The Changing Earth

Chapter Fourteen: Weathering and Erosion 14.3 Rivers Shape the Land

Human Impacts on Coastal Erosion 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 The image above is of a large valley that held a glacier during the last ice age. The valley floor rises up smoothly in a gentle curve to the ridge above. From the side, this glacial valley is U-shaped. Notice that the highest part of the ridge is rough. This is because the glacier didn’t get that high up before it melted. The change from smooth to rough rock is the “bathtub ring” left by the glacier that shows the highest point the glacier reached on the mountain.

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 knick-name?

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.