The Changing Earth Chapter Fourteen: Weathering and Erosion • 14.1 Weathering • 14.2 Erosion • 14.3 Rivers Shape the Land Investigation 14B Human Impacts on Coastal Erosion • How do people living and working in coastal areas affect erosion? 14.2 Erosion • Erosion is the process of moving pieces of rock and sediment by wind, water, ice, or gravity. 14.2 Moving Sediment • Weathering breaks rock into bits and pieces called sediment. How does sediment get from a mountain peak to a beach? 14.2 Moving Sediment • Weathering breaks rock into bits and pieces called sediment. • Wind erodes mountains and moves sediment, but not as well as flowing water. 14.2 Running water moves sediment • The process of depositing sediment after it has been moved by water, wind, or ice is called deposition. • The amount of sediment carried and deposited by water depends on many factors: – the volume of water, – the slope of the land, and – how rocky or smooth the land is. 14.2 Moving sediment • • A stream table can model how water flows over the land. The steeper the slope, the faster the water and sediment will move over land. 14.2 Moving sediment • • • A greater volume of water can move a lot of soil or sediment at once. Rocky landscapes can trap sediment so the sediment will not travel as far. A smooth river bed might mean sediment will be carried a long way. 14.2 Sorting sediment • • You can tell the speed of flowing water by the size of the rock pieces found on a stream bottom. The grains settle in order, making a pattern called graded bedding. 14.2 Interpreting layers of sediment • Sedimentary rocks hold clues to their past. • If you know the up direction, you know the direction of younging—this is the direction of younger layers. 14.2 Interpreting layers of sediment • Cross bedding, is easy to recognize in sedimentary rocks where one layer ends and another layer passed over it. 14.2 Moving sediment by ice • Particles that are trapped in ice or suspended in water can cause weathering. • As the ice of a glacier flows down a valley, it grinds the valley floor with pieces of rock caught up in the ice. 14.2 Moving sediment by ice 14.2 Moving sediment by ice • As the ice of a glacier flows down a valley, it grinds the valley floor with pieces of rock caught up in the ice. 14.2 Moving sediment by ice • The fine rock powder that results from glaciers is called “rock flour.” • Rock flour can be washed into lakes and make them a milky blue color. 14.2 More on moving sediment • Glaciers are formed from accumulation of snow over hundreds or thousands of years. • As snow piles up and pressure increases, it changes into ice. 14.2 More on moving sediment • • • Wind can move particles of sediment from one place to another. Beach dunes hold large amounts of wind deposited sand. Loess is another wind-blown deposit of fine sediment. 14.2 More on moving sediment • Mass wasting is the downhill movement of large amounts of rock and sediment due to the force of gravity. 14.2 More on moving sediment • A landslide occurs when a large mass of soil or rock slides down a steep slope. 14.2 More on moving sediment • Slumping describes what happens when loose soil becomes wet and slides or “slumps”. • Slumping can happen after a period of very heavy rainfall. 14.2 Erosion by people • In the 1930s, the Great Plains of North America experienced serious wind erosion events. What was this region’s knickname? 14.2 Erosion by people • Farming practices that protect sediment and soil from erosion include installing windbreaks, planting ground cover, and using contour plowing for farming.