3. Weathering

4. Weathering is the process that produces change in the surface of rocks exposed to the atmosphere and/or hydrosphere.

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.  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 1. Rocks formed deep in the Earth are made under high pressure. 2. When the pressure is released the rocks expand & crack. 3. May also be caused by alternate heating and cooling of rocks by weather conditions.

9.  Abrasion- rubbing by other rocks. Abrasion-

10.  Oxidation- Oxygen in the atmosphere chemically reacts with minerals. 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.

13.  Acid Rain: Sulfur Dioxide in the atmosphere dissolves in rain water forming a strong acid (sulfuric acid).  Wanna hear how acid rain was discovered?

14. Time For a Lab  Take out lab 3-1: Stream Abrasion

15. Rates of weathering will be influenced by: Surface area exposed - weathering occurs on the surface. More surface exposed, the faster the weathering will occur.

16. A full, solid block has the least surface area. The interior is safe from exposure. A smashed piece has greatest surface area exposed. The interior can now be attacked.

17.  Mineral composition- some minerals are more resistant than others. –ex.:Quartz is resistant to chemical and physical weathering. Rates of Weathering will depend on:

18. Where is the rock more resistant to weathering?

19. Where is the rock least resistant to weathering?

20. You might also see it like this…

23.  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:

24. 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.