|
||||||||||||||||||||||||||||||||
|
||||||||||||||||||||||||||||||||
|
|
Preparation
|
|
In the last two investigations students looked at weathering and how rocks break down into smaller pieces over time. In this investigation, students explore erosion, the process by which soil and sediment (the products of weathering) are moved from one location to another. Erosion is caused by gravity, wind, glaciers, and water in the form of ocean waves and currents, streams, and ground water. In this investigation, students explore river and stream erosion. Precipitation (rain) that falls to the Earth’s surface either soaks into the ground, evaporates, or flows across the land. Water that flows across the land runs downhill. Along the way, it can pick up and carry sediment ranging from fine clay to coarse sand or gravel. As the water runs downhill, it cuts into the soil, forming channels called gullies. When gullies reach a low-lying area, they merge together, forming a larger stream. Streams merge together to form larger streams or rivers. Most sediment carried downhill eventually ends up in a stream and is carried away. In this way, streams affect more of the Earth’s surface than any other agent of erosion. The amount of sediment a stream can carry depends on the speed and size of the stream. The speed of the water in a stream depends on its slope. The steeper the slope, the faster the water moves. Fast-moving or large streams can carry more sediment than slow-moving or small streams. Abrasion occurs as sediment in a stream collides with rock in and along the stream. Pieces of rock are chipped away and rough edges in rocks and sediments themselves become rounded. The bedrock beneath streams is also eroded by abrasion. Sediment flowing in the water can cut deeply into the bedrock. Over a long time, stream abrasion can cause great changes in the shape of a stream or river and Earth’s surface. In this investigation, students examine models of river erosion. Groups build different types of river beds by filling stream tables with sand. Each group perches one end of their stream table on some blocks to create a slope. They then pour water into the river bed through a spout. They watch as the water enters the stream bed and begins to carry away sand from the stream edges and the bottom. The sediment is deposited at the end of the stream where the water stops flowing. They see that as sediment is eroded, the shape of the stream changes.
|
For each student group:
For instructional purposes:
|
|
This investigation is generally considered safe to do with students. The sand should be dampened prior to the start of the investigation. Fine sand can be inhaled and is a major irritant. If the sand has not been dampened, provide disposable masks to students. Ensure that students wash their hands thoroughly after handling the sand. Make sure that water is well away from any electrical outlets or equipment. Also, review the investigation for your specific setting, materials, students, and conventional safety precautions. |
|
||||||||||||||||||||||||
|
||||||||||||||||||||||||||||||||
|
||||||||||||||||||||||||||||||||
