Earth Science - Weathering and Soils

Weathering

A response of Earth's materials to a changing environment; the disintegration and decomposition of rock at or near the surface of Earth

Erosion

Removal and transport of weathered rock by gravity-driven agents, such as wind, water, or ice

Types of weathering

Chemical and mechanical

Chemical weathering

Breaking down rock by changing chemical composition. Includes dissolution, hydrolysis, oxidation

Mechanical weathering (definition)

Breaking down rock without changing chemical composition. Includes frost wedging, sheeting, jointing, biological forces

Chemical weathering (types)

Dissolution, hydrolysis, oxidation

Mechanical weathering (types)

Frost wedging, sheeting, jointing, biological forces

Frost wedging

The mechanical breakup of rock caused by the expansion of freezing water in cracks and crevices

Joint

A fracture in rock along which there has been no movement

Sheeting

A mechanical weathering process that is characterized by the splitting off of slab-like sheets of rock

Exfoliation

The peeling off in flakes of layers of rock on an igneous intrusion, such as granite

Biological weathering

Accomplished by the activities of organisms, including plants, burrowing animals, and humans

Dissolution

The process of dissolving certain minerals in water

Carbonic acid

Acid that creates limestone caves

Sulfuric acid

Acid that is produced by chemical weathering of rocks with ore minerals; results in acid mine drainage

Oxidation

Occurs when electrons are lost from an atom or ion during a chemical reaction; electrons are lost to oxygen

Hydrolysis

A chemical weathering process in which minerals are altered by chemically reacting with water and acids; hydrogen ion replaces other positive ions in the crystal structure

Hydrolysis and oxidation

Chemical weathering processes combine to form acid mine drainage

Water

The universal solvent

Formation of carbonic acid

Rainwater combines with CO2 in the atmostphere

Formation of sulfuric acid

Chemical weathering of rocks with ore minerals (sulfides like pyrite)

Spheroidal

Rocks that are "attacked" more on corners and edges take on a spherical shape

Quartz

Rock that is very resistant to chemical weathering

Mass wasting

Rubble at the bottom of mountains due to the pull of gravity causing landslides

Transgression

Sea levels rising; limestone on top of shale on top of sandstone

Regression

Sea levels falling; sandstone on top of shale on top of limestone