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

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
Alluvial fan: shaped like a triangle
Delta: sediments not deposited until river enters ocean, gulf, or lake
Alluvial fan
Delta

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