WeatheringWeathering

Topic 9

Regents Earth Science

WeatheringWeathering

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

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Physical weathering aka mechanical weatheringPhysical weathering aka mechanical weathering

The breakdown of rock into smaller pieces without chemical change

1. Frost action1. Frost action

Weathering of rock by the alternate freezing and thawing of water in the pores or cracks in the rock

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Frost WedgingFrost Wedging

2. Plant action2. Plant action

Occurs when cracks in rock are widened by the forces exerted by growing plants

Plant ActionPlant Action

3. Pressure unloading3. 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. Abrasion4. 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.**As time increases, particles become more rounded.*

5. Exfoliation5. 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 ExfoliationPressure Unloading and Exfoliation

Chemical weathering aka decopositionChemical weathering aka decopositionThe 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 includeThe agents of chemical weathering include

1. oxygen1. oxygen

The chemical reaction of oxygen with another element is called oxidation

2. water2. water

Speeds up chemical reactionsDissolves many materialsReacts directly with many mineral

substances (hydrolysis)

Caves formCaves form

3. Carbon dioxide3. 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

SinkholeSinkhole

4. acids4. 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