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Chapter 8 Erosion and Deposition Along mountaintops and hillsides, weathering is breaking down rock into small pieces. The pieces vary in size. These materials are then moved from place to place by erosion. Gravity is always pulling things from high places to low places. Mass Wasting- The downhill movement of Earth material caused by gravity. Mass wasting depends largely on how steep a slope is. It can happen gradually or it can happen quickly. Deposition – The dropping off of Earth’s material at the bottom of a hill or places where the hill becomes less steep. Erosion and deposition work together. The shape of the land changes because of them Wind is another way for erosion and deposition to work. The faster speed of the wind, the larger the size of the particles it can carry. Wind easily picks up a fine particles such as clay and sand. Wind causes changes in the shape of a sand dune, making it appear to drift forward in the wind direction. +++++++++++++++++++++++++++++++++++ Flowing Water • Changes the shape of Earth’s surface • Bits and pieces of rock carried by moving water act as tiny drills. • In most streams, large particles are carried along by rolling, sliding, or bouncing along the bottom. View Diagrams on page D 60 – D 61 +++++++++++++++++++++++++++++++++++ How Streams Change A river or stream carries particles downhill and cuts into the bottom to create a steep valley with a V shape. As a river wears down the land, it slows down and widens, causing curves called meanders to develop. On the outside of the curve, waters flows faster and eats away the land. On the inside of the curve, water slows down and drops off sediment (sand, small rock, & dirt). +++++++++++++++++++++++++++++++++++ How Glaciers Shape The Land Glaciers – Huge moving sheets of ice. Glaciers form when more snow falls in the winter than melts in the summer. Glaciers are usually at least 328 feet thick. The weight above makes the ice at the bottom like a superthick syrup. The whole sheet of ice then moves down hill. View diagrams on p. D 62 As a glacier moves through a valley, the glacier digs deep into the valley’s walls and floor so that a once narrow valley becomes U shaped. ************************************************* When Glaciers Melt: Till - A jumble of many sizes of sediment that is frozen into a glacier. Moraine - A deposit of many sizes of sediment from a glacier that collects in front or along the sides of the glacier. When chunks of ice buried in till melt, the till collapses to form bowl-like holes that may become ponds or lakes. Drumlins - tear shaped pieces of till that were smoothed out when glaciers flowed over them. More Vocabulary: Icebergs - Formed when a glacier reaches the edge of a continent. Sand dune - Windblown sand is dropped off and built into this. FACTS: 3 forces that reshape earth: Water, wind, and ice. A deep, fast river becomes slower and shallower because of sediment which is carried downhill. |