Erosion and Deposition

1. Erosion and Deposition Chapter 8

2. What is Erosion? • A process that wears away surface materials and moves them from one location to another • Causes of erosion: • Gravity • Water • Wind • Glaciers

3. Deposition Deposition- the “dropping” of sediments that have been eroded or weathered away This is the final step in the erosion process.

4. Gravity Erosion • Mass movement – when gravity alone moves materials down slope • Four types: • Slump • Creep • Rockslides • Mudflows

5. Slump Mass movement that happens when loose materials or rock layers slip down a slope

6. Creep Gets name from way sediments inch down a hill Look for slopes where trees, poles or fences lean downhill The entire hill moves downward slowly (like an inch per year)

7. Rockslides Large blocks of rock break loose from steep slope, start falling, crash into more rocks, knock them loose, etc. Often occur in winter because of freezing & thawing in cracks causing fractures

8. Mudslides Thick mix of sediments and water flowing down a slope

9. Video Clips creep clip Rockslide in Tennessee Mudslide in Italy

10. Water Erosion Runoff Stream and River Ocean Shoreline Groundwater

11. Runoff Rills Gully Sheet Water that doesn’t soak into the ground or evaporate; it flows across the Earth’s surface Can create rills, gullies, or sheets

12. Results of water erosion: Combined

13. Stream/River Erosion Water flows along a channel Water picks up light sediments and moves them Large, heavy things just roll along the bottom of the channel Heavy things scrape and bump against bottom and sides of channel Stream continues to cut a deeper and wider channel

14. Streams/River Erosion

15. Two Types of Water Deposits Delta Alluvial fan Alluvial fan: shaped like a triangle Delta: sediments not deposited until river enters ocean, gulf, or lake

16. Ocean Shoreline Waves move sediments back and forth, eroding and re-depositing sediment Beaches are a result of sand being deposited Waves can also erode rocky cliffs to make caves

17. Groundwater Water that soaks into the ground and fills holes in rocks below the surface Can create wells, springs, and geysers

18. Erosion from Groundwater Water mixes with carbon dioxide to form a weak acid Limestone is easily dissolved by acid, so as acidic groundwater moves through cracks, the cracks are enlarged until a cave is formed

19. Wind Erosion Air movement picks up loose materials and transports them Deflation: wind removes small particles such as clay, silt, and sand, leaving behind coarse materials Abrasion:when windblown sediments strike and erode rocks Wind erosion usually happens in deserts, beaches, and plowed fields

20. Sandstorms and Duststorms

21. Wind Deposition: Dunes A mound of sand drifted by the wind Windward side has a gentle slope Leeward side has a steeper slope

22. Reducing Wind Erosion • Windbreaks: • People plant vegetation to reduce wind erosion and trap snow moisture • Grasses make good root systems on steep slopes and on the coastline

23. GLACIERS • Moving mass of ice and snow is a glacier • Snow piles up, compressing the ice on bottom • Ice partially melts & becomes putty-like • Whole mass begins to slide on putty layer and moves downhill

24. Glacial Erosion Plucking:ice cracks rocks, pieces are lifted up by the glacier Grooves:rocks scrape the dirt under the glacier leaving long parallel grooves Striations: smaller scrapes than grooves Cirque: bowl-shaped hole left by glacier Arete: ridge formed when two glaciers erode mountain from different directions Horn:sharp peak left by multiple glaciers eroding mountain

25. Glacial Erosion

26. Glacial Depostion Till: mix of sediment left at glacier base Moraine: ridge of sediment left in front of the glacier when it stops pushing forward Outwash: sediment deposited by melted water from the glacier Kettle: lake left behind by the glacier