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Topic IV: Weathering & Erosion. The “Destructive Geologic Forces”. When You Have Finished This Unit, You should be able to answer the following questions. How is the Earth’s crust affected by its environment ? What are the products of weathering ? - PowerPoint PPT Presentation
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Topic IV: Weathering & Erosion
The “Destructive Geologic Forces”
When You Have Finished This Unit, You should be able to
answer the following questions...• How is the Earth’s crust affected by its
environment ?
• What are the products of weathering ?
• How are the products of weathering transported ?
• How are eroded materials deposited ?
• How is the Earth’s surface shaped by weathering, erosion, and deposition ?
Definitions:……..
• Weathering - the slow continuous process by which nature breaks down rock material into smaller particles. The two major types of weathering are mechanical & chemical
• Erosion - the breakdown and transport of weathered material by the agents of erosion - running water, wave and current action, glaciers, wind, and gravity.
Mechanical Weathering
• The breakdown of rock material into smaller particles of the same material.
• Example - Granite bedrock breaks down into smaller particles of granite
Agents of Mechanical (aka “Physical”) weathering include...• Ice wedging
• Frost action
• Unloading
• Plant Action
• Animal Action
Ice Wedging• As water seeps into
the pre-existing cracks in rocks, it may freeze.
• As the water freezes, it expands.
• The expanding freezing water wedges the crack in the rock further open.
Frost Action• As rock material is
heated, it expands. • The exterior of the
rock may be heated while the interior is still cold and contracted from the cold night temps.
• This pulls the outer layer of rock away in a process called exfoliation.
“Unloading”
• When rock which has been buried by other sediment, rock, or ice is exposed, it may expand under the released pressure.
• This expansion causes the outer layers of rock to “exfoliate”
Animal Action
• As animals burrow into rock and soil, they break the material down into smaller particles of the same material.
• Examples include worms, ground hogs, chipmunks, etc.
Plant Action• The roots of growing
plants will grow into existing cracks of rock and enlarge the openings.
• Smaller plants (lichens, e.g.) dig their tiny roots into small cracks with the same result.
Chemical Weathering…...
• involves the breakdown of rock material into new material with a new chemical make-up. In other words, the rock has turned into new rock material. (decomposition)
• Agents of chemical weathering include oxidation, carbonation, hydration, and dissolution.
Oxidation
• Oxidation is the chemical union of oxygen with a molecule within the rock. “Rust” is a common form of oxidation and is seen on many iron rich rocks around the O’Neill campus.
Carbonation
• As water falls through the atmosphere, a mild acid forms which can dissolve away limestone to form caves.
Hydration • The chemical union of
water molecules with mineral molecules is known as “hydration”.
• Iron and magnesium minerals will alter to clay minerals due to hydration. Feldspar also hydrates to form clay minerals.
Dissolution...
• Certain minerals will actually dissolve when exposed to water or mild acids. The sample shown here is halite, a highly soluble mineral more commonly known as “rock salt”
In order for erosion to occur...
• Material must first be broken down by weathering so that it can be transported by the agents of erosion.
• Remember that chemical weathering can only occur on exposed surfaces.
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