Lecture14 weathering

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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