Chapters 4 & 5

Weathering and Erosion

Weathering

• Weathering is the breaking down of rocks and other materials

• 2 types of weathering– Mechanical– Chemical

Mechanical/Physical Weathering

• Mechanical Weathering occurs when rocks are broken down into smaller pieces, but the chemical composition is not changed

• Examples: temperature, frost, tree roots, gravity (abrasion)

Physical Weathering

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Mechanical Weathering• Temperature - rocks expand when they

are heated up, and contract when they are cooled. This process breaks rock.

• Frost Action- water gets into cracks of rock and freezes when it gets cold. Crack expands

• Organic Activity - roots of trees break rocks

• Gravity - rocks are pulled downward by gravity

• Abrasion - wind blown sand wears away rocks (also water running over rocks)

Chemical Weathering

• Chemical weathering occurs when rocks are broken down and their chemical composition is changed

• Examples: water, carbon dioxide, oxygen, plants

Chemical Weathering

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Chemical Weathering• Water - most chemical weathering occurs

w/ water/CO2. Water dissolves minerals.• Oxidation - process in which oxygen

chemically combines with another substance. (iron in rocks can rust)

• Carbonation - occurs when CO2 dissolves in water and forms carbonic acid.

• Plant Acids - moss and lichens produce weak acids that dissolve minerals in rocks

Soil Formation

• Soil is formed when rocks are continuously broken down by weathering.

• Soil that stay close is called residual, soil that is moved is called transported.

• Bedrock is the layer of rock beneath the soil

Erosion

• Erosion is the process by which weathered rock is moved.

• Grand Canyon was formed by erosion.

• Causes of erosion: gravity, wind, running water, glaciers, and waves.

• Deposition is the process by which sediments are laid down in a new place.

Erosion

Erosion• Gravity pulls rocks and soil down slopes.

Examples: landslide or mudflow• Wind is most active agent of erosion in

deserts and on beaches. Wind erosion can form dunes or caves.

• Running water is the major cause of erosion. Examples: rivers, streams, and runoff.

• Glaciers ice erodes rocks beneath it by abrasion.

• Waves erode and shape shorelines.

Erosion Caused by Wind

Humans Impact Erosion

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