Weathering Topic 9 Regents Earth Science

Weathering  The break down of rock material as a result of chemical and/or physical action

Physical weathering aka mechanical weathering  The breakdown of rock into smaller pieces without chemical change

1. Frost action  Weathering of rock by the alternate freezing and thawing of water in the pores or cracks in the rock

Frost Wedging

2. Plant action  Occurs when cracks in rock are widened by the forces exerted by growing plants

Plant Action

3. Pressure unloading  Occurs when rocks split along the planes of weakness when the pressure of overlying material is removed  Usually occurs as the result of natural processes such as landslides, erosion, and earthquakes  But humans also cause this through quarrying and mining

4. Abrasion  The physical action of scraping, rubbing, grinding, or wearing away of rock surfaces due to the movement of solid sediment in an erosional system such as stream or wind

*As time increases, particles become more rounded.*

5. Exfoliation  The scaling or peeling of successive shells from the surface of rocks  Generally occurs in coarse-grained rocks that contain feldspar (like granite)

Pressure Unloading and Exfoliation

Chemical weathering aka decoposition  The breakdown of rock by chemical action, during which there is a change in chemical composition of the minerals in the rock

The agents of chemical weathering include

1. oxygen  The chemical reaction of oxygen with another element is called oxidation

2. water  Speeds up chemical reactions  Dissolves many materials  Reacts directly with many mineral substances (hydrolysis)

Caves form

3. Carbon dioxide  Easily dissolves in water to form carbonic acid  Calcite, limestone, and marble react with carbonic acid  Reaction of carbonic acid with other substances is known as carbonation

Sinkhole

4. acids  Produced in the atmosphere by lightning and on the surface by decay of organic wastes  Also gases released by people and industry combine with water to form acids