chapter 7 section 1 and 2
TRANSCRIPT
- 1. Section I:Erosion by Gravity
Chapter 7:Erosion Forces
2. I.Erosion and Deposition
Erosion
The process of erosion wears away surface materials and moves them
from one place to another.
The mud sediments laying on a road following a flood or landslide
comes from material that was further up the hillside or
upstream.
3. I.Erosion and Deposition
What Wears Away Sediments?
Gravity:The force of attraction that pulls objects toward Earths
center.
Other causes of erosion, also called agents of erosion, are water,
wind, and glaciers.
Water and Wind erode materials only when they have enough energy of
motion to do the work.
Air cannot move sediments on a calm day.
Strong wind can move dust and even larger particles.
Glacial Erosion
Works differently by slowly moving sediment that is trapped in
solid ice.
As the ice melts, sediment is deposited, or dropped.
Sometimes the sediment is carried even further by moving melted
water.
4. I.Erosion and Deposition
Dropping Sediments
Deposition:Agents of erosion drop the sediments they are carrying
as they lose energy.
When sediments are eroded, they are not lost from Earth, they are
just relocated.
5. II.Mass Movement
Mass Movement is any type of erosion that happens as gravity moves
materials downslope.
Some mass movements occur so slowly they are hardly notices.
Some occur so quickly they cause catastrophes.
The greater the an objects mass is, the greater its gravitational
force is.
Common types of mass movements include slump, creep, rock falls,
rock slides, and mudflows.
Landslides are mass movements that can be one of these types of
combination of these types of mass movements.
6. II.Mass Movement
Slump
When a mass of material slips down along a curved surface , the
mass movement is called slump.
7. II. Mass Movement
B. Slump
Occurs when a slope becomes too steep, the base no longer can
support the rock and sediment above it.
The soil and rock slip down slope as one large mass or break into
several sections.
8. II. Mass Movement
Slump
Sometimes a slump happens when water moves to the base of a
slipping mass of sediment.
Water weakens the slipping mass and can cause material
downhill.
Sometimes a strong rock layer lies on top of a weaker layer
(commonly clay or mud); the clay can weaken under weight of the
rock and cannot support the rock causing slump to occur.
9. II. Mass Movement
Creep
Creep occurs when sediments slowly shift their positions downhill,
as figure 3 illustrates.
Creep is common if areas of frequent freezing and thawing.
Trees and fence posts leaning downhill are examples of creep.
10. II. Mass Movement
Creep
Stages of Creep
The ground freezes.
Expanding the ice in the soil pushes sediments up.
The frozen soil thaws.
Sediments slowly fall down slope.
11. II. Mass Movement
Rock Falls
Rock falls happen when blocks of rock break loose from a steep
slope and tumble through the air.
As they fall these rocks hit more and more rocks and knock them
loose.
Ice wedging plays part in rock falls occurring.
When large rocks fall; serious damage can occur at the bottom of
the slope.
12. II. Mass Movement
Rock Slides
Rock Slides occur when layers of rock (usually steep layers), slip
down slope suddenly.
Rock Slides, like Rock Falls, are fast and can be destructive in
populated areas.
Commonly occur in mountainous areas or in areas with steep
cliffs.
Happen most often after heavy rains or during earthquakes , but can
happen on any rocky slope without warning.
13. II. Mass Movement
Mudflows
Thick mixture of water and sedimentsflowing down a slope.
Usually occur in dry areas that have layers of loose
sediments.
Often happen after vegetation has been removed or after fire.
Gravity causes this thick, pasty mixture flow downhill.
Whenmudflow reaches bottom it loses energy and deposits sediment
and everything else it has carried.
These deposits often form a mass that spreads out in a fan/cone
shape.
14. II. Mass Movement
Mass Movement Summary
Mudflows, rock slides, rock falls, creep, and slump are similar in
some ways.
Most likely to occur on steep slopes and all require gravity to
occur.
All types of mass movements are more likely to occur after heavy
rain.
15. Developing Land Prone to Erosion
Chapter 7 Section 2:
16. I.Consequences of Erosion
Building on Steep Slopes
When people build on steep slopes, they constantly must battle
naturally occurring erosion.
Sometimes builders make erosion worse by removing vegetation.
This speeds up the erosion process and creates additional
problems.
Some steep slopes are prone to slumps because of weak sediment
layers below.
May increase the chance of mass movement due to change in
vegetation, more traffic, and change in natural landscape.
17. I.Consequences of Erosion
Making Steep Slopes Safe
One of the best ways to reduce erosion is to plant
vegetation.
Plants can be beautiful or weed like, but they all have root
structures that hold soil in place.
Deep tree roots and fibrous grass roots bind soil together,
reducing the risk of mass movement.
Plants also absorb large amounts of water.
Drainage pipes can prevent water from building up.
These materials help increase the stability of the slope by
allowing excess water to flow out of a hillside more easily.
18. I.Consequences of Erosion
Making Steep Slopes Safe
Retaining walls made of concrete or boulders can reduce erosion by
keeping soil in place.
Terraces can also slow down soil erosion by causing the water to
lose its energy as it flows down the hillside.
19. I.Consequences of Erosion
Summary
People who live in areas of erosion problems spend a lot of time
and money trying to preserve their land.
They can never eliminate erosion and the danger of mass
movement.
Earthquakes, floods, and mudslides are unpredictable.
Eventually Gravity wins!!
Sediment moves from place to place, constantly shaping reducing
elevation and changing the shape of the land.