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GEOL 102 week 8-10
Terms in this set (110)
Water erosion is unsually effective in desert areas because
rainfall tends to run off more quickly because of thin soils.
Why is the Great Salt Lake salty?
it has no outlet, so dissolved salts tend to accumulate as water evaporates.
Large cross-beds in fine-grained sandstone tend to develop in which environment?
Which of the following best characterize deserts?
Deserts support vegetation that covers less than 15% of their surface areas.
are asymmetric ridges made of gently tilted sedimentary rocks.
Wind is generally more effective at erosion in desert areas than in other places because
the sparse vegetation of deserts means that wind has easier access to the bare ground.
What is glacial till?
A random mix of large and small rock fragments deposited by a glacier.
Different types of glacial moraines
all consist of till, but are named differently depending on their location with respect to the glacier.
result from fluctuations in Earth's orbit and axial tilt.
Compared to the land record of glaciation, the marine record is
Longshore drift causes the formation of which landform(s)?
Active continental margins are those
that lie near a plate margin.
Parts of Oregon's coastline are marked by marine terraces that exist at different elevations. These terraces
originated by wave erosion at sea level.
Oregon's Physiographic map (below) shows a vast dry area as brown in the south-central and southeastern parts of the state. What most likely explains this region's aridity?
it lies in the rain-shadow of the Cascade Range.
what is a glacier?
a body of ice that flows in response to gravity
How do you know its a glacier ?
crevasses form b/c of stretching of the ice during movement.
After the ice melts, what would you excpect to see at X?
Below is a Roche Moutonee in Yosemite National Park, California. Which statement is true?
Ice flowed from Y towards X; side Y experienced abrasion while side X experienced plucking.
What impact did that have on river channels east of, but within about 10 miles of today's coastline?
It caused them to cut more deeply into their channels
which statement below best describes the effect in which elevated levels of CO2 can increase temperatures on Earth?
CO2 can absorb much or the radiation traveling from Earth to Space and so increase the temperature in the atmosphere.
What creates the sawtooth pattern in the CO2 curve?
Sea stacks mostly form by which process?
Erosion of headlands
Absence of water and vegetation cover defines a desert. About how much water, vegetation?
-vegetation covers <15% of ground
-low rainfall <10"/yr.
How does this absence of water affect physical vs. chemical weathering rates? Soil development?
-low rainfall means low rates of chemical weathering.
- thin soils
- low vegetation cover.
-lots of bedrock
-as a time dependent process: the darker a surface, the longer it's been exposed. Derived from windblown dust.
Main causes for desert landscapes
LOW RAINFALL AND CIRCULATION OF DRY AIR
How do rain shadow deserts form?
1. warm moist air blows inland
2. Air risese over mountains + cools > loses water
3. Cold dry air sinks on other side of range. Picks up remaining moisture + warms > keeps moving
4. Dries out the "rain shadow"
different type of deserts
-continental interior deserts
-coastlines next to cold ocean currents
How does erosion take place in deserts?
wind, water, gravity
Water, wind, gravity. Water is the most important factor. Why?
why are flash floods common in deserts?
flash flooding occurs when it rains rapidly on saturated soil or dry soil that has poor absorption ability.
What does a hydrograph in a desert look like?
Wind erosion -deflation and abrasion.
More effective in deserts than elsewhere. Not much vegetation to hold down or protect the bare surface. With less water, silt + sand is less cohesive.
removal of material
sand blasting effect
What determines how resistant a rock is to erosion?
cemetation, bedding thickness, grain size, composition
-required sand, wind, wind block
-sand dunes create a characteristic large-scale cross-bedding
-important source of evaporites and dust and fine sand.
-during wet periods, playas flood and become temporary lakes. But then they dry up!
-most typical of the Great Basin of the United States.
a fan-shapes mass of alluvium deposited ....
a broad slope of alluvial material at the foot of an escarpment or mountain.
Role of resistant and less-resistant rock in shaping the landscape.
-more resistant rock is on top and the bottom
-least resistant rock is in the middle
-differences in resistance to erosion caused by cementation, bedding thickness, grain size, composition
how will that upper sandstone erode?
breakage + falling of resistant rocks
-less resitant rock erodes + undercuts the more resistant rock - which then breaks + falls
large, flat-topped area with steep side. area: 10s - 100s of square miles.
flat-topped area with steep sides. several miles square up to several 10s square miles.
Butte + Chimney
all these landforms have flat tops. -b/c bedding is horizontal. Some buttes are igneous.
-rock tilt is <30 degrees
-make stripes in the landscapes
-make stripes in the landscapes
2.6 Ma to 10 Ka
body of ice that flows under the influence of gravity.
-mostly high elevations
-glacial flow accomplished by movement down steep gradients in landscape
-glacial flow accomplished by spreading from highly thickened to thinner problems
where accumulation = ablation
ice budget, ice movement
Movement of Glaciers occurs by basal sliding and internal deformation (flow). How do crevasses indicate glacial movement? how deep do they go? why?
crevasses - flowing of ice causes stretching
flow of ice is faster over steeper slope
Zones of accumulation
more gain of snow than loss in a given year
zone of ablation
more loss of snow than gain in a given year
what happens to the equilibrium line during advance or retreat?
-if the climate warms or less snowfall: equil line will rise in elevation
-if the climate cools or more snowfall: equil line will drop in elevation
How does advance or retreat of a glacier take place?
takes place by abrasion and plucking
scratching of bedrock by rocks embedded in the ice
pulling-off of loose bedrock by the ice itself
how does abrasion and plucking occur? also much weathering by frost-wedging.
asymmetric bedrock feature formed by both abrasion and plucking
-direction of ice flow was towards the steep side.
they have a characteristic U shape, with steep straight sides and a flat or rounded bottom
bowl-shaped areas at the head of a glacier (the main source area of the glacier)
peaks with cirques on 3 or more sides
cliffs behind the cirques
narrow ridges between cirques
a valley which is cut across by a deeper valley or a cliff
When the ice melts, the mixture of unsorted sediment deposits carried by the glacier either by till or outwash.
till glacial deposition
-unsorted, chaotic material deposited directly by glaciers.
-no bedding, unsorted and NOT stratified
outwash glacial deposition
-material deposited by streams running off glaciers.
-bedding, sorting of sed. sizes
-sediment deposited by the streams running off the ice.
-glacier that makes it to the ocean
arms of sea that invaded former glacial valleys.
ridge-like land from made of till.
a product of rock fall onto the margin of a glacier.
a moraine deposited at the point of furthest advance of a glacier or ice sheet.
small "terminal" moraines deposited at the glacier's terminus as it recedes.
-found within the glacier
-if you go upstream, medial moraines become lateral moraines.
-in joining another glacial > medial moraines.
is a high-magnitude, low-frequency catastrophic flood involving a sudden release of much water
lowered sea levels
estuaries in the PNW
streamlined hill - made of till
depositional feature - but sculpted by the ice
ice-marginal lakes and their deposits
role of greenhouse gases
1. short wavelength 9UV) radiation reaches and warms Earth.
2. Earth re-radiated long wavelength (infrared) radiation into space
3. CO2 and other "greenhouse gases" absorb some of the outgoing infrared radiation.
high erosion rates at headlands
-extremely variable water pressures
-abrasion from material suspended in the water
-rapid + irregular
-water will exploit any irregularity in the rock: fractures, fault, bedding surfaces
role of plate motions in climate
understand how waves evolve as they approach the shore.
wave energy focuses on headlands and less intense on embayemens. why?
Active vs. passive contiental margins
Active: near plate margin, tend to be rocky and steep. Passive: far from a plate margin, tend to be sandy and gentle.
frequently last connection of the sea stack to the mainland
flat areas of bedrock at sea level, erode flat by wave action
differential erosion produces many of the more interesting features
movement of sand restricted by headlands and rivers
causes of cooling
-plate motions: land masses to polar latitudes, disrupt ocean currents.
-orbital motions: Milankovitch cycles
-greenhouse gases: lower concentrations
-albedo effect: more ice = more reflectance = more cooling.
large intertidal areas typically covered by mud
spits vs barrier islands
-spits: connected to the land
-barrier islands: actual islands
headland erosion produces sea arches, sea stacks, wavecut platforms, sea cliffs
-movement of sand restricted by headlands and rivers
-beach morphology: intertidal zone, beach face, berm, backshore, dunes
-the sand is always in motion
oregon lies on an active margin
-rocky headlands where there's resistant rock; sandy stretches where it's less resistant.
-evidence for ongoing uplift in the marine terraces at different elevations.
-waves primarily driven by wind
-water particles move in circular motion as waves move towards coast; wave asymmetry increases as the cell "touches bottom" - at 1/2 the wavelength.
-headlands are made of relatively resistant rock.
-headlands receive the brunt of wave energy because of wave refraction. They erode irregularly depending on the rock's weaknesses.
---sea stacks, sea caves, sea arches, wave-cut benches (platforms)
-active margin - near a plate boundary
-well-defined boundary between shoreline + ocean
-passive margin - far from a plate boundary
-more irregular coastline not such a clear demarcation between shoreline + ocean.
typical speed of movement
slowest (1) >> fastest (6)
describes the movement of water particles from one reservoir to another.
-water is a polar molecule
-water has high surface tension
-water has a high heat capacity
from high hydraulic head to low hydraulic head
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