are swift and straight, with very few tributaries, and all flow in the same direction.

icehouse period

A period of time when the Earth's temperature was cooler than it is today and ice ages could occur.

geothermal region

A region of current or recent volcanism in which magma or very hot rock heats up groundwater, which may discharge at the surface in the form of hot springs and/or geysers.

Karst landscape

A region underlain by caves in limestone bedrock; the collapse of the caves creates a landscape of sinkholes separated by higher topography, or of limestone spires separated by low areas.

flood-hazard map

A representation of a portion of the Earth's surface that is designed to show how the danger of flooding varies with location.

arete

A residual knife-edge ridge of rock that separates two adjacent cirques.

esker

A ridge of sorted sand and gravel that snakes across a ground moraine; the sediment of an esker was deposited in subglacial meltwater tunnels.

salt dome

A rising bulbous dome of salt that bends up the adjacent layers of sedimentary rock.

Sinkholes & Karst

A sinkhole is a depression or hole in the ground caused by dissolution of limestone in the subsurface. Sinkholes develop when weakly acidic groundwater dissolves limestone. CO2 is added to rainwater as it falls through the air and to groundwater from decaying organic matter in the soil. CO2 reacts with water to form carbonic acid.

Talus

A sloping apron of fallen rock along the base of a cliff.

talus

A sloping apron of fallen rock along the base of a cliff.

Slump

A slow slide of unconsolidated material that travels as a unit. Slumping is mass movement by sliding of regolith as coherent blocks. Slip occurs along a spoon-shaped "failure surface." The body of the slump may be further subdivided into discrete blocks, each bounded by faults. Slumps occur in a variety of sizes and have highly variable rates of motion. Slumps have a characteristic head scarp (exposed upper part of the failure surface) and a bulging toe (where material piles up).

permanent stream

A stream that flows year-round because its bed lies below the water table, or because more water is supplied from upstream than can infiltrate the ground

disappearing stream

A stream that intersects a crack or sinkhole leading to an underground cavern, so that the water disappears into the subsurface and becomes an underground stream.

Formation of a Superimposed Stream System

A stream that keep its course through different preexisting lithologies and structures it encounters as it erodes downward into the underlying rock.

ephemeral (intermittent) stream

A stream whose bed lies above the water table, so that the stream flows only when the rate at which water enters the stream from rainfall or meltwater exceeds the rate at which water infiltrates the ground below

drumlin

A streamlined, elongate hill formed when a glacier overrides glacial till.

trap

A subsurface configuration of seal rocks and structures that keep oil and/or gas underground, so it doesn't seep out at the surface

debris slide

A sudden downslope movement of material consisting only of regolith.

Rockslide

A sudden downslope movement of rock. 1. The rapid movement of large blocks of detached bedrock sliding more or less as a unit.

Lahar

A thick slurry formed when volcanic ash and debris mix with water, either in rivers or from rain or melting snow and ice on the flank of a volcano.

Debris Slide

A type of mass of material in which rock material and soil move largely as one or more units along planes of weakness.

distillation column

A vertical pipe in which crude oil is separated into several components.

artesian well

A well in which water rises on its own

Desert Landscapes: Desert Pavement

A well-developed desert pavement in the Sonoran Desert, Arizona. The inset shows a close-up of the pavement. Students standing at the edge of a trench cut into desert pavement. Soil lies between the pavement and the underlying alluvium. The inset shows the top surface of the pavement (lens cap diameter = 8 cm).

Identify statements true of submarine landslides and tsunamis. Choose one or more: A. As a submarine slide occurs, it can result in a depression in the sea surface above the slide. A tsunami can form when water rushes in to fill the depression. B. Because submarine slides take place underwater, they do not displace surface water, and are thus not likely to result in tsunami initiation. C. As a submarine slide occurs, it can push water into a sea-surface bulge ahead of its path; this can result in tsunami initiation. D. Large submarine slides of rock or sediment can create earthquake waves, which can initiate a tsunami.

A. As a submarine slide occurs, it can result in a depression in the sea surface above the slide. A tsunami can form when water rushes in to fill the depression. C. As a submarine slide occurs, it can push water into a sea-surface bulge ahead of its path; this can result in tsunami initiation.

Hypothesize about drawbacks to hydrofracking. Although hydrofracking makes gas shales economically viable, which of the following are disadvantages to hydrofracking? Choose one or more: A. It uses water, which is a valuable resource. B. It requires dangerous human labor underground. C. It requires the extraction of large amounts of soil and rock, scarring the landscape. D. It is very labor intensive.

A. It uses water, which is a valuable resource. D. It is very labor intensive.

Which of these regions has a Δ-shaped delta? Choose one: A. Nile Delta B. Niger Delta C. Mississippi Delta

A. Nile Delta

Which of the following statements are correct? Choose one or more: A. Playas are dried-up temporary lakes. B. Bajadas are elongated sediment wedges. C. Bajadas form from multiple alluvial fans. D. Playas are channels that form during flash floods.

A. Playas are dried-up temporary lakes. B. Bajadas are elongated sediment wedges. C. Bajadas form from multiple alluvial fans.

Identify possible consequences of rapid groundwater withdrawal. Choose one or more: A. Pore collapse occurs. B. Swamps form. C. Wells go dry.D.A cone of depression forms.

A. Pore collapse occurs. C. Wells go dry.D.A cone of depression forms.

Which of these are characteristics of either porosity or permeability? Choose one or more: A. Porosity is a measure of the amount of the substance composed of empty spaces. B. Permeability is a measure of how well the pores are connected. C. Permeability is the same thing as secondary porosity. D. Porosity describes the ability of pores to form conduits through the material.

A. Porosity is a measure of the amount of the substance composed of empty spaces. B. Permeability is a measure of how well the pores are connected.

How does the rate of groundwater flow compare with that of ocean currents or river currents? Choose one: A. The rate of groundwater flow is slower than that of surface-water currents. B. The rate of groundwater flow can be faster or slower than that of surface-water currents, depending on conditions. C. The rate of groundwater flow is faster than that of surface-water currents. D. The rate of groundwater flow is about the same speed as that of surface-water currents.

A. The rate of groundwater flow is slower than that of surface-water currents.

This image shows the Platte River in eastern Nebraska. Which of the following terms best describes the morphology of this stream? Choose one: A. braided river B. alluvial fan C. meandering river D. delta

A. braided river

Identify clues to detect slumps before they move very far. Choose one or more: A. broken fences B. localized flooding C. tilted utility poles D. cracked or displaced roadways

A. broken fences C. tilted utility poles D. cracked or displaced roadways

The image below depicts an alluvial fan at the mouth of a small canyon along the edge of Death Valley. The alluvial fan is composed of sediment that has eroded from the mountains above, and the sediment tends to be immature in nature. In order for an alluvial fan such as the one shown above to develop, what must be present, even in the desert? Choose one: A. flowing water B. snow C. tornadoes D. earthquakes

A. flowing water

Which of these are causes of desertification? Choose one or more: A. natural droughts B. agricultural grazing C.diversion of water D. excessive heat

A. natural droughts B. agricultural grazing C.diversion of water

Which characteristics are essential to defining a geologic occurrence as an ore deposit? Choose one or more: A.It contains enough ore to make mining economical. B.It has a high concentration of a metal. C.The ore is visible to the naked eye. D.The ore is easily extractable.

A.It contains enough ore to make mining economical. B.It has a high concentration of a metal.

Types of Deserts: Polar Deserts

Above 66º N and S latitude there is very little moisture in the air due to cold temperatures. Air circulation carries air to the polar regions, but it is so cold, the air can't hold any moisture.

Floodplain Settlements: two trends taken by people in the past

Accelerate programs to control floods or Continued growth of flood damages as populations increased

groundwater contamination

Addition of chemicals or microbes (e.g., from agricultural and industrial activities, and landfills or septic tanks) to the groundwater supply.

Example of Urban Stream Restoration

Addition of trees and riprap to stabilize banks. Note that riprap is used to stabilize the cut banks (main erosional areas)

The Pleistocene Ice Age: Life and Climate

All climate and vegetation belts were shifted southward. The tundra limit was ~48o N. Today, it is above 68o N. Southern states had forests like those in New England today. Vegetation evidence is preserved as pollen found in bogs. Cold-adapted, now extinct, large mammals roamed regions that are now temperate. Pleistocene fauna were well adapted. Mammals included now-extinct giants: Giant beaver, Giant ground sloth, and Mammoths and mastodons. Modern humans proliferated.

Desert Depositional Environments: Alluvial Fans

Alluvial fans are conical accumulations of sediment that accumulate where the water exiting a canyon spreads out and drops sediment. Alluvial fans grow outward from a source over time. Alluvial fans emerging from adjacent valleys along a mountain front may merge to form a continuous apron of sediment called a bajada.

Formation of an Antecedent Stream System

An antecedent stream is a stream that maintains its original course and pattern despite the changes in underlying rock topography

Unconfined & Confined Aquifers

An aquifer is a high-porosity, high-permeability rock that transmits water easily. An aquitard is lower-permeability rock that hinders water flow. Aquifers and aquitards are commonly interlayered. An unconfined aquifer lies at the surface. Because it is in contact with human activities, it is easily contaminated. A confined aquifer lies beneath an aquitard. Being isolated from the surface, it is less susceptible to pollution.

Drainage Basin

An area of land that funnels all water that fall on it into a network of streams. The boundaries of the drainage area are called divides

Desert Landscapes: Inselbergs

An inselberg is an eroded remnant rock resulting from almost-complete cliff retreat. The remnant rock is surrounded by erosional alluvium.

Types of Deserts: Continental Interior Deserts

Areas in the continental interiors, far from source of moisture where hot summers and cold winters prevail. Example: Gobi, Mongolia

Will There Be Another Glacial Advance?

Are we living in an interglacial? Will ice return? Very likely. Interglacials last ~10,000 years. It has been ~11,000 years since the last one. A cool period (1300 to 1850) resulted in the Little Ice Age in Europe. Today, a warming trend has caused glaciers to recede. Earth's climate changes without consulting humanity. During the last 150 years, temperatures have risen and most mountain glaciers have dramatically retreated. Earth's climate could now be in "super-interglacial" period.

Artesian Wells and the Potentiometric Surface

Artesian wells tap confined, tilted aquifers that are pressurized by upland recharge. Water rises in artesian wells to the potentiometric surface, which is an analogue of the water table for a confined aquifer. A well casing below this surface will flow without pumping. City water distribution systems are designed like artesian aquifers. A water tower establishes the potentiometric surface.

Identify statements true of landslides and tsunamis. Choose one or more: A. Landslides and rockfalls are capable of producing only local tsunamis. B. Large landslides, such as those involving partial collapse of steep-sided islands, have triggered tsunamis of regional or global extent. C. Landslides can trigger tsunamis by creating earthquake waves. D. Landslides can trigger tsunamis by rapidly displacing a mass of ocean water.

B. Large landslides, such as those involving partial collapse of steep-sided islands, have triggered tsunamis of regional or global extent. D. Landslides can trigger tsunamis by rapidly displacing a mass of ocean water.

This illustration shows the conditions that existed just before heavy rains caused the 1925 Gros Ventre Slide in Wyoming. The Gros Ventre Slide occurred as a slump that dammed the Gros Ventre River and created the Lower Slide Lake. Which of the following was primarily responsible for this famous event? Choose one: A. Hillside C was responsible because it was undercut by the river. B. Shale A was responsible for the failure because it was mechanically weak and dipped in a downslope direction. C. Limestone D was responsible because it contained numerous sinkholes developed because of acid rain. D. Sandstone B was responsible because it was deeply weathered, and the cement holding the sand grains together was largely dissolved by the rain.

B. Shale A was responsible for the failure because it was mechanically weak and dipped in a downslope direction.

The diagram provided illustrates a typical rain-shadow desert. Select the statements that accurately describe the processes shown in this diagram. Choose one or more: A. The prevailing wind direction is right to left. B. The prevailing wind direction is left to right. C. The air cools as it rises over the mountains. D. The prevailing wind blows parallel to the coast.E.The air warms as it rises over the mountains.

B. The prevailing wind direction is left to right. C. The air cools as it rises over the mountains.

Identify the materials that are made from nonmetallic resources. Choose one or more: A. electrical wire B. drywall C. concrete D. granite countertops E. nuts and bolts

B. drywall C. concrete D. granite countertop

This sand dune in Death Valley National Park was created by the wind. Evidence of its origin comes from the small wind ripples that ornament its surface and the pronounced asymmetry of the two sides of the dune (obvious in the foreground). What is the primary wind direction in this area? Choose one: A. right to left B. left to right C. into the image (away from you) D. out of the image (toward you)

B. left to right

Caves commonly form in what rock type? Choose one: A. coal B. limestone C. silt D. sandstone

B. limestone

Upon seeing this photograph of karst topography, one could infer that Choose one or more: A. the area is tectonically active. B. solution caves have formed below the ground. C. there are faults in the region. D. the region most likely has extensive limestone layers.

B. solution caves have formed below the ground. D. the region most likely has extensive limestone layers.

Hydrothermal Deposits - Black Smokers

Black Smokers are forming massive sulfide deposits around midocean ridges right now. Hydrothermal deposits are also associated with black smokers at mid-ocean ridges.

Alteration of Landscapes

By definition, Landscape alteration implies habitat fragmentation, habitat loss (i.e. reduction in the total amount of the habitat), habitat isolation and modification of the structure of the landscape. As geologist's we first look at alteration of the structure of the landscape

Retention Pond

Comparison of runoff from a paved area through a storm drain with runoff from a paved area through a temporary storage site (retention pond).

Which of the following statements is true about lakes? Choose one: A. The presence of a lake indicates a lack of groundwater in a region. B. A lake is surface water; it is not associated with groundwater. C. The surface of a lake corresponds to the surface of the groundwater table nearby. D. The bottom of a lake bed represents the groundwater table in the region.

C. The surface of a lake corresponds to the surface of the groundwater table nearby.

This image shows a layer of gravel found in a flat area between sand dunes in Death Valley National Park. Which of the following processes was most likely responsible for the creation of this feature? Choose one: A. deposition of gravel by strong winds B. deposition in an ancient lake bed C. concentration of gravel caused by the removal of sand and silt D. fragmentation of larger boulders by wind abrasion

C. concentration of gravel caused by the removal of sand and silt

This image shows a layer of gravel found in a flat area between sand dunes in Death Valley National Park. Which of the following terms is used to describe this type of feature? Choose one: A. ventifact B. desert varnish C. lag deposit D. playa

C. lag deposit

This image shows the aftermath of mass movement in a steep-sided glacial valley in Switzerland. This impressive scar and talus pile likely records which of the following types of mass movement? Choose one: A. turbidity current B. debris flow C. rockfall D. creep

C. rockfall

This image shows mass movement on a vegetated hillside near the Dietrich River in Alaska. Which of the following terms best describes this type of mass movement? Choose one: A. debris flow B. rockslide C. solifluction D. slumping

C. solifluction

Caves and Karst

Caves develop when weakly acidic groundwater dissolves limestone. CO2 is added to rainwater as it falls through the air and to groundwater from decaying organic matter in the soil. CO2 reacts with water to form carbonic acid.

Portland cement

Cement made by mechanically mixing limestone, sandstone, and shale in just the right proportions, before heating in a kiln, to provide the correct chemical makeup of cement.

Nuclear Fission

Certain radioactive atoms can be fragmented, a process called fission, to yield tremendous quantities of energy. Fission energy is used to run nuclear power plants.

Meandering Streams

Channels form intricately looping meanders along the lower gradient portion of the longitudinal profile.

Biogeochemical Cycles

Chemical fluxes between living and nonliving. Involve storage and transfer between reservoirs. Nonliving reservoirs: Atmosphere, Lithosphere, and Hydrosphere. Living reservoirs: All living organisms: Microbes, Plants, and Animals

Cirque Glacier

Cirque glaciers fill the amphitheater-shaped bowl where mountain glaciers start.

Milankovitch cycles

Climate cycles that occur over tens to hundreds of thousands of years, because of changes in Earth's orbit and tilt.

Lag Deposits

Coarse clasts cannot be lifted and moved by the wind. Lag deposits form when all finer sediment is blown away leaving coarse material behind. Desert pavement is an erosion-resistant surface lag of stones that develops in stages. Dust that falls between pebbles and cobbles is protected from erosion and builds up as a soil. Stones crack into smaller bits and settle to form a mosaic.

Peat

Compacted and partially decayed vegetation accumulating beneath a swamp.

Long-Term Climate Change: Oceanic Circulation

Complex interactions across the Earth system are responsible for long-term climate changes. Plate tectonics modifies the positions of continents, which alters the nature of oceanic current circulation. When the Isthmus of Panama closed during the Miocene, circulation between the Atlantic and the Pacific was restricted, contributing to global cooling.

Landslide Potential Mapping

Computer modeling is used to identify areas of potential risk that may not show obvious signs of mass movement. It assesses multiple factors: Slope steepness, Strength of substrate, Degree of water saturation, Orientation of planar features, Bedding, Joints, Foliation, Vegetation cover, Heavy rain potential, Undercutting potential, and Earthquake probability

Interactions between surface water and groundwater

Considered parts of the same resource. Nearly all surface water environments have strong linkages with groundwater. Effluent versus influent streams. Effluent streams: perennial streams (flow all year). Influent streams: above the water table and flow only in direct response to precipitation.

Types of Deserts: Coastal Deserts

Cool air over cold ocean water holds little moisture. This air absorbs moisture when it interacts with land.

petroglyph

Drawings formed by chipping into the desert varnish of rocks to reveal the lighter rock beneath.

River Slope or gradient

Drop of channel over horizontal distance.

What is the greatest contributor to tide generation? Choose one: A. Changes in water levels through storms B. Gravitational attraction of the Sun C. Geometry of ocean basins D. Gravitational attraction of the Moon

D. Gravitational attraction of the Moon

Which of the following statements accurately describes the formation of such features? Choose one: A. Lags form where sediment has been stabilized by a biofilm. B. Lags form as pebbles settle from suspension deposition. C. Lags form when windblown dust sticks to condensation on the surface of the soil. D. Lags form when the wind preferentially removes relatively fine-grained sand and dust.

D. Lags form when the wind preferentially removes relatively fine-grained sand and dust.

Which of the following provides the source of heat for the water that erupts from this geyser? Choose one: A. solar energy B. friction from motion along a fault C. underground coal fires D. heat from molten rock in the subsurface

D. heat from molten rock in the subsurface

This image shows a close-up view of a piece of pumice that was washed up onto a beach in Italy. Which of the following sets of properties allow this volcanic rock to float on water? Choose one: A. high porosity, high permeability B. low porosity, high permeability C. low porosity, low permeability D. high porosity, low permeability

D. high porosity, low permeability

Consider the various ways in which oil pollution can reach the North American oceans. The greatest amount of oil pollution comes from which of the following sources? Choose one: A. large oil tanker accidents near ports and in rivers B. purposeful dumping of oil-contaminated bilge water from cruise ships C. oil leakage from offshore drilling platforms D. oil residue on roadways and oil dumped in storm drains

D. oil residue on roadways and oil dumped in storm drains

What is the primary weathering process in desert conditions? Choose one: A. chemical weathering B. temperature weathering C. water weathering D. physical weathering

D. physical weathering

Which of the following is not an environmental hazard of large-scale mining? Choose one: A. tailings piles that create large areas of unvegetated land B. massive holes in the Earth's surface visible from space C. ore-processing plants that can release harmful chemicals that mix with rain and damage surrounding life D. sediment liquefaction that can compromise mining tunnels and neighboring processing plants E. acid mine runoff from ore-bearing rock reacting with rainwater

D. sediment liquefaction that can compromise mining tunnels and neighboring processing plants

Wind Erosion: Deflation

Deflation is a lowering of the desert land surface via wind erosion. Concentrated wind erosion creates a depression in the desert surface called a blowout.

Desert Landscapes: Cuestas and Hogbacks

Desert landforms are different where bedding dips at an angle. At lower bedding angles, an asymmetric linear ridge called a cuesta develops. A cuesta has a steep cliff scarp and a more gentle dip slope. At higher bedding dip angles a hogback develops. The steeply dipping beds of a hogback create a more symmetric ridge.

Desertification

Desertification is the aridification of nondesert areas as the result of human activity. The Sahel is the semiarid region along the southern edge of the Sahara. Large parts have undergone desertification. Desertification is caused by overpopulation, overgrazing, careless agriculture, and the overuse of ground and surface water supplies. Desertification leads to famine. Desertification facilitates large dust storms that cross entire ocean basins and carry dangerous chemicals and disease organisms.

Weathering and Erosional Processes in Deserts

Deserts are characterized by special processes of erosion by water and wind, weathering, soil formation, and sediment deposition. These processes result in the unique landscapes that typify deserts. Because of the lack of plant cover, variations in soil and bedrock color stand out. Trace elements add to wide color variations creating beautiful landscapes.

Dry Regions: The Geology of Deserts

Deserts are lands of extremes—extreme dryness, heat, cold, and beauty. Deserts cover ~25% of land surfaces.

Desert Landscapes

Deserts exhibit a diverse set of landscape styles that reflect a complex interplay of erosional and depositional processes over time. Because physical weathering dominates, rock strength is a major control over erosion. Resistant rock forms cliffs; weaker rock forms gradual slopes.

Preventing Mass Movements: Drainage

Dewatering reduces weight and increases material strength, especially of weak layers.

Karst Landscapes: Stages of Development

Dissolution takes place near the water table in an uplifted sequence of limestone. Downcutting by an adjacent river lowers the water table. The caves drain and speleothems grow. With additional dissolution, roof collapse creates a landscape pockmarked with sinkholes.

Preventing Mass Movements

Drainage control: Reducing infiltration and surface runoff. Slope grading: Reducing the overall slope. Slope supports: Retaining walls or deep supporting piles. Avoid landslide hazards: Warning of and correcting landslides

Drainage Networks: Dendritic

Drainage networks often form geometric patterns that reflect underlying geology. A dendritic drainage pattern is the most common form and looks like the branching pattern of tree roots. It develops in regions underlain by homogeneous material.

Desert Landscapes: Transverse Dunes

Dune form depends on the direction and velocity of the wind and the abundance or scarcity of sediment. Abundant barchan dunes may merge into barchanoid ridges, which then grade into linear (or slightly sinuous) transverse dunes. In transverse dunes the wind direction is perpendicular to the ridge crest.

Desert Landscapes: Barchan Dunes

Dune form depends on the direction and velocity of the wind and the abundance or scarcity of sediment. Common landform in sandy deserts. Possesses two "horns" that face downwind, with the steeper slope known as the slip face, facing away from the wind, downwind, at the angle of repose of the sand in question, approximately 30-35 degrees for medium-fine dry sand.

Desert Landscapes: Longitudinal Dunes

Dune form depends on the direction and velocity of the wind and the abundance or scarcity of sediment. Large, elongated dunes lying parallel to the prevailing wind direction. They form in areas that are located behind an obstacle where sand is abundant and the wind is constant and strong. They are usually tens of meters high and up to 100 km (62 mi) long.

Desert Landscapes: Star Dunes

Dune form depends on the direction and velocity of the wind and the abundance or scarcity of sediment. Star dunes form in area's where the wind regime is complex. The wind blows from varied directions over the course of a year.

Desert Landscapes: Parabolic Dunes

Dune form depends on the direction and velocity of the wind and the abundance or scarcity of sediment. U-shaped mounds of sand with convex noses trailed by elongated arms are parabolic dunes. These dunes are formed from blowout dunes where the erosion of vegetated sand leads to a U-shaped depression.

The Pleistocene Ice Age: Glaciers

During the Pleistocene, several distinct ice sheets formed. In several places, neighboring sheets came into contact.Young (<2.6 Ma) glacial remnants are abundant: Northern North America, Scandinavia and Europe, and Siberia. Landscapes in these regions are clearly glacial.

Effects of land-use changes

Dynamic equilibrium: A steady state between sediment transported and sediment delivered to stream and Any changes in amount of water or sediment will bring changes in channel slope or cross-section

Types of Deserts

Each desert has unique characteristics of landscape and vegetation. Geologists group deserts into one of five classes: Subtropical deserts (Sahara, Arabian, Kalahari), Rain-shadow deserts (Eastern Oregon), Coastal deserts (Atacama), Continental interiors (Gobi), and Polar deserts (Antarctica).

Energy Drives Landscape Evolution

Earth's Internal Heat Engine: heat engine: a system that converts thermal energy into useful work (mechanical energy). The two biggest engines in the Earth's interior are in the mantle and outer core. Both regions are undergoing vigorous convection - that is they are transferring heat by mass movement (due to buoyancy). Leads to plate tectonics, volcanoes, earthquakes, mountain building, etc., and Landscape Evolution

Global Climate Change

Earth's climate has changed many times. Long-term climate change. Millions to tens of millions of years in scale. Short-term climate change. Tens to hundreds of thousands of years in scale. Climate studies reveal our past and suggest our future. Distinguish kinds of climate changes. Establish rates at which these changes occur. Determine the effects on Earth and its inhabitants. Methods of study: Paleoclimates—investigations of past climatic variation and Computer simulations—modeling past and future changes. Paleoclimates—past climates are interpreted by datable Earth materials that are climate-sensitive. Stratigraphic records—sequences of rock strata Depositional environments are often climate-sensitive. Glacial tills—cold and continental. Coral reef— tropical marine.

Long-Term Climate Change

Earth's climate history has been largely deciphered: Greenhouse—warmer climates and Icehouse—colder climates. Today, we live in an "Icehouse" but in an interglacial period in that icehouse. There have been at least five major icehouse periods in Earth's geologic history. Over the last 100 million years, Earth experienced a warm climate at the end of the Mesozoic and climate cooling since the Oligocene. What causes long-term climate changes? Complex interactions across the Earth System. Plate tectonics modifies the position of continents. Uplift of land surfaces influences atmospheric circulation. Formation of coal and oil removes carbon from atmosphere. Evolution of life affected atmospheric composition.

Geothermal

Earth's internal (geothermal) energy has two sources: residual heat from planet formation and heat from radioactivity in the crust and mantle. It is geothermal energy that drives tectonic plates. Heat lost through the crust can be harnessed.

Human Impact on the Earth System: Ecosystem Modification

Ecosystem modification—balances are destabilized. Human-caused changes occur faster than indigenous organisms can adapt. Rainforest decline is largely the result of human activity. Human-induced ecosystem destruction is a consequence of deforestation, overgrazing, agriculture, and urbanization.

Preventing Mass Movements: Engineered Structures

Engineered safety structures can be built to improve slope stability or to reduce movement hazards. Retaining walls are barriers that pin the base and trap rock. Fencing or coating can be used to cover an outcrop that has loose rocks. Rock staples are rods drilled into rock to hold loose facing. Avalanche sheds are structures that shunt avalanche snow.

Ephemeral Streams

Ephemeral streams do not flow all year. They are common in places with low annual rainfall, a low water table, and high rates of evaporation. (c and d)

Desert Landscapes: Arches

Erosion produced hoodoos, chimney-like columns of rock, in Bryce Canyon, Utah. Erosion along joints in sandstone produces fins. Erosion at the base of these fins then produces arches.

Desert Landscapes: Fins

Erosion produced hoodoos, chimney-like columns of rock, in Bryce Canyon, Utah. Erosion along joints in sandstone produces fins. Erosion at the base of these fins then produces arches.

Desert Landscapes: Hoodoos

Erosion produced hoodoos, chimney-like columns of rock, in Bryce Canyon, Utah. Erosion along joints in sandstone produces fins. Erosion at the base of these fins then produces arches. Hoodoos form in areas where a thick layer of a relatively soft rock, such as mudstone, poorly cemented sandstone, or tuff (consolidated volcanic ash), is covered by a thin layer of hard rock, such as well-cemented sandstone, limestone, or basalt.

External Heat Engine Alteration of Landscapes: Erosion and Deposition

Erosion: the grinding away and removal of the Earth's surface. Deposition: the accumulation of transported sediment. Both occur at different rates. This is a good time to talk about the fact that energy drives landscape evolution. Internal energy: the heat within the Earth. External energy: energy coming to Earth from the Sun. Gravitational energy: the downward pull on material at higher elevation.

Erosion Landforms

Erosional landforms: result from the breakdown and removal of rock and sediment; develop where agents of erosion (water, ice, air, etc.) carve into land surface.

Eskers

Eskers are long, sinuous ridges of sand and gravel. They form as meltwater channels within or below ice. Channel sediment is released when the ice melts.

The Theory of Glaciation

European farmers broke plows on large rocks. Buried in fine-grained soils, often of enormous size. Unlike local bedrock, they had come from hundreds of kilometers away. These rocks became known as erratics. The origin of erratics became a scientific mystery. Louis Agassiz, a Swiss geologist, observed glaciers. He saw glaciers as agents of landscape change. They carried sand, mud, and huge boulders long distances. They dropped these materials, unsorted, upon melting. He realized that glaciers could explain erratic boulders. Agassiz proposed that an ice age had frozen Europe.Ice sheets covered land. Ice carried and dropped: Fine-grained unsorted sediment and Erratic boulders. When first proposed, Agassiz's idea was criticized. By the 1850s, many geologists agreed that he was right. Agassiz saw evidence for a North American ice age.

Unidirectional Changes

Evolution of the solid Earth: Planetesimal accretion and Melting and differentiation. Formation of the Moon: Mars-sized protoplanet collides, Mantle blasted into space, and Debris coalesced to form the Moon. Evolution of the atmosphere and oceans: Volcanic gases created an early atmosphere. CO2, H2O, N2. Liquid water condensed to form the oceans. Photosynthetic organisms appeared. O2 becomes a significant component of the atmosphere. Evolution of Life. Life appeared on Earth before 3.8 Ga. Multicellular organisms appeared in Late Proterozoic and early Phanerozoic. Life inhabits all regions, within a few km of Earth's surface.

Human Impact on Earth System: Landscape Modification

Excavation, agriculture, and construction modify the topography, drainage, infiltration, and ecology. Human-induced erosion may exceed natural processes.

storm surge

Excess seawater driven landward by wind during a storm; the low atmospheric pressure beneath the storm allows sea level to rise locally, increasing the surge.

Groundwater Problems: Depletion - Groundwater Mining

Excessive groundwater removal has created depletion problems in California and India.

Cut Bank Slumping

Exposed slump failure surface along a river in Costa Rica. Slump blocks that fall into water are often removed quickly by erosion. Slumping is a common process along the outer (cut bank) bend of a meandering river.

Desert Varnish

Exposed surfaces develop desert varnish, a dark surface coating of iron and manganese oxides and clay. Desert varnish forms very slowly; thickness is a relative indicator of age of exposure. Native Americans left petroglyphs in desert varnish across the southwestern United States.

Debris Avalanche

Fast* downhill movements of soil and rock, usually occurring in humid mountainous regions. -up to 280 km/hr

Definitions

Flooding is the natural process of overbank flow. Flood discharge: channel discharge at the point where water overflows the channel. Stage: the height of the water in the river at any time. Flood stage: a high-water condition likely to cause property damage.

Nature and Extent of Flood Hazards

Flooding is universally experienced. In USA, #1 natural disaster during 20th century. Costs ~100 lives/year (10,000 in 20th century). Much higher in developing countries

Hydroelectric

Flowing water turns potential energy into kinetic energy as water is directed past turbines to create electricity. Some dams generate electricity via tidal flux.

Wind Erosion: Rock Pedestals or Mushroom Rocks

Formed by the sand blasting effect of winds against any projecting rock masses. It wears down the softer layer leading to formation of irregular edges on alternate bands of softer & harder rocks. Grooves & hollows cut in the rock surfaces, carve them into pillars known as rock pedestals. Such rock pillars will be further eroded near their bases where friction is greatest. This process of undercutting produces rocks of mushroom shape called mushroom rocks. Grains in wind often "sandblast" exposed surfaces. Ventifacts are stones that have been sandblasted by the wind. Yardangs are wind-sculpted bedrock knobs.

Topographic Profile

Geologists represent variations in elevation along a given traverse by means of a topographic profile, the trace of the ground surface as it would appear on a vertical plane that sliced into the ground.

The Changing Earth

Geology verifies that Earth changes constantly. Why does it change constantly? A plastic asthenosphere permits tectonic plate motion. A star is close enough to warm Earth and its atmosphere. Liquid water is possible; thus, weathering and erosion. Biotic evolution continually modifies the biosphere.

Hydrothermal Systems & Geysers

Geyser: Boiling water and steam erupt cyclically from geysers. Groundwater is heated by shallow magma, but the weight of overlying water prevents boiling. Pressure drops as bubbles form; the water transforms to vapor and the water all boils at once erupting at the surface. The cycle repeats after the emptied chamber is refilled.

Glacial Consequences: Ice Dams

Gigantic proglacial lakes formed near the ice margin. Glacial Lake Agassiz covered a huge area. Existed for 2,700 years. It drained abruptly. Exposed mud-rich, extremely flat land.

Depositional Landforms

Glacial sediments create distinctive landforms: End moraines and terminal moraines, Recessional moraines, Ground moraine, Drumlins, Kettle lakes, and Eskers. End moraines form at the stable toe of a glacier. Terminal moraines form at the farthest edge of flow. Recessional moraines form as retreating ice stalls. Cape Cod, Nantucket, Martha's Vineyard, Block Island, Long Island, and other prominent landforms in northeastern United States formed at the end of the continental ice sheet. Drumlins are elongate, tapered, and aligned hills of molded glacial till that formed underneath the continental ice sheet. They have an asymmetric form—steep up-ice, tapered down-ice—and are common as swarms aligned parallel to ice-flow directions. They are likened to a "field of swimming whales."

Earlier Glaciation

Glaciations have occurred before in Earth history. They are indicated by fossil tills and striated bedrock: Pleistocene, Permian, Ordovician, and Late Proterozoic—tillites at equatorial latitudes suggest an ice-covered world ("Snowball Earth").

Glacial Deposition: Transport of Sediment by Ice

Glaciers act as large-scale sediment conveyor belts. Sediment falls onto a glacier and gets plucked up from below. This material is transported to the toe where it piles up as an end moraine. They pick up, transport, and deposit a lot of sediment. Sediment transport is always in one direction (downhill). Debris at the toe of a glacier is called an end moraine.

Transport of Sediment by Ice

Glaciers are dirt machines; they carry an enormous amount of sediment. Lateral moraines form along either side of a valley glacier. Medial moraines occur in the middle of a valley glacier and result from the merging of two lateral moraines. Moraines—unsorted debris deposited by a glacier. Lateral—forms along the flank of a valley glacier. Medial—mid-ice moraine from merging of lateral moraines.

Carving & Carrying by Ice

Glaciers are important forces of landscape change: Erosion , Transport, and Deposition.

Glacial Advance & Retreat

Glaciers behave like bank accounts. Zone of accumulation—area of net snow addition. Colder temperatures prevent melting. Snow remains across the summer months. Zone of ablation—area of net ice loss. Zones meet at the equilibrium line. The equilibrium line separates the zone of accumulation from the zone of ablation. Ice flows downward in the zone of accumulation and upward in the zone of ablation. Toe position: The position of the toe represents a balance between addition by accumulation and loss by ablation and If accumulation = ablation, the glacial toe stays in the same place. If accumulation > ablation, the glacial toe advances. If accumulation < ablation, the glacial toe will retreat upslope.

Glacial Erosion & its Products

Glaciers carve deep valleys, such as Yosemite Valley. Polished granite domes and vertical cliffs are the result of glacial erosion. Glacial abrasion—a "sandpaper" effect on substrate. Substrate is pulverized to fine "rock flour." Sand in moving ice abrades and polishes bedrock. Large rocks dragged across bedrock gouge striations. Boulders crack crescentic chatter marks into bedrock. Striations run parallel to direction of ice movement. nErosional features of glaciated valleys: Cirques, Tarns, Aretes, Horns, U-shaped valleys, Hanging valleys, and Fjords. Before glaciation, valleys are V-shaped, and tributary mouths are the same elevation as the trunk stream - River dominated. During glaciation, the valleys fill with ice and are aggressively eroded and over steepened - Glacier dominated. After glaciation, the landscape is transformed, containing U-shaped valleys, hanging valleys, cirques, arêtes, horns, and other evidence of the erosive power of glaciers - Erosional Features. Cirques—bowl-shaped basins high on a mountain. Form at the uppermost portion of a glacial valley. Freeze-thaw mass wasting chews into the cirque headwall. After ice melts, the cirque often becomes a tarn (lake). Arete—a "knife-edge" ridge. A narrow ridge of rock that separates two U-shaped glacial valleys. Horns: A horn is a pointed mountain peak formed by three or more cirques that coalesce and In other words, there were at least three glaciers that started near the Matterhorn, and they eroded there way back toward each other, eventually forming this pyramidal peak. Glacial erosion creates a distinctive U-shaped trough valley. These are easily discerned from V-shaped fluvial valleys. A hanging valley results from the intersection of a tributary glacier with a trunk glacier. The larger trunk glacier incises much deeper into the bedrock than the smaller tributary glacier. When the ice melts, the troughs have different elevations and a waterfall results. Glaciers can also erode by plucking. Ice freezes around bedrock fragments and plucks chunks as glacier advances. It forms a distinctive asymmetric hill called a roche moutonée. An asymmetric bedrock hill shaped by the flow of glacial ice. Abrasion rasps the upstream side and plucking carries away fracture-bounded blocks on the downstream side. Fjords are U-shaped glacial troughs that have become flooded by the sea.

Glaciers & Ice Ages

Glaciers: Thick masses of recrystallized ice, Last all year long, Flow via gravity, and Two Types: Mountain/Alpine and Continental. Presently cover ~10% of Earth. During ice ages, coverage expanded to ~30%. The most recent ice age ended ~11 ka. Covered New York, Montreal, London, and Paris. Ice sheets were hundreds to thousands of meters thick.

Wind Erosion - Ventifacts

Grains in wind often "sandblast" exposed surfaces. Ventifacts are stones that have been sandblasted by the wind. Yardangs are wind-sculpted bedrock knobs.

Wind Erosion: Yardangs

Grains in wind often "sandblast" exposed surfaces. Ventifacts are stones that have been sandblasted by the wind. Yardangs are wind-sculpted bedrock knobs. Rocks are aligned in the direction of prevailing winds. Winds abrasion excavates the bands of softer rocks into long, narrow corridors, separating the steep sided overhanding ridges of hard rocks called Yardangs.

Kettle Lakes

Ground moraine is till left behind by rapid ice retreat. Creates a hummocky, mostly flat land surface. Kettle lakes form from stranded ice blocks. Ice blocks calve off of glaciers and become buried in sediment. When the ice melts, a kettle forms. Hummocky knob-and-kettle topography typifies ground moraine. If the water table is high, the kettle will fill to become a kettle lake.

Note the Difference Between:

Groundwater Table: the level to which water will rise in an unconfined aquifer. Potentiometric Surface: the level to which water will rise in a confined aquifer* *If the potentiometric surface is above the ground surface, the water will flow freely out of the ground. Such wells are called flowing artesian wells.

Contamination Cleanup

Groundwater contamination can be cleaned up by utilizing engineering principles and natural processes. Contamination can be cleaned up but it is expensive. Most remedial strategies include removing the source. Bioremediation is a technique that utilizes bacteria to clean groundwater.

Groundwater Flow

Groundwater flow occurs on a variety of time and spatial scales. Some groundwater may flow hundreds of kilometers across sedimentary basins. The transit time depends on the flow path. Deeper flow paths take longer. Dependent on: 1. hydraulic gradient: approximately the slope of the water table. 2. hydraulic conductivity: The ability of a particular material to allow water to move through it (m3/day/m2) 3. Darcy's Law: represents the quantitative relationship between hydraulic gradient and hydraulic conductivity.

Groundwater Recharge

Groundwater flows from recharge areas to discharge areas along curving flow paths. Groundwater infiltrates at recharge areas, which are at higher elevations. Groundwater exits the subsurface at discharge areas, which occur at lower elevations.

Human-Caused Contamination

Groundwater transports pollutants away from a source of input and creates a contaminant plume. Contaminant plumes have high concentrations near the pollutant source. Concentrations decrease with distance.

Global Climate Change: Growth Rings

Growth rings in tree rings can be easily dated. The ring thickness reflects climatic changes. Wetter and warmer conditions generate thicker rings. Drier and colder conditions produce thinner rings. The sequence of alternating thick and thin rings forms a time sequence that can be matched with other tree data. Overlapping sequences yield a time scale.

Urbanization and Flooding

Has increased magnitude and frequency of floods in small drainage basins. Percent impervious cover and percent of area served by storm sewers are a measure of the degree of urbanization. Impervious cover - parking lots, sidewalks, buildings, i.e., thinks that do not absorb water, but the water just runs off.

Global Climate Change: Historical Records

Historical records are useful in the reconstruction of past climate change. Written documents. Archaeological evidence. Paintings. Crop records (eg. Grape vines in Newfoundland and wheat crops in Greenland circa 1000 -1200.)

Adjustments to flood hazards

Historically, humans have attempted to prevent flooding: creating physical barriers, straightening streams, widening streams, and deepening streams. Recent years, alternative adjustments: flood insurance and controlling land use on floodplains

Hot Springs and Geysers

Hot springs develop in two settings: where deep groundwater discharges along faults and in geothermal regions. Deep groundwater is warm. The source of heat is the geothermal gradient. In geothermal regions, high geothermal gradients are linked to shallow magma. Circulation returns heated groundwater to the surface.

Human Alteration of Landscapes

Humanity has become a major agent of landscape change.

Hydraulic Head

Hydraulic head, the potential energy driving flow, is due to elevation above sea level and the pressure exerted by the weight of overlying water. A piezometer is a small device used to measure hydraulic head. Flow always moves from high to low hydraulic head.

What is ice?

Ice is solid water (H2O) that grows as hexagonal crystals when water cools below the freezing point. Natural ice is a mineral that forms many types of rock. Igneous ice crystallizes from a melt. Sedimentary ice, such as falling snow, accumulates under the influence of gravity. Metamorphic ice is deformed by plastic flow. Ice moves through the rock cycle quickly. Snow falls like sediment and accumulates in layered strata. Layers of snow recrystallize to become metamorphic glacial ice.

Consequences of Continental Glaciation: Ice Loading and Rebound

Ice sheets depress the lithosphere into the mantle. Slow crustal subsidence follows flow of asthenosphere. This process continues slowly today. After ice melts, the depressed lithosphere rebounds and the land rises.

Minimizing Mass Movement Hazards

Identifying potential mass movements: Photographic analysis, Topographic map and detailed field check, and Historic data. Landslide hazard inventory map: Grading code from the least stable to the most stable

Factors Affecting Slope Strength

Important factors: Relief—steeper slopes have more mass movement, and Climate—more rainfall creates larger water problems and accelerates rates of chemical weathering.

Short-Term Climate Change: Changes in Earth's Orbit and Tilt

In 1920, Milankovic recognized that changes in the Earth's orbit and rotational axis resulted in variation in the amount of heat reaching the surface. Earth's axis wobbles (precession) with a 23,000-year periodicity. The angle of Earth's rotational axis (obliquity) changes with a 41,000-year periodicity. The shape (eccentricity) of Earth's orbit around the Sun varies with a 100,000-year periodicity.

The Pleistocene Ice Age: Timing

In North America, multiple Pleistocene glacial advances are recognized. Youngest to oldest: Wisconsinan, Illinoian, and Pre-Illinoian. Ice ages separated by interglacials intervals. Oxygen isotopes suggest twenty or more glaciations throughout Earth history. Higher 18O/16O = colder. Lower 18O/16O = warmer. The "original four" ice ages may simply have been the largest.

Withdrawal of Subsurface Fluids

In exploration and extraction processes: Petroleum and natural gas, Groundwater, and Geothermal water and steam

The Longitudinal Profile

In general, the longitudinal profile of a stream (elevation change along its length) resembles a concave-up curve

The Carbon Cycle

In the carbon cycle, carbon transfers between several near-surface reservoirs, including the ocean, the atmosphere, organisms (living and dead), and rocks. A biogeochemical cycle that regulates climate. Volcanic CO2 adds carbon to the atmosphere. Atmospheric CO2 is removed in several ways: It dissolves in water as carbonic acid and bicarbonate, Photosynthesis removes CO2, and Weathering. Carbon may be stored for long periods of time in: Limestones, Fossil fuels (coal and oil), Organic shales, and Methane hydrates. Carbon is returned to the atmosphere. Biotic respiration creates CO2 from organic matter. Rapid oxidation (burning) of organic matter creates CO2. Metamorphism of carbonate rocks liberates CO2. Degassing removes dissolved CO2 from water.

Case History of a Seasonal Flood: the Mississippi and Missouri Rivers, 1993

In the spring of 1993, the jet stream moved over the midwestern United States. This trapped moist humid air from the Gulf of Mexico and rain fell in great abundance. In July of 1993, floodwaters invaded large areas. Flooding lasted 79 days, covering 40,000 square miles. The toll was enormous: 50 people died, 55,000 homes were destroyed, and the damage totaled $12 billion.

Head Scarp

Incipient slump along a highway in Utah displaying a developing head scarp. This slump will continue to develop unless remedial stabilization is applied.

Glacial Consequences: Pluvial Features

Large lakes occupied today's Basin and Range deserts. The Great Salt Lake is a small remnant of the much larger Lake Bonneville. Weather patterns were different during glaciation; the American southwest was much wetter. Pluvial features—large lakes formed during ice age. The American Southwest was much wetter. Large lakes occupied today's deserts. Lake Bonneville (remnant is Great Salt Lake).

Climate Change - Aerosols in the Stratosphere

Largely injected by volcanic eruptions. the stratosphere is a stable layer, so lighter, smaller aerosols will have long residence times aerosols reflect and absorb short wave radiation. As a result aerosols produce warming in the stratosphere and cooling in the troposphere. Recent significant eruptions: El Chichon - April 1982 and Mount Pinatubo - June 1991.

Caves and Jointing

Joints, which are conduits for water, are dissolved by the flow, creating a network of caves and passageways. Soluble beds dissolve more rapidly.

Interactions between surface water and groundwater - KARST

Karst topography Definition - landscape underlain by limestone that has been eroded by dissolution, producing ridges, towers, fissures, caves, sinkholes and other characteristic landforms. Karst topography causes many environmental problems: water pollution sources, Collapse (subsidence), and groundwater mining

Factors that cause flood damage

Land use on floodplain. Magnitude of flood. Rate of rise and duration of flooding. The season. Sediment load deposited. Effectiveness of forecasting, warning, and emergency systems

Landforms

Landforms are the individual shapes (valleys, cliffs, beaches, etc.) that make up landscapes.

Introduction

Landslide and other ground failures posting substantial damage and loss of life. In U.S., average 25 deaths; damage more than $1 billion. For convenience, definitions of landslide includes all forms of mass-wasting movements. Landslide and subsidence: naturally occurred and affected by human activities

Perception of the Landslide Hazard

Landslide hazard maps not preventing development in many areas. Common perception: "It could happen on other hillsides, but never on this one." Infrequency and unpredictability of large slides reducing awareness of the hazards. Often people taking the chances

The Earth System

Life on Earth is due to interactions among the: Lithosphere, Atmosphere, Hydrosphere, and Biosphere. The "Earth System" is composed of these physical components interacting with the biosphere. The interlinkage of the physical and the biological: Global changes transform or modify both realms. There are many ways to describe changes: Gradual change, Catastrophic change, Unidirectional change, and Cyclic change. The Earth has undergone and will continue to undergo changes of various, rates, frequencies, and agencies.

Summary - Karst Landscapes

Limestone dissolution creates unique karst landscapes, named for the Kras Plateau in Slovenia. Elements common in karst landscapes include disappearing streams, natural bridges, caves, speleothems, sinkholes, and springs.

Karst Landscapes

Limestone dissolution creates unique karst landscapes. Elements common in karst landscapes include disappearing streams, natural bridges, caves, speleothems, sinkholes, and springs.

Causes of Glaciation

Long-term causes—set the stage for ice ages. Plate tectonics - control factors that influence glaciation. Distribution of continents toward high latitudes. Sea-level flux by mid-ocean-ridge volume changes. Oceanic currents. Atmospheric chemistry. Changes in greenhouse gas concentrations. Carbon dioxide (CO2). Methane (CH4). Short-term causes - govern advances and retreats. Milankovitch cycles drive global climate and glacial cycles. Stage 1: average temperature drops, glaciers are born. Stage 2: glaciers grow, albedo causes further cooling. Stage 3: temperatures warm, glaciers shrink, interglacial begins.

Riprap

Loose boulders or concrete piled together along a beach to absorb wave energy before it strikes a cliff face.

Magmatic Activity

Magmatic deposits form from a cooling plutonic intrusion. Results in crystal settling from the magma. Often known as Massive Sulfide Deposits. -Common element (mineral): Chromium - Cr (chromite) and Copper - Cu (chalcopyrite) -Locations: Bushveld, South Africa, and Sudbury, Ontario

Sedimentary Deposits - Manganese Nodules

Manganese Nodules: potato-size (25% Manganese, 15% Iron, 2%, Nickel, 2% Copper). Chemistry of seawater in some places promotes the deposition of Mn-oxide nodules. Mining companies have begun to explore technologies to exploit these deposits as they have 720 years worth of Cu and 60,000 years of Mn (at current rates of composition).

Ice in the Sea

Marine glaciers are grounded in shallow water and float in deeper water. Floating ice is mostly (4/5ths) beneath the waterline. Icebergs form when the leading edge of the glacier breaks away (calves). Tidewater glaciers—valley glaciers entering the sea. Ice shelves—continental glaciers entering the sea. Sea ice—nonglacial ice formed of frozen seawater. Large areas of the polar seas are covered with ice. Global warming is causing a reduction in ice cover.

Catastrophic Changes & Extinctions

Mass Extinction events: the stratigraphic record contains evidence of dramatic decreases in biodiversity. Catastrophic changes. Large numbers of species disappear forever. Millions of years needed for biodiversity to recover. Major extinctions: Late Ordovician: Mid-Late Devonian, End Permian, Late Triassic, and End Cretaceous

Mass Movements

Mass movement is driven by gravity acting on any sloping surface. It is an important component of the rock cycle.

Initiating Mass Movements

Mass movements occur when Earth materials are subjected to topographic (slope) forces and are weakened or loosened from their attachments. Mass movement occurs on material that has been weakened by fragmentation and weathering. Chemical and physical weathering produce regolith. Surface material is much weaker than solid crustal rock.

Causes of Ice Ages

Milankovic hypothesized that climate variation over 100 to 300 Ka is predicted by cyclic changes in orbital geometry. Earth's axis wobbles (precession) with a 23,000-year periodicity. The angle of Earth's rotational axis (obliquity) changes with a 41,000-year periodicity. The shape (eccentricity) of Earth's orbit around the Sun varies with a 100,000-year periodicity. Ice ages may result when cooling effects coincide.

cement

Mineral material that precipitates from water and fills the spaces between grains, holding the grains together.

ore minerals

Minerals that have metal in high concentrations and in a form that can be easily extracted.

Types of Deserts: Rain-Shadow Deserts

Moist ocean winds are driven over coastal mountains. Windward air is forced to rise, expand, and cool. Moisture condenses, rains out, and creates a rainforest. Leeward air, stripped of moisture, sinks, warms, compresses, and wicks water out of the landscape, forming a rain-shadow desert.

Warning of Impending Landslides

Monitoring changes: Human surveillance, and Instrumental survey: Tilt meter and geophones. Landslide warning system: Info for public awareness and education, Enough time for public evacuation, Stop or reroute traffic flow, and Emergency services

Global Climate Change: The Role of Greenhouse Gases

Most of the incoming visible light from the Sun penetrates the atmosphere and warms Earth's surface. This absorbed energy is released from the surface as infrared (thermal) energy. Certain gases (H2O, CO2, CH4, NO2, and O3) in Earth's atmosphere absorb thermal energy and re-radiate it, warming the lower atmosphere. This is called the greenhouse effect because it operates in a manner similar to the way glass traps heat in a horticultural greenhouse.

Climate Change - Mt. Pinatubo's SO2 Plume

Mt. Pinatubo injected 20 million tons of sulfur dioxide into the stratosphere! The sulfur dioxide was observed around the globe in the equatorial regions. What was the effect on global temperatures???

Native Metals

Native metals (gold, silver, copper, iron) occur naturally in a pure form.

Undercutting

Natural—a river eroding the base of a slope. Human-induced—excavating the base of a slope

Mass Movement is Classified on the Basis of:

Nature of material, Velocity of movement, and Nature of movement

Factors Influencing Mass Movement

Nature of slope materials, Steepness of slope, Water content, and Slope stability

Groundwater supply

Nearly half of U.S. population uses groundwater as primary drinking water source. Total amount of groundwater in U.S. is enormous. Cost of water pumping and exploration reduces total quantity of available groundwater. Groundwater mining, the removal of groundwater faster than it can be recharged, is a problem, e.g., Ogallala aquifer.

Hydraulic Conductivity

Note: when working with groundwater you are typically in the saturate zone, and the density and viscosity of water is constant. Therefore, permeability becomes the defining characteristic of the hydraulic conductivity measurement. Dependent on: Permeability, Degree of saturation, Density of the fluid, and Viscosity of the fluid

Floodplain regulation

Objective: obtain most beneficial use of floodplains while minimizing flood damage and costs of protection 1. Need to recognize that the floodplain belongs to the river system 2. Requires flood hazard mapping 3. Requires floodplain zoning

Groundwater withdrawals, by State, 2015

Of the total fresh groundwater withdrawals nationwide (82,300 Mgal/d), irrigation accounted for 70 percent, primarily in California, Arkansas, Nebraska, Idaho, and Texas. Irrigation used greater than three times more fresh groundwater than public supply, which was the next largest use of fresh groundwater in the Nation.

Ore Minerals

Often, native metals are collected from ore minerals. Ore minerals: these are minerals that contain an element that, when mined, can be extracted for a profit. This image shows malachite, a copper carbonate ore mineral. It is mined to extract the copper.

Vajont Dam Case Study

On October 9, 1963 in Italy. ~ 2600 deaths. Landslide at 30 m/s or 60 mile/h occurred above a man-made reservoir pushing tons of material into the water. Generated waves of water up to 300 ft high that swept down the valley toward towns. Multiple factors: Weak carbonate rocks and clayey layer, Geologic fractures, sinkholes, and Steep slope surface and creep due to the increased water pressure of the reservoir

global change

The transformations or modifications of both physical and biological components of the Earth System through time.

Earth's Future

Our future on Earth requires sustainable growth. Growth based on balancing societal and human needs with our limitations are Earth's finite resources. Without sustainability, Earth and humans will be in conflict. Earth System disruption will reach a critical point based on: Natural resource limitations (fuels, metals, water), Shrinking land areas, and Increasing populations. Under such a scenario, a new equilibrium will need to be reached.

Global Climate Change: Oxygen Isotopes

Oxygen isotope ratios indicate the temperature of past environments. Two oxygen isotopes are used: 16O, which is lighter, and 18O, which is heavier. 16O water evaporates faster than 18O water. During ice ages, the 16O water evaporated more readily and was trapped on land as glacial ice. Seas then become 16O-depleted and 18O-enriched (the 18O/16O ratio increased). Shells grown in this seawater preserve the 18O/16O ratio. The oxygen isotope record is read from glacial ice (left) and fossil shells in sediment (right). Oxygen isotope ratios are preserved in carbonate shells of organisms. The oxygen in CaCO3 shells mirrors oceanic 18O/16O. Sea-floor sediments preserve ocean chemistry and temperature changes.

Rivers: Historical Use

People have lived on floodplains throughout human history. WHY? Enticed by rich alluvial soil, water supply, ease of waste disposal, and proximity to river commerce

Living with Floods

People living in floodplains face hard choices: move or realize eventual catastrophic loss. Defining floodways, places designed to transmit floods, and removing people and structures from these places may mitigate the magnitude of catastrophic loss.

Permanent Streams

Permanent streams are defined by water flowing all year. These streams are common where there is abundant rainfall, groundwater discharge, and low rates of evaporation. (a and b)

Physical Weathering

Physical weathering dominates. Lack of water diminishes chemical weathering, although it does still occur. Ions dissolved by moisture are precipitated as evaporation salts that cement grains and break them apart. Sometimes dissolved ions percolate into the soil and precipitate calcite, which creates a hard layer called calcrete. To the right, a calcrete layer has been exhumed by erosion.

Piedmont Glaciers

Piedmont glaciers spread out at the base of a mountain valley.

Playas

Playas are desert lakes that have no outlet streams. Playas are dry, vegetation-free, flat areas at the lowest part of an undrained desert basin. They are location where ephemeral (temporary) lakes form during wet periods, and is underlain by stratified clay, silt, and sand, and commonly, soluble salts. The water from flash floods flows into playas and then evaporates. Dissolved solids crystallize out as minerals as the water evaporates. Halite, gypsum, and borax are all evaporite minerals found in playas.

Human Impact on the Earth System: Stratospheric Ozone Depletion

Pollution causes depletion of stratospheric ozone (O3). Chlorofluorocarbons (CFCs) catalyze destruction of ozone. Stratospheric ozone protects Earth from UV radiation. Ozone depletion is harmful to many life forms. Note: Ozone depletion is unrelated to CO2 buildup.

Human Impact on the Earth System: Pollution

Pollution—materials that harm life forms and resources. Modern human society generates contaminants. Contaminating materials are numerous and diverse. They are produced so fast that the natural environmental systems can't absorb or modify/neutralize them. Pollution affects air quality. Smog (smoke + fog)—urban haze created by reaction of: Ground-level ozone, and Unburned hydrocarbons. Pollution causes water contamination. Pollutants frequently enter surface and groundwater: Sanitary wastes, Fuel and oil, Solvents, Fertilizers, and Pesticides. Pollution causes acidification. Acid runoff—sulfide minerals dissolve and release acid: Coal mining and Metal mining. Acid precipitation—sulfide-rich aerosols acidify rain: Coal-fired power plants and Ore smelters. Pollution—radioactive waste. Nuclear materials, mining and processing, generate wastes: Mine spoil and mill tailings, High-level nuclear wastes, and Medical radioactive isotopes.

Erosional Processes: Potholes

Potholes are formed by the sand and gravel swirled by turbulent eddies. This abrasive material drills holes in the bedrock.

Human Impact on the Earth System

Prehistoric humans were few, having a small impact. Today, humans are a huge force of planetary change. Exponential population growth aided by advancements in: Industry, agriculture, technology, and medicine, and Fueled by a suitable supply of natural resources. Human demands often rival or exceed some natural processes.

Effects of flooding

Primary effects: caused directly by the flood. Secondary effects: caused by disruption and malfunction of services and systems

What Can You Do?

Professional geologic evaluation for a property on a slope. Avoid building at the mouth of a canyon, regardless of its size. Consult local agencies for historic records. Watch signs of little slides—Often precursor for larger ones. Look for signs of structure cracks or damages prior to purchase. Be wary of pool leaking, tilt of trees and utility poles. Look for linear cracks, subsurface water movement. Put observations into perspective, one aspect may not tell the whole story

Cone of Depression

Pumping groundwater affects the water table. If groundwater is extracted faster than it can be replaced, a cone of depression develops around the well. Pumping by a large well may lower the water table enough to cause a nearby small well to go dry.

How is Recurrence Interval Calculated?

R = (N+1)/M -R = recurrence interval in years -N = number of years of record -M = rank of the individual flow in the recorded years.

Drainage Networks: Radial

Radial drainage develops from a point uplift (a mesa, volcano, etc.)

Human Impact on the Earth System: Recent Global Warming

Recent global warming—human greenhouse gas additions alter climate. CO2 in the atmosphere has steadily climbed since the industrial revolution began. Ice core data show atmospheric CO2 in 1750 was ~ 280 ppm. In 1958, CO2 was ~315 ppm; in 2010, CO2 was ~390 ppm; today, in 2018 it was 407 ppm and is increasing at >2 ppm/yr. The current value of ~407 ppm is beyond the range of natural variation for the last 800,000 years. From ice core studies, CO2 concentration varied from 180 to 280 ppm throughout glacial advances and retreats. Recent global warming—human greenhouse gas additions alter climate. Human additions of CO2 and CH4 exceed natural removals. Fossil fuel combustion (CO2). Rice-paddy decay (CH4). Cow flatulence (CH4). Atmospheric CO2 increase causes warming, but has warming taken place over the last 200 years? Thousands of published observations suggest that, yes, it has. Large ice shelves, like the Larsen B along the Antarctic Peninsula, are breaking up. The summer melt line indicates that melting of the Greenland ice sheet is accelerating. Thousands of published observations suggest that, yes, warming has occurred. Arctic summer sea ice coverage has decreased dramatically. Valley glaciers worldwide have been retreating rapidly. The Muir Glacier, Alaska, retreated 12 km between 1941 and 2004. Consensus now: global warming is fact. Surface air temperatures have warmed by ~ 1oC since 1880. Global average temperature is higher today than at any time in the last 2,000 years even warmer than during the medieval warm period. Temperature reconstructions during the past 2,000 years: each color represents the results of a study from a different location. Graph of the change in global average temperature since 1880: Both the southern and the northern hemispheres show warming. This model calculates the extent of global warming with variation in the input amount of CO2: Even the low emissions model shows substantial warming. Computer models predict climate changes: By 2050, average annual T will increase by 1.5oC to 2.0oC. By 2150, global T may be 5oC to 11oC warmer than present. What might we expect from global warming: Stronger storms due to a more vigorous hydrologic cycle: Higher sea-surface temperatures, Greater evaporation, Greater differential pressures - winds!, and 2005 set a number of storm records. The predicted effects of global warming: A rise in sea level Sea level is now rising at more than 2 mm/year. Warming will accelerate this trend by: Thermal expansion of seawater and Melting polar ice. Sea level has risen by about 120 m (400 ft) since the last glaciation, primarily from melting of continental ice sheets. Tide gauges document a steady rise in sea level over the last 130 years. The predicted effects of global warming: A rise in sea level. Many people live within 1 meter of sea level. Rising sea level will displace millions. Many scientists think that global warming could lead to: Interruption of the oceanic heat conveyor system. Polar ice meltwater is freshwater. Would dilute surface ocean water near the poles. This freshwater won't sink and move southward. Thermohaline circulation would stop preventing warm water from flowing northward.

Preventing Mass Movements: Regrading

Redistributing a slope by terracing (creating benches) removes some of the mass loading and catches debris.

greenhouse (hothouse) period

Relatively warm global climate leading to the rising of sea level for an interval of geologic time.

Desert Landscapes: Rocky Cliffs and Mesas

Resistant beds (sandstone or limestone) form cliffs while weak layers (shales) erode into a gradual slope. Flat-lying rocks create a specific suite of landform types. Cliffs break along joints as erosion undermines resistant rocks. Cliffs retreat to create plateaus and mesas. Over time, erosion creates buttes and chimneys as remnants of mesas.

Preventing Mass Movements: Revegetation

Revegetation has two positive effects: it removes water by evapotranspiration, and the roots help to bind and anchor regolith.

River Erosion

Rivers erode by: Headward erosion - erosion at the origin of a stream channel, which causes the origin to move back away from the direction of the stream flow, and so causes the stream channel to lengthen, Incision or downcutting erosion - the narrow erosion caused by a river or stream that is far from its base level. Forms a V-shaped valley, and Lateral erosion - the process by which a stream over time sweeps back and forth after initially incising, and changes a V-shaped into a U-shaped one: a floodplain is created increasing the stream valley's capacity to carry floodwaters and limit future downcutting.

reservoir rock

Rock with high porosity and permeability, so it can contain an abundant amount of easily accessible oil.

Physical Cycles: Sea-Level Cycle

Sea Level (SL) has risen and fallen many times over Earth's history. +/- 300 meters during the Phanerozoic.Transgression (SL rise): shorelines move landward. Regression (SL fall): shorelines move seaward. Sedimentary rocks preserve evidence of sea-level change. Sea-level cycles are bounded by unconformities.

Mass Wasting includes:

SLOPE PROCESSES, LANDSLIDES, and SUBSIDENCE

Sinkholes Caused by the Removal of Solid Materials

Salt and coal mining: Salt dissolution and pumping, Active coal mines and abandoned coal mines, Ground failure due to depleted subsurface pressure, and More than 8000 km2 of land subsidence due to underground coal mining

Salt Lakes

Salt lakes form when the water flowing into the lake, containing salt or minerals, cannot leave because the lake is terminal, i.e., there is no drainage. The water then evaporates, leaving behind any dissolved salts and thus increasing the lakes salinity, making a salt lake an excellent place for salt production. Playas are desert lakes that have no outlet streams. The water from flash floods flows into playas and then evaporates. Dissolved solids crystallize out as minerals as the water evaporates. Halite, gypsum, and borax are all evaporite minerals.

Groundwater Problems: Saline Intrusion

Saltwater intrusion renders groundwater unpotable. Beneath coastal land, freshwater "floats" on saltwater. Pumping causes the fresh/saltwater boundary to rise, contaminating the well.

Desert Landscapes: Sand Dunes

Sand dunes are windblown accumulations of sand. Dunes develop when sand carried by the wind accumulates around an obstacle. Over time, a dune grows and begins to move downwind. Dune form depends on the direction and velocity of the wind and the abundance or scarcity of sediment.

Secondary Porosity

Secondary porosity is new pore space created after the rock was first formed. Examples include fractures, fault breccia, and solution cavities.

Distribution of Mineral Resources - Continental USA

Sedimentary & residual deposits are found in shield areas of continents. Bauxite forms on granite that has experienced major leaching in tropical areas.

Seismic Reflection Profiling

Seismic reflection can create an image of the subsurface by bouncing sound off of layers. This permits geologists to look for traps without drilling. Seismic imaging is conducted both on land and at sea. These studies are technologically sophisticated and expensive.

Groundwater Problems: Depletion

Severe water table decline can alter surface water flow. Before groundwater withdrawal, the water table is high, discharging to a swamp and permanent stream. After protracted groundwater withdrawal, the water table falls and no longer intercepts the surface at the swamp and stream, which dry up.

Landscapes of the Moon

Shaped by ancient meteorite impacts and volcanic eruptions. No plate tectonics. No new mountains or volcanoes. No hydrologic cycle. No erosion from rivers, wind, or ice. Lunar highlands: light-colored areas with rocks over 4.0 Ga. Mare: flood basalt plains formed over 3.8 Ga.

Natural Removal of Solid Materials

Sinkholes in areas underlain by carbonate rocks: Dissolution of carbonate rocks, i.e. limestone & dolomite (dolostone), Affects most of the conterminous states, Natural or artificial fluctuations in water table increases the problem, and Triggers other problems: Sinkholes are often used as waste dumping sites

Canyons

Slot canyons form when rivers cut through hard rock.

Wind Storms

Sparsely vegetated ground is scoured by wind and fine sand and silt-sized sediment is lifted and moved. High winds can carry dust across entire oceans. Surface load consists of grains moved by saltation (sand skipped and bounced off the land surface). Suspended load is finer sediment carried in the air. Sometimes suspended load is transported as giant dust storms, or haboobs.

Speleothems

Speleothems are formed from precipitation of dripstone, which develops when groundwater entering a cave degasses CO2. CaCO3 is precipitated as a coating on interior surfaces and grows over time into spectacular forms. Stalactites hang down; stalagmites point up.

Groundwater & Springs

Springs are locations of natural groundwater discharge that have been important resources for humans for millennia. A spring develops where the water table intersects the surface, most often in a valley. Springs are marked by wetland vegetation, perennial wetlands, saturated soils, nonfreezing ground, and stream flow.

Springs

Springs form under a variety of conditions. Springs develop where there are strong permeability contrasts in layered sedimentary materials. A network of interconnected fractures facilitates spring flow.

Structural Springs

Springs form under a variety of conditions. Where flowing groundwater reaches a steep, impermeable barrier, the pressure pushes it up to the surface. A seep develops where a perched water table intersects the surface.

Channelization

Straightening, deepening, widening, clearing, or lining existing stream channels. Objectives: Controlling floods, Improving drainage, Controlling erosion, and Improving navigation. In many places, especially in arid settings, humans use so much river water for irrigation and industry that not enough is left to maintain hydrologic and ecologic functions.

Types of Glacial Sedimentary Deposits

Stratified drift is water sorted; unstratified drift is not sorted. Many types of sediment derive from glaciation. Called glacial drift, these include: Glacial till, Erratics, Glacial marine sediments, Glacial outwash, Loess, and Glacial lake-bed sediment. Glacial till—sediment dropped by glacial ice. Consists of all grain sizes—boulders to clay. Unmodified by water, hence: Unsorted and Unstratified. Accumulates: Beneath glacial ice, At the toe of a glacier, and Along glacial flan. Glacial erratics are cobbles and boulders that have been dropped by a glacier, often on glacially polished bedrock. These rocks are different from the underlying bedrock. Often, they have been carried long distances in ice. Glacial marine—sediments from an oceanic glacier. Calving icebergs raft sediments away from the ice. Melting icebergs drop stones into bottom mud. These sediments are called Dropstones. Glacial outwash—sediment transported by meltwater. Muds are removed. Sizes are graded and stratified. Grains are abraded and rounded. Outwash is dominated by sand and gravel. Lakes are abundant in glaciated landscapes. Fine rock flour settles out of suspension in deep lakes. Muds display seasonal varve couplets. Finest silt and clay are from frozen winter months. Coarser silt and sand are from summer months. Loess—wind-transported silt. Pronounced "luss." Glaciers produce abundant amounts of fine sediment. Strong winds over ice blow the rock flour away. This sediment settles out near glaciated areas as loess deposits. Deposits are unstratified and distinct in color.

River Terraces

Stream (river) terraces form when streams carve downward into their floodplains, leaving discontinuous remnants of older floodplain surfaces as step-like benches along the sides of the valley.

Wet Period

Streams bring in large amounts of water, which is stored and slowly released during dry periods. Recharge is High

Dry Period

Streams bring in small amounts of water and carry away small amounts. Recharge is Low

Forming Streams

Streams form at the headwaters, as the result of water precipitated (snow & rain) on Earth's surface. Some streamflow is temporarily stored in lakes and wetlands. Some infiltrates to become groundwater. Headward erosion occurs via intense scouring where sheet flow enters the uppermost part of a channel. Smaller tributaries join a larger trunk stream. The array of linked channels forms a drainage network. Drainage networks evolve over time.

Valleys and Canyons

Stronger rocks produce vertical cliffs, while weaker rocks produce sloped walls.

Types of Deserts: Subtropical

Subtropical deserts, Earth's largest, result from patterns of atmospheric convection. They are found from 20o to 30o N and S latitude across geologic time. At the Equator (0o latitude), solar energy evaporates water, which rises as hot moist air. The rising air cools and expands, dropping abundant rain. This air, stripped of moisture, flows to the N and to the S. In the subtropics (20o to 30o N and S latitude), the dry air moving N and S from the equator sinks back downward, warming and absorbing moisture from the landscape.

Natural Short-Term Climate Change: Solar Flux

Sunspots are magnetic storms that slow convection at the Sun's surface. The abundance of sunspots varies cyclically. When there is an increase in sunspot activity, the Sun radiates less heat. Measurements of the solar energy reaching the top of the atmosphere fluctuate periodically.

Surface Indicators

Surface features warn that a large slump is beginning to develop. Cracks that appear at the head scarp may drain water and kill trees. Power-line poles tilt and the lines become tight. Fences, roads, and houses on the slump begin to crack.

External Heat Engine

Surface processes are mostly driven by solar energy, the external heat engine. Water is evaporated from the oceans and rains down on the continents. Water chemically attacks (weathers) the silicate rocks and physically transports (erodes) the weathered products back to the ocean where they are laid down as horizontal sedimentary beds. This cycling of water is called the hydrologic cycle. Solar driven wind may also redistribute the sediments on the land surface.

Landscapes of Venus

Surface reshaped by volcanic eruptions 300 to 1,600 Ma. Dense atmosphere. Surface dominated by volcanic and tectonic features. No hydrologic cycle.

Effect of Tectonic Setting

Tectonic Setting can influence: high relief, steep slopes, fractured, tilted rocks, and frequent earthquakes (triggers)

wave refraction (ocean)

The bending of waves as they approach a shore so that their crests make no more than a 5° angle with the shoreline

Mass Movement Depends on Nature of Material

The angle of repose increases with increasing grain size. Angle of Repose: the maximum angle at which a pile of unconsolidated particles can rest

angle of repose

The angle of the steepest slope that a pile of uncemented material can attain without collapsing from the pull of gravity.

Recurrence Interval

The annual recurrence interval ( R I ) of an event of a particular magnitude is the average number of years between events of similar or greater magnitude. Thus, the 100 year flood is one which occurs, on the average, once every 100 years.

climate

The average weather conditions, along with the range of conditions, of a region over a year

water table

The boundary, approximately parallel to the Earth's surface, that separates substrate in which groundwater fills the pores from substrate in which air fills the pores.

cliff (scarp) retreat

The change in the position of a cliff face caused by erosion.

Global Climate Change: Paleontological Evidence

The changing proportion of spruce pollen to grass pollen in a sedimentary sequence records changes in vegetation linked to change in climate. Spruce forests grew much farther south 12,000 years ago. Paleoclimatic evidence: Paleontological—faunal assemblages reflect climate. Assemblage changes record climatic shifts. Pollen in pond sediments: Spruce (colder) versus hemlock (warmer) and Trees (colder, drier) versus grasses (warmer, wetter).

hydrologic cycle

The continual passage of water from reservoir to reservoir in the Earth System

The Hydrologic Cycle

The continuous movement of H2O from one reservoir to another. 1. River systems are part of the hydrologic cycle. Other components of the hydrologic cycle include: Evaporation, Transpiration, Precipitation, Infiltration, and Runoff

The Hydrologic Cycle

The continuous movement of H2O from one reservoir to another. Water moves among reservoirs (ocean, atmosphere, rivers, lakes, groundwater, living organisms, soils, and glaciers). Some of the water that falls on Earth's surface infiltrates and becomes soil moisture. Infiltrated water that percolates deeper becomes groundwater. Groundwater flows slowly underground, eventually resurfacing after months to thousands of years to rejoin the hydrologic cycle.

Coriolis effect

The deflection of objects, winds, and currents on the surface of the Earth owing to the planet's rotation

plastic deformation

The deformational process in which mineral grains behave like plastic and, when compressed or sheared, become flattened or elongate without cracking or breaking.

permeability

The degree to which a material allows fluids to pass through it via an interconnected network of pores and cracks.

Glacial Consequences: Periglacial Regions

The distribution of periglacial environments in North America. An example of patterned ground near a pond in Manitoba, Canada. Periglacial (near-ice) environments are unique. Characterized by year-round frozen ground (permafrost). Freeze-thaw cycles generate unusual patterned ground.

slope failure

The downslope movement of material on an unstable slope.

cone of depression

The downward-pointing, cone-shaped surface of the water table in a location where the water table is experiencing drawdown because of pumping at a well.

biogeochemical cycle

The exchange of chemicals between living and nonliving reservoirs in the Earth System.

creep

The gradual downslope movement of regolith.

mass movement (mass wasting)

The gravitationally caused downslope transport of rock, regolith, snow, or ice.

Erosion

The grinding away and removal of Earth's surface materials by moving water, air, or ice.

Bioremediation

The injection of oxygen and nutrients into a contaminated aquifer to foster the growth of bacteria that will ingest or break down contaminants.

Landscapes

The landscape is the character and shape of the land surface in a region.

glacial retreat

The movement of a glacier's toe back toward the glacier's origin; glacial retreat occurs if the rate of ablation exceeds the rate of supply.

saltation

The movement of a sediment in which grains bounce along their substrate, knocking other grains into the water column (or air) in the process.

Groundwater Problems: Reversing Flow Direction

The natural hydraulic gradient can be reversed by groundwater withdrawal. Before pumping, septic effluent is carried by the regional groundwater flow away from the home well. A large irrigation well creates a large cone of depression that reverses the hydraulic gradient and causes septic contamination of the home well.

paleoclimate

The past climate of the Earth.

Oil Age

The period of human history, including our own, so named because the economy depends on oil.

Rock Avalanche

The rapid* mass movement of broken rock material, often riding on a cushion of trapped air. Usually triggered by an earthquake. -10's to 100's of km/hr

beach erosion

The removal of beach sand caused by wave action and longshore currents

ablation

The removal of ice at the toe of a glacier by melting, sublimation (the evaporation of ice into water vapor), and/or calving.

stream rejuvenation

The renewed downcutting of a stream into a floodplain or peneplain, caused by a relative drop of the base level

thermohaline circulation

The rising and sinking of water driven by contrasts in water density, which is due in turn to differences in temperature and salinity; this circulation involves both surface and deep-water currents in the ocean.

glacial subsidence

The sinking of the surface of a continent caused by the weight of an overlying glacial ice sheet.

Physical Changes

The supercontinent cycle: Plate tectonics drives continental movement. Ocean basins open and close. Continental landmasses collide and rift apart. Supercontinents (like Pangaea) have formed several times.

porosity

The total volume of empty space (pore space) in a material, usually expressed as a percentage.

Conditions Needed for Glacier Formation

The transformation of fresh snow to blue glacial ice can take as little as tens of years in regions with abundant snowfall or as long as thousands of years in regions with little snowfall. nThree conditions are necessary to form a glacier: A cold local climate (which requires polar latitudes or a high elevation), Snow must accumulate; more snow must fall than melts, and Snow must not be removed by avalanches or wind.

Solifluction

The type of creep characteristic of tundra regions; during the summer, the uppermost layer of permafrost melts, and the soggy, weak layer of ground then flows slowly downslope in overlapping sheets.

submarine slump

The underwater downslope movement of a semi-coherent block of sediment along a weak mud detachment.

Subsidence

The vertical sinking of the Earth's surface in a region, relative to a reference plane.

Groundwater and the Water Table

The water table is found at the top of the saturated zone of groundwater. The water table is the level to which water will rise in a hole or well. The water table is the level to which water will rise in an unconfined aquifer. The water table is the top of the groundwater reservoir in the subsurface. The water table separates the unsaturated (vadose) zone from the saturated (phreatic) zone. The capillary fringe forms at the boundary. The subsurface layer in which groundwater seeps up from a water table by capillary action to fill pores. The depth to the water table varies with the climate and the seasons. In humid regions, the water table lies close to the surface. Ponds and streams are connected to the water table and remain filled. In dry regions, the water table sinks deep below the surface. Ponds and streams are disconnected from the water table and dry up. The water table is a subdued replica of the surface topography. It is high where the land is high and low where the land is low. Water flows from higher elevations to lower elevations. Topography can be used to estimate groundwater flow direction.

kerogen

The waxy molecules into which the organic material in shale transforms on reaching about 100°C. At higher temperatures, kerogen transforms into oil.

Groundwater Quality: Human-Caused Contamination

There are many human activities that are sources of groundwater contamination.

Principal Metals Used Today

There are three principal metals in most common use today:copper, iron, and aluminum.

Glaciers

Thick masses of recrystallized ice. Two categories of glaciers: mountain and continental

Groundwater Problems: Supply

This map shows the combination of surface water and recharge, as measured in cubic meters per capita per year. Given that, globally, per capita water consumption averages 1,000 m3 per year, the map emphasizes that freshwater supplies are becoming insufficient in many parts of the world.

Water Erosion

Though rare, water is the dominant force shaping landscapes. Desert landscapes reveal dry drainages. Sediment erodes quickly when torrential rains generate dangerous flash floods characterized by rapid flow of thick, muddy, and viscous water. Flash floods quickly infiltrate dry streambeds.

Topography

Topography is the variation in land surface elevation. It can be represented on a topographic map or on a shaded relief map.

global climate change

Transformations or modifications in Earth's climate over time.

Drainage Networks: Trellis

Trellis drainage develops in deformed strata with alternating resistant and weak rocks.

Floodplain Zoning

Typical zoning map before and after the addition of flood regulation.

How a Glacier Forms

Under a microscope, glacial ice has coarse grains and contains air bubbles. Air content decreases with age and degree of metamorphism. Snow compacts and melts to form firn, which recrystallizes into ice. Crystal size increases with depth. Snowfall accumulates and survives the following summer. Snow is transformed into ice. Snow is buried by later falls. Compression reduces volume. Burial pressure causes melting and recrystallization. Snow turns into granular firn. Over time, firn become interlocking crystals of ice. Glacial ice may form: Quickly (tens of years)or Slowly (thousands of years)

soil moisture

Underground water that wets the surface of the mineral grains and organic material making up soil, but lies above the water table.

Glacial Consequences: Sea-Level Changes

Uplifted beaches along the coast of Arctic Canada form terraces as the land undergoes post-glacial rebound. Apparent sea-level fall, but really the land is rising. Sea level—ice ages cause sea level to rise and fall. Water is stored on land during an ice age; sea level falls. Deglaciation returns water to the oceans; sea level rises. Sea level was ~100 m lower during the last ice age. If ice sheets melted, coastal regions would be flooded. The sea level rise between 17 Ka and 7 Ka was the result of deglaciation. Low sea level during the last ice age exposed continental shelves. Prehistoric people migrated to North America from Asia via the Bering land bridge.

Urban Flood Hazards

Urban flood hazards increase as impervious areas increase

Urbanization and Recurrence Interval

Urbanization increases floods for a particular recurrence interval.

Human Land Use and Landslides

Urbanization, irrigation, Timber harvesting in weak, relatively unstable areas, Artificial fillings of loose materials, Modification of landscape, and Dam construction

Valleys - Downcutting Erosion

V-shaped valleys form as rivers downcut through soft sediments. Below: the Andes of Peru.

Valley Glaciers

Valley glaciers are rivers of ice that flow through valleys. Here, a valley glacier in Alaska is draining a mountain ice cap.

Continental Glaciers

Vast ice sheets covering large land areas. Ice flows outward from thickest part of sheet. Two major ice sheets remain on Earth: Greenland and Antarctica

Finding Coal

Vast quantities of coal lie buried in continental sedimentary basins. Cretaceous and Carboniferous coal-bearing rocks occur in great abundance in the midwestern United States and Rocky Mountain regions.

Rivers are a transportation system involving erosion and deposition of sediments

Velocity varies along course, affecting erosion and deposition of sediment. Faster flowing river has greater erosional capacity and transports more sediment than does slower moving river

Lahars

Volcanic ash from recent or ongoing eruptions mixes with water from heavy rains or melted glacial ice.

Natural Short-Term Climate Change

Warmer or colder climates may last thousands of years. The past million years— dramatic climate flux. Around 20 to 30 glaciations. Separated by interglacials. Shorter-term climate changes may last decades to centuries. The past 15,000 years (the Holocene). Warming led to deglaciation; temperatures still fluctuate. Several cold periods have punctuated this interglacial: Younger Dryas, Holocene maximum, Medieval Warm Period, Little Ice Age, and Modern warming trend (human driven).

Process of Subsidence

Water fills pore spaces (holes) between grains. Water helps to hold the ground up. Water is removed to irrigate crops, to use for drinking water, flushing toilets, industrial uses, etc. Water is no longer filling the pore spaces (holes) and the pores collapse = subsidence

Describing Flow in Channels

Water in a stream doesn't usually follow a straight path. It swirls and twists, producing turbulence.

Groundwater Problems: Land Subsidence

Water in pore space acts to hold grains apart. When groundwater is removed, sediment grains compress and the pores collapse. This causes the land surface to crack and subside irreversibly.

Origin of Surface Tension

Water molecules in a liquids interior are attracted in all directions whereas surface molecules have a net inward attraction that results in surface tension that acts like a membrane, allowing objects to float.

Groundwater

Water that resides under the surface of the Earth, mostly in pores or cracks of rock or sediment.

Sediment in Rivers

Waterfall formed by headward erosion

How Long Will Mineral Resources Last?

We can estimate the expected lifetime of mineral resources based on consumption rates and the amount of calculated reserves. Some mineral resources are running out. Strategic Metals: Metals needed for national security - Mn (100%); Pt (92%); Cr (73%); Co (95%). Percentages shown = amount needed to be imported annually.

People have historically settled on or near Flood Plains

What are Flood Plains? The flat surface adjacent to the river channel that is periodically inundated (flooded) and produced by processes associate with flooding

erratic

a boulder of cobble that was picked up by a glacier and deposited hundreds of kilometers away from the outcrop from which it detached

pothole

a bowl-shaped depression carved into the floor of a stream by a long-lived whirlpool carrying sand or gravel

sinkhole

a circular depression formed when an underground cavern collapses

kettle hole

a circular depression in the ground made when a block of ice calves off the toe of a glacier, becomes buried by till, and later melts

contaminant plume

a cloud of contaminated groundwater that moves away from the source of the contamination

feedback mechanism

a condition that arises when the consequence of a phenomenon influences the phenomenon itself

beach profile

a cross section illustrating the shape of a beach's surface

logitudinal profile

a cross-sectional image showing the variation in elevation along the length of a river

geologic cross section

a depiction of contacts in the subsurface as represented by their traces on an imaginary vertical slice into the earth

wave

a disturbance that transfers energy from one point to another in the form of periodic motions

patterned ground

a polar landscape in which the ground splits into pentagonal or hexagonal shapes

scouring

a process by which running water removes loose fragments of sediment from a streambed

sand spit

an area where the beach stretches out into open water across the mouth of a bay or estuary

sheetwash

a film of water less than a few mm thick that covers the ground surface during heavy rains

coastal wetland

a flat-lying coastal area that floods during high tide and drains during low tide, and hosts salt-resistant plants

flash flood

a flood that occurs during unusually intense rainfall or as the result of a dam collapse, during which the floodwaters rise very fast

slow-onset flood

a flood that takes days to weeks to develop; these include seasonal floods that cover flood plains and delta plains

alluvial fan

a gently sloping apron of sediment dropped by an ephemeral stream at the base of a mountain in arid or semiarid regions

beach

a gently sloping fringe of sediment along the shore

hanging valley

a glacially carved tributary valley whose floor lies at a higher elevation than the floor of the trunk valley

coastal fjord

a glacially carved valley that became submerged when sea level rose, so it is now an elongate bay of the sea

mountain (alpine) glaciers

a glacier that exists in or adjacent to a mountainous region

tidewater glacier

a glacier that has entered the sea along a coast

drainage divide

a highland or ridge that separates one watershed from another

well

a hole in the ground dug or drilled in order to obtain water

drainage network (basin)

an array of interconnecting streams that together drain an area

hydrocarbon reserve

a known supply of oil and gas held underground

pluvial lake

a lake formed to the south of a continental glacier as a result of enhanced rainfall during an ice age

erosional landform

a landform that results from the breakdown and removal of rock or sediment

crevasse

a large crack that develops by brittle deformation in the top 60 m of a glacier

tropical cyclone

a large spiral-shaped rotating storm that forms over the ocean in tropical latitudes; the categories includes hurricanes, typhoons, and cyclones.

mesa

a large, flat-topped hill (with a surface area of several square km) in an arid region

topographic profile

a line representing the intersection of the land surface with an imaginary vertical plan at a locality

discharge area

a location where groundwater flows back up to the surface and may emerge at springs

artesian spring

a location where the ground surface intersects a natural fracture (joint) that taps a confined aquifer in which the pressure can drive the water to the surface

recharge area

a location where water enters the ground and infiltrates down to the water table

debris fall

a mass event in which fragments of various sizes, including large chunks and fine sedimnet, free fall down a slope

Rockfall

a mass of rock that separates from a cliff, typically along a joint, and then free-falls downslope. 1. A very rapid mass movement in which newly detached blocks of rock suddenly fall from a steep slope or cliff.

oxbow lake

a meander that has been cut off yet remains filled with water

coral reef

a mound of coral and coral debris forming a region of shallow water

submarine canyon

a narrow, steep canyon that dissects a continental shelf and slope

spring

a natural outlet from which groundwater flows up onto the ground surface

natural levees

a pair of low ridges that appear on either side of a stream and develop as a result of the accumulation of sediment deposited naturally during flooding

landform

a particular land-surface shape at a location

dune

a pile of sand generally formed by deposition from the wind

waterfall

a place where water drops over an escarpment

horn

a pointed mountain peak surrounded by at least three cirques

perched water table

a quantity of groundwater that lies above the regional water table because an underlying lens of impermeable rock or sediment prevents the water from sinking down to the regional water table

rapids

a reach of a stream in which water becomes particularly turbulent; as a consequence, waves develop on the surface of the stream

meandering stream

a reach of stream containing many meanders (snake-like curves)

desert

a region so arid that it contains no permanent streams, except for those that bring water in from elsewhere, and has very sparse vegetation cover

stream

a ribbon of water that flows in a channel

glacier

a river or sheet of ice that slowly flows across the land surface and lasts all year long

tillite

a rock formed from hardened ancient glacial deposits and consisting of larger clasts distributed through a matrix of sandstone and mudstone

guyot

a seamount that had a coral reef growing on top of it, so that it is now flat-crested

moraine

a sediment pile composed of till deposited by a glacier

braided stream

a sediment-choked stream consisting of entwined subchannels

slump

a semi-coherent volume of regolith that slipped down a slope above a spoon-shaped failure surface at slow to moderate speed

tributary

a smaller stream that flows into a larger stream

meander

a snake-like curve along a stream's course

hotspring

a spring that emits water ranging in temperature from about 30 C to 104 C

u-shaped valley

a steep-walled valley shaped by glacial erosion into the form of a U

turbidity current

a submarine avalanche of sediment and water that speeds down a submarine slope

landslide

a sudden movement of rock and debris down a nonvertical slop

mass-extinction event

a time when vast numbers of species abruptly vanish

channel

a trough dug into the ground surface by flowing water

canyon

a trough or valley with steeply sloping walls, cut into the land by a stream

valley

a trough with sloping walls, cut into the land by a stream

V-shaped valley

a valley whose cross-sectional shape resembles the shape of a V; the valley probably has a river running down the point of the V

continental glacier (of a glacier)

a vast sheet of ice that spreads over thousands of square km of continental crust

oasis

a verdant region surrounded by desert, occurring at a place where natural springs provide water at the surface

conventional reserve

a volume of oil or gas in a reservoir rock within a trap; it can be pumped relatively easily from the reservoir rock

failure surface

a weak surface that forms the base of a landslide

Delta

a wedge of sediment formed at a river mouth when the running water of the stream enters standing water, the current slows, the stream loses competence, and sediment settles out

point bar

a wedge-shaped deposit of sediment on the inside bank of a meander

ordinary well

a well whose base penetrates below the water table and can thus provide water

Climate Change - Aerosols in the troposphere

aerosols are tiny liquid and solid particles. they enter the troposphere by: factory and auto emissions, agricultural burning /wild fires, and ocean - phytoplankton produce dimethylsulphide (DMS) - DMS forms SO2 in atmosphere which in turn produces sulfate aerosols. Aerosol concentrations are increasing with time. Tropospheric aerosol effect on climate: reflects incoming solar radiation - cooling affect and absorbs LW radiation - warming affect (especially the black sooty aerosols emitted through fossil fuel and biomass burning). The net effect of tropospheric aerosols is thought to be one of cooling.

Other Factors that affect Climate

amount of dust and aerosols in the atmosphere, reflectivity of ice sheets, concentrations of trace gases, and amount of clouds

flood

an event during which the volume of water in a stream becomes so great that it covers areas outside the stream's normal channel

stalactite

an icicle-like cone that grows from the ceiling of a cave as dripping water precipitates limestone

estuary

an inlet in which seawater and river water mix; created when a coastal valley is flooded because of either rising sea level or land subsidence

seamount

an isolated submarine mountain

cave

an opening in the side of a cliff, or completely underground, which remains dark all day long; larger underground caves are also know as caverns

oil shale

an organic shale containing abundant kerogen

stalagmite

an upward-pointing cone of limestone that grows when drips of water hit the floor of a cave

Regolith

any kind of unconsolidated debris that covers bedrock

greenhouse gases

atmospheric gases, such as carbon dioxide and methane by absorbing infrared radiation

Climate Change - Mt. Pinatubo's effect on Global Temperatures

average hemispheric temperatures dropped by 0.2-0.5｡C for a period of 1-3 years.

firn

compacted granular ice (derived from snow) that forms where snow is deeply buried; if buried more deeply, firn turns into glacial ice

seasonal floods

floods that appear almost every year during seasons when rainfall is heavy or when winter snows start to melt

glacial striation

grooves or scratches cut into bedrock when clasts embedded in the moving glacier act like the teeth of a giant rasp

dissolved load

ions dissolved in a stream's water

weather

local-scale conditions as defined by temperature, air pressure, relative humidity, and wind speed

costal plain

low-relief regions of land adjacent to the coast

pollution

natural and synthetic contaminant materials introduced to the earth's environment by the activities of humans

agent of erosion

natural entities that remove material from the earth's surface, and transport it elsewhere; examples include rivers, glaciers, and wind.

shale oil

oil extracted directly from a source rock

permafrost

permanently frozen ground

acid rain

precipitation in which are pollutants react with water to make a weak acid that then falls from the sky

snow avalanche

rapid downslope movement of a mass of snow; tupically. the movement transforms the snow into a turbulent cloud

ore

rock containing native metals or a concentrated accumulation of ore minerals

Types of Rock Mass Movement

rock fall, rock slide, and rock avalanche

Alluvium

sorted sediment deposited by a stream 1. A rise in the base level or a decrease in discharge causes the valley to fill with alluvium. Later, if the base level falls or the discharge increases, the stream downcuts through the alluvium and a new, lower floodplain develops. The remnants of the original alluvial plain remain as a pair of terraces. Definition: a deposit of clay, silt, sand, and gravel left by flowing streams in a river valley or delta, typically producing fertile soil.

sustainable growth

the ability of society to prosper without depleting the supply of natural resources, and without destroying the environment

energy density

the amount of energy contained by a unit volume of material

Runoff

the water the flows on the surface of the earth to drain the land; it includes streamflow and sheetflow

steady-state condition

the condition when proportions of a chemical in different reservoirs remain fairly constant even though there is a constant flux (flow) of the chemical among the reservoirs

tide

the daily rise and fall of sea level at a given point on the earth

salinity

the degree of concentration of salt in water

wave base

the depth, approximately equal in distance to half a wavelength in a body of water, beneath which there is no wave movement

relief

the difference in elevation between adjacent high and low regions on the land surface

tidal range

the difference in sea level between high tide and low tide at a given point

Hydrosphere

the earth's water, including surface water (lakes, rivers, and oceans), groundwater, and liquid water in the atmosphere 1. Hydrosphere: all the water on Earth in all reservoirs. 2. Residence time: the time water stays in a reservoir; varies among reservoirs. The average length of time that water stays in a particular reservoir during the hydrologic cycle is called the residence time. Water in different reservoirs has different residence times. For example, a typical molecule of water remains in the oceans for 4,000 years or less, in lakes and ponds for 10 years or less, in rivers for 2 weeks or less, and in the atmosphere for 10 days or less.

terminal moraine

the end moraine at the farthest limit of glaciation

Sublimation

the evaporation of ice directly into vapor without first forming a liquid

Distributaries

the fan of small streams formed where a river spreads out over its delta

Floodplain

the flat land on either side of a stream that becomes covered with water during a flood

playa

the flat, typically salty lake bed that remains when a,, the water evaporates in drier times; form in desert regions

longshore current

the flow of water parallel to the shore just off a coast, because of the diagonal movement of waves toward the shore

glacial advance

the forward movement of a glacier's toe when the supply of snow exceeds the rate of ablation

backwash

the gravity-driven flow of water back down the slope of a beach

Pleistocene Ice Age

the ice age that began about 2.6 Ma, and involves many advances and retreats of continental glaciers

annual probability

the likelihood that a flood of a given size or larger will happen at a specified locality during any given year

base level

the lowest elevation a stream channel's floor can reach at a given locality

competence (of a stream)

the maximum particle size a stream can carry

Saltation

the movement of a sediment in which grains bounce along their substrate, knocking other grains into the water column (or air) in the process

Migration

the movement of oil gas from a source rock into a reservoir rock

longshore drift

the movement of sediment laterally along a beach; it occurs when waves wash up a beach diagonally

mouth

the outlet of a stream where it doscharges into another stream, a lake, or a sea

landscape

the overall shape and character of the land surface in a region

hydraulic head

the potential energy available to drive the flow of a given volume of groundwater at a location; it can be measured as an elevation above a reference

headward erosion

the process by which a stream channel lengthens up its slope as the flow of water increases

Deposition

the process by which sediment settles out of a transporting medium

downcutting

the process in which water flowing through a channel cuts into the substrate and deepens the channel relative to its surroundings

deflation

the process of lowering the land surface by wind abrasion

desertification

the process of transforming nondesert areas into desert

carbon cycle

the progressive transfer of carbon, from reservoir to reservoir in the earth system

albedo

the reflectivity of a surface

shore

the region of land adjacent to a body of water

watershed

the region that collects water that feeds into a given drainage network

stream gradient

the slope of a stream's channel in the downstream direction

Hydraulic Gradient

the slope of the water table. Measured by the difference in elevation between two points on the slope of the water table and the distance of flow between them.

Evapotranspiration

the sum of evaporation from bodies of water and the ground surface and transpiration from plants and animals

capillary fringe

the thin subsurface layer in which water molecules seep up from the water table by capillary action to fill pores

capacity (of a stream)

the total quantity of sediment a stream can carry

greenhouse effect

the trapping of heat in the earth's atmosphere by carbon dioxide and other greenhouse gases, which absorb infrared radiation; somewhat analogous to the effect of glass in a greenhouse

downslope movement

the tumbling or sliding of rock and sediment from higher elevations to lower ones

swash

the upward surge of water that flows up a beach slope when breakers crash onto the shore

discharge

the volume of water in a conduit or channel passing a point in 1 second

Urbanization shortens lag time

time between rainfall and peak discharge

suspended load

tiny solid grains carried along by a stream without settling to the floor of the channel

bathymetry

variation in depth

Discharge (Q)

volume of water moving past a particular location in a river (in a unit of time) continuity equation: Q=W*D*V -W = width -D = depth -V = velocity Discharge = water cross section (width x depth) x velocity (distance/time)

rogue wave

waves that are two to five times the size of most of the large waves passing a locality in a given time interval

Exceedence Probability

ØThe probability (p) of an event of a particular magnitude being equaled or exceeded any given year is: P=1/R (R = Recurrence Interval). Therefore, a 100- year flood has a 1 in 100 (=1%) probability of being equaled or exceeded any given year

stream terrace

when a stream downcuts through the alluvium of a floodplain so that a new, lower floodplain develops and the original floodplain becomes a step-like platform

drainage reversal

when the overall direction of flow in a drainage network becomes the opposite of what it once had been

Sedimentary Deposits

1. Banded iron formations (BIFs) consist of alternating layers of gray hematite (Fe2O3) and iron-rich red chert (jasper). BIFs formed from 2.5 to 1.8 Ga and record the onset of oxygen buildup in Earth's atmosphere. 2. Banded Iron Formations (BIFs): Fe2+ is soluble in water, but Fe3+ is not. BIFs are found in the Proterozoic and contain Hematite (Fe2O3) and Magnetite (Fe3O4) in layers that alternate with Fe-rich chert (jasper). They present evidence for an oxygenated atmosphere. 3. Another type of sedimentary ore deposit is Manganese nodules. These nodules grow slowly on the sea floor and are rich in MnO2 and trace elements 4. Avery Island is one of five salt dome islands rising above the flat Louisiana Gulf Coast. These islands formed over the eons when alluvial sediment covered a vast plain of salt left behind by an ancient saltwater ocean. Surficial Precipitation: Evaporite deposits Two types: marine evaporites (salts of Na, K, Ca - halite, sylvite, anhydrite, gypsum and bedded phosphates); non-marine evaporites (Ca & Na carbonates, nitrate, sulfate, and borate minerals).

Coal in the United States

1. Coal has been one of most valuable natural resources since the 1300s when the Hopi Indians used it for the first time. European settlers began to use coal in the late 1740s and as immigration to the US grew and energy demand increased, coal production quickly climbed from 9.3 million tons in 1850 to 750 million in 1918. Eventually coal replaced wood as the primary energy source, and by the 1940s it provided up to 75% of US energy 2. Bituminous coal was the first main target of US mining. This changed between 1843 and 1868 when more anthracite began to be mined. Anthracite was used in iron smelting, and this cleaner and smokeless alternative became the preferred fuel in cities. Limited anthracite resources could not fulfill increasing demand. Production of sub-bituminous coal began to slowly rise; as of 2010 it was higher than bituminous coal production. 3. Until the 1950s coal was primary mined underground east of the Mississippi River. By the 1970s, the development of cheaper surface mining proved a viable alternative for the coal industry. Currently the Powder River Basin, the Appalachian Basin, and the Illinois Basin are among the largest coal producers in the US. In the early 1950s, oil and natural gas became the primary source of US energy. Today, petroleum, natural gas, and coal provide 87% of US energy, and coal is used mostly for electricity generation, steel and liquid fuels production, and cement manufacturing. 4. U.S. coal production dropped 37% in the last 10 years, from over 1.2 billion to about 800 million tons in 2017, cutting the number of coal mines. Coal consumption declined due to the increased supply of cheaper and cleaner natural gas, growth of renewable energy sources, and rigorous environmental regulations. Coal provided close to 60% of US electricity in the mid-1980s, and only about 30% in 2017. From 1,436 coal-powered plants in the US in 2009, about 600 remain as they are shut down due to aging, replacement by natural gas, and environmental guidelines

Indiana Coal Production

1. Coal in Indiana was discovered along the banks of the Wabash River in 1736. Organized development of Indiana's coal resources began in the 1830s and by 1918, production exceeded 30 million short tons 2. Coal production declined following World War I, but underground (deep) mining remained the primary mining method in Indiana until the 1940s. Following World War II, the advent of large-scale excavation equipment made surface mining more cost efficient and by 1965, surface mining accounted for more than 80% of the state's annual production. Surface mining continues to be the primary method of coal removal in Indiana, with nearly 70% of the current production coming from surface mines. 3. Indiana has approximately 57 billion tons of unmined coal, of which nearly 17 billion tons is recoverable using current technology. Of the mineable reserves, about 88 % is recoverable by underground mining and only 12% is recoverable using surface mining methods. Based on current production rates, Indiana's 17 billion tons of available coal could last more than 500 years. Note that since the mid-1990s underground mining has increased as surface mining has decreased. The coal that is left is deeper and harder to reach.

Coal: Energy from Swamps of the Past

1. Coal is a black, brittle, carbon-rich sedimentary rock made up of the altered remains of fossil vegetation that grew in swamps. Coal is an important global energy source and a dominant CO2 emitter. It is only found in rocks younger than 420 Ma (after land plants had evolved). 2. Coal swamps formed on top of marine deltas and along tropical coasts. Sea level fluctuations bury former swamps. Coal-forming periods include the warm climate and broad epicontinental seas of the Carboniferous (354-286 Ma) and the tropical deltaic wetlands of the Cretaceous (144-65 Ma).

Environmental Issues

1. Energy production has clear adverse environmental impacts. Oil drilling and production scars the landscape. Spills from oil storage tanks, pipelines, and ships contaminate surface water and groundwater and may devastate large areas of coastline. Coal mining creates pits, spoil piles, and acid mine runoff. 2. The Deepwater Horizon oil-drilling platform as it appeared in the Gulf of Mexico in July of 2009. Fireboats dousing the burning Deepwater Horizon rig before it sank. 3. Kingston Fossil Plant Coal Ash Slurry Spill. Coal ash slurry is a mixture of solids (mined coal) and liquids (water or organic) produced by a coal preparation plant. Coal slurry can contain hazardous chemicals such as arsenic and mercury and can kill aquatic wildlife (not good for people either).

Drilling

1. Expensive drilling is required to tap into a potential trap. A diamond rotary bit pulverizes rock, while high-density mud cools the bit and lifts cuttings out of the hole. The heavy mud reduces the risk of high-pressure blowouts. Steel casing is cemented to the upper 1,500 ft (or more) of the borehole to protect aquifers and surface water supplies. 2. Drilling can proceed in any direction. Many wells are now drilled horizontally after reaching a target depth to increase yields. Many wells today are artificially stimulated by hydrofracturing, a process that cracks subsurface rock using high-pressure water with additives and sand. 3. After the packers and the fluid are removed, oil and gas can seep into the pipe and flow to the drill head. There is potential for groundwater contamination from hydrofracturing.

The Oil Crunch

1. M. King Hubbert correctly predicted the peak of U.S. oil production to be 1971. We are now close to the peak of global oil production. Oil extinction is likely to occur between 2050 to 2150. Humanity faces many changes as oil runs out. 2. Oil prices have been fluctuating dramatically in recent times. Despite short-term dips, the consumption rate of oil has increased over time but the rate of new discovery has not. Other sources of energy have more abundant reserves.

Traps and Seals

1. Oil and gas traps, sometimes referred to as petroleum traps are below ground traps where a permeable reservoir rock is covered by some low permeability cap rock (the seal). Anticlinal traps are formed when rock layers are folded into an anticlinal arch. The structural arch traps oil. 2. Salt-dome traps are formed when deeply buried salt flows like a plastic. Less dense than overlying rock, salt will flow upward and deform overlying strata. 3. Fault traps are created when displacement creates permeability contrasts on offset strata. 4. Stratigraphic traps are created when depositional features create changes in permeability and porosity.

Methods of Mineral Exploration

1. Originally, exploration entailed looking for a "show" of minerals in a hillside, cliff-face, etc. This "show" would include quartz veins or oxidative staining that included the element(s) of interest. The rock was then assayed (analyzed) to see what the concentration of the element of interest was. A claim could be staked by simply staking off the area. These days, laws are more stringent and exploration techniques are more sophisticated 2. Geophysics: gravity and magnetism. Gravity: Force of gravity increases between two objects with an increase in mass of either one. Use gravity meter to explore local variations in rock density: (mass=density x volume) 3. Magnetic Field Positive magnetic anomaly: magnetic field strength above the average - vice versa for negative magnetic anomaly 4. Geochemical Prospecting - looking at concentrations of metals in the weathered rock (soil) over a wide area. Plants can also be analyzed. Even soil gases and groundwater can be used.

Coal Classification

1. Peat - spongy material formed by the partial decomposition of organic matter, primarily plant material, in wetlands such as swamps, muskegs, bogs, fens, and moors. 2. With increasing temperature, peat is converted to lignite, a very soft, low-rank coal. 3. With further increases in temperature, lignite is transformed into subbituminous coal, a dark brown to black coal, intermediate between lignite and bituminous coal. Contains 42% to 52% carbon. 4. and then into bituminous coal, the most abundant type of coal ranked between subbituminous coal and anthracite. Contains 60% to 80% carbon. 5. At even higher temperatures, usually accompanied by intense deformation generated by the folding and faulting of the Earth's crust, anthracites, the highest rank of coal, are produced. Contains greater than or equal to 86% carbon.

Coal Mining

1. The mining method depends on the depth of the coal seam. Within 100 m, coal is strip mined. For deeper coal seams, underground mining is required. Strip mining removes the rock and soil overlying the coal seam using a large drag-line bucket. Spoil is stockpiled nearby for later use during reclamation. Exposed coal is removed and the excavation is reclaimed. Excavation is backfilled with spoil and soil, then replanted. 2. Underground mining is much more specialized, expensive, and dangerous. The coal is removed by tunneling. Coal mining is hazardous: tunnels can collapse, methane gas can lead to explosions and asphyxiation, and miners can contract black lung disease.

Hydrocarbon Systems

1. The oil window refers to the depth or maturity range within which a source rock generates and expels liquid petroleum. Creation of an oil reserve is dependent on correct timing. After a source rock enters the oil window, kerogen is converted to oil. The oil is buoyant and begins to seep upward. 2. Oil migrates out of the source rock following a higher permeability migration pathway. Migration pathways are created long before oil generation by faulting and fracturing or variations in strata. Oil will accumulate in a structural trap as long as a seal rock is in place. Without a seal, reservoirs can leak to form an oil seep at the surface. 3. Oil and gas accumulate in a trap to form a reserve. Oil floats above groundwater; gas floats above oil. A well is drilled into the trap and the fluids are pumped out. In the context of geologic time, hydrocarbon trapping is temporary. Erosion will eventually breach a seal and hydrocarbons will be lost. Many oil fields that existed in the past have vanished.

coal

A black, organic rock consisting of greater than 50% carbon; it forms from the buried and altered remains of plant material.

hydrocarbon

A chain-like or ring-like molecule made of hydrogen and carbon atoms; petroleum and natural gas are hydrocarbons.

seismic reflection profile

A cross-sectional view of the crust made by measuring the reflection of artificial seismic waves off boundaries between different layers of rock in the crust.

blowout

A deep, bowl-like depression scoured out of desert terrain by a turbulent vortex of wind.

Refining

A distillation column works by gravity. Heated oil separates into bubbles of lighter hydrocarbons and droplets of heavier ones. Heavier ones sink and light ones rise.

strategic mineral

A mineral containing elements, typically metals, of strategic importance to technology

hydrofracturing (fracking)

A process by which drillers generate new fractures or open preexisting ones underground, by pumping a high-pressure fluid into a portion of the drill hole, in order to increase the permeability of surrounding hydrocarbon-bearing rocks.

hydrocarbon generation

A process in which oil shale warms to temperatures of greater than about 90°C so kerogen molecules transform into oil and natural gas molecules.

seal rock

A relatively impermeable rock, such as shale, salt, or unfractured limestone, that lies above a reservoir rock and stops the oil from rising further.

drilling mud

A slurry of water mixed with clay that oil drillers use to cool a drill bit and flush rock cuttings up and out of the hole.

pore

A small, open space within sediment or rock.

metal

A solid composed almost entirely of atoms of metallic elements; it is generally opaque, shiny, smooth, malleable, and can conduct electricity.

ore deposit

An economically significant accumulation of ore.

fossil fuel

An energy resource such as oil or coal that comes from organisms that lived long ago and thus stores solar energy that reached the Earth then.

dimension stone

An intact block of granite or marble to be used for architectural purposes.

Coal Formation

Compaction and decay turn plant debris into peat. In coal-forming swamps, dead vegetation falls into stagnant, O2-poor water. The absence of oxygen prevents decay. Burial to depths of 4-10 km compacts and heats the peat. Chemical reactions drive off hydrogen, nitrogen, and sulfur as gases. The remaining residue, coal, is greater than 70% carbon (C).

biofuel

Gas or liquid fuel made from plant material (biomass). examples of biofuel include alcohol (from fermented sugar), biodiesel from vegetable oil, and wood

Geothermal Energy

Geothermal is energy from Earth's internal heat. Geothermal plants utilize hot groundwater in places that have a high geothermal gradient (mostly located in volcanic regions). Geothermal energy is also useful in nonvolcanic areas. Groundwater can be used to heat and cool buildings very efficiently with no wastes, no greenhouse gases, or air pollution.

Placer Deposits

Heavy (high density) minerals concentrate in regions of low flow. Placer deposits form as the result of hydraulic sorting in high-velocity water. Low-density minerals are suspended and washed away while high-density grains are concentrated.

Energy Resources

Human energy needs have greatly increased in the past 150 years, and the mix of energy resources required to address those needs has changed dramatically. Today, fossil fuels total more than 75% of energy supplies.

Hydrothermal Deposits

Hydrothermal deposits are formed by the action of hot water, which is very chemically reactive. Circulation of reactive hot water solutions through a magma or rocks surrounding an igneous intrusion. Metallic ions are dissolved. They are redeposited when the fluids enter a region of lower temperature/ lower pressure/different acidity/different oxygen availability. This creates a hydrothermal deposit. Common elements (minerals): Lead - Pb (galena), Zinc - Zn (sphalerite), and Silver - Ag (native silver)

Banded Iron Formation (BIF)

Iron-rich sedimentary layers consisting of alternating gray beds of iron oxide and red beds of iron-rich chert.

Natural Gas

Natural gas was the United States' largest source of energy production in 2016, representing 33 percent of all energy produced in the country. Natural gas has been the largest source of electrical generation in the United States since July 2015. U.S. natural gas production growth was concentrated in the Appalachian, Permian, and Haynesville regions. Pennsylvania and Ohio, states that overlay the Appalachian Basin, had the first- and third-largest year-over-year increases for 2018, increasing by 2.0 Bcf/d and 1.7 Bcf/d, respectively.

Where Does Oil Occur?

Oil reserves are distributed on all continents—some onshore and some offshore. Regions bordering the Persian Gulf contain the world's largest reserves.

How Do Ore Deposits Form?

Ore-forming geologic processes: Magmatic activity, Hydrothermal alteration, Secondary enrichment, Groundwater transport (MVT), Sedimentary processes, Residual weathering, and Placer Deposits

Secondary-Enrichment Deposits

Original deposit is sub-economic. Secondary enrichment processes allow concentration of the ore minerals to economic levels. This is also called Supergene Enrichment. These deposits can form when dissolution occurs in oxygenated waters and the water moves to a deoxygenated region.

tar sand

Sandstone reservoir rock in which less viscous oil and gas molecules have either escaped or been eaten by microbes, so that only tar remains.

Solar Power

Solar energy is, by far, the most abundant source of energy to the surface of the Earth. But, solar energy is hard to use because it is diffuse, highly variable on a seasonal and daily basis, and difficult to convert into more usable forms of energy. There are two ways to use solar energy directly. Solar collectors concentrate sunlight for heating, and photovoltaic (PV) cells convert light directly into electricity. Both are useful for small buildings, not large cities.

Wind Power

Steady winds drive a large turbine to produce electricity. Wind-derived electricity is renewable and carbon-free. High-tech wind farms are sprouting worldwide. Wind farms have negative aesthetic impacts and turbine blades are noisy and kill birds.

Energy Choices, Energy Problems

The Oil Age, for future historians, will span about 300 years. Global energy use continues to increase dramatically, reflecting rapid expansion of industrialization. Oil, the dominant energy source, is a nonrenewable resource that is declining. In the future, humans will need to have a different energy mix.

grade (of an ore)

The concentration of a useful metal in an ore—the higher the concentration, the higher the grade.

What is an Ore?

The difference between an ore and other rock is that metals are concentrated in the ore.

oil window

The narrow range of temperatures under which oil can form in a source rock.

directional drilling

The process of controlling the trajectory of a drill bit to make sure that the drill hole goes exactly where desired.

coal reserve

The quantities of discovered, but not yet mined, coal in sedimentary rock of the continents.

Porosity

The total volume of empty space (pore space) in a material, usually expressed as a percentage. amount of spaces in-between sediments depends on size, shape, and sorting of sediments 1. The percent void space in a rock or sediment. A void is a hole or fracture. It is a measure of the potential volume of water that can be stored in a rock. 2. Groundwater resides in subsurface pore spaces, the open spaces within any sediment or rock. The total volume of open space is termed porosity. Porosity can be filled with water or air. Pores can also become filled with mineral cement and other fluids, like oil or natural gas.

Completion

When the hole is completed, the drill rig is removed and a pump is set up. Oil pumped out of the ground is stored in on-site tanks for periodic removal by truck or is added to a pipeline for transport across the countryside. Only 30% of the oil can be removed from a reservoir by pumping (primary recovery). Secondary recovery uses enhanced techniques to retrieve oil, including injecting fluids (steam, CO2) to heat or push the oil.

photovoltaic cell

a devise capable of transforming solar energy directly into electricity

oil seep

a location where oil bubbles out of the ground on its own, without pumping

source rock

a rock (organic-rich shale) containing the raw materials from which hydrocarbons eventually form

chain reaction

a self-perpetuating process in a nuclear reaction, whereby neutrons released during the fission trigger more fission

fuel

a substance that can be used to produce energy

unconventional reserve

a supply of oil or gas that cannot be easily pumped; it includes forms of hydrocarbons that are too viscous to pump, or occur in impermeable rock; examples include tar sand, oil shale, shale oil, and shale gas

Biomass

amount of organic material in a specified volume

mineral resource

an accumulation of a useful ore, in which valuable elements are sufficiently concentrated to be worth mining

shale gas

gas extracted directly from a source rock (organic shale)

manganese nodules

lumpy accumulations of manganese-oxide minerals precipitated onto the sea floor

Permeability

the degree to which a material allows fluids to pass through it via an interconnected network of pores and cracks. The ability of a fluid to flow through pore space in a rock 1. The ability of a material to transmit a fluid. It is a measure of how fast the fluid can travel through the rock or sediment. Permeability is the ease of water flow due to pore interconnectedness. High-permeability material allows water to flow readily. Water flows slowly through low-permeability material.

Hubbert's Peak

the high point on a graph of production vs. time; the concept that we can define hubbert's peak for a resource emphasizes that supplies of resources are limited

meltdown

the melting of the fuel rods in a nuclear reactor that occurs if the rate of fission becomes too fast and the fuel rods become too hot

nuclear reactor

the part of a nuclear power plant where the fission reactions occur

coal gasification

the process of producing relatively clean-burning gases from solid coal

nuclear waste

the radioactive material produced as a byproduct in a nuclear plant that must be disposed of carefully due to its dangerous radioactivity