Lecture14 weathering
Transcript of Lecture14 weathering
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
Weathering
Bedrock to regolith to soil
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
Denudation
= wearing away of landforms
Involves
• Weathering
• Mass wasting
• Erosion
Agents: moving water, air, waves, ice
Weathering – breakdown of rock materials
Erosion – transport of broken-down materials
Processes that weather/alter/destroy bedrock (Pw)
versus
Processes that expose bedrock (Pe)
Yosemite, California
Pw < Pe
Pw > PeWest Virginia
Champaign, France
Moab, Utah
Wind River Range, Wyoming
Illinois
Amazon Basin, Brazil
Svalbard Islands, Norway
Canadian Rockies
bedrock regolith soil
Weathering
Disintegration and decomposition of rock near Earth’s surface
Regolith = rock fragments made by weathering
Bedrock = parent rock producing regolith
2 Types of Weathering
Chemical alteration
yes no
1. Physical Weathering(disintegration)
2. Chemical Weathering(decomposition)
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
Joint-controlled weathering
Joints in sandstone, Canyonlands NP, Utah
Sandstone, Escalante basin, Utah
Sandstone, Rainbow Arch, northern Arizona
Sandstone, central AustraliaGranite, central Australia
Granite, Missouri
Granite, Vedauvoo, Wyoming
Granite, Sinai peninsula, Egypt
Joint-controlled weathering
Aspect (Orientation)
Biological differences w/ slope aspectBiological differences w/ slope aspect
NN SS
Aspect (Orientation)
“South Facing”“South Facing” ““North Facing”
North Facing”
• 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
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
Physical Weathering: Water and Ice
Mechanism for fracturing rocks?
Physical weathering processes1. Frost action
- repeated freeze-thaw breaks rocks
Frost action
Freeze/ThawFreeze/ThawAdequate WaterAdequate Water
2. Salt crystal growth
- salt crystal growth
- caused by evaporation of H2O in dry climates
Physical weathering processes
3. Unloading (e.g., granites)- as surface rock erodes, pressure on buried
rock decreases
- sheets form & slide off = exfoliation
Physical weathering processes
Unloading
Granite, Yosemite National Park, California
Sandstone, Arches National Park, Utah
Granite, Poudre drainage, Colorado
Thermal Expansion
Granite blockGranite block
Wedging byVegetation
Chemical weathering= involves reactions between air,
water, & minerals
Chemical weathering processes1. Hydrolysis
- minerals + H2O
- silicate minerals
2. Oxidation
- metals + O
- e.g., rusting
Chemical weathering processes
3. Acid action
- minerals dissolve into solution
- often involves C
- e.g., marble tombstones, limestone caves
Solution
Sandstone, Zion Canyon National Park, Utah
Sandstone, Uluru, central Australia
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