Weathering and Erosion

Weathering

• The breakdown of rock material by physical and chemical processes.

Physical Weathering

• Process by which rocks are broken down into smaller pieces by physical changes.

• Causes of physical weathering include:– Changes in temperature– Pressure changes– Actions of plant and animals– Water– Wind and Gravity

Temperature Change

• Changes in temperature can cause a rock to break apart.

• A decrease in temperature can cause a rock to contract and a rise in temperature can cause a rock to expand.

• Ice wedging can cause rocks to physically break apart when water collects in the cracks of rocks and the temperature drops

Ice Wedging

Pressure Change

• Physical weathering can be caused by pressure changes.

• Rocks formed under pressure deep within earth can become exposed at the surface and changes in pressure can cause layers of rock to separate.

• Exfoliation- the process by which the outer layers of rock slowly peel away due to pressure changes.

Pressure Change

Effects of Animals on Weathering

• Many animals dig burrows into the ground, allowing for more rock to become exposed

• Common burrowing animals include:

- Ground squirrels

- Prairie Dogs

- Ants

- Earthworms

Burrowing of Animals

Wind, Water, and Gravity

• Abrasion- the breaking down and wearing away of rock material by the mechanical action of other rocks.

• Wind- the small particles carried by wind hit the surface of rocks and slowly wear them away

• Water- moves rocks causing them to collide with other rocks

• Gravity-can cause landslides where large rocks can fall from above and break more rocks below.

Water Erosion

• Rivers, streams, and runoff

Plant Growth

• The roots of plants can grow in small cracks in rocks causing the rock to expand due to the increase in pressure.

Plant Growth

Chemical Weathering

• The process that breaks down rock through chemical reactions.

• The agents of chemical weathering– Water– Oxygen– Carbon dioxide– Living organisms– Acid rain

Erosion

• The process by which water, ice, wind or gravity moves fragments of rock and soil.

Oxygen• Iron combines with

oxygen in the presence of water in a processes called oxidation

• The product of oxidation is rust

Water

• Water weathers rock by dissolving it

Wind Erosion

Acid Rain• Compounds from burning coal, oil and gas

react chemically with water forming acids.

• Acid rain causes very rapid chemical weathering

Reactions with Acids in Groundwater

• As groundwater moves through spaces or cracks in rock, acids in the water can cause rocks to dissolve.

• A small crack in a rock can result in the formation of extensive cave systems that are carved out over time.

Reactions with Acids in Groundwater

Caves

Living Organisms

• Lichens and mosses can grow on rocks and produce weak acids that chemically weather rock

Sinkholes