Changing Earth’s Surface
Jan 03, 2016
Changing Earth’s Surface
Changing Earth's Surface
• Weathering
– The process that breaks down and changes rocks that are exposed at Earth’s surface
8.1 Weathering
• Erosion
– Moving weathered material from one place to another
• Deposition
– Sediment is laid down at a new location
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Shaping the Earth with Water
• Most erosion is done by water.
• Rivers, ocean currents, and ice (p. 334, 342)
2.1 Landforms
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Rivers
Rivers
• Streams and rivers are active systems that erode land, transport sediment, and deposit sediment.
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Deposition• Sediment and rock that are eroded and carried by river systems
are transported and eventually deposited at a new location.
8.2 Erosion and Deposition
– Oxbow lakes
– Delta
– Alluvial fans
1(Page 345)
Flooding
Flood• When the water level in a river rises above the usual
height and overflows its banks
8.2 Erosion and Deposition
• Floodplain: a wide, flat valley located along the sides of rivers and streams
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Levees
• Protect area from flooding
8.2 Erosion and Deposition
– Natural levees: long, low ridges formed by sediment carried by floodwaters and deposited along the floodplain
– Artificial levees: human–made structures built to help control floodwaters (p. 348)
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Beaches
Beaches
• Landform consisting of loose sand and gravel
8.2 Erosion and Deposition
• Dynamic, actively changing systems
• Sand supplied by the continuous flow of rivers to oceans
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Erosion Features
• Cliffs: formed by the cutting action of waves• Eroded cliffs move back from the shoreline and leave behind a flat area called a wave-cut
platform
• Sea caves, sea stacks, and sea arches can form when waves erode the softer portions of rocks.
8.2 Erosion and Deposition
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Longshore Current
8.2 Erosion and Deposition
• Movement of the water that moves large amounts of sediment along coasts
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Erosion Prevention• Shoreline armoring: retaining walls, harbor channels, and
groins
8.2 Erosion and Deposition
• Changes natural shoreline processes but is necessary to prevent collapse of cliffs or the complete destruction of a beach. (p. 349)
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Glaciers
Glaciers
• Large masses of ice and snow
8.2 Erosion and Deposition
• Form in areas where amount of annual snowfall is greater than the meltoff
• Formation takes hundreds to thousands of years
• Movement is about 2.5 cm/day
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Glaciers (cont.)
• Valley glaciers (alpine glaciers): form in existing stream valleys high in the mountains
8.2 Erosion and Deposition
• Continental glaciers (ice sheets): cover entire land areas, only located in Antarctica and Greenland
• Video
(Page 350)
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Glaciers shape the land
Glaciers and Erosion• Glaciers erode surfaces as they
pass over them. U-shaped valleys.
• Trapped rocks and boulders at the bottom of the ice create grooves and scratches as the glacier moves.
• Grooves and scratches show the direction the glacier was moving. (striations)
8.2 Erosion and Deposition
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Deposition and Glaciers• Till: sediment deposited by glacier. Often builds up along the
sides and fronts of glaciers into long, high ridges called moraines
• Outwash: sediment deposited by glacial river; consists mostly of sand and gravel (p.351)
8.2 Erosion and Deposition
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MassWasting
Mass Wasting
• Downhill movement of rocks and/or soil in one large mass
• Usually occurs when the ground is saturated with rainwater but can be triggered by vibrations from earthquakes, heavy machinery, and blasting
• Steeper the slope of hillside, the more likely mass wasting will occur
• Form of erosion caused by gravity
8.2 Erosion and Deposition
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Mass Wasting (cont.)8.2 Erosion and Deposition
• Landslides: rapid, gravity-caused events that move soil, loose rock, and boulders
• Mudslides: mixtures of soaked soil and rock
• Rock falls: loosened rock falling from steep cliffs
• Slumps: a block of rock and overlying soil slide down as one large mass
• Creep: sediment moves slowly downhill
• (p.343) 1
Climate & Erosion
Climate and Erosion• Climate determines amount of water a region receives
• Regions with large amounts of rain more likely to experience mass wasting
• Presence of thick vegetation on slopes tends to prevent landslides because the plants’ root systems hold sediment in place (p.344)
8.2 Erosion and Deposition
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