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Erosion |
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Erosion is the destructive breakdown of rock and soil by a variety of agents that, together with weathering, forms denudation, of the land surface. Erosion occurs because of the mechanical action of material carried by agents: water (rivers, currents, waves), ice (glaciers) and wind. Wind laden with sand can scour rock, rocks embedded in glaciers grind down the rocks which they pass and gravel and pebbles in streams and rivers excavate their own course and may create pot holes, undercut banks, etc. Water can also carry material in solution. There are six different kinds of erosion processes, each with a different effect: |
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| Process | Effect |
| Abrasion | Wearing away through grinding, rubbing and polishing. |
| Attrition | The reduction in size of particles by friction and impact. |
| Cavitation | Characteristic of high energy river waters (e.g. waterfalls, cataracts) where air bubbles collapse sending out shock waves that impact on the walls of the river bed (a very local occurence). |
| Corrasion | The use of boulders, pebbles, sand etc., carried by a river, to wear away the floor and sides of the river bed. |
| Corrosion | All the erosion achieved through solution and chemical reaction with materials encountered in the water |
| Deflation | The removal of loose sand and silt by the wind. |
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The effect of these processes can be very marked, with time, and can combine to deepen gorges, create and enlarge waterfalls and result in the movement of a waterfall upstream. The latter occurs through undercutting of lower, softer rocks which then cause the collapse of overhanging ledges. 
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