-
Weathering
- A. Physical and chemical breakdown of rocks at/near Earths surface
- B. Weathering occurs because the minerals that compose rocks arent stable at conditions found at Earths surface.
- 1. As granite is exposed at the surface, feldspar, minerals arent stable, so they begin to break down and become down and become more stable under the lower temperatures and pressures found at Earths surface
- C. Mechanical and chemical weathering work together at Earths surface
- 1. Mechanical weathering increases the surface area for chemical weathering to attack
- D. Erosion
- 1.Removal and transportation of material
-
Mechanical Weathering
- A. Frost Wedging
- 1. Alternate freezing/ thawing of water in fractures in rocks causes rocks to break down over time
- 2. Common in mountainous areas
- 3. May create talus slopes
- a.Cone-shaped deposits of loose material at the base of a slope
- b.When talus lithfies, it may form breccia
- B. Unloading
- 1. As rocks (especially granites) are exposed at the surface, the pressure is relieved
- 2. The outer surface of the granite fractures along sheet joints, which are parallel to the surface
- 3. Over time, pieces of rocks break off along the sheet joints
- 4. Unloading creates exfoliation domes
- a. Enchanted Rock, TX
- b. Stone Mountain, GA
- C. Activity of Animals and Plants
- 1. Burrowing animals may help break down rocks
- 2. Root weding
- a. Plant roots grow into fractures in rocks and over time may cause rocks to break down
-
Chemical Weathering
- A. Minerals are alterred by the addition and / or removal of ions
- B. Water is very important in chemical weathering
- C. Types of chemical weathering
- 1. Dissolution
- a. Halite dissolves in water
- b. Rainwater+ CO2 produces H2CO3 (carbonic acid)
- i. Carbonic acid dissolves calcite
- 2. Oxidation
- a.Iron in water reacts with oxygen to form hematite
- 3. Hydrolysis
- a. H+ in carbonic acid replaces elements such as Al, K, Na, in feldspars in granites
- b. Chemical weathering of feldspars produces clay minearls
- c. Al, Na , K ions go into solution , as well as some SiO2
- d. Quartz grains, which are resistant to chemical weathering, are released and transported, then deposited to become part of new rock
|
|
