(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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