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a.k.a. THE MOLDING OF THE EARTH’S UPPER LITHOSPHERE Erosion •A natural process by which the earth’s particles are removed with the forces of water, wind, gravity and/or glaciers Deposition •A natural process by which the earth’s particles which were removed from their origin by the forces of water, wind, gravity and/or glaciers - accumulate in a new place The natural processes of erosion and deposition form many geographical features of the continental crust of the earth’s lithosphere Wind Erodes mainly through deflation (a fancy name for the blowing of surface material). The stronger the wind the heavier the material that can be moved. As the wind weakens or when an immobile barrier occurs, the wind drops the particles (deposits them) Wind Erosion The two major landforms created by wind deposition are: Sand dunes Loess regions Glaciers There Are Two Types of Glaciers • valley glaciers, long narrow glaciers which usually move down valleys cut by rivers • continental glaciers which spread out in all directions covering the land Glacial Erosion Glaciers erode in two ways: plucking and abrasion. Plucking: When glaciers flow over the land they pick up rocks beneath them often breaking the rocks apart into fragments which then freeze to the glacier (these rock fragments can be huge boulders) Abrasion: As the glacier moves it drags the rocks with it gouging and scratching the bedrock as it goes Some landforms due to the glacial erosion process Horn: glacier carves away the sides of a mountain, leaving a sharpened peak Fiord: valley carved by a glacier in a coastal region that fills when the level of sea rises Cirque: bowl-shaped hollow eroded by a glacier Lakes: long basins created by plucking and abrasion Glacial Deposition As the glacier melts it deposits the sediment and rock (called till) it eroded from the land creating various landforms. Drumlin: deposits shaped by retreating glacier Moraine: glacier deposit mounds or ridges of particles from sand to boulders along the edge of the glacier Kettle lake: forms when a depression left by a retreating glacier fills with water Gravitational Erosion The downhill mass movement of rocks and other materials. The four kinds of gravitational erosion are: • • • • creep, landslide, slump, mudslide. creep Slow slide of soil. Note the bending of the trees’ trunks. Landslides and Slumps are very similar in nature. Landslides are when rock and soil move quickly down hill. Slumps are large masses that move down in a single “lump” of soil and rock. Slump Landslide Mudslides The rapid downhill movement of a mixture of water, rock and soil. The amount of water in a mudflow can be as high as 60 percent. Clay soils suddenly become extremely fluid. Water Erosion Water is the most common source of erosion on the Earth. Water Erosion Water erosion occurs with the movement of water on Earth’s solid surface (called surface water) and below it (called groundwater). It occurs with both fresh water and salt water. When it rains-it erodes! • Raindrop impact begins the process of erosion. As drops hit unprotected soil they dislodge some particles making it easier to move the soil with the water during runoff. •Rain and the soil it carries moves downhill, with the aid of gravity, forming rills and then gullies until it reaches a “permanent” holding place such as a stream, river, lake or ocean. Rills Gully Creeks, streams and rivers are just gullies that stay filled with water year round. They constantly erode the soil around them cutting into the ground and soft rock below. One of the most famous formations caused by river erosion is the Grand Canyon. Waterfalls form when the river erodes the bed beneath unevenly. Softer rock gets removed first. Harder rock erodes more slowly. Click here to see animated version of waterfall formation. The amount of sediment a river carries with it is called its load. Load is affected by the river’s slope, volume flow and streambed shape. – The steeper the slope, the faster the river flows and the more sediment the river carries – The greater the volume of water the more sediment the river carries – The wider and shallower a river is the more soil surface area is exposed to the moving water and the more sediment the river carries Water Deposition As the river’s flow begins to slow, the river begins to drop its sedimentary load. This is called deposition. Two common landforms created by these depositions are below. Delta Alluvial fan A floodplain is a flat area along a river that receives river deposition when the flood waters recede. 1 Meanders and oxbow lakes are formations created by a river’s erosion and deposition. They form on flat plains with an overall slow current. 2 3 4 Groundwater Erosion After a storm some rain gets absorbed into the ground and becomes groundwater. When groundwater combines with carbon dioxide it forms a weak acid called carbonic acid. When this acidic water comes into contact with limestone it chemically weathers the stone away forming pockets or caves. stalactites – C for ceiling Different formations inside caves are a result of deposition, such as stalactites. and stalagmites stalagmites – G for ground If the roof of the cavern collapses a sinkhole is formed. This can happen when water in the cavern, which is supporting the ceiling, is removed. WAVE ACTION • Waves are constantly working on the shoreline, mainly by mechanical action (impact and abrasion) also known as mechanical weathering. Beaches change through longshore drift. This movement of the beach sediment with the current and motion of the waves is a natural process that makes beaches ever changing Waves create sea caves by erosion. If the cave deepens enough to work its way to the other side of the rock it opens up to a sea arch. If the arches top erodes it becomes a sea stack. WAVE DEPOSITION Many landforms are created by wave deposition such as spits, tombolos and barrier islands Images and Data courtesy of: Van Buren County Community Center Clark County Soil and Water Conservation District NRCS canyoneers.co.uk David Miller, USGS. GeoBytesGCSE http://www.monsted-kalkgruber.dk swfwmd.state.fl.us www.winona.edu Landsat 7 ETM+ image faculty.weber.edu Power point created by Donna Marcelo