General Geographical Features Test - 4

Sheet erosion is the uniform removal of soil in thin layers by the forces of raindrops and overland flow. It can be a very effective erosive process because it can cover large areas of sloping land and go unnoticed for quite some time.

Sheet erosion occur in wide range of settings such as coastal plains, hillslopes, floodplains and beaches. Water moving fairly uniformly with a similar thickness over a surface is called sheet flow and is the cause of sheet erosion.

Soil erosion is the displacement of the upper layer of soil, one form of soil degradation. This natural process is caused by the dynamic activity of erosive agents, that is, water, ice (glaciers), snow, air (wind), plants, animals, and humans. In accordance with these agents, erosion is sometimes divided into water erosion, glacial erosion, snow erosion, wind (aeolean) erosion, zoogenic erosion, and anthropogenic erosion.

Valley or stream erosion occurs with continued water flow along a linear feature. The erosion is both downward, deepening the valley, and headward, extending the valley into the hillside, creating head cuts and steep banks. In the earliest stage of stream erosion, the erosive activity is dominantly vertical, the valleys have a typical V cross-section and the stream gradient is relatively steep. When some base level is reached, the erosive activity switches to lateral erosion, which widens the valley floor and creates a narrow floodplain.

Weathering is a term which describes the general process by which rocks are broken down at the Earth's surface into such things as sediments, clays, soils and substances that are dissolved in water.The process of weathering typically begins when the earth's crust is uplifted by tectonic forces. After the physical breakup and chemical decay of exposed rocks by weathering, the loosened rock fragments and alterations products are carried away through the process of erosion.

Chemical Weathering results from chemical reactions between minerals in rocks and external agents like air or water. Oxygen oxidizes minerals to alteration products whereas water can convert minerals to clays or dissolve minerals completely.

Weathering is the breaking down of rocks, soil, and minerals as well as wood and artificial materials through contact with the Earth's atmosphere, water, and biological organisms.

Soil conservation is the preventing of soil loss from erosion or reduced fertility caused by over usage, acidification, salinization or other chemical soil contamination. Slash-and-burn and other unsustainable methods of subsistence farming are practiced in some lesser developed areas.

Coastal lagoons are common, occurring along nearly 15 percent of the world's shorelines. In the United States, lagoons are found along more than 75 percent of the Eastern and Gulf coasts. Coastal lagoons are usually connected to the open ocean by inlets between barrier islands.

Coastal lagoons are created as a shallow basin near the shore gradually erodes, and the ocean seeps in between the sandbars or barrier islands. The size and depth of coastal lagoons often depend on sea level. When the sea level is low, coastal lagoons are swampy wetlands.

The simplest and most natural way to prevent erosion is through planting vegetation. Plants establish root systems, which stabilizes soil and prevents soil erosion. Geotextiles: Using geotextiles is an effective method because it also stabilizes soil.

Corrie or Cirque Formation. Corries or cirques are mountain valley heads which have been shaped into deep hollows by the erosion of small glaciers. In Britain, many corries were last filled by glacier ice around 12, 000 years ago but these corries have held glaciers on many occasions during the last 2.4 million years.

Thermal stress weathering, sometimes called insolation weathering, results from the expansion and contraction of rock, caused by temperature changes. For example, heating of rocks by sunlight or fires can cause expansion of their constituent minerals. This is referred to as mechanical weathering.

Cave features are usually formed by slow-moving water that has a high calcium carbonate content. Chemical changes inside the cave make the minerals harden and form deposits, such as icicle-like stalactites (which hang from the ceiling) and stalagmites (which rise up from the ground).

Limestone stalagmites. The most common stalagmites are speleothems, which usually form in limestone caves. Stalagmite formation occurs only under certain pH conditions within the cavern. They form through deposition of calcium carbonate and other minerals, which is precipitated from mineralized water solutions.