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 2

Shaping the Earth with Water Most erosion is done by water. Rivers, ocean currents, and ice (p. 334, 342) 2.1 Landforms 1

Rivers

Streams and rivers are active systems that erode land, transport sediment, and deposit sediment. 2

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 lakesOxbow lakes –DeltaDelta –Alluvial fansAlluvial 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 2

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) 1

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 4

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 3

Longshore Current 8.2 Erosion and Deposition Movement of the water that moves large amounts of sediment along coasts 2

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) 1

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 2

Glaciers (cont.) Valley glaciers (alpine glaciers): form in existing stream valleys high in the mountainsValley glaciers 8.2 Erosion and Deposition Continental glaciers (ice sheets): cover entire land areas, only located in Antarctica and GreenlandContinental glaciers Video (Page 350) 1

Glaciers shape the land

Glaciers and Erosion Glaciers erode surfaces as they pass over them. U-shaped valleys. 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 2

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 1

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 2

Mass Wasting (cont.) 8.2 Erosion and Deposition Landslides: rapid, gravity-caused events that move soil, loose rock, and bouldersLandslides: Mudslides: mixtures of soaked soil and rockMudslides Rock falls: loosened rock falling from steep cliffsRock falls Slumps: a block of rock and overlying soil slide down as one large massSlumps: Creep: sediment moves slowly downhillCreep (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 1