1. Agents, Forces, and Results
Erosion
Agents, Forces, and Results

2. What Causes This?

3. What Is Erosion?
Erosion – moving of rock material from one place to a new location
Three processes must take place:
detachment of particles
lifting them
transporting them
Agents of erosion:
water
moving ice
gravity
wind
Sand consists of small pieces of rock that have been:
weathered from a parent rock
eroded
deposited somewhere else

4. What Is Wind Erosion
Wind – responsible for wearing away rocks and creating great deserts like the Sahara Desert and Gobi
Most effective in moving loose material
Main effects:
Wind causes small particles to be lifted and moved away.
Suspended particles may impact on solid objects causing erosion by abrasion (rubbing).
Occurs in areas where there is not enough
rainfall to support vegetation

5. Wind Erosion
Wind will carry fine, dry sediments over
long distances.

6. Wind Transport of Dust
Photo shows Sahara Desert sand being transported over
the Atlantic Ocean.

7. What Is Water Erosion Water – most influential force in erosion
Moves materials
Transports large objects with fast moving streams
Wears away rocks:
streams (rills, gullies, creeks, rivers, etc.)
lakes
oceans

8. Stream Erosion Flowing water will lift and carry small
sediments such as silt and sand.

9. Stream Erosion and Deposition
Where water moves more swiftly there will be more
erosion.
Where the water slows down, sediments will be
deposited.

10. Wave Erosion Waves – relentless pounding Erodes:
softer/weaker rock first
harder/more resistant left behind
Can take over 100 years to erode a rock to sand
Energy of waves and chemical content of the water erodes the rock off the coastline.

11. Ocean Dynamics
Tidal action and waves carry away weathered materials.

12. What Is Gravity Erosion?
When sediments are weathered they may be transported downward by gravity.
Mass wasting – downward movement of rock and sediments, mainly due to the force of gravity

13. Gravitational Erosion
When sediments are weathered they may be transported downward by gravity as a slump.
Slump

14. Gravitational Erosion
Loose sediments transported by gravity are called creep.
Creep Field

15. What Is Glacial Erosion?
Ice – moves and carries rocks, grinding the rocks beneath the glacier
Most powerful agent of erosion because of size, weight, and density
Plucking occurs when water enters cracks under the glacier.
freezing
breaking off pieces of rock that are then carried by the glacier
Abrade (abrasion)
Scratches and cuts grooves into the rock under the glacier
Smoothes and polishes the rock surface
Forms U-shaped valleys

16. Glaciers
Form at Earth’s poles and in high elevations (mountainous areas)
Valley Glaciers
Form in valleys of mountainous areas
Occurs when ice is too heavy, flows down the mountain like liquid
Continental Glaciers
Cover a continent-sized area
Thickest at center
Callled Ice Sheets

17. Glacial Erosion