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 waterDeposition – dropping of sediment in a new location.The final stage of erosion.Erosion and Deposition by GravityGravity – force of attraction that exists between all objectsGravity 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.CreepCreep – sediments that slowly inch their way down a hill.Frequent in areas of freezing and thawingRockslidesLarge blocks of rock break loose form a steep slope ad start tumblingOccur in mountainous areas or where there are steep cliffsMost 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 sedimentsOften after a heavy rainErosion-Prone LandBuilding on Steep SlopesProne to slumps because of weak sediment layers underneath.Removal of vegetation or increasing slope speeds up erosion.Making Steep Slopes SafePlant vegetationBuild walls or terracesCan only slow erosion, never eliminatePg
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 GlaciersGlaciers 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 ErosionGlaciers 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-shapesGlacial DepositionTillTill – 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 OutwashMore snow melting causes glacier to melt and retreat.Outwash – material left by the meltwaterMeltwater leaves sediments and deposits in layers like a riverCan 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
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.SandstormsSandstorm – low cloud, just above the groundOccur in deserts and sometimes on beaches and dry riverbedsDust StormsDust storms – higher off the ground and can be carried far distancesStorms 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 erosionRootsPlants with fibrous root systems, help to stop erosionDeposition by WindLoessLoess – glacial outwash of fine-grained sediments, deposited by windCreates much of the fertile farmland of the Midwestern USDunesFormed when sediments build up behind an obstacleBuild 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 MovementSide facing wind has gentler slope, side away is steeperWithout grasses, dunes will migrate form the direction of the windDune ShapeShape can tell the direction of the windIn a crescent shaped dune, the points are directed downwind.