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112 Cards in this Set

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Weathering
Disintegration and decomposition of ricks in place, due to pressure release, fire, ice, plants, water, acids
Microcracking-mechanical weathering
Unequal expansion of different minerals as pressure drops
Other mechanical weathering
Water expanding, fire expanding outside of rocks, plant roots
Chemical weathering
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
Mechanical-->chemical weathering
Mechanical weathering creates surface area, allows chemical weathering to begin
Chemical weathering includes...
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
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
Dissolution is accelerated by acid waters, where does additional acidity come from
Gasses mixing with rain-VERY COMMON, IN ALL RAINWATER
Plants creating strong organic acids
To discourage browsing by animals, changes color
Soil
Column of weathered material formed in place from underlying bedrock and flowing groundwater (plus organic deposits)
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
Pedalfer soil-temperate zone
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
Pedocal-desert
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
Tropical laterite
A-hydrated Fe and Al oxides
B-missing, nothing precipitates
C-laterite veins in bedrock
Forming a new soil and damage
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
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
Water constantly cycles
ocean to rain to groundwater to rivers to ocean
Why study groundwater
Scarce resource in arid lands, transports natural chemical elements, transports pollution
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
Below the water table...
pores are saturated, pressure is proportional to depth from water table (head)
Water table
Surface separating unsaturated from saturated rocks
Head
Pressure
Pressure gradient
Height of column of groundwater above a certain point
weight of water overhead/unit area
Horizontal change of pressure
Flux
Permeability
measure of average speed of groundwater
Ease of water movement
When permeability is uniform...
when it is not...
Flow follows surface slopes
Follow slope of a pressure surface in an aquifer between aquicludes
Aquifer vs. aquiclude
High permeability
Low permeability
Potentiometric surface
Thermal effect
level to which the water would rise if unconfined
Transports heat from earth
Groundwater transports..
immense amounts of matter, causes weathering, caves, hard water, spreads pollution
What must be done about pollution in groundwater
Must be put in a discharge zone and not a recharge area or whole aquifer will be contaminated
Hot springs
Effectively move and concentrate elements whose solubility increases with water temp
Groundwater in aquifers is finite
recharge-discharge=change in groundwater volume
local increase in discharge causes decrease in discharge elsewhere or a drop in water table
When is the time for a landslide
After hillside is weakened by mechanical and chemical weathering and an intense rain raises the water table
Landslide importance
Transports soil from hillsides into streams, creates valleys shaped like v's instead of vertical slots
River erosion
River erosion plus landsliding
Slot canyon
V-shaped canyon
Landslides and slumps
Mudflows and avalanches
More slowly according to the laws of friction
Move rapidly as fluid flows
Fault under a typical slow moving landslide
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
Piles of rock steeper than critical angle...
will slide unless they have cohesion
Critical angle depends on the friction of the rock, usually about 40, but only 7 for some clays
How is cohesion lost
Slowly by weathering
More rapidly by slope-steepening erosion
Very rapidly by earthquake shaking
Failure can be accelerated by anything that increases shear stress such as
Slope steepening or increase of shear stress by seismic S waves
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
How can wet slides be stopped
By dewatering (rerouting streams, pumping)
Or by buttressing the toe (piling up earth to reduce the average slope)
More dangerous rockfalls/mudflows/avalanches have...
a lot of air or water mixed in, creating a dense but weak fluid that can travel at high speeds for many kilometers
Why does mass of bouncing rock behave like fluid?
Bouncing=friction doesn't apply, compressed air or melted snow beneath, compressed steam
Slides underwater danger?
Can generate tsunami waves hundreds of meters tall
Rivers have many converging...forming a...pattern
Complete system is referred to as...
Tributaries
Dendritic
Catchment
Water flows downhill and...
Meanders, expends energy over its full course due to principle of least work
River deposits...
Fine sediment to establish equilibrium, causing meandering
Fluvial river sediments
Sand, gravel, silt, clay
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
If total sediment flux increases/decreases downstream...
there is erosion/deposition
Steady state requires
Equal sediment transport past all points otherwise deposition or erosion occurs
Dissolved load
Everything in solution
Sediment transport
Saltation, rolling, suspension
Meandering verses braided
Fine sediment, gentle slope, not much flow variation, single channel
Coarse sediment, steep slope, variable flow, multiple channels
Terminal rivers
Do not reach the ocean but drain internally
What rivers end in
Deltas with branching distributaries
Slope which continuously decreases downstream
Total sediment flux and largest bedload particle increase with
Greater water velocity
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
Faulting the builds mountains leads to....
Leads to erosion of a canyon upstream and construction of an alluvial fan downstream
Top and bottom of each river, what is inevitable? What happens in central part?
Erosion and deposition
Both
Eroding tributaries...
Depositing distributaries...
Therefore deltas are good places for farms but not for...
Merge
Diverge by flooding
Cities
Rainwater contains no sediment but picks it up so...
There is always erosion at the headwater end of river systems
At sea, slope is zero so velocity is zero so there is...
Deposition
3 beds
Topset, foreset, bottomset
Deltas are good places for farms BUT
not for cities
Deltas accumulate at the mouths of great rivers because...
Elsewhere sand is transported along the coast by longshore transport, net effect of many waves arriving at an angle
Waves arrive at angle, push sand up, backwash runs straight down, net effect is...
To transport both sand and water along the beach
Beach is a coastal river of sand, interrupting its flow causes...
Local deposition upstream and erosion downstream
What are harbor mouths? What are dredges used for?
Unnatural gaps in the river, dredges used to carry sand across each one
Beaches end where sediment flows down submarine canyons as...
Turbidity currents
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
Turbidity currents are the major mechanism of...
Sediment transport from coastline to continental rises, abyssal plains, and trenches
Mechanism of turbidity currents
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
Current and how it runs
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
Erosion of...in the continental shelf due to acceleration of turbidity currents
Submarine canyons
Deceleration on continental rise causes deposition of delta like forms, including (2)
Branching distributaries and natural levees
Turbidites eventually bury all bedrock hills and valleys, creating...
Abyssal plains and flat floors in some trenches
Far from land, main sources of sediment are...
Coral, oolites, wind blown dust, volcanic ash, and CaCO3 and SiO2 tests of 1-celled plants and animals living as plankton
Currents cannot cross trenches so...
Large parts of of ocean floor are protected for sediments far from land
Off continental shelves, seawater is free of sediment (blue water) so...
Coral can grow in shallow water without being choked
Warming of clean seawater on shallow offshore banks can cause inorganic precipitation of...
Oolites
Wind blown dust comes from...
Desert sandstorms and volcanoes
Volcanic ash weathers quickly to form..
Slip planes where many landslides which occur in marine sedimentary rocks
CaCO3 plants and animals (limestone)
SiO2 plants and animals (opal)
Chalk, foraminifera
Diatoms, radiolarians
Deserts description
Regions of little or no plant cover, in some regions wind transport exceeds transport by water, can be cold or hot
Where are desert belts and what is the process?
30 deg N/S latitude, air sinks and warms adiabatically, reducing humidity
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
Shortage of rain encourages eolian (wind) landforms to dominate over fluvial landforms in what 3 ways
Less frequency of running water
Low water table, rain sinks in quickly before traveling far
Between rains, little surface tension to hold surface down
Deserts can be cold-where and describe
Earth's poles produces the Antarctic dry valleys
Precipitation minimum due to converging and descending air and high pressure
Deserts on Mars
Rain is scarce despite low T
Sand dunes and wind transported
Sand transported eastwards by westerly and north westerly winds
Air flow around sand grains is...
Competence law relates...
Laminar
Grain size transported to wind speed
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)
When is wind turbulent? What is the horizontal wind speed required to lift a grain compared to vertical component?
Large length scales
2-3x larger
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
When clay travels far enough to reach the deep sea far from land what does it form?
Thin deep-sea sediments such as ocean sediments and loess
Loess
"Loose"
predominantly silt-sized sediment, which is formed by the accumulation of wind-blown dust
Because of weathering, far-traveled .3mm sand is...
Mostly quartz
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
Fluvial
Eolian
River transported
Wind transported
Desert pavement-where it forms, what it is
Forms by accumulation of immovable stones on the surface in source erosion areas
Fragile and slow to reform
Source material is alluvial fan debris
Surface sand layer moves by...
Saltation, flux-V^3
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
Wind erosion-where expressed, examples
Very close to ground, undercut cliffs, "mushrooms"
Yardangs
Ventifacts
Forming in soft and hard rocks
Wind-eroded rocks
Sand flux increases non linearly with V because...
Whole sand sheet moves faster
Landing grains hit harder and kick up more neighbors
If available, larger grains join the flux
Most action in desert occurs when...
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
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
Dunes grow by...
Collecting smaller dunes that arrive from the upwind side
How do dunes move?
Up and over caterpillar tractor motion
Acts like a conveyor belt that moves the dune forward
Beds within a dune are tilted up to 30 deg because...
They were deposited by mini-landslides down the slip face
Direction of tilt varies with the wind direction, leads to cross bedding
What is dune size and spacing controlled by...
the height of the atmosphere
Dune forms (5)
Transverse Dune, Barchans, Parabolic Dune, Star Dune, Longitudinal Dune