Weathering and the Effect of Type of Ground Cover on the Rate of Soil Erosion
Category: Earth Science—Physiography
Project Idea by: Alex and Drake Conner
The physical nature of Earth's crust (the outer layer of Earth) is in a constant state of change. The changes are the result of erosion, the process by which rocks and other materials of Earth's crust are broken down and carried away. The part of erosion that involves only the breakdown of crustal materials is called weathering. Two weathering processes are mechanical weathering and chemical weathering.
Mechanical weathering is the breakdown of crustal material by physical means.
Mechanical weathering is a physical change, meaning the appearance of a material changes, but its properties and makeup remain the same. For example, when a seed germinates in a crack in a rock, the growing plant that forms may push hard enough to split the rock. The rock has been physically changed in that it has been split into smaller pieces.
Chemical weathering is the breakdown of crustal materials due to chemical changes in the substances making up the crust. A chemical change produces one or more kinds of substances that are different from those present before the change. For example, iron in rocks combines with oxygen in the air, forming iron oxide (rust).
The moving part of erosion is caused by natural agents such as water and ice. For example, water in a river erodes a riverbank, forming both a solution and a suspension. When water in a river hits against the riverbank, material breaks away, and some dissolves in the water, forming a solution. Other materials that break away from the bank don't dissolve, but they mix with the water, forming a suspension (a liquid mixture made of parts that separate upon standing). The moving water carries the weathered materials away.
When new roads are built, material such as hay is often placed over the newly formed roadside to help prevent erosion. A project question might be, "What effect does the type of ground cover have on the rate of soil erosion?"
Clues for Your Investigation
Cover four or more equal-sized pieces of boards, with dirt. Cover the dirt with different types of material such as leaves, hay, and grass. Raise one end of each board the same amount so that it is at a slant to the ground.
Design a way for equal amounts of water to rain down on the separate testing surfaces. One way to measure erosion is to collect and measure the amount of soil washed off the surface and collected at the lower end of each surface.
Independent Variable: Type of ground cover
Dependent Variable: Degree of erosion (measured by the amount of material washed away)
Controlled Variables: Size and slope of surfaces, type and amount of dirt, amount of water, type of watering method, measuring devices
Control: Soil without a covering
Other Questions to Explore
- what effect does the slope of the land have on the rate of soil erosion?
- what effect does plant growth have on the rate of soil erosion?
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