1. Weathering and Erosion
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2. Weathering breaks rocks into smaller pieces.
Weathering is the process by which natural forces break down rocks.
July 22, 2012
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3. Mechanical Weathering
Mechanical weathering is the breaking up of rocks by physical forces.
For example:
Ice wedging
Pressure release
Plant root growth
Abrasion
Abrasion is the process of wearing down by friction, which is the rubbing of one object or surface against another.
July 22, 2012
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4. Chemical Weathering
Chemical weathering is the breakdown of rocks by chemical reactions that change the rocks’ makeup or composition. When minerals in rocks come in contact with air and water, some dissolve and others react and are changed into different minerals.
July 22, 2012
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5. Types of Chemical Weathering
Dissolving
Water is the main cause of chemical weathering. Many minerals dissolve in ordinary water, like Halite (salt).
Other minerals dissolve in acidic water. Carbon dioxide in the atmosphere dissolves into rainwater and causes the water to become acidic.
Air pollution makes rainwater even more acidic. Acid rain causes rocks to weather much faster than they normally would.
July 22, 2012
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6. Types of Chemical Weathering, continued…
Rusting
Many minerals contain iron. When these minerals dissolve in water, oxygen in the air and the water combines with the iron to produce iron oxides, or rust.
The iron oxides form a coating that colors the weathered rocks.
July 22, 2012
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7. Weathering occurs at different rates.
It can take hundreds, thousands, or even millions of years for some rocks to break down only a few millimeters. A few things determine the time it takes for weathering to occur.
Surface area: the more of a rock’s surface that is exposed to the elements, the faster the rock will break down.
Rock composition: some rocks break down faster than others. For example: limestone breaks down more quickly than granite.
Climate: heat speeds up chemical weathering. So areas with hot, wet climates experience greater rates of chemical weathering. At the same time, freezing and thawing in cold areas causes mechanical weathering to occur at a faster rate.
July 22, 2012
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8. Review: Exit Ticket
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July 22, 2012
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