Transcript Chapter 8: Erosional Forces

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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
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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
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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
Is when a mass of material slips down slope as
one large mass
 3 ways this can happen:
1. when a slope becomes too steep and the base
can no longer support the sediments above
2. When water weakens the base and the slipping
sediments move downhill
3. Strong rock layer lays on top of a weaker layer
and it can not support the strong rock
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
2.
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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
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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
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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
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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
Wind picks up loose sediments and materials
 It can’t pick up very large sediments
 Wind erodes earth’s surface by deflation and
abrasion
1. 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
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2.
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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
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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
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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
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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
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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
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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
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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