Great 8 Science: Erosion

Erosion

    Erosion is the moving of rock material from one place to another, whether by flowing water, moving ice, waves, gravity, or wind. While mechanical, biological or chemical weathering is the breaking down of rock; erosion is the moving of it to another area. For example, when Mt. Saint Helens erupted in 1980, the north side of that mountain rushed down to the valley below. Erosion can take as long as a second to thousands of years, can be considered as the movement of sand grains to hundreds of tones of matter, going anywhere from a few meters to thousands of kilometers, to create eventually create sedimentary rock.

    Water Erosion: As water rushes along in rivers and streams, it gradually digs a valley for itself, by picking up the pebbles and sand on the bottom of the bed; tumbling and twirling down to a delta at a lake or the ocean, where the loose gravel and soil are deposited. A young river would be narrow, fast-flowing and pretty much straight, forming a narrow valley with high banks. Once a river leaves the mountains and gullies, it would probably reach a delta or flood-plain before getting to the sea. A flood-plain has very rich silt soil for growing bountiful crops, like Mesopotamia, or Ancient Egypt. However, if there would be a large spring melt then most of the farmer's fields would be flooded. As for a delta, it is a triangular shaped area mouth where the river expands from one large flow into several smaller channels, created by sediment.

    Wind Erosion: Just the same as water erosion, the wind can carry rock particles and silt, except that soil would be placed down where-ever the air movement stopped.

    Moving Ice Erosion: See Glacial Advance and Retreat

    Wave Erosion: Every time a wave hits the shore or a cliff, a few grains of sand return to the sea. Sooner or later, the cliff would be overhanging itself, or would have caves at shore level likely to collapse because of the scrub-brush motion of waves. As for the shore, eventually there would only be smooth rocks left, and all of the sand from the beach would have collected underwater.

    Gravitational Erosion: As mentioned above, the overhanging cliffs are likely to collapse, so, as soon as a crack or weak spot might occur, gravity would pull down and send the cliffs crashing down to the shore, creating a slight beach. Other examples are rockslides, avalanches, dirt falling off upturned tree roots, and many others.

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