Weathering and Erosion

1. Weathering and Erosion Objectives: Define weathering, mechanical weathering, chemical weathering, erosion, and deposition Predict how weathering might reshape surface features (topography)

2. What’s The Big Idea? • The top part of the lithosphere—the earth’s surface—changes as rocks are broken down to smaller pieces and carried away. • These processes are weathering and erosion, respectively.

3. Mechanical Weathering • Weathering is the process by which rock is broken down to smaller pieces. • Mechanical weathering breaks rock into smaller pieces by physical means without changing chemical composition. • Agents of mechanical weathering include: • Water • Wind • Ice • Changing temperatures • Gravity • Living things

4. Ice Wedging Drop in temperature below 0oC (32oF) causes water in joints to freeze and expand. This can happen over and over again breaking rock.

5. Abrasion Wind and water can carry small pieces of rock and sand. When theses particles hit other rock, they break off tiny bits like sandpaper.

6. Abrasion by Glaciers Glaciers are large masses of slowly moving ice. As they move across the earth’s surface, they pick up weathered rock material. This material scratches and abrades the rock surfaces over which the glaciers flow.

7. Living Things Living things cause weathering by growing into and moving over rock. Plant roots can produce enough force to break rock. Burrowing animals dig into the ground and can bring rocks to the surface.

8. Chemical Weathering • Chemical weathering breaks down rock into smaller pieces as a result of chemical reactions. • Changes the chemical composition of rocks. • Result: Rock is weakened and can break, dissolve, or wash away. • Agents of chemical weathering: • Water, which can dissolve rock. • Carbon dioxide, makes a weak acid called carbonic acid. • Acid rain, can react with minerals breaking down rocks. • Oxygen, can oxidize some minerals breaking down rocks. • Living organisms, plant roots and lichens produce acids.

9. Lichens, organisms made up of algae and fungi living together, symbiosis. Oxygen can cause oxidation of iron in some rocks causing rust. Effects of acid rain.

11. Erosion • Erosion is the process by which weathered rock, sand and soil is picked up an moved to new places. • Together weathering and erosion change the earth’s surface. • Agents of erosion • Wind • Water (running) • Glaciers • Gravity

12. Erosion is a problem on nearly all beaches on the Gulf Coast of Texas. Jetties at Mansfield Channel. View is toward northwest. Note that sediments have accumulated on the south side of the jetties, which indicates that net longshore drift is northward at this location. Erosion has occurred on the north, or downcurrent, side of the jetties.

13. Wave Erosion

14. View looking west along the New Jersey shore. Storm waves and surge cut across the barrier island at Mantoloking, NJ, eroding a wide beach, destroying houses and roads, and depositing sand onto the island and into the back-bay. Construction crews with heavy machinery are seen clearing sand from roads and pushing sand seaward to build a wider beach and protective berm just days after the storm. The yellow arrow in each image points to the same feature.

15. River Valleys • Rivers remove rock and soil from their channels. • Over time, rivers carve out v-shaped valleys.

16. Wind • Wind erodes sand and soil by lifting it and blowing it away.

17. Erosion in Texas • Water erosion is mainly a problem in eastern Texas, esp. along the coast. • In the far west region and High Plains, erosion caused mainly by wind. • In areas where land is plowed for farming, soil can be blown away. • Sand and soil can make its way in to streams which can muddy up the water causing problems for plants and fish.