Corrosion
Korrasion (from Latin corradere “to scratch”, “to grind”) primarily describes the removal of rock by wind grinding , but also comparable processes in flowing waters as well as in machines and technical systems.
Corrosion from wind
Corrasion or wind abrasion refers to the removal of rock by moving material (dust, grains of sand, fine gravel) similar to the mode of action of a sandblasting fan . The surface of the rock receives a cut (wind cut). The extent and strength of the corrosion depend on the wind speed , the wind direction and its persistence as well as on the ground cover (absence of vegetation ), the precipitation and the possibilities for the wind to attack and absorb particles ( deflation ). A low level of soil vegetation combined with a high proportion of sediments or loose rock of small to medium grain size ( coarse silt , sand , fine gravel ) favor corrosion. Such conditions are found mainly in deserts on earth .
The rock forms caused by corrosion show different characteristics depending on the above conditions, which is why a distinction is made between mushroom rocks , yardangs , wind canters , grooves and windstrokes .
There is also the appearance of scree deserts , which are caused by the wind-induced abrasion of areas previously covered with sharp-edged fragments of rock.
Wind abrasion is also referred to as aeolian weathering or wind weathering , but this process is not weathering in the actual sense of the word, as it involves a more or less penetrating (profound) change in the structure and / or the mineral stock of a rock, but not a simple one natural mechanical treatment of the rock surface. However, wind can play a supporting role in the formation of certain forms of weathering, for example in the formation of tafone .
Corrosion from water
In rivers, the term refers to the breaking up of debris carried along with it and the associated removal from the walls of cave systems.
Corrosion in technology
In the technical field, corrosion is the mechanical destruction or wear and tear of machine parts by solids. This problem is particularly a problem in the Pelton and Francis turbines of high-pressure pumped storage power plants , and the ultimate solution is still a long way off, despite modern settling systems upstream of the pressure lines .
However, corrosion is also used as a technical process with the desired result of material removal in sandblasting .
literature
- Radim Kettner: General geology. Vol. IV, The external geological forces, the earth's surface and the geological activity of ice, wind, gravity, organisms and humans . Berlin 1960, pp. 119-126, 156-157