Geology Test 4
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3 types of flow:
- 1. slow aka CREEP only detected by dislocation or bending of features at the surface
- 2. fast aka FLOW of rock, regolith, vegetation and/or ice
- 3. very fast aka AVALANCHE
...the loose material that piles up at the base of steep slopes
The lack of vegetaion or soil on .... indicates that material is actively accumulating
landscape feature that indicate a .....
main & minor scarp
swampy low area
cracked walls and roof, sinking foundation of a house
tiltled utility poles
cracked & displaced highway
broken face in earth
....favors slope instability or motion
3 factors between driving & resisting forces
- increasing slope
- smooth surfaces (decreasing friction)
- presence of water
...a resisting force that opposes motion between two objects that are touching one another.
...the other component of resisting strength, the attraction of particles at the atomic level.
- loose sand/gravel have little cohesion
- clay has high cohesion
causes of mass movements
- weakening by fragmentation & weathering
- interplay of downslope force (weight of soil)
- resistive force (friction)
...interface between rock and soil
...the max angle of a stable slope as determined by
angle of repose
2 factors that determine slope stability
- angle of repose
- influence of local geology (joints, bedding planes, foliation, faults; water; physical & chemical weathering)
3 triggers of a mass movements:
- 1. earthquakes (liquefaction)
- 2. volcanoes
- 3. tsnamis
...the process that causes mass movements of water-saturated regolith when it is shaken by strong earthquake waves. Vibrations cause teh grans to compact closer together, however when there is water between the grains, the compacting grains displace water and that forces other grains apart, which decreases cohesion and friciton, and causes flow.
how do mass movement and mountain building go together?
- 1. max stable slope angle
- 2. erosion & uplift
- 3. oversteepened slopes
- 4. unstable rock mass removed by mass movement
- 5. more mass movement
...the primary agents of regolith movement in mountains. The downcutting by streams steepens valleys, and periodic slides, flass and flows will occur.
GIS data layers are used to make....
rock type layer
mass-movement inventory layer
a hazard susceptibility map
Americans pump ~....billion liters of ground water every day
~... percent of the nation's drinking water comes from ground sources
~...of the ground water pumped is used for agriculture
Ground water represents ... of earth's unfrozen fresh water
evidence for ground water is visible at the....
fractures, joints and other open spaces below the regolith and rock below are collectively known as .... for ground water.
....the percentage of the total volume of the regolith/rock that consists of pores
varies according to the type of:
- 1. pore space and
- 2. material
....water that soak into regolith and rock at the surface, percolates through fractures, pores, and other open spaces, and resides for some period in these subterranean zones
Typical porosity range:
well-sorted sand & gravel
mixed sand & gravel
silt & clay
- well-sorted sand & gravel 25-50%
- mixed sand & gravel 20-35%
- silt & clay 30-60%
- shale 0-10%
- sandstone 3-30%
- limestone/dolostone 1-30%
- plutonic/meta rocks 0-5%
- volcanic rocks 1-50%
...the top surface of the ground water, which
mimics the topography of the ground surface above
seperates the saturated zone from the unsaturated zone
the water table
what is the difference from the saturated and unsaturated zone?
- saturated is the region where all pores are completely filled with water
- unsaturated is region above that contains at least some air in the pores and where most plants draw water.
in the unsaturated zone above the water table, the soil feel moist because a thin film of water adheres to the surfaces of small particles due to minute.....
Porosity and permeability .... downward into Earth
- therefore infiltration of rain water is limited as it soaks into the surface
- and the uneven land suface allows ground water to only rise to discharge points where it is taken away by surface flow in streams
Ground water flows from .... areas to ... areas
from recharge areas to discharge areas
Crust is made of complex folded and titled layers of various composition. There are areas wehre impermeable layers overlain by porous layers trap pockets or water near the surface, or even at high elevation. These bodies of ground water are called...
perched ground water
...a body of ground water with sufficient porosity and permeability to provide useful quantities of water to well or springs
- the best aquifers have high porosity and permeability
- water that leaves
- water added to the ground water system
why do some streams flow year-round?
Streams may either gain water from ground water or lose as it contributes to recharge. During a rain storm, the stream that has a water table closer to its surfaces could flow year-round because it doesn't have to lose to recharge (the ground water system)
...the practice of using injection well or infiltration ponds to assist ground water recharge
- artificial recharge
- injection well.injection recharge.infiltration recharge.evapotranspiration/runoff.
minerals that precipitate from ground water (in between grains or in your water pipe)
These can be removed used water softeners, but soft water leaches ions from metal pipes.
What 3 ores are associated with hot, circulating ground water?
...a naturally-occuring toxic material found in ground water with an EPA acceptable level of 10 ppb
Describe how Ground Water shapes the landscape.
- soluble rocks such as limestone interact with water (acidic) by dissolving
- dissolved material is mobile, leaving voids in its wake
- these voids can become large enough to be expressed on the surface (subsidence or sinkholes)
- regions exhibiting such feature are said to have karst topography
disappearing stream, sinkholes and caverns indicate...
development of early karst features
how is a cave formed?
- the CO2 in the soil mixes with the infiltrating water, causing the acidic water to dissolve limestone and form caves
- the CO2 escapes from water into cave atmosphere, decreasing the acidity which causes calcite to precipitate and create cave formations
what happens when perched water seeps from a juncture of layers in a canyon wall?
the high permeability sandstone allows water to flow to a low permeability sandstone, where the water seeps to edge, then freeze-thaw weathers the rock until an overhanging cliff is formed. Overtime the overhanding cliff with fail in rock fall.
confined aquifer : .... permeability
unconfined aquifer : .... permeability
- confined aquifer : low permeability
- unconfined aquifer : high permeability
ground water flows .... to hydraulic gradient
evapotransipration moves water into atmosphere
precipitation bring it back to earth
Surface water flows in streams or infiltrates down to ground water.
This cycle is the ....
A drainage basin is the area that ....
Basins are separated by ridges called .....
Major rivers contain the drainage basins of all the .... that feed into it.
- drains into a stream.
largest river drainage basin is ....
does not drain into the a sea or ocean, but instead exits into lakes and playas is called...
- Mississippi Basin
- The Great Basin
3 ways of how streams procure sediment
- surface runoff with eroded particles
- mass movement
- erosion from the stream itself
sediment moves by ....
force (not velocity)
moving water has a shear stress parallel to the direction of motion and depends on the weight of the water and the steepness of the slope
for motion to occur with a sediment, the shear stress must exceed the .... of the grain, plus ... and .... at grain contacts
- must exceed the weight of the grain
- plus friciton and cohesion at grain contacts
shear stress .... with increasing water depth
shear stress ... with increased slope
...large grains that cannot be picked up, but still are able to be moved. they roll, bounce and slide along the bottom. may form dunes and cross bedding
...small sediment grains that mix with teh flowing water are transported above the bed, rarely touch bottom and can make the water cloudy or muddy
...ions in water
- suspended load
- dissolved load
why do streams deposit sediment?
when a flow broadens out, the depth goes to zero as well as the power and the sediment falls out quickly, forming an alluvial fan
.....form in fault-block valleys/down-dropped block/grabens
salty playa lakes
...form where streams enter the ocean or a lake
-elevation of channel bed
-slope of channel bed
-grain size of bedload
stays the same down stream:
stream power per area of stream bed remains the same
flow velocity is .... close to banks and bed because of friction, forming a .... on the inside of the shallow curve
- to form a point-bar
explain alteration of stream dynamics by tectonic change
uplift alters power, as the headwater end of a stream is raised, it begins to incise in an effort to acheive a base level condition
as the meandering pattern .....,
-more suspended sediment load
-finer grained sediment
-increasing bank stability
-low discharge variablity
-low channel slope
....are formed by shifting channels, oxbow lakes, suspended deposits
1. ... deposition upstream due to decreased velocity
2. ... erosional capacity downstream due to increased slope below the dame
3. produce sediment free water
- 1. increase deposition upstream
- 2. increase erosional capacity downstream
- 3. produce sediment free water
....% of the us pop lives on coasts
~ .... km of coasts on earth
.... % of world's pop lives within 60km of a coast
Are typical .... elements:
muddy tidal flats
all are related to wave energy/sediments
typical coastal elements
sea-level change affects the base level of any stream ....
..vertical distance between adjacent crest and trough
... distance between successive crests
... the time it takes for successive crests to pass a point
- wave height
- wave length
- wave period
wave crests become higher, steeper, and more closely spaced apart as waves .... the shore
when waves end on the shore at an angle, the net energy is down the beach and is known as a ..... current and water flows back off the beach more directly as .... currents
- longshore current
- rip current
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