Erosional Forces

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Chapter 8
Erosional Forces
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Flatten the soil in your plate. Find 3 ways to
move the soil from one side of the plate to the
other. You may not touch the soil with your
hands! But, you can touch the plate. Do not
spill!
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• Erosion process that wears away surface material
  and moves them from one place to another
• major causes gravity, glaciers, wind, water
• they all need energy for motion!
• Deposition the dropping of sediments that occur
  when an agent of erosion looses its energy of
  motion and is no longer able to carry the load
• drop when energy of motion decreases!
• What causes erosion and deposition?
• - Gravity! What is gravity? The force of
  attraction that exists between all objects
• - Since Earth is so large, all objects are
  attracted to it.
• - The Earth is the source of all our gravity.
• - Any loose material will be pulled down a slope
  (hill), due to gravity.
• - When gravity alone causes material to slide
  down a slope this is called mass movement.

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• Examples of mass movement
• Slump mass movement that happens when loose rock
  layers slip down a slope.
• When a slope becomes too steep, the base material
  no longer can support the rock and sediment above
  it.
• The soil and rock slip downslope as one large
  mass or break into several sections.
• 2) Creep sediments slowly inch their way down a
  hillmost common in freezing areas.
• Ex Leaning trees and fence posts that lean
  downhill.

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• Rockfalls and Rock Slides when large rocks break
  loose and tumble down a hillcan be very
  destructive!
• Rockfalls - As rocks fall and tumble through the
  air, they crash into other rocks and knock them
  loose. More and more rocks break loose and
  tumble to the bottom.
• Rock Slides occur when layers of rocks
  usually steep layers slip down a slope
  suddenly. Happen most after heavy rain or
  earthquakes.
• 4) Mudflows a thick mixture of sediment and
  water flowing down a slopedry areas with thick
  layers of sediment that suddenly get really wet
  from rain

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• All mass movements
• Occur on slopes
• Occur more often after a rain
• Increase if vegetation has been removed
• How can you prevent these problems?
• Strengthen slopes with vegetationroots hold
  soil together
• Walls made of concrete
• We can try all we want to avoid erosion and
  deposition problems, but in the long rungravity
  will still be too powerful!
• IE video of mudslide

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Review 1. Define erosion. What force causes
it? 2. Explain how deposition changes the
surface of the Earth. 3. Describe the
characteristics that all types of mass movements
have in common. 4. Describe ways to help slow
erosion on steep slopes. 5. What are the
similarities and differences between rock falls
and rock slides?
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• Erosion by Glaciers!
• Glacier a large mass of ice and snow moving on
  land under its own weight.
• As glaciers pass over land, they erode it,
  changing features on the surface.
• They then carry eroded material along and
  deposit it somewhere else.
• Change large areas of the earths surface.
• Plucking process that adds gravel, sand and
  boulders to a glaciers bottom and sides as water
  freezes and thaws, breaking off pieces of
  surrounding rock.

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• Transporting and Scouring as glaciers move
  forward over land, they can transport huge
  volumes of sediment and rock.
• Plucked rock fragments and sand at its base
  scour and scrape the soil and bedrock like
  sandpaper against wood, eroding the ground below
  even more.
• When bedrock is gouged deeply by rock fragments
  being dragged along, marks are left behind.
• Deep, long parallel scars are called grooves.
• Shallow marks are called striations.
• These indicate the direction in which the
  glacier moved.

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• Ice Depositing Sediment
• When glaciers begin to melt, they are unable to
  carry much sediment and that sediment drops, or
  is deposited, on the land.
• When a glacier melts and begins to shrink back,
  it is said to retreat.
• As it retreats, a jumble of boulders, sand, clay
  and silt is left behind.
• The mixture of different sized sediments is
  called till.
• Till deposits can cover huge areas of land.
• Thousands of years ago, huge ice sheets in the
  northern US left enough till behind to fill
  valleys completely and make these areas appear
  flat.
• Ex areas of Montana, Iowa, Ohio, Illinois,
  Indiana and New England.

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• Moraine Deposits large ridges of rocks and
  soil deposited by a glacier when it stops moving
  forward.
• Outwash Deposits material deposited by
  meltwater from a glacier.
• Eskers a winding ridge of sand and gravel left
  behind when a glacier melts.
• Pg. 217

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• Continental Glaciers huge masses of ice and
  snow that cover 10 of Earthmostly near the
  poles of Antarctica and Greenland.
• Thicker than some mountain ranges and make it
  impossible to see most of the land features of
  those regions.
• Valley Glaciers occur in high mountains where
  the average temperature is low enough to prevent
  snow from melting during the summerthese grow
  and creep along.
• Importance of Glaciers
• Shaped mountain tops and transformed valleys.
• Left behind sediments that are economically
  important
• Ex sand and gravel deposits are excellent
  starting materials for the construction of roads
  and buildings.

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• Wind!
• Wind erosion air moves and picks up particles
  and deposits them in other places
• Air differs from other erosional forces because
  it cant normally pick up heavy objects, but it
  can deposit sediment over a large area
• Wind erodes Earths surface by deflation and
  abrasion
• Deflation wind blows across loose sediment and
  removes small particles and leaves behind heavy
  materialbig rocks
• Abrasion windblown sediment hit rocks and
  surface gets worn away occurs everywherebut
  mostly in deserts, beaches plowed fields
• WHY? fewer plants to hold sediment
• Sandstorms - sand is normally too heavy for
  windwind blows forcefully sand bounces hits
  other grains causing them to rise into air (low
  cloud just above ground)
• Dust storms - dry soil picked up by wind and
  blown high into atmosphere because they weigh
  less than sandcarries particles far distances
• IE 1930dust picked up in Kansas was found in
  New England
• important part of soil erosion

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• Reduce wind Erosion
• Erosion is most common in areas with no plants
• Stop erosion?PLANTS!
• Vegetation will reduce erosion
• Roots hold soil in place
• Windbreaks with trees slow down wind
• Stop energy of motion
• IE row of cottonwood trees reduced wind to 66
  of normal speed
• Butstrong wind with dry soilnothing will stop
  erosion by wind!

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Deposition by wind sediments are eventually
deposited in new areas Creates a variety of
land forms Loess wind deposits of fine-
grained sedimentpacked together creates a thick
unlayered yellowed- brown colored deposit What
happens when wind blows sediment against an
obstacle? dune! Dunes created when sediment
settles behind an obstacle Dunes can be moved as
sand is lifted and deposited downwind(picture
) OverallErosion and Deposition constantly
shape and reshape the land!
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• Create a Study Guide!
• Using key terms and main ideas from chapters 7
  and 8, create a study guide AND answer key (on
  separate sheets of paper).
• 10 fill in the blank questions
• 5 multiple choice questions
• 5 true or false questions
• Ex ______ is a mixture of weathered rock,
  organic matter, mineral fragments, water and air.