Weathering and Erosion

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Mrs. Arnold Pages 86-115

Weathering

the breaking down of rocks into smaller pieces by physical or chemical processes.

Mechanical weathering

(also called physical weathering) the breaking down of rocks by physical processes including temperature extremes, ice, water, and the activities of living things (biological weathering).

Ice wedging

the mechanical weathering process in which water in the cracks of rocks freezes and expands, widening the cracks.

Chemical weathering

the breaking down of rocks by chemical processes. The reactions change the chemical structure of the minerals, producing an entirely new mineral.

Hydrolysis

(the most common form of chemical weathering) the breaking down of a compound by a chemical reaction with water. During hydrolysis, water dissolves minerals, which drain into lower layers of rock and soil, causing the minerals to concentrate into mineral ore deposits below the Earth's surface.

Acid rain

the result of sulfur dioxide, nitrogen oxides, and carbon dioxide reacting in the atmosphere with water and returning to the Earth as rain, fog, snow, sleet, or dew.

Carbonation

the process in which carbonic acid reacts chemically with other substances. The process can form underground caverns, stalactites, and stalagmites.

Oxidation

a chemical change in which a substance combines with oxygen. Example--iron (Fe) combines with oxygen (O) to form rust (Fe2O3). (the 2 and 3 should be subscripts)

Topography

the surface features of a place or region, which affects the rate of weathering.

Landslide

the rapid downhill movement of a large amount of rock and soil. Landslides can be triggered by earthquakes, volcanic eruptions, spring thaws, or heavy rains.

Mass wasting

the downhill movement of loose rocks and soil due to gravity.

Regolith

the loose layer of rock and soil.

Slump

a large block of soil and rock that slides downhill along a curved slope, forcing the rock mass to tilt backward.

Mudflow

the rapid downhill movement of a large mass of mud.

Soil creep

the extremely slow downhill slide of soil.

Earthflow

the slow movement of soil down a steep slope.

Permafrost

the lower layer of soil in Arctic regions that stays permanently frozen.

Abrasion

the wearing down of rock surfaces by other rocks or sand particles.

Rock pedestals

mushroom-shaped rocks that form when sand particles eat away at the rock's bases. The sand particles are too heavy to reach the top of the rock, so the top does not get worn away.

Deflation hollows

soil depressions scooped out by the wind.

Dunes

mounds of sand deposited by the wind; they usually form in deserts and on beaches.

Runoff

water—usually from precipitation—that flows over the land; it is a constant source of erosion because it washes away particle of silt and soil. Note--because of gravity, water always flows to the lowest point.

Gully

a narrow ditch formed when water runs down a hill or mountain.

Watershed

an area of land that drains into a particular river system. For example, the Chesapeake Watershed includes Delaware, the District of Columbia, Maryland, New York, Pennsylvania, Virginia, and West Virginia. All of these states have land that sends water into the Chesapeake Bay.

Channel

the path that a stream flows. Networks of channels drain into a river to form a watershed.

Divides

the ridges and other elevated regions that separate watersheds.

Floodplain

a flat area along a river formed by sediments deposited when the river overflows, usually providing rich soil for farming.

Dams & Levees

built to control floods; dams are concrete structures built on a river to regulate its flow, while levees are made of an earthwork construction built up to stop water from flowing in a specific direction. The protection of a levee is temporary, and as rivers deposit more sediment, the levee must be made higher.

Delta

a fan-shaped deposit of sediments deposited at the mouth of a river.

Estuary

a wide, shallow bay at the mouth of a river valley that shelters fish and birds.

Glacier

a large mass of moving ice. (An iceberg is a large floating mass of ice that has detached from a glacier and has been carried out to sea.)

Glacial drift

sediments deposited by glaciers.

Till

unsorted rocks and sediments left behind when a glacier melts.

Moraine

a large ridge or mound developed from till; pronounced muh-reyn'.

Drumlins

long tear-shaped mounds of till formed by advancing glaciers; example: Bunker Hill.

Eratics

large boulders transported by glaciers; they give us clues about the direction and distance that glaciers traveled.

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