Geology Interlude B

Sediment

An accumulation of loose mineral grains, such as boulders, pebbles, sand, silt, or mud, that are not cemented together. (page 173)

Weathering

The processes that break up and corrode solid rock, eventually transforming it into sediment. (page 173)

Physical weathering

The process in which intact rock breaks into smaller grains or chunks. (page 174)

Clast

A fragment or grain produced by the physical or chemical weathering of a pre-existing rock. (page 174)

Erosion

The grinding away and removal of the Earth's surface materials by moving water, air, or ice. (page 176)

Chemical weathering

The process in which chemical reactions alter or destroy minerals when rock comes in contact with water solutions and/or air. (page 177)

Soil

Sediment that has undergone changes at the surface of the Earth, including reaction with rainwater and the addition of organic material. (page 179)

Zone of leaching

The layer of regolith in which water dissolves ions and picks up very fine clay; these materials are then carried downward by infiltrating water. (page 182)

Zone of accumulation

(1) The layer of regolith in which new minerals precipitate out of water passing through, thus leaving behind a load of fine clay; (2) the area of a glacier in which snowfall adds to the glacier. (page 182)

Soil horizon

Distinct zones within a soil, distinguished from each other by factors such as chemical composition and organic content. (page 182)

Soil profile

A vertical sequence of distinct zones of soil. (page 182)

Topsoil

The top soil horizons, which are typically dark and nutrient-rich. (page 182)

Subsoil

The B-horizon, or zone of accumulation, in a soil; it underlies the topsoil. (page 182)

Soil order

A given type of soil in a common soil classification scheme.

Soil erosion

The removal of soil by wind and runoff. (page 186)

Thalweg

a line connecting the lowest points of successive cross-sections along the course of a valley or river.