Shaping the Land : Lecture Notes - Erosion

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3.  Erosion - is the process of wearing away the land or carrying away the results of weathering. Erosion is performed by three major agents:    a) Water - running water (sreams, rivers, waves), is probably the greatest of all         erosive actions         As running water flows over even the hardest rocks it will, in time, wear them away.         A it flows it carries minerals resulting from weathering with it and dumps them into         ponds, lakes, river beds and oceans as mud, sand and silt.         The continuous beating of ocean waves and the rolling of waves on the beach of          lakes and ponds, washes up rocks and soil which in turn shapes and changes the          shore line.  When streams and rivers run for a long time they produce a "V"          shaped valley by eroding away the rock beneath it.  This process can take hundreds          or even thousands of years.   b) Wind - the wind carries away tiny particles of sand and soil which sometimes become         great dust or sand storms that can cause a great deal of damage.  The dust and sand         storms are very erosive and as the wind blown sand hits solid rock, the abrasive         action slowly wears the rock away.         The wind can also pile up sand into dunes.  Dunes are formed when something          interferes with the wind causing it to slow down and drip particles of sand it was          carrying.     c) Ice and Snow - as masses of ice and snow move over the land they wear it away         and carry rocks, soil and other materials along with them.  Large masses of ice         and snow are called glaciers and the rocks, soil and other materials are deposited         along the sides and the ends of the glaciers.         Glaciers erode "U" shaped valleys.         The mud, silt and rock left along the edges, middle and front of glaciers is called          moraine.         Large stones or boulders which have been carried away by the glacier and are         different from the rock beneath them are called erratics.  Erratics come in different         sizes and some weigh many tons and are found hundreds of miles from the place         of origin.