Changing Earth’s Surface

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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