Chapter 8 Erosional Chapter 8 Erosional ForcesForces

Section 8-1 Erosion by GravitySection 8-1 Erosion by Gravity

Notes GuideNotes Guide

Erosion and DepositionErosion and Deposition► The process that wears away surface materials and The process that wears away surface materials and

moves them from one place to another is called moves them from one place to another is called erosion.erosion.

► Causes of erosionCauses of erosion-1. Gravity-1. Gravity-2. Water-2. Water-3. Wind -3. Wind -4. Glaciers-4. Glaciers

► Gravity is the force of attraction that pulls objects Gravity is the force of attraction that pulls objects towards Earth’s center.towards Earth’s center.

► Agents of erosion drop the sediments as they lose Agents of erosion drop the sediments as they lose energy. This is called deposition.energy. This is called deposition.

► When sediments are eroded, they are not lost, they When sediments are eroded, they are not lost, they are just relocated.are just relocated.

Mass Movement Mass Movement

► Any type of erosion that happens as gravity Any type of erosion that happens as gravity moves materials down slope is called mass moves materials down slope is called mass movement.movement.

► Some happen very slowly, others happen Some happen very slowly, others happen quickly and cause catastrophes.quickly and cause catastrophes.

►When a mass of material slips down along a When a mass of material slips down along a curved surface, the mass movement is curved surface, the mass movement is called a slump.called a slump. This can be caused by water weakening the This can be caused by water weakening the

mass, or if a strong rock layer lies on top of a mass, or if a strong rock layer lies on top of a weak rock layer, commonly clay.weak rock layer, commonly clay.

A curved scar is left where the slumped materials A curved scar is left where the slumped materials originally rested.originally rested.

SlumpSlump

CreepCreep

►Creep occurs where sediments slowly Creep occurs where sediments slowly shift their positions downhill.shift their positions downhill.

►    Leaning trees and human-built structures, Leaning trees and human-built structures,

such as houses show evidence of creep.such as houses show evidence of creep. Creep is common in areas of frequent Creep is common in areas of frequent

rainfall and snowfall.rainfall and snowfall.

Mass Movement Cont.Mass Movement Cont.

► Rock falls happen when blocks of rock break Rock falls happen when blocks of rock break loose from a steep slope and tumble down, loose from a steep slope and tumble down, causing more and more rocks to crash into causing more and more rocks to crash into each other and break loose.each other and break loose.-This can be caused when water freezes in -This can be caused when water freezes in rocks and the cracks expand.rocks and the cracks expand.

► Rock slides occur when steep layers of rock Rock slides occur when steep layers of rock slip down slope suddenly.slip down slope suddenly.-Rock slides are common in mountainous -Rock slides are common in mountainous areas or areas with steep cliffs. They can areas or areas with steep cliffs. They can occur after heavy rains or during occur after heavy rains or during earthquakes.earthquakes.

Mass Movement Cont.Mass Movement Cont.

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

LandslideLandslide

RockslideRockslide

MudslideMudslide

How would you like to own that How would you like to own that house?house?

Landslide!!Landslide!!

Consequences of ErosionConsequences of Erosion

► People live on steep slopes because they like to People live on steep slopes because they like to have a great view and live in scenic areas.have a great view and live in scenic areas.

► When people build homes on steep slopes, they When people build homes on steep slopes, they make slopes steeper or remove vegetation. This make slopes steeper or remove vegetation. This speeds up erosion.;speeds up erosion.;

► One of the best ways to reduce erosion is to plant One of the best ways to reduce erosion is to plant vegetation.vegetation.

► Drainage pipes can help prevent water from building Drainage pipes can help prevent water from building up.up.

► Walls or boulders can reduce soils erosion by holding Walls or boulders can reduce soils erosion by holding soil in place.soil in place.

► Eventually, regardless of time and money spent to Eventually, regardless of time and money spent to preserve land, gravity always wins.preserve land, gravity always wins.