1. Chapter 23: Earth’s Changing Surface Objectives: What is weathering & erosion? Give examples of mechanical and chemical weathering. How do weathering & erosion change Earth’s surface? How do you “read” sedimentary rocks that are formed as a result of erosion and deposition?

2. Weathering Weathering by wind and water causes rocks to break apart into smaller pieces or SEDIMENTS (SEDIMENT = END PRODUCT).

3. Types of Weathering 1. Mechanical – Rocks are broken apart physically Water seeps into cracks of rocks and freezes when temps. drop. Ice expands and wedges apart rocks Examples of Mechanical Weathering 1A. Frost Wedging

4. Frost Wedging creates rock spires and pot holes. Frost wedging happens in environment where temperatures alternate between hot and cold or where there are seasons

6. Examples Mechanical Weathering 1B. Abrasion = Wind or water SCRAPES the surface of rock to break it up. (sand blasting)

7. Examples of Mechanical Weathering 1 C. Plant roots – help break apart rocks

8. Chemical Weathering Rocks containing calcium (limestone, marble, etc.) dissolve in acidic water. Rain can be acidic because of dissolved carbon dioxide (carbonic acid) Example: Caves form in limestone rocks. Water seeps through ground and dissolves rock to form caverns.

9. Erosion Erosion is when the sediments (made by weathering) are carried away to a new location by wind or water. AGENTS OF EROSION: 1.Water 2.Wind 3.Gravity

10. Mass Movements= Erosion w/ help of gravity. Once weathering has broken rock up, gravity can move rocks down slopes! (H2O usu. helps) Land slides – rapid, large amounts of rock & soil Mudflows – rapid, large amounts of soil, sediments & water Creep – gradual, soil moves down slope (alt. freezing & cold temps) Slump – rapid, small amount of hillside move down a “step” (Wet soil)

11. Types of Mass Movement (aka, mass wasting)

12. Sediments are deposited in layers and cement into new layers of sedimentary rock Layer A was laid down first. Then layer B. Layer I is the most recent.

13. “Story of Rocks” Lower layers came first. Index fossils are used to guess the age of rocks. Magma intrusions come after the layers they cross through. Folding can change the direction of layers.