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Erosional Forces. 7 .1 Gravity. 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.

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Erosional forces
Erosional Forces

7.1

Gravity


  • 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.


  • Slump

    • 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


  • Mudflows

    • 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. 189 1-4


  • Erosional forces1
    Erosional Forces

    7.2

    Glaciers


    • 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.


    • 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.


    • Evidence of valley Glaciers

      • 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


    • 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 196 1-3


    Erosion forces
    Erosion Forces

    7.3

    Wind


    • Wind Erosion

      • Deflation and Abrasion

        • Deflation – blowing loose sediment, removing small particles such as clay, silt, and sand.


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