Erosion

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Erosion has removed soil from this forest.

Erosion is the process of natural forces moving rocks and soil. Rocks and soil can be referred to as earth materials. The natural forces that make erosion happen are water, wind, ice, and gravity.

Geology is the study of the structure of the earth and the processes that change the earth. Erosion is a geological process. Erosion occurs at the earth's surface, and has no effect on earth's mantle and core.

Most of the energy that makes erosion happen is provided by the sun. The sun's energy causes the movement of water and ice in the water cycle and the movement of air to create wind. If the sun did not provide energy for erosion, only gravity erosion would still occur.

Erosion can cause problems that affect humans. Soil erosion, for example, can create problems for farmers. Soil erosion can remove soil, leaving a thin layer or rocky soil behind. Erosion can also cause problems for humans by removing rocks or soil that support buildings.

Erosion by water[change | change source]

Water moving downhill can carry away pieces of rock and soil.

Temperature changes cause pieces of rock to flake away from the surface. Also, the acid in rainwater dissolves rocks containing calcium carbonate. These processes are called weathering.

Water erosion happens when water moves the pieces of rock or soil downhill. Waves also carry away small pieces of material. A wave can wash up onto the surface of rock or soil and then carry away pieces of material as it flows back into the ocean or lake.

The size of earth materials that can be moved by water depends on how fast the water is moving. A fast-flowing stream can carry large rocks while a slow moving stream might only be able to carry very small things like clay. Canyons are among the most obvious features made by erosion.

Tropical rivers[change | change source]

Drainage basin of the Amazon
The Aletsch Glacier is the biggest glacier in the Alps
Wind is blowing sand off this dune in the Mojave desert, California.

Huge tropical rivers like the Paraná, Indus, Brahmaputra, Ganges, Zambezi, Mississippi and the Amazon carry huge amounts of sediment down to the sea. The Nile, perhaps the world's longest river, carries much less sediment than the others because, part of the way, it runs through less fertile regions than the other great rivers.

The Amazon has by far the largest waterflow, with an average discharge greater than the next seven largest rivers combined. It has the largest drainage basin in the world, about 7,050,000 square kilometres (2,720,000 sq mi), accounts for approximately one-fifth of the world's total river flow.[1][2]

The sediment discharged by the gigantic mouth of the Amazon stains the sea brown for hundreds of miles out to sea.

Erosion by ice[change | change source]

Ice erosion happens when a glacier moves downhill. As the ice of the glacier moves downhill, it pushes and pulls earth materials along with it. Glaciers can move very large rocks. Ice erosion can happen in another way. Cold weather causes water inside tiny cracks in rocks to freeze. As it freezes, the ice gets bigger, and pushes hard against the rock. This can break the rock.

Erosion by wind[change | change source]

Wind erosion occurs when wind moves pieces of earth materials. Wind erosion is one of the weakest kinds of erosion. Small pieces of earth material can be rolled along the ground surface by wind. Very small pieces can be picked up and carried by the wind. Sometimes, wind can carry small pieces of earth materials over large distances. Some sediment from the Sahara Desert is carried across the Atlantic Ocean by wind.

One of the most famous examples of wind erosion occurred in the Dust Bowl, when wind erosion severely damaged farming communities.

Erosion by gravity[change | change source]

Gravity erosion is the simplest kind of erosion. Gravity simply pulls loose earth materials downhill. Landslides are dramatic examples of gravity erosion.

Erosion and tectonics[change | change source]

Interactions and feedback pathways for tectonics and erosional processes

Tectonic effects on erosion has long been recognized. For example, rivers form as a result of tectonic uplift (as Himalayas and Tibetan Plateau). On the other hand, erosional effects on tectonic activity has only recently been understood.[3][needs to be explained]

The Earth's landscape is a product of two factors. Tectonics builds up height by surface and rock uplift, and climate controls the erosion. Erosion wears away upland areas over time.[4] The interaction of these processes can form, modify, or destroy features of the Earth’s surface.

References[change | change source]

  1. Sterling, Tom 1979. Der Amazonas. Time-Life Bücher, 7th German printing, p. 19
  2. Smith, Nigel 2003.. Amazon sweet sea: land, life, and water at the river's mouth. University of Texas Press. pp. 1–2. ISBN 978-0-292-77770-5. http://books.google.com/books?id=SywgnV96puYC&pg=PA1.
  3. "Tectonics, climate and landscape evolution". Geological Society of America 398. 2006. http://specialpapers.gsapubs.org/content/398.
  4. Whittaker, Alexander C. (2012). "How do landscapes record tectonics and climate?". Lithosphere 4 (2): 160–164. doi:10.1130/RF.L003.1.