Erosional ForcesErosional Forces

FACTORS SUCH AS WIND FACTORS SUCH AS WIND AND WATER MOVE AND WATER MOVE

MATERIALS !MATERIALS !

ErosionErosion Wearing away and moving of surface Wearing away and moving of surface

materials by gravity, water, wind or materials by gravity, water, wind or glaciers.glaciers.

Through the process of deposition, Through the process of deposition, sediments are dropped by erosion sediments are dropped by erosion

agents as they lose energy.agents as they lose energy.

Mass movement occurs as gravity Mass movement occurs as gravity moves materials down a slope as moves materials down a slope as

one large mass.one large mass.

Slump: material slips down a Slump: material slips down a curved surface as one large mass.curved surface as one large mass.

Sediments slowly shift down hill in Sediments slowly shift down hill in the process of creep.the process of creep.

Rockfalls and rock slides occur Rockfalls and rock slides occur when rocks break off or slip when rocks break off or slip

suddenly down a hill.suddenly down a hill.

A mudflow is a thick mixture of water A mudflow is a thick mixture of water and sediments flowing downhill.and sediments flowing downhill.

Consequences of erosion:Consequences of erosion: Buildings on slopes eventually have Buildings on slopes eventually have

problems due to erosion by gravity.problems due to erosion by gravity.

Another source of instability is the Another source of instability is the removal of vegetation.removal of vegetation.

Steep slopes can be made safer with Steep slopes can be made safer with vegetation, drainage pipes, and walls of vegetation, drainage pipes, and walls of

concrete or railroad ties.concrete or railroad ties.

Glacier: large mass of ice and Glacier: large mass of ice and snow; moves slowlysnow; moves slowly

Glaciers are the most powerful Glaciers are the most powerful erosion agent.erosion agent.

As glaciers move they pick up As glaciers move they pick up boulders, gravel and sand in an boulders, gravel and sand in an erosion process called plucking.erosion process called plucking.

Plucked rocks at the base of the Plucked rocks at the base of the glacier scour the soil and bedrock.glacier scour the soil and bedrock.

Dragged rock fragments leave scars Dragged rock fragments leave scars on bedrock called grooves.on bedrock called grooves.

Striations are shallower scars on Striations are shallower scars on bedrockbedrock

Grooves and striations indicate the Grooves and striations indicate the direction a glacier moveddirection a glacier moved

As a glacier moves forward over land it can As a glacier moves forward over land it can transport huge volumes of sediment and transport huge volumes of sediment and

rockrock..

When glaciers melt and retreat they When glaciers melt and retreat they leave behind till (boulders, sand, leave behind till (boulders, sand,

clay and silt)clay and silt)

A moraine is a ridge, or pile, of A moraine is a ridge, or pile, of deposit left at the end of a glacierdeposit left at the end of a glacier

Outwash: material deposited in layers Outwash: material deposited in layers by the meltwater of a glacier, with by the meltwater of a glacier, with

largest pieces closer to the glacier.largest pieces closer to the glacier.

Esker: type of outwash deposit formed as Esker: type of outwash deposit formed as meltwater rivers within the ice deposit sand meltwater rivers within the ice deposit sand

and gravel within their channels.and gravel within their channels.

Continental glacier: huge masses of Continental glacier: huge masses of ice and snow now covering only about ice and snow now covering only about 10% of Earth in areas near the poles.10% of Earth in areas near the poles.

In the past, as much as 28% of In the past, as much as 28% of Earth was covered with glaciers.Earth was covered with glaciers.

Ice ages: periods of widespread glaciation Ice ages: periods of widespread glaciation over the last 2 million to 3 million years.over the last 2 million to 3 million years.

The average air temperature on Earth The average air temperature on Earth was about 5 degrees Celsius lower was about 5 degrees Celsius lower

during ice ages than todayduring ice ages than today

The last major ice age was about The last major ice age was about 18,000 years ago.18,000 years ago.

Valley glaciers exist in mountains.Valley glaciers exist in mountains.

Cirques: bowl-shaped basins in the Cirques: bowl-shaped basins in the sides of mountains, created by sides of mountains, created by

valley glaciers.valley glaciers.

Arete: long ridge that forms when Arete: long ridge that forms when two valley glaciers erode a two valley glaciers erode a

mountain side by side.mountain side by side.

Horn: forms when valley glaciers erode Horn: forms when valley glaciers erode a mountain from several directions.a mountain from several directions.

Glacially eroded valleys have a U Glacially eroded valleys have a U shape, as opposed to the V shape shape, as opposed to the V shape

left by stream erosion.left by stream erosion.

Glaciers have changed, and Glaciers have changed, and continue to change, the shape of continue to change, the shape of

Earth’s surface.Earth’s surface.

Wind ErosionWind Erosion

Can scatter dust or volcanic ash over Can scatter dust or volcanic ash over thousands of kilometersthousands of kilometers

DeflationDeflation

Wind removes small particles of Wind removes small particles of loose sediment, leaving behind loose sediment, leaving behind heavier materialsheavier materials

Wind behaves like a sandblaster Wind behaves like a sandblaster blowing sand grains against rocks blowing sand grains against rocks wearing them down and pitting them wearing them down and pitting them in the process of abrasionin the process of abrasion

Deflation and abrasion happen most Deflation and abrasion happen most often in areas where there is little often in areas where there is little vegetation to hold sediment in placevegetation to hold sediment in place

When strong winds blow in the When strong winds blow in the deserts, beaches, or dry riverbeds, deserts, beaches, or dry riverbeds, an airborne sand cloud or sandstorm an airborne sand cloud or sandstorm occursoccurs

Dust storms occur when winds blow Dust storms occur when winds blow dry topsoil from open fields, dry topsoil from open fields, overgrazed areas, or places with little overgrazed areas, or places with little or no vegetationor no vegetation

Reducing Wind ErosionReducing Wind Erosion

Plant vegetationPlant vegetation Windbreaks – rows of trees can slow Windbreaks – rows of trees can slow

down wind reducing erosion; they down wind reducing erosion; they can also trap snow and increase can also trap snow and increase moisturemoisture

RootsRoots

fibrous root system plants such as fibrous root system plants such as grasses help anchor soil particlesgrasses help anchor soil particles

Deposition by wind – airborne Deposition by wind – airborne particles eventually return to earthparticles eventually return to earth

Fine-grained sediments known as Fine-grained sediments known as loess helped form fertile soils in the loess helped form fertile soils in the Midwestern USAMidwestern USA

A mound of sediments drifted by A mound of sediments drifted by the wind is called a dunethe wind is called a dune

Dunes move as the wind continues Dunes move as the wind continues to blow against themto blow against them

the more gently sloping side of a the more gently sloping side of a dune faces the winddune faces the wind

Dunes have different shapes, such as Dunes have different shapes, such as crescents, lines, or starscrescents, lines, or stars

This is based on sediments, wind This is based on sediments, wind speed and direction, and vegetationspeed and direction, and vegetation