1. Erosional Forces
7.1
Gravity

2. Erosion and Deposition
Erosion – process that wears away surface materials and moves them from one place to another.
Major causes – gravity, glaciers, wind, and water
Deposition – dropping of sediment in a new location.
The final stage of erosion.
Erosion and Deposition by Gravity
Gravity – force of attraction that exists between all objects
Gravity causes loose materials to move down a slope.
Mass Movement – erosion that occurs due to gravitational pull on a down slope.

3. Slump Creep Rockslides
Slump- mass movement that happens when loose materials or rock layers slip down a slope.
Happens when layers underneath can not support the rock and sediment above.
Creep
Creep – sediments that slowly inch their way down a hill.
Frequent in areas of freezing and thawing
Rockslides
Large blocks of rock break loose form a steep slope ad start tumbling
Occur in mountainous areas or where there are steep cliffs
Most often happen after heavy rains, or during earthquakes

4. Erosion-Prone Land Pg. 189 1-4 Mudflows Building on Steep Slopes
Occur in dry areas where there are thick layers of dry sediments
Often after a heavy rain
Erosion-Prone Land
Building on Steep Slopes
Prone to slumps because of weak sediment layers underneath.
Removal of vegetation or increasing slope speeds up erosion.
Making Steep Slopes Safe
Plant vegetation
Build walls or terraces
Can only slow erosion, never eliminate Pg

5. Erosional Forces
7.2
Glaciers

6. Continental and Valley Glaciers
Weight of snow becomes great enough to press the bottom layers into ice.
Pressure on ice on the bottom causes partial melting and becomes putty-like.
Glacier – moving mass of ice and snow.
Continental Glaciers
Glaciers covered up to 28% of Earth during the last ice age (2 to 3 million years ago)
Average air temperature was 5 degrees C lower than today.
20,000 years ago ice sheets began to melt.
Today glaciers only cover 10% of Earth.

7. Glacial Erosion Valley Glaciers
Occur in current climate in high mountains where temperature is low enough to stop snow from melting.
These glaciers grow and creep along.
Glacial Erosion
Glaciers pull loose material and deposits it in a new location.
Plucking - Glacial ice melts and water flows into crack in rocks. As it refreezes rocks break apart and results in boulders, gravel, and sand being added to the moving glacier.
As the glacier moves, plucked rock fragments rub against soil and bedrock speeding up erosion.
The rocks leave grooves or striations.

8. Glacial Deposition Evidence of valley Glaciers Till
In mountains look for striations and plucking.
Valley glaciers make bowl-shaped basins called cirques.
Two or more glaciers will form arete, a ridge, or a horn.
Glaciers erode valley in U-shapes
Glacial Deposition
Till
Till – different size sediment dropped from a melting glacier.
During the last ice-age glaciers dropped till in the northern United States to fill valleys and make land appear flat.
Moraine – ridge formed when a glacier stops moving and a large amount of till is dropped

9. Outwash
More snow melting causes glacier to melt and retreat.
Outwash – material left by the meltwater
Meltwater leaves sediments and deposits in layers like a river
Can make fan-shaped deposits.
When meltingwater under a glacier forms a river in the ice, eskers, a winding ridge of sand and gravel is formed. Pg

10. Erosion Forces
7.3
Wind

11. Wind Erosion Deflation and Abrasion Sandstorms Dust Storms
Deflation – blowing loose sediment, removing small particles such as clay, silt, and sand.
Abrasion – windblown sediments strike rock, and wear away the surface.
Abrasion and deflation happened mainly in deserts, beaches, and plowed fields.
Abrasion works like sandblasting, with the wind acting as the machine.
Sandstorms
Sandstorm – low cloud, just above the ground
Occur in deserts and sometimes on beaches and dry riverbeds
Dust Storms
Dust storms – higher off the ground and can be carried far distances
Storms blow top soil from open fields, overgrazed areas, and place where vegetation has disappeared.

12. Reducing Wind Erosion Deposition by Wind Windbreaks Roots Loess Dunes
Rows of trees used to reduce the energy of motion in wind to stop soil erosion
Roots
Plants with fibrous root systems, help to stop erosion
Deposition by Wind
Loess
Loess – glacial outwash of fine-grained sediments, deposited by wind
Creates much of the fertile farmland of the Midwestern US
Dunes
Formed when sediments build up behind an obstacle
Build where there is sand and winds or sea breezes that blow daily.

13. Dune Movement Dune Shape Sand builds up becoming an obstacle itself
Sand will continue to build and form a dun until the sand runs out or the obstacle is removed.
Dune Movement
Side facing wind has gentler slope, side away is steeper
Without grasses, dunes will migrate form the direction of the wind
Dune Shape
Shape can tell the direction of the wind
In a crescent shaped dune, the points are directed downwind.