carbonic acid

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A weak acid (H₂CO₃) that forms from the reaction of water and carbon dioxide. Most rain water is a very weak carbonic acid solution formed by the reaction of rain with small amounts of carbon dioxide in the atmosphere.

chemical weathering

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The breaking down of surface rock material by solution or chemical alteration. Common alteration processes are oxidation and hydrolysis.

creep

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The slowest form of mass movement, measured in millimeters or centimeters per year and occurring on virtually all slopes.

erosion

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The process by which particles of rock and soil are loosened, as by weathering, and then transported elsewhere, as by wind, water, ice, or gravity.

exfoliation

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A physical weathering process in which concentric layers of rock are removed from an outcrop.

hydrolysis

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A chemical reaction involving water that results in the breakdown of mineral material.

ice wedging

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One of the many kinds of mechanical weathering, ice wedging is the most common.

 

Water fills up cracks in rock, and when it freezes, it expands and cracks the rock, similar to driving an axe into wood.

landslide

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A downslope movement of rock and soil over a failure surface and under the influence of gravity. Slumps, rockslides, debris flows and debris slides are examples.

mass movement

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Also called 'Mass Wasting'.

A general term used for any downslope movement of rock, soil, snow or ice under the influence of gravity. Includes: landslides, creep, rock falls and avalanches.

mechanical weathering

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A general term applied to a variety of weathering processes that result in the particle size reduction of rock materials with no change in composition.

 

Frost action, salt crystal growth and pressure relief fracturing are examples. Also known as physical weathering.

 

mudflow

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A type of mass movement composed mainly of clay-size materials with a high enough water content that it flows readily.

oxidation

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A chemical reaction in which substances combine with oxygen. For example, the combination of iron with oxygen to form an iron oxide or rust.

parent material

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Rock material from which a soil is formed. An example is bedrock or organic material.

residual soil

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Soil that has the local bedrock as it's parent material.

soil

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Soil is the naturally occurring, unconsolidated or loose covering of broken rock particles and decaying organic matter (humus) on the surface of the earth, capable of supporting life.

soil erosion

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The processes by which soil is removed from one place by forces such as wind, water, waves, glaciers, and construction activity and eventually deposited at some new place.

 

The loss of plants often makes soil erosion worse as the roots of many plants resist wind and water. 

soil profile

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A vertical strip of soil stretching from the surface down to the bedrock and including all of the successive soil horizons.

subsoil

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General term for the layers of soil below the uppermost layer or topsoil (or A-Horizon).  It can consist of sand, silt and clay but has little, if any, humus or other organic matter. Subsoil or B-Horizon provides structure, holds moisture, and is a good foothold for rooting plants.
 

topsoil

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Surface layer of soil with higher organic content. Also called the A-Horizon it is the uppermost layer of soil, usually darker and richer than the subsoil.

transported soil

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Soil not formed from the local rock but from parent material brought in from some other region and deposited, usually by running water, wind, or glacial ice.

weathering

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The group of processes that change rock at or near Earth’s surface.

 

Chemical or physical processes in which rocks exposed to the weather are worn down by water, wind, or ice.