Aim: How does erosion by gravity

occur?Chapter 8

What is erosion?

Erosion is the process that wears away surface materials and moves the sediments from one place to another.

What is erosion?

Don’t let Gravity get you Down!!! Gravity is the force of attraction that pulls

all objects toward the Earth’s center.

Gravity and Erosion

Water and wind erode materials only when they have enough energy of motion to do work.◦ Example: Strong winds can move dust sediments.

Glacial erosion is another agent of erosion.◦ Glacial erosion slowly moves sediments that is

trapped in solid ice.◦ As the ice melts, sediment is deposited, or

dropped. ◦ Sometimes sediment is carried further by moving

meltwater.

What are some other agents of erosion?

Deposition is the dropping of sediments that occurs when an agent of erosion, such as gravity, a glacier, wind, or water loses its energy and can no longer carry its load.

Dropping Sediments

Mass Movement is any type of erosion that happens as gravity moves materials downslope.

Mass movement can be slow or quick.

The greater an object mass is, the greater its gravitational force is.

Gravity is a major force of erosion and deposition.

Common mass movements include slump, creep, rockfalls, rock slides, and mudflows.

Mass Movement

When a mass of a material slips down along a curved surface, the mass movement is called slump.◦ Usually occurs:

Steep hills Movement of water down hill Strong rock layers laying on weaker rock layers

What is a slump?

A creep is a type of mass movement in which sediments move down-slope very slowly.

It is common in areas of freezing and thawing, and can cause walls trees, to lean downhill.

What is a creep?

Signs along mountainous roadways warn people of a mass movement called a rockfall.

Rockfalls occur when blocks of rock break loose from a steep slope and tumble through the air.

As the rock fall, they hit other rocks and break them loose.

Rock slides occur when layers of rock, usually steep layers, slip downslope suddenly.

Rockfalls and Rock Slides

A mudflow is a thick mixture of sediment and water flowing down a slope.

They often occur:◦ When vegetation has been removed by a fire◦ Thick layers of loose sediment◦ Areas of heavy rainfall

Why might mudflows be more dangerous than flood waters?

What are mudflows?

All types of mass movement occur more often after heavy rain.

Mass Movement

What are some consequences of erosion?