1. Weathering and Erosion
Painted Desert, Arizona

2. Weathering Vs. Erosion Weathering Erosion
The general process in which rocks are broken down at the Earth’s surface
Mechanical – rocks broken w/o changing composition
Chemical – minerals are altered or dissolved
Erosion
Move weathered materials under influence of gravity on grain-by-grain basis

3. Intertwined Processes
Weathering breaks rocks down
Erosion carries away loose material exposing new, fresh surface to weathering

4. Mechanical Weathering: Pressure-Release Fracturing
Igneous and meta rx generally form deep in the crust
Tectonic forces may cause rocks to rise forming a mtn
As mtn erodes, less pressure on stuff beneath it
Rx expand due to lower pressure--fractures

5. Mechanical Weathering: Wedging
Frost wedging
Can also occur when
Salt water seeps into cracks and evaporates—-haloclasty
Or when
Tree roots=wedge—organic activity

6. Rocks wedged apart by growing
Tree roots
Honeycomb texture
Characteristic of a rock that
Has undergone haloclasty

7. Mechanical Weathering: Abrasion
Weathering of rocks by friction and impact
Actions make jagged edges round
Natural sandblasting in desert environments—weird shaped rocks

8. Mechanical Weathering: Thermal Expansion
Occurs only in areas with dramatic diurnal temperature variation
i.e. deserts
Outside of rock cools/heats more quickly than interior—may cause fractures to form

9. Chemical Weathering Dissolution: dissolving stuff in water Ex: Halite
Polar water molecule
Water can pull
apart ionic bonds

10. Acids and Bases Acidic solution Basic solution
High concentration of H+
Basic solution
High concentration of OH-
Acids and bases dissolve minerals faster than water because they have more H+ and OH- ions to pull atoms away from minerals
Acid rain

11. What Governs Weathering?

12. Properties of the Parent Rock
Different minerals weather at different rates
Different solubilities
The extent to which their minerals will dissolve in water

13. Properties of the Parent Rock
Type of rock and structure
Determines rate of P and C. weathering
Ex. Niagara
Falls

14. Climate Amount of rainfall and temperature
Water is the best agent for dissolving
Can hold lots of dissolved ions
Chemical weathering
Fastest where water abundant, hot (humid)
Slower in dry, hot climates
Slowest in cold climates because water frozen, inert

15. Soil
Fragments of rock, clay formed by altering minerals, and organic matter
Can trap rainwater, host vegetation, bacteria, and organisms
Create an acidic environment which speeds weathering
Roots and organisms create fractures
A positive-feedback process

16. Length of Exposure
Obviously, the longer the exposure time, the more the weathering
But dependent on other factors

17. Colorado Rockies: Short Exposure

18. Appalachians: Long Exposure

19. Surface Area vs. Volume
The more surface area compared to volume, the faster that part will weather

20. Works Much Like Coffee Add hot water to coffee beans
Water can only affect the surface of the beans
Smaller beans means more reactions (Hooray!)