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GEOL 120: FINAL EXAM
Deserts |
water deficient (receive <25 cm precipitation/year
have high evaporation rates
dominated by mechanical weathering (due to lack of water)
very little vegetation (due to lack of water)
two types:
- low-latitude
- middle-latitude |
Low-Latitude Deserts |
- largest of the world's deserts occur at 30⁰ N and 30⁰S of the equator
- the Earth is driest along these latitudes because of its circulation |
Low-Latitude Deserts (Circulation Pattern) |
1. Air is warmed at the equator (low pressure) where land gets the most sun
2. Warm air rises at the equator
3. Warm air cools as it rises
4. Cool air expands and precipitation occurs (at 20⁰ latitude)
5. At 30⁰ latitude, Cool air sinks back to the surface (high pressure), compresses and warms and results in:
- clear skies
- sunshine
- drought |
Two Types of Low-Latitude Deserts |
1. Continental Interiors: deserts that are too far away from the ocean for it to be a source of moisture
- air masses lose moisture as they travel across the continent
2. Rainshadow Deserts: leeward (dry) sides of mountains
- as moist coastal air rises, it becomes cooler, the moisture then condenses and precipitates and the air that gets to the other side of the mountain is dry, cool, and sinks |
Weathering in deserts is a ___ process because ______. |
SLOW
of the scarcity of water and organic acids (from plants) |
Ephemeral Streams |
stream beds that only carry water during rain events, not all year round |
Rain events often result in flooding because _____. |
of scarce vegetation and slow infiltration |
Significant erosion can occur after ___ rain event(s) |
one |
Wind (As an Erosional Agent in Deserts) |
- able to pick up and transport sediment over large areas
- like water, wind carries a bed load and a suspended load |
Bed Load |
sand grains carried by wind move by saltation (moving by skipping and bouncing) close to the ground |
Suspended Load |
Finer (silt and clay) dust that is transported into the atmosphere for great distances |
Deflation |
erosion caused by wind where the entire land surface is lowered due to removal of sediment |
Erosional Features Created by Wind |
Blowout: scoop-shaped depressions carved out by wind through deflation
- Ventifacts: sharp, polished stones shaped by the wind by abrasion
- indicate wind direction
- Yardangs: streamlined wind sculpted landform; about 5 m tall that is narrower at the base than at its top |
Depositional Features Created by Wind |
- Dunes: mounds and ridges of sand
- Loess: blankets of silt
|
Dunes |
- up to 100 m high
- form in groups with regular spacing
- balance between erosion and deposition (tractor tread motion)
- types:
1. Transverse 6. Star
2. Barchan
3. Parabolic
4. Longitudinal
5. Coppice |
What does the type of dune depend on? |
1. Wind direction
2. Velocity
3. Availability of Sand
4. Amount of Vegetation
|
Loess |
-homogeneous, unstratified silt
- thick
- highly porous
- keeps vertical slopes
- decreases in thickness with increasing distance from its source
- widespread and distinctive
- soils derived from loess are among the world's most fertile |
Glacier |
a thick mass of ice that forms over hundreds or thousands of years by snow:
- accumulation
- compaction
- recrystallization |
Glaciers today cover __% of the Earth's surface |
10 |
What areas of the globe reflect a prior glacial presence? |
- Alps
- Cape Cod
- the Great Lakes
- Alaska |
Glaciers move ______ and have a ______ erosive power. |
Slowly
Strong |
Glaciers are part of what cycle(s)? |
Hydrologic Cycle
Rock Cycle |
Types of Glaciers |
1. Valley (Alpine): in mountainous areas where valleys that were once water are now ice; flow down-valley
2. Ice Sheets: much larger than valley glaciers; flow out in all directions; include Greenland and the Antarctic Ice Sheets today
-Ice Caps
-Outlet
-Piedmont |
Snowline |
marks the elevation above which snow remains all year |
How do glaciers move? |
1. Plastic Flow: movement within ice (50 m depth)
2. Basal slip: ice mass slipping along the ground
|
Crevasses |
cracks that form at the surface of a glacier (zone of fracture) due to tension as the glacier moves over irregular terrain |
Where do glaciers move the fastest? |
in the center of the channel (similar to water streams)
- friction caused by bedrock floor and valley walls slows glacial movement at its bottom and sides |
Zone of Ablation |
glacial loss due to melting, calving, and sublimation
|
Zone of Accumulation |
Snow accumulation and ice formation |
If ice accumulation exceeds ablation, the glacier _____. A |
Advances |
If warming increases ablation or snowfall decreases accumulation, the glacier ____. |
Retreats |
How do glaciers erode? |
1. Plucking: the loosening and lifting of rock and incorporating into the glacial ice
2. Abrasion: the ice and rock fragments that are carried by a glacier act like sand paper against the bedrock it is sliding over
(smooths & polishes the underlying bedrock but can also scratch the surface, causing glacial striations) |
Glacial Erosional Features: |
- cirques
- trough valleys
- hanging valleys
- aretes
- horns
- finger lakes
- tarns, cirque lakes |
V-shaped Valleys are _____ valleys. |
Stream |
U-shaped valleys are _____ valleys. |
glacial |
Cirque |
- at the head of an alpine glacial valley
- bowl shaped depression with downvalley side open
- where snow and ice accumulate |
Horn |
- sharp, pyramid-like peak in alpine glacial terrain
- produced by the convergence of three cirques
- ex: Matterhorn |
Arete |
- sharp-edged ridge in alpine glacial terrain
- the ridge divide separating two cirques or two adjacent glacial troughs |
Hanging Valley |
- when a tributary glacial valley is higher in elevation (due to less erosion) than the main glacial valley
- rivers reoccupying these valleys therefore produce waterfalls because of elevation difference |
Roche Moutonnee |
- terrain modified by continental glaciation
- formed by glacial abrasion and plucking
- abrasion smooths the gentle sloping side; plucking produces a steep edge on the opposite side
- once the glacier is no longer present, these features can be used to determine the direction of glacial flow |
Tarn |
- after the glacier has melted away the cirque is often filled with a small lake, this is called a tarn |
Glacial Drift |
sediment of glacial origin
2 types:
1. Till: material deposited directly by the glacier
- unsorted mixtures of particle sizes
2. Stratified Drift: material deposited by glacial melt water
- sorted by size and weight of the sediment |
Moraines |
- ridges of glacial till
- form under alpine and continental glaciers
types:
1. Lateral
2. Medial
3. End
4. Ground |
Kettles |
pits formed when blocks of ice buried in till melt
can be filled with water to become kettle lakes |
Drumlins |
- ground moraine smeared into tear-drop hills
- formed during glacial advance
- steep side faces the direction from which the ice advanced
-- occur in clusters |
Varves |
Glacial lake sediments |
What were the consequences of ice age glaciation? |
1. forced migration of organisms and some became extinct
2. changes in stream courses and the formation of large lakes
3. sea-level changes due to the formation and melting of ice sheets
4. adjustments of Earth's crust due to the addition or removal of ice
5. climate changes |
Glacial Rebound |
the continent bounces back after ice sheet melts |
What causes ice ages? |
- Plate tectonics
- Variations in Earth's Orbit
- eccentricity
- obliquity
- precession
- chemical composition of atmosphere
- reflectivity of Earth's surface
- ocean circulation |
Eccentricity |
changes in Earth's orbit from more ellipitical to less elliptical (100,000 year cycle) |
Axial Tilt |
Earth's spin axis changes angle over time (41,000 year cycle) |
Precession |
Earth's spin axis points to different directions over time (23,000 year cycle) |
The Hydrosphere includes all water in: |
- oceans
- glaciers
- rivers
- lakes
- air
- soil
- living tissue |
5 Processes of the Hydrologic Cycle: |
1. Evaporation (water evaporates into the atmosphere--mostly from oceans)
2. Transpiration (water released into the atmosphere by plants)
3. Precipitation (water condenses into clouds in the atmosphere and falls as precipitation (rain or snow))
4. Infiltration (water that is precipitated back to the land can be infiltrated (soaked) into the ground)
5. Runoff (water that is not infiltrated flows off the land and into lakes and streams/rivers) |
Whether water is infiltrated or runoff the land depends on the _______________. |
the infiltration capacity of the ground (i.e. soil) |
What is the infiltration capacity of the ground dependent on? |
1. intensity and duration of rainfall
2. how we the soil already is
3. soil texture
4. the slope of the land
5. the amount and type of vegetation |
The higher the intensity& the longer the duration of precipitation, the __ the soil, the __ the texture, the __ the slope, the __ vegetative cover, the more water runoff and surface erosion possible. |
wetter
finer
steeper
less |
Drainage Basin |
land area that contributes water to a river system |
Divide |
separates one drainage basin from another
- can be a ridge or it can be a mountain range |
Drainage Patterns |
networks of streams that form patters which depends primarily on the underlying geology:
-Dendritic: Tree-like branching pattern due to underlying lithology
-Radial: streams diverge from a central point like on a volcano
-Rectangular: right-angle bends are evident from underlying faults
-Trellis: streams are parallel to each other due to alternating bands of resistant and non-resistant underlying lithology |
What are the 3 parts of river morphology? |
1. a zone where erosion occurs (creates steep v-shaped valleys)
2. a zone where sediment is transported
3. a zone where sediment is deposited |
River morphology helps to shape the Earth's surface in what 3 ways? |
1. they erode their channels
2. they transport sediment
3. they produce erosional and depositional landforms |
The time it takes for water to travel from its headwaters to its final destination, the ocean, depends on ____. |
velocity |
Velocity of water is dependent on |
1. gradient (slope/distance) of the land surface
2. the size, shape, and roughness of the channel
3. the discharge: the volume of water flowing past a certain point in a given unit of time |
Zone of Erosion |
when the ground is saturated to the point where it can no longer hold any more water, the water then starts to run off the surface causing small channels to erode, and eventually streams and rivers form |
Zone of Transportation |
Streams transport 3 types of material:
1. Dissolved load: material in solution (dissolved ions)
- not dependent on stream velocity
2. Suspended load: material in suspension (particles)
- makes up greatest portion of stream material; mostly silt and clay
- dependent on water velocity
3. Bed load: material sliding/rolling along the bottom of the stream bed |
Zone of Deposition |
stream beds slow down, allowing for particles to fall out of solution and be deposited by the stream |
Alluvium |
Material deposited by a stream |
Depositional Landforms |
Deltas: when a stream enters a still body of water like a lake or ocean, the velocity drops abruptly causing the sediment particles to fall out of the water
Levees: built by successive floods that deposit sediment on both banks of a channel
Alluvial fans: when streams leave narrow valleys in mountainous terrain and enter a broad flat plain or valley |
What are the 2 types of stream channels? |
1. Bedrock channels: stream eroding into bedrock
2. Alluvial channels: stream eroding into alluvium |
What are the 2 types of Alluvial Stream Channel morphology? |
1. Meandering channel
- consists mostly of fine material in suspension
2. Braided Channel
- consists mostly of coarser material (sand and gravel)
- channels are highly erodable and are thus wide and shallow |
Base Level |
the lowest elevation to which a stream can erode its channels |
What are the 2 types of base levels? |
1. Ultimate base level: the lowest level a stream can lower the land; this is sea level
2. Local base level: lakes, resistant layers of rock, and the trunk stream that tributaries flow to |
Shorelines |
- mark the boundary where air, land, and sea interact
- transitional zones between marine and continental environments where sediment is continuously moving toward, away, and along the coast |
Shore |
the area between the highest and lowest tide
- divided into foreshore & backshore |
What are foreshores and backshores? |
Foreshores are the area exposed when the tide is out (low tide) and submerged when the tide is in (high tide) while backshores are the areas that are only affected by storms and are landward of high tide. |
Coast |
the area between the shore and all the ocean-related features that can be found farther inland |
Coastline |
the line that marks the coast's seaward edge |
Beach |
the accumulation of sediment along the water's edge |
Berm |
flat platforms seaward of coastal dunes |
Beach |
the area of sand or gravel that covers the shoreline from the lower water edge to a well defined upper elevation such as a bluff or a vegetative surface |
Marine Terraces |
Offshore beyond beach face, gently sloping; deposited by retreating waves |
Waves |
energy that is dependent on weather conditions, the length of the wave, wind speed, duration of the wind, and distance the wind travels of water |
What is the dominant agent of erosion in coastal environments? |
waves |
Wave Morphology |
- crest: the top of the wave
- trough: the lowest point of the wave
- height: the vertical distance between the crest and the trough
- the most powerful waves have the greatest wave height
- normal wave 5 m height; tropical wave 15 m height |
Wave Morphology (Continued) |
- wavelength: the horizontal distance between 2 adjacent crests or troughs (30 - 300 m)
- wave period: the time it takes for one wavelength to pass a fixed point |
Describe wave movement |
- waves approach the shore at an angle
- individual water molecules aren't transported by the wave, instead energy moves through the water molecules, moving in a circle path between returning to its original position
- circular pattern decreases with ocean depth
- circular pattern becomes oval as wave approaches shallow water due to increased friction slowing the wave down |
Wave Refraction |
waves adjust to the bottom land surface and bend to become more parallel with the shoreline |
Surf |
when wave speed and length decrease as it approaches the shore, and collapses or breaks because it is too steep to support itself |
What are tides and how often do they occur? |
- the rise and fall of sea level caused by gravitational forces exerted on Earth by sun and moon
- occur 2x a day |
What is the significance of tides on shores/coasts? |
tides create tidal flats (low relief areas of mudflats between high and low tides) |
Wave Refraction determines the degrees of what? |
1. erosion
2. sediment transport
3. deposition |
What impact is made by the backwash of water being straight down a slope on a shore? |
- beach drift and longshore currents are caused by the sediments moving in a zigzap pattern along the beach face |
What are the two currents that control water movement in beach zones? |
1. Longshore current: generated by waves striking at an angle to the prevailing direction of the shoreline
2. Rip currents: the narrow zone of strong flowing water that flows back through the surf after its waves have broken |
Name some erosional shoreline features |
- cliffs, platforms, and terraces form when the surf erodes the base of the coastal land
- sea arches and sea stacks form when surf erodes away the softer portions of the rock at a faster rate
- (arch collapses form multiple sea stacks) |
Name some depositional shoreline features |
- Spits and Bars: elongated ridge that projects from the land and blocks open bays from the ocean
- tombolos: bar of sediment connecting island and mainland forming a peninsula
- barrier islands: elongated islands parallel to coast
- reefs: hard framework of skeletal living and nonliving marine organisms
- keys: accumulation of sand (broken coral) that form islands |
Sandy Beaches |
balance between input and output of sediments
- rivers bring sediment from upcoast (input)
- longshore drift, storms, wind (output) |
What are some types of beach engineering that protect beaches and harbors from sand drift and natural development of these areas? |
- jetties: parallel walls built on the sides of the harbor and extend into the ocean to protect the harbor from excessive sedimentation and destructive waves
- groins: walls built perpendicular to the coast to widen beaches that are losing sediment to longshore drift
- breakwater: built parallel to shoreline for recreational boating |
What is the category of hurricane based on? |
Saffir-Simpson Scale
range: 1 (minimal damage) to 5 (catastrophic) |
What is hurricane damage categorized into? |
1. storm surge
2. wind damage
3. inland flooding |
Groundwater |
- water soaked into the ground to become part of the groundwater reservoir if it isn't surface/runoff or evaporated water
- the most important freshwater reservoir for humans (drinking water, irrigation, industry needs)
- moves below the surface of the Earth and dissolves rock that can create sinkholes and caverns |
What are the 3 zones of groundwater? |
1. soil moisture zone
- zone near surface of the soil
- water here is used by plants and animals, some evaporation
2. saturation zone
- zone where water completely fills all open spaces in sediment
- where water is considered groundwater
- top surface of this is zone is called the water table
3. unsaturated zone
- zone between soil moisture and saturated zones where open spaces in sediment aren't totally filled |
Depth of water table varies seasonally & depends on: |
1. quantity
2. distribution
3. timing |
Depth of water table measured using wells where: |
1. the highest elevations are beneath hills
2. the lowest beneath valleys
3. the surface where there is a wetland/swamp or local body of water (pond or lake) |
What are the 3 types of interactions between groundwater and streams? |
1. Gaining Streams: streams gain water from groundwater
- occurs when elevation of water table is higher than surface of stream
2. Losing Streams: streams lose water to groundwater
- elevation of water table below surface of stream
3. Combination of 1 &2 (some sections are losing streams, some are gaining |
Water moves from areas where the water table is ____ to to zones where the water table is ____. |
higher, lower |
Movement of groundwater, its amount and rate are influenced by: |
1. porosity: open spaces in rock
2. permeability: ability to transmit water |
Porosity depends on: |
1. size and shape of grains
2. how the grains are packed together
3. degree of sorting
4. amount of cementing material (only with sedimentary rocks) |
Well-sorted sediments have ____ porosity |
greater |
Which rocks have the greatest and lowest porosity? |
In order from greatest to least:
1. unconsolidated sediment
2. sedimentary rocks
3. igneous rocks
4. metamorphic rocks |
What are the most and least permeable rocks? |
In order from most permeable to least:
1. sands and gravels
2. partially-cemented sandstones, conglomerates
4. well-sorted sandstones
5. shales, mudstones |
Wells |
device used to retrieve groundwater from the saturation zone, below the water table
- water must be pumped to surface |
Artesian well |
kind of well where water rises on its own because:
1. water is confined to an aquifer that is inclined (one end exposed at surface where it receives the water)
2. aquitards both above and below the aquifer to prevent water from escaping |
What are some environmental concerns with groundwater? |
1. groundwater is a nonrenewable resource in regions where aquifers don't recharge fast enough to keep up with the demand in which water is being withdrawn
2. contamination from landfills, pollution, chemicals, etc. |
L.U.S.T. |
Leaking Underground Storage Tanks
- from many sources, usually gas station tanks leaking
- commonly old gas station tanks that are often single-walled or abandoned tanks |
What are 2 types of hydrothermal systems? |
1. hot springs: hot water that rises to the Earth's surface
- cooling igneous rocks are a common heat source here in the western US
2. Geysers: hot water ejected into the air |
Caverns |
- softer rock like limestone eroded by groundwater
- form just below water table in zones of saturation |
Spaleothems |
left behind calcium carbonate that form above water table in unsaturated zone that was once filled with water
2 types:
- stalactites: hang from ceilings of caves
- stalacmites: form on floors of caves |
Glaciers are commonly given this nickname because they move large quantities of rock, soil, & sediment |
earth-movers |