1. Chapter 8: Erosional Forces

2. Aim: What is the difference between erosion and deposition?

3. Erosion
is a process that wears away surface materials and moves them from one place to another
Agents of erosion include gravity, water, wind and glaciers
Water and wind need to have large amounts of energy to move materials
Glacial erosion moves sediments trapped in the ice by melting

4. Deposition
Agents of erosion drop sediments they are carrying as they lose energy
Eroded sediments are not lost from earth
They are moved by erosional forces and relocated to other areas

5. Aim: How does gravity act as an erosional force?

6. Mass Movement
Is an type of erosion that happens as gravity moves materials down slope
Some are so slow you can’t see them happening
Other happen rapidly and you can see
Landslides are one of the 5 types or a combination of them
5 types: slump, creep, rock falls, rock slides and mudflows

7. Slump Is when a mass of material slips down slope as one large mass
3 ways this can happen:
when a slope becomes too steep and the base can no longer support the sediments above
When water weakens the base and the slipping sediments move downhill
Strong rock layer lays on top of a weaker layer and it can not support the strong rock

8. Creep Occurs when sediments slowly shift their positions downhill
Is common in places where there freezing and thawing are common
Evidence of creep includes: leaning trees or human-built structures

9. Rockfalls
Happens when rocks break loose from a steep slope and fall to the ground
As they fall they knock other rocks loose
Falling rocks can cause serious damage to structures on the ground
This is caused by the ice wedging
On roadways signs warn of falling rock areas

10. Rock Slides Occurs when layers of rocks slide downslope
They move quickly and can be destructive
Occur in areas with steep, mountainous slopes
Mostly happen after heavy rainfall or during earthquakes

11. Mudflows
Occur in places that have thick layers of loose sediments, like soil
Happen after vegetation has been removed because of fires
With the lose of vegetation and heavy rainfalls the loose sediments are carried downhill by gravity
While it moves down slope it gains energy and can destroy anything in its path

12. Aim: How can we slow down erosion on steep slopes?

13. Preventing Erosion on Slopes
Building on steep slopes, you must worry about erosion
By building we quicken the process of erosion by removing vegetation and makes slopes steeper
There are ways to prevent erosion
By planting vegetation on slopes we keep soil in place, which reduces the risk of mass movements
Construction of draining systems prevents water from building up

14. These methods help build a stronger stability of the slope
We can also help stability by building walls to hold soil in place
Large amounts of money are spent on trying to prevent mass movements
Earthquakes and rain make it difficult to completely prevent erosion on slopes
Eventually materials will weaken and gravity takes over causing mass movements

15. Aim: How do glaciers cause erosion?

16. Glaciers Glaciers form in regions where snow accumulates
As snow builds up the weight of snow compresses the lower layers into ice
With enough pressure the mass of ice and snow begins to move, which are known as glaciers
Are agents of erosion
When moving over land they erode, and change features of earth
While the move the take eroded materials and deposit them somewhere new

17. Plucking Glaciers weather and erode solid rock
When glaciers melt the water flows into cracks in rocks
Water refreezes , expands and pieces of rock are plucked out by the ice
During this process, boulders, gravel, and sand are added to bottom and sides of the glacier

18. Transporting and Scouring
As the glacier moves large amounts of sediments are transported
Sand and plucked rock fragments scour and scrape the soil and bedrock
Glaciers cause grooves to form along bedrock
Grooves are deep, long, parallel scars
Striations are shallower scars
Grooves and striations show the direction that the glacier is moving

19. Aim: How do glaciers deposit sediments?

20. Types of Deposits
As glaciers melt boulders, sand, clay and silt are left behind
Till Deposits
Mixture of different sized sediments
Can cover huge areas of land
Till areas in the US span from northwestern Iowa and northern Montana, which are wheat fields
Some farmland in Ohio contain till deposits
Rocky pastures of New England have till deposits

21. Moraine Deposits
Form at the end of glaciers
Type of till deposit
This deposit doesn’t cover a large area of land
Materials pile up and form a ridge known as a moraine
Can also form at the sides of glaciers

22. Outwash Deposits
Materials deposited my the meltwater from a glacier is called outwash
Carries sediments and deposits them in layers
Heavier materials drop first
Can form a fan-shaped deposit

23. Eskers
Type of outwash deposit
Looks like a winding ridge
Forms in a melting glacier when meltwater forms a river within the ice
River carries sand and gravel and deposits them within their channel

24. Aim: What are the 2 types of glaciers?

25. Continental Glaciers Are huge masses of ice and snow
Are thicker than some mountain ranges
In the past covered as much as 28% of earth
Today they cover 10% of the earth
Many of them melted after the last ice age

26. Valley Glaciers
Occur in mountains where the temperature is very low all year round
To find evidence of glaciers look for striations and plucking
They erode bowl-shaped basins called cirques
Arete forms when 2 valley glaciers side by side erode a mountain
Horns form when the glacier erodes the mountain from several directions
Valleys eroded by glaciers have a U-shape

27. Aim: How does wind cause erosion?

28. Wind Erosion Wind picks up loose sediments and materials
It can’t pick up very large sediments
Wind erodes earth’s surface by deflation and abrasion
Deflation
wind blows across loose sediment, removing small particles like silt and sand
Larger materials are left behind
Occur mostly in deserts, plowed lands and beaches

29. Abrasion
Windblown sediments strike rocks and change the surface and shape of the rocks
The impact of the sand is so strong it breaks off small fragments
Occurs mostly in beaches, deserts and plowed lands

30. Aim: How can we reduce wind erosion?

31. Sandstorms occur when wind blows forcefully in deserts
Dust storms occur when soil dries out
Soil particles weigh less than sand-sized particles and they move higher through the air
Dust storms can cover hundreds of kilometers
Blow soil from places where vegetation has been removed

32. Reducing Wind Erosion
Planting vegetation is one of the best ways to prevent wind erosion
Farmers plant trees along their fields to act like windbreaks
The trees reduce the energy of the wind and it is unable to pick up loose sediments
Tree belts also trap snow, which makes the soil more moist
Moist soil helps prevent erosion

33. Vegetation is planted along seacoasts and deserts too
Grasses, which have fibrous root systems are the best at stopping wind erosion
Their roots are shallow and twist between particles to hold them in place
planting vegetation is a good way to reduce the effects of abrasion and deflation, but can’t complete stop it

34. Aim: What do wind deposits develop into?

35. Loess Loess is deposits of fine-grained sediments
Sediments settle on hilltop and in valleys
The particles pack together and create a thick, yellowish deposit
Is as fine as talcum powder
Many farmlands have fertile soil that developed from loess deposits

36. Dunes Dune is a mound of sediments drifted by the wind
Common in desert regions
Sediments being blown by the wind build up against a rock or bundle of vegetation
Side of dune facing the wind has a gentler slope
Side away from the wind is steeper
Shape of a dune depends on the amount of sediment, wind speed and direction and amount of vegetation present

37. Crescent-shaped dune (barchan dune): open side faces the direction that the wind is blowing
This type of dune forms on hard surfaces where the sand supply is limited
Transverse dune: forms where sand is abundant
The direction of this dune is perpendicular to the wind direction
Star dune form in areas where the wind direction changes and form pointed structures