(WES) Weathering, Erosion, and Soil Module Overview
Weathering, Erosion, and Soil Module Overview
We often think of weathering as destructive and a bad thing because it ruins buildings and statues. However, as rock is destroyed, valuable products are created. The major component of soil is weathered rock. The growth of plants and the production of food is dependent on weathering. Some metallic ores, such as copper and aluminum, are concentrated into economic deposits by weathering. Dissolved products of weathering are carried in solution to the sea, where they nourish marine organisms. And finally, as rocks weather and erode, the sediment eventually becomes rock again--a sedimentary rock.
Soil is a critical natural resource teaming with life. Most, but not all, of Earth's land is covered with soil. Soil may be just a thin layer over solid rock or it may be over one hundred feet thick in some places. Soil is a mixture. Most soil is about fifty percent rocks and minerals. The other fifty percent is made up of decayed organic matter, air, and water. Soil is formed when forces such as wind, water, or ice weather rocks. These forces break apart rocks into smaller and smaller pieces. For one inch of soil to form can take hundreds, even thousands of years. Soils vary by type, color, texture, and chemicals.
These traits come from the parent rock the soil came from, the minerals present, and the organic matter in the soil.
Essential Questions
- What are the characteristics of weathering, and how does weathering differ from erosion?
- What is meant by weathering? How many different kinds of weathering processes are there?
- How are weathering and erosion different?
- How are weathering and erosion related?
- How does the formation of soil relate to the processes of weathering and erosion?
Key Terms
- Weathering - any of the chemical or mechanical processes by which rocks exposed to the weather undergo changes in character and break down
- Mechanical weathering - any of the destructive effects of the atmosphere and the exposure of rocks to the extremes of the surface
- Chemical weathering - chemical effects of water, carbon dioxide, and oxygen attacking and destroying the minerals that are near the surface of the Earth
- Frost wedging - a collective term for several mechanical weathering processes induced by stresses created by the freezing of water into ice
- Exfoliation - the sheeting of rocks and their disintegration, thought to be due to thermal expansion, at least on small structures
- Oxidation - the absorption by a mineral of one or more oxygen ions. The major type of chemical weathering, particularly in rocks containing iron
- Acid rain - acid precipitation falling as rain
- Weathering rates - a measurement of the amount of weathering over a given time period
- Surface area - measurement of the extent of the area covered by a surface
- Topography - detailed, precise description of a place or region
- Climate - the meteorological conditions, including temperature, precipitation, and wind, that characteristically prevail in a particular region
- Soil - the top layer of the Earth's surface, consisting or rock and mineral particles mixed with organic matter
- Soil profile - the vertical section of soil showing the nature and sequence of the various layers, as developed by deposition or weathering, or both
- Soil horizon - a layer of soil, approximately horizontal, which differs in structure and composition from the adjacent layers
- Humus - the amorphous, ordinarily dark colored, colloidal matter in soil; a complex of the fractions of organic matter of plant, animal, and microbial origin that are most resistant to decomposition
- Regolith - the layer of loose rock resting on bedrock, constituting the surface of most land
- Parent bedrock - the original rock from which something else was formed
- Deposition - the dropping of material which has been picked up and transported by wind, water, or ice
- Erosion - a group of natural processes, including weathering, dissolution, abrasion, corrosion, and transportation, by which material is worn away from the Earth's surface
- Rill erosion - the formation of numerous, closely spaced rills due to the uneven removal of surface soil by stream-lets of running water
- Gully erosion - erosion of soil by running water
- Wave erosion - erosion of the ocean floor by sediment moved by ocean waves
- Glacial erosion - movement of soil or rock from one point to another by the action of the moving ice of a glacier
- Dust bowl - a region reduced to aridity by drought and dust storms
- Mass movement - the movement downslope of rock fragments and soil under the influence of gravity
- Slides - a form of mass movement in which material slides in a relatively straight plane
- Flows - the mass movement of material held in suspension by water
- Creeps - the slow movement of rock debris and soil down a weathered slope
- Abrasion - the process of wearing down or rubbing away by means of friction
- Deflation - the erosion of soil by the wind
- Ventifact - a stone that has been shaped, polished, or faceted by wind-driven sand
- Deforestation - the act process of removing trees from or clearing a forest
- Erosion - a group of natural processes, including weathering, dissolution, abrasion, corrosion, and transportation, by which material is worn away from the Earth's surface
- Tillage erosion - erosion that moves soil from the top of the field downward, exposing subsoil at the crest while burying soil at the bottom
- Contour farming - cultivation of land along lines connecting points of equal elevation, to prevent water erosion
- Slash and burn - a form of agriculture in which an area of forest is cleared by cutting and burning, and is then planted, usually for several seasons, before being left to return to forest
- Fallowing - plowed but left unseeded during a growing season
- Soil conservation - management of soil to prevent or reduce soil erosion and depletion by wind and water
- Terracing - a method of shaping land to control erosion on slopes of rolling land used for cropping and other purposes
- Strip cropping - the growing of a cultivated crop, such as cotton, and a sod-forming crop, such as alfalfa, in alternating strips following the contour of the land, in order to minimize erosion
- Contour plowing - farming practice of plowing across a slope following its elevation contour lines
- No-till farming - cultivation technique in which the soil is disturbed only along the slit or hole into which seeds are planted
- Wind breaks - a hedge, fence, or row of trees serving to lessen or break the force of the wind
- Ground cover - a low-growing dense growth of plants planted to prevent soil erosion in areas where turf is difficult to grow, as in deep shade, or on a steep slope
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