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112 Cards in this Set
- Front
- Back
Weathering
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Disintegration and decomposition of ricks in place, due to pressure release, fire, ice, plants, water, acids
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Microcracking-mechanical weathering
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Unequal expansion of different minerals as pressure drops
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Other mechanical weathering
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Water expanding, fire expanding outside of rocks, plant roots
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Chemical weathering
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Surface process, follows mechanical weathering
Chemical breakdown in water of minerals which were stable where they were formed but are not stable where they are now |
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Mechanical-->chemical weathering
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Mechanical weathering creates surface area, allows chemical weathering to begin
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Chemical weathering includes...
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Dissolution-any mineral will lose ions to a constant flow of pure water
Oxidation-reaction with O2 which increases the + charge of cations, accelerated by acid groundwater |
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Leaching
Coffee example with feldspar |
Ions replaced by H+, OH-, of O2- to preserve charge balance
Rainfall, feldspar altars to kaolinite, soil or groundwater containing dissolved substances from feldspar |
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Dissolution is accelerated by acid waters, where does additional acidity come from
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Gasses mixing with rain-VERY COMMON, IN ALL RAINWATER
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Plants creating strong organic acids
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To discourage browsing by animals, changes color
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Soil
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Column of weathered material formed in place from underlying bedrock and flowing groundwater (plus organic deposits)
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Typical simple soil horizons
Caution |
O-Organic layer
A-Leached layer (organic rich and clay poor) B-Zone of accumulation (clay-rich) C-Zone barely altered from pristine rock Unaltered rock Immature soils incomplete, O directly on C |
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Pedalfer soil-temperate zone
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A-Quartz rick sand (Fe, Mg, Ca, K leached away)
B-Rusty clay C-Rotted bedrock Soil is a loam=equal mixture of sand, silt, and clay |
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Pedocal-desert
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A-Sand and rock (leaching incomplete due to low rainfall)
B-Sand and rock and carbonates (caliche) deposited by evaporating groundwater C-commonly missing due to protection by caliche in B |
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Tropical laterite
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A-hydrated Fe and Al oxides
B-missing, nothing precipitates C-laterite veins in bedrock |
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Forming a new soil and damage
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New soil profile takes 10^3-10^6 years so human damage is basically permanent
Damage from excess pop pressure, overgrazing, plowing, acid rain, desert irrigation |
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Irrigation of deserts
Slash and burn Overgrazing Plowing |
buildup of alkali salts, poisons plants
wasteful of soils, converts O layer to ash Erosion and desertification Soil erosion by removing sheltering trees and grasses |
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Water constantly cycles
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ocean to rain to groundwater to rivers to ocean
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Why study groundwater
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Scarce resource in arid lands, transports natural chemical elements, transports pollution
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Pore
Porosity Saturated Unsaturated |
Space in rock not occupied by crystals (includes cracks)
Volume of pores/volume of rock Pores filled with water Pores empty or partly filled with water |
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Below the water table...
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pores are saturated, pressure is proportional to depth from water table (head)
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Water table
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Surface separating unsaturated from saturated rocks
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Head
Pressure Pressure gradient |
Height of column of groundwater above a certain point
weight of water overhead/unit area Horizontal change of pressure |
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Flux
Permeability |
measure of average speed of groundwater
Ease of water movement |
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When permeability is uniform...
when it is not... |
Flow follows surface slopes
Follow slope of a pressure surface in an aquifer between aquicludes |
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Aquifer vs. aquiclude
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High permeability
Low permeability |
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Potentiometric surface
Thermal effect |
level to which the water would rise if unconfined
Transports heat from earth |
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Groundwater transports..
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immense amounts of matter, causes weathering, caves, hard water, spreads pollution
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What must be done about pollution in groundwater
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Must be put in a discharge zone and not a recharge area or whole aquifer will be contaminated
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Hot springs
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Effectively move and concentrate elements whose solubility increases with water temp
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Groundwater in aquifers is finite
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recharge-discharge=change in groundwater volume
local increase in discharge causes decrease in discharge elsewhere or a drop in water table |
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When is the time for a landslide
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After hillside is weakened by mechanical and chemical weathering and an intense rain raises the water table
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Landslide importance
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Transports soil from hillsides into streams, creates valleys shaped like v's instead of vertical slots
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River erosion
River erosion plus landsliding |
Slot canyon
V-shaped canyon |
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Landslides and slumps
Mudflows and avalanches |
More slowly according to the laws of friction
Move rapidly as fluid flows |
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Fault under a typical slow moving landslide
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Appears as a normal fault on top
Strike-slip faults on the sides Thrust fault at the base All part of one listric fault or sliding surface |
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Piles of rock steeper than critical angle...
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will slide unless they have cohesion
Critical angle depends on the friction of the rock, usually about 40, but only 7 for some clays |
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How is cohesion lost
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Slowly by weathering
More rapidly by slope-steepening erosion Very rapidly by earthquake shaking |
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Failure can be accelerated by anything that increases shear stress such as
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Slope steepening or increase of shear stress by seismic S waves
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Rainwater encourages failure by...
Effect of water on fine sand (think sandcastle) |
Adding weight, raising water table, reducing cohesion
if dry or wet can't do anything, moist increases cohesion |
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How can wet slides be stopped
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By dewatering (rerouting streams, pumping)
Or by buttressing the toe (piling up earth to reduce the average slope) |
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More dangerous rockfalls/mudflows/avalanches have...
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a lot of air or water mixed in, creating a dense but weak fluid that can travel at high speeds for many kilometers
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Why does mass of bouncing rock behave like fluid?
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Bouncing=friction doesn't apply, compressed air or melted snow beneath, compressed steam
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Slides underwater danger?
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Can generate tsunami waves hundreds of meters tall
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Rivers have many converging...forming a...pattern
Complete system is referred to as... |
Tributaries
Dendritic Catchment |
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Water flows downhill and...
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Meanders, expends energy over its full course due to principle of least work
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River deposits...
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Fine sediment to establish equilibrium, causing meandering
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Fluvial river sediments
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Sand, gravel, silt, clay
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Rivers move fine sediment as?
Course sediment as? |
Suspended load-fine particles suspended in turbulent water, rivers red/brown/grey
Bed Load-moving sand and cobbles and boulders that roll and bounce along the bed |
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If total sediment flux increases/decreases downstream...
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there is erosion/deposition
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Steady state requires
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Equal sediment transport past all points otherwise deposition or erosion occurs
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Dissolved load
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Everything in solution
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Sediment transport
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Saltation, rolling, suspension
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Meandering verses braided
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Fine sediment, gentle slope, not much flow variation, single channel
Coarse sediment, steep slope, variable flow, multiple channels |
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Terminal rivers
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Do not reach the ocean but drain internally
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What rivers end in
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Deltas with branching distributaries
Slope which continuously decreases downstream |
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Total sediment flux and largest bedload particle increase with
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Greater water velocity
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In turbulent (eddying) flow, drag force is caused by...
Eddies allow... Floods carry much much more... |
Randomizing momentum into smaller and smaller scales
Local rapid flow to support particles Sediment |
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Faulting the builds mountains leads to....
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Leads to erosion of a canyon upstream and construction of an alluvial fan downstream
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Top and bottom of each river, what is inevitable? What happens in central part?
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Erosion and deposition
Both |
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Eroding tributaries...
Depositing distributaries... Therefore deltas are good places for farms but not for... |
Merge
Diverge by flooding Cities |
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Rainwater contains no sediment but picks it up so...
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There is always erosion at the headwater end of river systems
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At sea, slope is zero so velocity is zero so there is...
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Deposition
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3 beds
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Topset, foreset, bottomset
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Deltas are good places for farms BUT
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not for cities
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Deltas accumulate at the mouths of great rivers because...
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Elsewhere sand is transported along the coast by longshore transport, net effect of many waves arriving at an angle
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Waves arrive at angle, push sand up, backwash runs straight down, net effect is...
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To transport both sand and water along the beach
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Beach is a coastal river of sand, interrupting its flow causes...
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Local deposition upstream and erosion downstream
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What are harbor mouths? What are dredges used for?
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Unnatural gaps in the river, dredges used to carry sand across each one
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Beaches end where sediment flows down submarine canyons as...
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Turbidity currents
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Turbidity currents erode canyons in the...
And deposit the... Finest clays come to rest in a...which buries the seafloor topography |
Continental shelf and continental slope
Continental rise Abyssal plain |
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Turbidity currents are the major mechanism of...
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Sediment transport from coastline to continental rises, abyssal plains, and trenches
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Mechanism of turbidity currents
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Earthquake or major storm shakes the seafloor
Sediment at right angle is loosened and compacts Starts underwater landslide Suspension of sediment in water has strength like water but more dense |
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Current and how it runs
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Hugs the bottom, accelerates downhill to high speed
Major drag is on the top from turbulent mixing with seawater Current runs out of slope, then slows and deposits sediment |
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Erosion of...in the continental shelf due to acceleration of turbidity currents
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Submarine canyons
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Deceleration on continental rise causes deposition of delta like forms, including (2)
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Branching distributaries and natural levees
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Turbidites eventually bury all bedrock hills and valleys, creating...
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Abyssal plains and flat floors in some trenches
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Far from land, main sources of sediment are...
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Coral, oolites, wind blown dust, volcanic ash, and CaCO3 and SiO2 tests of 1-celled plants and animals living as plankton
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Currents cannot cross trenches so...
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Large parts of of ocean floor are protected for sediments far from land
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Off continental shelves, seawater is free of sediment (blue water) so...
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Coral can grow in shallow water without being choked
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Warming of clean seawater on shallow offshore banks can cause inorganic precipitation of...
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Oolites
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Wind blown dust comes from...
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Desert sandstorms and volcanoes
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Volcanic ash weathers quickly to form..
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Slip planes where many landslides which occur in marine sedimentary rocks
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CaCO3 plants and animals (limestone)
SiO2 plants and animals (opal) |
Chalk, foraminifera
Diatoms, radiolarians |
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Deserts description
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Regions of little or no plant cover, in some regions wind transport exceeds transport by water, can be cold or hot
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Where are desert belts and what is the process?
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30 deg N/S latitude, air sinks and warms adiabatically, reducing humidity
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Adiabatic warming process
Why lower relative humidity? Weather? |
During descent, air is squeezed by inc P, causing higher T (adiabatic effect)
Higher T, with no change in water content, rarely rains and evaporation is common |
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Shortage of rain encourages eolian (wind) landforms to dominate over fluvial landforms in what 3 ways
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Less frequency of running water
Low water table, rain sinks in quickly before traveling far Between rains, little surface tension to hold surface down |
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Deserts can be cold-where and describe
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Earth's poles produces the Antarctic dry valleys
Precipitation minimum due to converging and descending air and high pressure |
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Deserts on Mars
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Rain is scarce despite low T
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Sand dunes and wind transported
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Sand transported eastwards by westerly and north westerly winds
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Air flow around sand grains is...
Competence law relates... |
Laminar
Grain size transported to wind speed |
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Why are fine particles hard to pick up?
What is the grain size that travels most easily? 2 modes of fluid flow? |
Electrostatic cohestion
0.3mm Laminar (smooth, steady) and turbulent (eddying and changing) |
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When is wind turbulent? What is the horizontal wind speed required to lift a grain compared to vertical component?
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Large length scales
2-3x larger |
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Clay crystals bond weakly to each other, what does this mean for wind?
What helps break up grains? |
Hard for wind to break up and pick up
Salt crystallization |
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When clay travels far enough to reach the deep sea far from land what does it form?
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Thin deep-sea sediments such as ocean sediments and loess
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Loess
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"Loose"
predominantly silt-sized sediment, which is formed by the accumulation of wind-blown dust |
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Because of weathering, far-traveled .3mm sand is...
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Mostly quartz
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What is evidence that sand has traveled a long way?
What will multiple impacts along the way do? |
Well sorted sand
Shatter any crystal that has cleave, quartz is slightly chipped |
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Fluvial
Eolian |
River transported
Wind transported |
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Desert pavement-where it forms, what it is
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Forms by accumulation of immovable stones on the surface in source erosion areas
Fragile and slow to reform Source material is alluvial fan debris |
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Surface sand layer moves by...
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Saltation, flux-V^3
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When are most eolian landforms formed?
Sand moving in the wind is like... |
During sandstorms
Like the bedload of rivers, bounces and never rises very high |
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Wind erosion-where expressed, examples
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Very close to ground, undercut cliffs, "mushrooms"
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Yardangs
Ventifacts |
Forming in soft and hard rocks
Wind-eroded rocks |
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Sand flux increases non linearly with V because...
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Whole sand sheet moves faster
Landing grains hit harder and kick up more neighbors If available, larger grains join the flux |
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Most action in desert occurs when...
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When you can't easily study it
One day of 60mph winds moves as much sand as 200 days of 10mph breezes Turbidity currents, mudflows, pyroclastic flows, earthquakes |
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What are instabilities in the transport system? (2)
Ripples form quickly from flat surfaces because of... Small dunes to large dunes |
Ripples and dunes
Slight waviness Small dunes move faster, collide and merge with larger ones adding to their volume |
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Dunes grow by...
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Collecting smaller dunes that arrive from the upwind side
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How do dunes move?
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Up and over caterpillar tractor motion
Acts like a conveyor belt that moves the dune forward |
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Beds within a dune are tilted up to 30 deg because...
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They were deposited by mini-landslides down the slip face
Direction of tilt varies with the wind direction, leads to cross bedding |
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What is dune size and spacing controlled by...
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the height of the atmosphere
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Dune forms (5)
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Transverse Dune, Barchans, Parabolic Dune, Star Dune, Longitudinal Dune
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