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Erosion – the carrying away of weathered rock by gravity, water, wind, and ice Running Water Wind Ice Gravity Erosion: mass movements of materials down hill • • • • Soil creep (slow, 1 cm/year) Debris flow (slow to fast, mm/day – km/hr) Mud flow (fast, 1-5 km/hr) Rock fall (very fast, >4 km/hr) SOIL CREEP Rock Fall Rock fall Most erosion is caused by water moving across the Earth’s surface (runoff) Random runoff – this is rain water that runs down any exposed slope and often produces gullying 1. slope 3. low permeability RECALL: What factors favor runoff? 2. lack of vegetation 4. saturated ground Notice the many gullies Badlands National Pa (South Dakota) Similar gullying in Bryce Canyon in Utah Random runoff –produces gullying Organized runoff – this is water that moves through a series of developed channels until it eventually reaches the ocean. Also referred to as a drainage pattern. The area drained by a river and its tributaries is called a WATERSHED or DRAINAGE BASIN Organized runoff ^ ^ Continental Divide ^ This is the Mississippi River drainage basin or WATERSHED ^ ^ ^ ^ ^ The small rivers are tributaries of the Mississippi River Every location in green, drains into the Mississippi River Which way is the river flowing? Which are the tributaries? Grand Canyon from space Young Mature Old Rivers and streams can be grouped into 3 stages of development Summary of Young Stream 1. Mostly erode down 2. High velocity, steep gradient 3. Characterized by rapids and waterfalls 4. Narrow and carve a “V” shaped valley 5. Straight unless forced to curve by topography 6. canyons may form Streams start out high in the mountains as young streams These young mountain steams have a high velocity and can move even large boulders Their velocity and eroding power grows as smaller streams join the main stream Young rivers often carve “V” shaped valleys The young stage usually produces a “V” shaped valley Waterfalls and rapids are common In this stage Grand Canyon When a young river cuts through a plateau, a canyon is created Velocity of any stream is determined by: 1. Gradient or slope of land 2. Volume of water in stream Streams usually flow fastest In spring, why? Glacier Nat. Park solution Rivers and streams transport rock and sediment in 3 ways suspension Rolling and tumbling Abrasion causes rocks in a stream to become rounded