Engineering geology

What is erosion?

In geologic terms, erosion is the lifting and physical removal of rock particles, dirt, sand, and other natural materials by agents such as streams or glaciers. Erosion can be by physical (or mechanical) means (for example, by wind, waves and currents, running water such as rainfall, or moving glacial ice), or it can be by chemical means, when particles are moved in watery solutions that dissolve rocks and minerals.

Both forms of erosion take place everywhere on Earth, from rock fragments sliding down the slope of a mountain to particles carried down a submarine canyon. Erosion takes place at varying rates and depends on many variables. For example, erosion of harder (more resistant) granites produces less sediment than softer (less resistant) sedimentary siltstone over the same period. Erosion also depends on the climate and surrounding environment. Waves pounding on an outcrop of sandstone wilt carry away particles faster than an intermittent stream wearing away at the same material.

And in certain circumstances, catastrophic events are also a factor. For example, a half-mile~wide asteroid striking the Earth would obviously cause extensive local erosion in only a few seconds.

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