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physical geology exam 4


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mass wasting
horizontal and vertical movement, any material can move, provides the bulk of the material for streams to carry.
direct cause: gravity
low slope - friction exceeds shear, high slope - shear exceeds friction
freefall of any size fragments, cliffs, roadcuts
coherent movement along a well-defined surface, faults, joints, bedding plains, may create its own surface.
non-coherent movement, like a fluid. fragments move independently of each other. often produces lobe or tongue-like edges.
combination of slide and flow. slide at head, flow at toe.
slowest, most widespread form
precipitating problems
too much rainfall, earthquakes, fires, fluid soils like quick clays, planes of downslope weakness in the rock
anthropogenic causation
undercutting/overweighting slopes, creating oversteepened slopes, reactivating ancient landslides
mitigating mass wasting
easy to study and easy to ignore
hazard mapping
-bedrock & soil nature
-bedding planes, joints, foliations
-prior movement

modifying construction
removing or terracing overhanging slopes, improving water drainage, rock bolts, retainer walls, vegetation/erosion control, shelters
purely vertical motion, mostly caused anthropogenically, few fatalities, but large property losses
mitigating subsidence
by the time it starts sinking, it's too late. adding a fill is an expensive band-aid. prevention is the key: surface mapping bedrock and soils, subsurface testing
stream - any channelized surface flow - collect, transport, dispense water and sediments.
drainage networks
an array of interconnecting streams, developing channels caused by water moving overland in the shortest/steepest route.
separated by divides
stream piracy
(capture) - when the headward erosion of a stream crosses a divide, one stream steals the upper network of another
drainage patterns and topography
dendritic- network of branches (tree), rectangular- joints, radial- volcano, trellis- resistant ridge
antecedent stream
existed before typography
superposed stream
superimposed on older rocks
high gradient streams
far from base level, narrow, V-shaped valleys, features like rapids and waterfalls, stream cuts downward
low gradient streams
close to base level, wide,flat bottomed valleys, features like meanders and floodplains, stream cuts sideways
(meanders) - grow, get cutoff, grow again. oxbow lakes and meander scars. over time, plain develops. covers with water during floods, floodplain.
natural levees
forms during floods. velocity slows when it leaves channel. lower velocity causes deposition.
incised meanders
when a low gradient river is rejuvenated, meanders stop cutting sideways, and start cutting down.
braided streams
form when stream has more sediment than it can carry. water flows through multiple channels.
form when sediment-laden water enters a body of quiet water.
alluvial fans
form when sediment-laden water enters a dry valley.
volume of water per unit time in a stream
most destructive natural hazard. normal, natural and cyclical.
(flash) - small streams, begin and end quickly
(riverine) - large streams, begin and end slowly
plots of stream discharge as a function of time for a given station. usage dependent on time period chosen. short-period (hours to days) used for flooding, long-period (months to years) used for water resources.
100-year flood
a probability, not a deterministic idea. a 100-year flood = 1% chance per year.
control structures: walls parallel to channel on floodplain. intended to keep floodwater off floodplain
results of levees
armored riverbanks - river completely walled off from its floodplain, levee failure results in catastrophic flood.

sediment stored in channel. river bottom raised, so river levels higher.

flood mitigation
retention structures - collect and hold impervious surface runoff, allows discharge downstream slowly.

zoning, flood insurance, buy outs

oceanic sedimentation near continents
fine-grained detrital rocks - siltstones, mudstones, shales.
oceanic sedimentation not near continents
shallow water - limestones. deep water - cherts. carbonates become soluble under pressure.
spring tides
when the pull is in the same direction
neap tides
when they pull at 90 degrees to each other.
emergent coastlines
formerly submerged features now exposed on land (ocean terraces).
submergent coastlines
formerly exposed features now submerged (estuaries, fjords)
ocean terraces
wave-cut benches that have been uplifted
drowned river valleys
drowned glacial valleys
west coast processes
steep slopes: quick sand loss, small beach zones, littoral cells. california.
east coast processes
gentle slopes: slow sand loss. large beach zones, barrier islands. north carolina.
barrier islands
large sand bars that stand above sea level.
intercepting longshore drift, walls perpendicular to beach trap sand on one side. current picks up new sand on the other.
maintaining inlets. wall perpendicular to beach block longshore current. blocked current drops sand on one side, current picks up new sand on the other.
block waves. walls parallel to beach stop waves. longshore current dies, sand dumped behind wall.
armoring the dune line.
mitigating coastal hazards
planning: geologic and emergency.

zoning: limit modifications in vulnerable areas.

the percentage of a material that is open space
primary porosity
forms during deposition and lithification
secondary porosity
develops after rock forms
how easily a fluid passes through a material. permeable materials have connected pores, impermeable materials have isolated pores.
rock/sediment layer that allows fluid to pass (highly permeable)
rock/sediment layer that prevents fluids from passing (highly permeable)

also called aquiclude.

unconfined aquifers
not restricted by aquitards, local recharge, water level dependent on local conditions
confined aquifers
restricted by aquitards, remote recharge, water level independent of local conditions.
pressurized confined aquifers
artesian aquifers. recharge at a higher elevation, pressure surface above aquifer elevation. effect like a water main.
filled with caves, sinkholes, sinking creeks. only forms in humid regions with carbonate bedrock.
systems of flowing ice. relatively little impact currently.
alpine (valley) glaciers
found in mountainous regions worldwide.
continental glaciers
greenland and antarctica
glacier formation
snow, compact, repeat
glaciers move by two means
by flow and slip
glacial erosion by plucking
loosening and removing blocks from the bedrock
glacial erosion by abrasion
filing and grinding rock
bowl-shaped depression at the head of a glacier, u-shaped valleys
finger lakes
u-shaped valleys
glacial deposition
occurs at the margins of the ice, sediments can be deposited directly by ice
sediments carried from glacier by meltwater. may be sorted, rounded and stratified.
out of place rocks deposited by glaciers. igneous/metamorphic boulders on sedimentary layers.
seasonal layers deposited in meltwater lakes. silt in spring; clay during winter.
till at the margins of the ice. names based on location: end, terminal, lateral, medial, ground.
sub-ice stream channels. meltwater deposits, so may be sorted and stratified.
glacial period hypotheses
changes in the sun, changes in the relationship of the Earth to the sun, changes in heat budget due to land arrangement, changes in heat budget due to atmospheric transparency

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