Weathering and Erosion Chapter 14 Weathering and Erosion

Section 1: Weathering Processes 1. weathering the natural process by which atmospheric and environmental agents, such as wind, rain, and temperature changes, disintegrate and decompose 2. 2 types a. mechanical b. chemical

B. mechanical weathering the process by which rocks break down into smaller pieces by physical means 1. Common agents of mechanical weathering are ice, plants and animals, gravity, running water, and wind. 2. Ice Wedging a. occurs in cold climates b. occurs when water seeps into the cracks in rock and freezes. c. When the water freezes, its volume increases by about 10% and creates pressure on the surrounding rock. d. eventually splits the rock apart.

3. abrasion the grinding and wearing away of rock surfaces through the mechanical action of other rock or sand particles a. caused by gravity, running water, and wind. C. Organic Activity 1. As plants grow, the roots grow and expand to create pressure that wedge rock apart. 2. Earthworms and other animals that move soil expose new rock surfaces to both mechanical and chemical weathering.

D. Chemical Weathering 1. Chemical weathering changes both the composition and physical appearance of the rock 2. oxidation the process by which an element combines with oxygen a. commonly occurs in rock that has iron- bearing minerals, such as hematite and magnetite. b. 4Fe + 3O2  2Fe2O3

3. hydrolysis a chemical reaction between water and another substance to form two or more new substances 4. carbonation the conversion of a compound into a carbonate 5. acid precipitation precipitation, such as rain, sleet, or snow, that contains a high concentration of acids, often because of the pollution of the atmosphere 6. Acid precipitation weathers rock faster than ordinary precipitation does.

Section 2: Rates of Weathering Rates of Weathering depends on 1. rock composition, 2. climate 3. topography. B. differential weathering - the process by which softer, less weather resistant rocks wear away at a faster rate than harder, more weather resistant rocks

C. Rock Composition 1. Limestone and other sedimentary rocks that contain calcite are weathered most rapidly. 2. shales and sandstones that are not firmly cemented together gradually break up to become clay and sand particles D. Amount of Exposure 1. Surface Area a. The part of a rock that is exposed to air, water, and other agents of weathering is called the rock’s surface area. b. As a rock breaks into smaller pieces, the surface area that is exposed increases.

a. These structures are natural zones of weakness within the rock. 2. Fractures and Joints a. These structures are natural zones of weakness within the rock. b. increase the surface area of a rock and allow weathering to take place more rapidly. c. form natural channels through which water flows. E. Climate 1. climates that have alternating periods of hot and cold weather allow the fastest rates of weathering. 2. slowest rates of weathering occur in hot, dry climates.

F. Topography Because temperatures are generally cold at high elevations, ice wedging is more common at high elevations than at low elevations G. Human Activities 1. Mining and construction often expose rock surfaces to agents of weathering. 2. exposes rock to strong acids and other chemical compounds that are used in mining processes. 3. Recreational activities such as hiking or riding all- terrain vehicles can also speed up weathering by exposing new rock surfaces.

H. Plant and Animal Activities 1. Rock that is disturbed or broken by plants or animals also weathers more rapidly than undisturbed rock does. 2. The roots of plants and trees often break apart rock. 3. Burrowing animals dig holes into rock and soil.

Section 3: Soil Soil 1. soil a loose mixture of rock fragments and organic material that can support the growth of vegetation 2. Bedrock is the solid, unweathered rock that lies beneath the soil. B. Soil Composition 1. refers to the materials of which it is made. 2. The color of soil is related to the composition of the soil. 3. Soil moisture can also affect color.

C. Soil Texture 1. Rock material in soil consists of three main types: a. Clay particles have a diameter of less than 0.004 mm. b. Silt particles have a diameter from 0.004 to 0.06 mm. c. Sand particles have diameters from 0.06 to 2mm. 2. The proportion of clay, silt, and sand in soil depends on the soil’s parent rock.

D. Soil Profile 1. soil profile a vertical section of soil that shows the layers of horizons 2. humus dark, organic material formed in soil from the decayed remains of plants and animals 3. The A horizon, or topsoil, is a mixture of organic materials and small rock particles. 4. The B horizon or subsoil, contains the minerals leached from the topsoil, clay, and sometimes, humus. 5. The C horizon consists of partially- weathered bedrock.

E. Soil and Climate 1. Climate is one of the most important factors that influences soil formation. 2. Climate determines the weathering processes that occur in a region F. Soil Erosion 1. Soil erosion is considered by some scientists to be the greatest environmental problem that faces the world today. 2. This erosion prevents some countries from growing the crops needed to prevent widespread famine.

3. One farming technique that can accelerate soil erosion is the plowing of furrows, or long, narrow rows -> these become gullies 4. sheet erosion the process by which water flows over a layer of soil and removes the tops