3. Weathering

4. Weathering - is the natural process that changes the surface of rocks.

5. Two Types OF Weathering:  Physical weathering is breaking rock by force. ex: hitting, scratching, cracking  Chemical weathering is where the rock material is changed into another substance by reacting with a chemical.

6.  PHYSICAL WEATHERING  Frost action (ice wedging) 1. Water seeps into small cracks in rocks. 2. When the water freezes it expands creating great pressure. 3. The crack widens and allows water to seep deeper into the rock. 4. (Robert Frost’s Mending Wall.)

7.  Plant action- 1. Tiny root hairs seek out small cracks and pits in rock. 2. Once the root hairs find a place they grow and expand. 3. The expansion causes great pressure and cracks the rock.

8.  Exfoliation – peeling of sheets of rock from surface. 1. Rocks formed deep in he Earth are made under high pressure. When large rocks are removed the pressure is released the rocks expand & crack. (Called sheet jointing). 2. May also be caused by alternate heating and cooling of rocks by weather conditions.

9.  Abrasion- rubbing by other rocks. Abrasion-  Wetting & Drying when rocks swell and shrink they crack.  Gravity moves water which weathers rocks.

10. CHEMICAL WEATHERING  Oxidation- Oxygen in the atmosphere chemically reacts with minerals. Dissolves rocks ex.: rusting of a nail

11.  Water (hydrolysis) Minerals are dissolved in water. ex.: Halite, calcite

12.  Acid- Carbonic acid: C0 2 dissolves in rain water forming a weak acid. Dissolves rock

13.  Sulfuric acid: Sulfur Dioxide in the atmosphere dissolves in rain water forming a strong acid.  Acid rain

14. Where is the rock more resistant to weathering?

15. Where is the rock least resistant to weathering?

16. You might also see it like this…

18.  Climatic Conditions: Cold and/or dry climates favor physical weathering. Warm and wet climates favor chemical weathering. Frost action works best in areas where the temperature fluctuates wildly. Rates of Weathering will depend on:

19. Soil - The product of weathering  Soil- rocks, minerals (mainly sand and clay), and organic material (regolith and organic matter)  Soil forms layers of different characteristics called horizons.

20. Videos :  http://www.youtube.com/watch?v=Xdg1lpQfLbo& safe=active http://www.youtube.com/watch?v=Xdg1lpQfLbo& safe=active