1. Chapter 8 Erosional Forces
Section 8-1 Erosion by Gravity
Notes Guide

2. Erosion and Deposition
The process that wears away surface materials and moves them from one place to another is called erosion.
Causes of erosion
-1. Gravity
-2. Water
-3. Wind
-4. Glaciers
Gravity is the force of attraction that pulls objects towards Earth’s center.
Agents of erosion drop the sediments as they lose energy. This is called deposition.
When sediments are eroded, they are not lost, they are just relocated.

3. Mass Movement
Any type of erosion that happens as gravity moves materials down slope is called mass movement.
Some happen very slowly, others happen quickly and cause catastrophes.
When a mass of material slips down along a curved surface, the mass movement is called a slump.
This can be caused by water weakening the mass, or if a strong rock layer lies on top of a weak rock layer, commonly clay.
A curved scar is left where the slumped materials originally rested.

4. Slump

5. Creep
Creep occurs where sediments slowly shift their positions downhill.
Leaning trees and human-built structures, such as houses show evidence of creep.
Creep is common in areas of frequent rainfall and snowfall.

6. Mass Movement Cont.
Rock falls happen when blocks of rock break loose from a steep slope and tumble down, causing more and more rocks to crash into each other and break loose.
-This can be caused when water freezes in rocks and the cracks expand.
Rock slides occur when steep layers of rock slip down slope suddenly.
-Rock slides are common in mountainous areas or areas with steep cliffs. They can occur after heavy rains or during earthquakes.

7. Mass Movement Cont.
Mudflows occur in areas that have thick layers of loose sediments.
-These happens after vegetation has been removed.
-When heavy rains fall on the area, the water mixes with sediments causing it to be thick and pasty.
-Gravity causes the mass to flow downhill, where it loses energy and deposits everything it has been carrying.

8. Landslide

9. Rockslide

10. Mudslide

11. How would you like to own that house?

12. Landslide!!

13. Consequences of Erosion
People live on steep slopes because they like to have a great view and live in scenic areas.
When people build homes on steep slopes, they make slopes steeper or remove vegetation. This speeds up erosion.;
One of the best ways to reduce erosion is to plant vegetation.
Drainage pipes can help prevent water from building up.
Walls or boulders can reduce soils erosion by holding soil in place.
Eventually, regardless of time and money spent to preserve land, gravity always wins.