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Erosion and Deposition Grinding down and washing away What is sediment? (notes) • Sediment is a naturally occurring material that has been broken down. • Common examples would be clay, peat, and sand Betsiboka River, Madagascar What is erosion? (notes) • Erosion is the process of moving sediment from one location to another. • The most important force that powers erosion is gravity. • However, there are many different agents that directly cause the erosion. Newton and his amazing gravity Sometimes erosion takes us by surprise What is deposition? (notes) • Deposition (“to deposit”) is the dropping off of sediment • The size, density, and shape of the particles affect how fast deposition occurs. Particle sizes Particle shapes Agents of Erosion (not notes) • Each agent we discuss will have certain properties to the sediment that it creates. • The two main points will be: • The general appearance of the sediment produced. • Whether the sediment is sorted or unsorted. Agents of SHIELD Erosion Agents of Erosion – Water (notes) • The most common and powerful agent of erosion. • Sediment appears rounded and smooth • Sediment is sorted Water – Sorting (not notes) • Running water starts with a whole mixture of materials in it at the beginning. • But as it flows the biggest rocks drop out first, followed by the smaller ones, and finally the very smallest particles fall out. • This sorts the material along the path of the river. Boulders Cobbles Gravel Sand Silt Clay Water – Movement of Particles (notes) • Suspension is when particles that are of low size and density are picked up and carried by the water. • Saltation is when particles that are of medium size and density bounce along the river bottom. • Rolling is when large particles (“rocks”) are pushed along the bottom of the river. Water – River Structure (not notes) • When rivers flow across an open area they begin to meander (curve). • This is because where the river flows faster on the outer bank it wears away at the bank. • Where the river flows slower on the inner bank it drops off sediment. • In extreme cases the river bends so far that the tip breaks off and forms an “oxbow lake”. Oxbow lakes beginning to form in Sandakan, Malaysia An oxbow lake on the Danube River Water – Waterfalls (not notes) • Waterfalls occur when a hard layer of rock is on top of a softer layer. Agents of Erosion – Ice (notes) • Glaciers are massive sheets of ice that move slowly along the land. • Glaciers are the only erosive force that can transport large boulders. • Sediment appears scratched and grooved • Sediment is completely unsorted Glacial “till” Boulder in Madison, New Hampshire, that was transported by a glacier Ice – Sorting (not notes) • As glaciers grind along they pick up rocks of various sizes. • However, when it becomes warmer the glacier melts and drops all of them in a big pile. Valley Shape (notes) • You can tell what formed a valley depending on its shape. A U-shaped valley is formed by a glacier because the ice squashes out and flattens the bottom. A V-shaped valley is formed by running water as it cuts down through the layers. Agents of Erosion – Wind (notes) • Wind can only transport very small particles. • Sediment appearance is…well…small. • Sediment is sorted (same reason water sorting occurs) Wind – Shaping the Land (not notes) Even though it can only move small particles, given time it can wear away a large volume of rock. Agents of Erosion – Gravity (notes) • Gravity can act as a direct agent as well as the force that drives erosion. • Sediment appears jagged and angular • Sediment is unsorted (same reason that glaciers are unsorted) (Rocks fall; aren’t you glad you came to school to learn this?) ->