Weathering - refers to the group of destructive processes that change the physical and chemical character of rocks at or near the earth's surface. Weathering is to be distinguished from Erosion which is the picking up or physical removal of rock particles by an agent such as streams or glaciers.

Mechanical Weathering - physical disintegration of rocks.

Frost Action - water commonly collects in cracks and wedges the rock apart upon freezing.

Abrasion - grinding or rock by friction and impact during transportation in streams or under glaciers.

Stress release - removal of great weight allows rock expansion which causes sheet joints.

Temperature - constant diurnal and annual heating and cooling causes exfoliation which is similar to peeling of layers from an onion.

Chemical Weathering - the transformation of rocks and minerals exposed to water and air into new chemical products.

Role of Oxygen - rusting of an iron nail exposed to dampness and air is a simple example of chemical weathering. Iron oxide (hematite) is a product of weathering. If water is present iron oxide combines with water to form limonite. product of numerous minerals containing iron.

Role of Acid - Natural acids disrupts the atomic structure of many minerals. The source of natural acid for rock weathering is dissolved carbon dioxide in water. Acid causes feldspars to alter to clay.

Solution weathering - some minerals such as calcite will dissolve in water.

Soil - the layer of weathered, unconsolidated material on top of bed rock.

Soil Horizons -layers of soil are distinguishable by characteristic physical or chemical properties.

A horizon - the zone of leaching characterized by the downward movement of water. In a humid (wet) climate, clay minerals, iron oxides, and dissolved calcite are most typically leached downward.

B horizon - the zone of accumulation of material leached downward from the A horizon. This layer is often quite clayey and stained red or brown by hematite and limonite.

C horizon - incompletely weathered parent material.

Pedalfer - are marked by effective downward leaching due to high rainfall and to the acids produced by the decay of abundant humus. These soils contain a high content of aluminum and iron.

Pedocal - tend to be thin and characterized by little leaching, scant humus, and upward movement of soil water beneath the land surface. Evaporation of water beneath the land surface can cause the precipitation of salts within the soil and formation of alkali soils.

Caliche - a hardpan soil which forms by calcium carbonate and other salts that precipitate in the soil as water evaporates.