A Dreikanter is a type of
ventifact
A ventifact (also wind-faceted stone, windkanter) is a rock that has been abraded, pitted, etched, grooved, or polished by wind-driven sand or ice crystals. These geomorphic features are most typically found in arid environments where there is li ...
that typically forms in
desert or
periglacial
Periglaciation (adjective: "periglacial", also referring to places at the edges of glacial areas) describes geomorphic processes that result from seasonal thawing of snow in areas of permafrost, the runoff from which refreezes in ice wedges and o ...
environments due to the abrasive action of
blowing sand.
Dreikanters exhibit a characteristic
pyramid
A pyramid (from el, πυραμίς ') is a structure whose outer surfaces are triangular and converge to a single step at the top, making the shape roughly a pyramid in the geometric sense. The base of a pyramid can be trilateral, quadrilat ...
al shape with three wind-abraded facets. The word ''Dreikanter'' is
German
German(s) may refer to:
* Germany (of or related to)
** Germania (historical use)
* Germans, citizens of Germany, people of German ancestry, or native speakers of the German language
** For citizens of Germany, see also German nationality law
**Ge ...
for "three-edged."
Similarly, a zweikanter ("two-edged") has two wind facets, an einkanter ("one-edged"), has only one wind facet.
[Greeley, R., N. T. Bridges, R. O. Kuzmin, and J. E. Laity, Terrestrial analogs to wind-related features at the Viking and Pathfinder landing sites on Mars, J. Geophys. Res., 107(E1), doi:10.1029/2000JE001481, 2002.]
Most places on the planet have several weathering processes acting at the same time, so finding good examples of Dreikanters is often difficult.
Antarctica
Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...
is a good location for finding such ventifacts since wind is usually the only active weathering agent. Many specimens in the Northeastern United States were formed during the Pleistocene era when the absence of vegetation made for little cover from wind-blown sediment.
Common features
Some common features of Dreikanters include
fluting, high polish, sharp ridges, pits, grooves, and helical forms.
image:Bradley_1930_dreikanter.jpg, 300px, Unusually large dreikanter of granite, Sweetwater County, Wyoming. This dreikanter measures 71 cm by 46 cm deep and 37 cm wide. Photo by Bradley, W.H., USGS (1930).
[U.S. Geological Survey Photographic Library ( http://libraryphoto.cr.usgs.gov/ )]
Formation
In areas where there is a prevailing wind, sand and debris cause a rock face to become flattened and polished. This changes the mass distribution of the rock, and may cause it to turn another surface toward the wind. If this process continues undisturbed, the resulting rock will have three distinct flattened and polished faces.
Dreikanters generally form in dry, arid environments from hard rocks.
See also
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References
External links
An image of a DreikanterGlossary of Meteorology
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Geomorphology
Petrology
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