Erosion & Deposition Ch 10 8 th grade

What processes wear down and build up Earth’s surface? Gravity, moving water, glaciers, waves, and wind are all agents of erosion. The process of erosion moves sediment and deposits it somewhere else. Deposition changes the shape of the land. Weathering, erosion, and deposition act together in a cycle that wears down and builds up Earth’s surface.

What are the different types of mass movement? mass movement Gravity causes mass movement of sediment downhill. The different types of mass movement include: –Mudflow is a rapid downhill movement of a mixture of water, rock, and soil. –Landslide occurs when rock and soil slide quickly down a steep slope. –Slump happens when a mass of rock and soil slip out from under a landmass. –Creep is the very slow downhill movement of rock and soil.

How does moving water cause erosion? Moving water is the major agent of the erosion that has shaped Earth’s land surface. As water moves over the land, it carries particles with it. The amount of runoff depends on: –Amount of rain –Type of vegetation –Type of soil –Shape of land –How land is used

Stream formation Because of gravity, runoff and its sediment flow downhill. Often, it runs together to form rills, gullies, and streams. Rills are tiny grooves in soil that move water. Many rills run together to create a gully that moves water, soil, and rocks. Gullies only contain water during rain.

Drainage Basin Erosion enlarges the gullies to form a larger channel called a stream. Streams carry water almost all the time, and may be called creeks or brooks. Streams flow together to create a river. Tributaries add more water to the river. A drainage basin, or watershed, is the area from which a river and its tributaries collect their water.

What land features are formed by water erosion & deposition? Through erosion, a river creates valleys, waterfalls, flood plains, meanders, and oxbow lakes. When rivers begin at steep mountains, the fast moving water erodes land rapidly creating valleys. Waterfalls occur when water flows over harder rock and erodes softer rock underneath.

As land becomes more level, rivers flow slower and spreads out forming a wide river valley. As the river floods, it covers this flood plain with new soil making it a fertile valley. When a river flows through easily eroded rock, it creates loop-like bends called meanders. The river erodes the outer bank and deposits sediment on the inner bank causing the meander to become more curved. Over time, a meander gets cut off from the river causing an Oxbow lake.Oxbow lake

Water Deposition Deposition creates landforms such as alluvial fans and deltas. Sediment deposited where a river flows into an ocean or lake, builds up land, and creates a delta.delta When a stream flows out of a steep, narrow mountain valley, the stream suddenly becomes wider and shallower. An alluvial fan is created from the wide, sloping deposit of sediment.

Groundwater Erosion When rain falls and snow melts, some water soaks into the ground filling openings in the soil and spaces in layers of rock. Groundwater can cause erosion through a process of chemical weathering. Rainwater contains a weak acid called carbonic acid that can break down limestone when groundwater flows into cracks. Limestone dissolves to hollow out pockets in the rock creating caves or caverns.

Cave formations Inside limestone caves, deposits called stalactites (that look like icicles from the roof) and stalagmites (that look like a cone-shape) on the floor often form.

Karst topography In areas where there is a layer of limestone near the surface, water easily sinks down into the weathered limestone creating deep valleys and caverns. If the roof of a cavern collapses due to erosion of underlying limestone, a sinkhole is created.sinkhole This type of landscape is called karst topography.

How do glaciers form and move? Glaciers can form only in an area where more snow falls then melts.Glaciers Continental glaciers cover about 10% of Earth’s land- mostly Antarctica and most of Greenland. Continental glaciers can flow in all directions as they move and many times in the past have covered larger parts of Earth’s surface during ice ages. They advanced and retreated, the last about 10,000 years ago.advanced and retreated

Continental Glaciers Continental glaciers can flow in all directions as they move. What are some changes in elevation and ice depth on this chart? Glacial Erosion

Valley glaciers build up high in a mountain valley and the sides of the mountain keeps it from spreading out so it moves down the valley that has been carved by rivers. The weight of snow compacts at the bottom of the valley since gravity constantly pulls a glacier downhill and once it is 30-40m deep, the glacier begins to move. Velley glaciers can move from a few centimeters to a few meters per day.

Valley Glaciers When glaciers recede, they leave behind evidence of their existence. Glacial Erosion

How do glaciers cause erosion and deposition? Two processes by which glaciers erode the land are plucking and abrasion. As a glacier flows over the land, it picks up rocks called plucking. The weight of the glacier can break apart a rock and the pieces freeze to the bottom. The rocks remain on the bottom, are dragged across the land, and gouge the bedrock. This process is called abrasion.

Glacial Deposition A glacier can gather a huge amount of rock as it erodes the land. When the glacier melts, it deposits the rock creating new landforms. Till: mixture of sediments deposited on the surface. Moraine: ridge created by till at the end of a glacier –Terminal moraine forms at the farthest point of a glacier. Kettles: a depression formed when ice is left in a deposit of till then melts –Kettle lakes form when kettles fill with water See glaciers melt before your eyes

How do waves cause erosion and deposition? The energy in wind is transferred to the water creating waves. The friction between the waves and land creates a force that changes the shoreline. Waves shape the coast through weathering by breaking down rock and through erosion by moving sand and sediment.

Energy in waves can break apart rocks. Waves can pick up sediment in shallow water. This sediment can wear away rock and can deposit when the wave looses energy.

Landforms caused by wave erosion Harder rock that resists erosion is called a headland and sticks out into the water. When rock is soft, the land erodes faster and creates a hallow called a sea cave and eventually the rock collapse creating a wave-cut cliff. A sea arch may form instead of a sea cave. If the arch collapse, the pillar remaining is a sea stack.

Landforms caused by deposition Beaches are wave-washed areas covered in deposited sediment usually sand. Beach sediment can move down the beach due to a parallel current called longshore drift and creates spits that projects into the water. Sand bars and barrier beaches can also build up parallel to the shore