1. Weathering The natural breaking down of rocks and other materials on the Earth’s surface. A slow continuous process that affects all substances exposed to the atmosphere. Two types of weathering: Mechanical Chemical

2. Weathering

3. Mechanical Weathering Forces of nature break rock into smaller pieces without changing the chemical make up of the rock. Rocks are broken into smaller pieces Fragments tend to become rounder as weathering continues. 5 types of Mechanical Weathering

4. Mechanical Weathering Video Clip

5. Temperature Repeated heating and cooling of outer surface of rock causes outer layers to break off. Breaking of outer layers called: Exfoliation.

6. Ice Wedging Water seeps into cracks in rocks. Temperature drops and water in cracks freezes and expands widening the crack.

7. Organic Activity Mechanical Weathering caused by plants or animals. Could be animals simply walking. Root-pry: roots in cracks of rocks widen cracks as the root grows.

8. Examples of Weathering

9. Gravity Pulls loose material down. As rocks fall they collide and break.

10. Abrasion Wearing away by solid particles carried by wind or water.

11. Chemical Weathering Weathering which changes the mineral composition of rocks through chemical reactions. Most often involves water.

12. 3 Types of Chemical Weathering 1. Water Water dissolves minerals and carries them away. Water can form weak acid with many chemicals. 2. Acid formation Mild acids form and breakdown minerals Plants (Lichens) can often form mild acids that breakdown rock material 3. Oxidation Oxygen in the air combines with minerals to form new compounds Rusting is an example

13. Chemical Weathering

14. Factors That Influence the Rate of Weathering Type of rock Rock that is more resistant to chemical weathering are called a Stable Rock. Amount of moisture present: Climate The more moisture, the faster weathering occurs. The amount of living organisms. The amount of exposed surface a rock has. Time