lecture14 weathering
TRANSCRIPT
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Announcements
Problem Set 1 Answer Key is posted. Check your graded set. If there are any discrepancies talk to me.
Exam 1 review session: Monday at 5pm, here in McG-S room 20. Bring questions!
Exam 1 itself: Wednesday the 23rd
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Weathering
Bedrock to regolith to soil
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Endogenic vs. exogenic
Internal vs. external systems
plate tectonics
folding
faulting
volcanism
weathering
water erosion
wind erosion
Building up Breaking downtug of war
glacial erosion
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Denudation
= wearing away of landforms
Involves
• Weathering
• Mass wasting
• Erosion
Agents: moving water, air, waves, ice
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Weathering – breakdown of rock materials
Erosion – transport of broken-down materials
Processes that weather/alter/destroy bedrock (Pw)
versus
Processes that expose bedrock (Pe)
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Yosemite, California
Pw < Pe
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Pw > PeWest Virginia
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Champaign, France
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Moab, Utah
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Wind River Range, Wyoming
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Illinois
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Amazon Basin, Brazil
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Svalbard Islands, Norway
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Canadian Rockies
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bedrock regolith soil
Weathering
Disintegration and decomposition of rock near Earth’s surface
Regolith = rock fragments made by weathering
Bedrock = parent rock producing regolith
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2 Types of Weathering
Chemical alteration
yes no
1. Physical Weathering(disintegration)
2. Chemical Weathering(decomposition)
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What controls weathering?1. Bedrock
- hardness,
- jointing, solubility, etc.
2. Water availability- precipitation, water table, & movement
3. Climate- precipitation, temperature, freeze-thaw
4. Vegetation
5. Aspect (Orientation)- exposure to sun & weather
Res
istin
g F
orce
Driv
ing
For
ces
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Joint-controlled weathering
Joints in sandstone, Canyonlands NP, Utah
Sandstone, Escalante basin, Utah
Sandstone, Rainbow Arch, northern Arizona
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Sandstone, central AustraliaGranite, central Australia
Granite, Missouri
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Granite, Vedauvoo, Wyoming
Granite, Sinai peninsula, Egypt
Joint-controlled weathering
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Aspect (Orientation)
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Biological differences w/ slope aspectBiological differences w/ slope aspect
NN SS
Aspect (Orientation)
“South Facing”“South Facing” ““North Facing”
North Facing”
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• depends on climate
Physical or chemical?
precipitation
tem
pera
ture
physical
chemical
This combination of temp and precip doesn’t occur anywhere
both, but at very low rates
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Physical or chemical?
precipitation
tem
pera
ture
physical
chemical
This combination of temp and precip doesn’t occur anywhere
both, but at very low rates
• depends on climate
Physical = cooler, drier Chemical = warmer, wetter
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Physical Weathering: Water and Ice
Mechanism for fracturing rocks?
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Physical weathering processes1. Frost action
- repeated freeze-thaw breaks rocks
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Frost action
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Freeze/ThawFreeze/ThawAdequate WaterAdequate Water
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2. Salt crystal growth
- salt crystal growth
- caused by evaporation of H2O in dry climates
Physical weathering processes
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3. Unloading (e.g., granites)- as surface rock erodes, pressure on buried
rock decreases
- sheets form & slide off = exfoliation
Physical weathering processes
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Unloading
Granite, Yosemite National Park, California
Sandstone, Arches National Park, Utah
Granite, Poudre drainage, Colorado
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Thermal Expansion
Granite blockGranite block
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Wedging byVegetation
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Chemical weathering= involves reactions between air,
water, & minerals
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Chemical weathering processes1. Hydrolysis
- minerals + H2O
- silicate minerals
2. Oxidation
- metals + O
- e.g., rusting
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Chemical weathering processes
3. Acid action
- minerals dissolve into solution
- often involves C
- e.g., marble tombstones, limestone caves
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Solution
Sandstone, Zion Canyon National Park, Utah
Sandstone, Uluru, central Australia
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Chemical Weathering
• Geochemical weathering: Natural, inorganic processes, that break down bedrock into regolith
• Pedochemical weathering: Natural organic and inorganic processes, that lead to soil formation