Inselberg
In geomorphology, an island mountain is a single mountain or a mountain group that rises like an island and suddenly from a flat shape. It is a stopped Restform on a through denudation deep down trunk space . Their formation typically takes place in the semi-humid to semi-arid climates of the tropics.
The German name Inselberg has also established itself in the Anglo-Saxon and Francophone-speaking areas.
A distinction is made between azonal shield island mountains , which often arise in connection with flushing areas , and zonal island mountains, which arise when a fuselage surface is erosively relocated. The Sugar Loaf in Rio de Janeiro and the Uluṟu (Ayers Rock) in the Australian outback are shield island mountains (flushed, resistant, standing rock).
Free-standing volcanoes are not part of the island mountains .
Emergence
In the humid tropics with strong chemical weathering during the hot and humid season, island mountains can arise if the denudation rate is greater than the weathering rate. With an equilibrium of the two rates, the trunk area is evenly lowered. Where however, due to locally higher resistance to weathering of the rock weathering rate is lower, which is bedrock on the surface of the weathering material ( regolith exposed). Since the rate of weathering of the exposed rock is subsequently even lower than with a moisture-storing regolith layer, the erosion of this hardened part can no longer keep pace with the lowering of the surrounding area - it is increasingly carved out of the hull surface (Schildinselberg), whereby the Slopes often steeper towards the foot and take on a convex shape (e.g. Sugar Loaf , Ayers Rock ). Typical slope profiles of the Inselbergs result in different climatic zones. Both island mountains and the hull surfaces on which they stand are typical sculptural forms . The material of the island mountains does not necessarily have to differ petrographically from that of the surrounding area . Deviations in the weathering resistance can also be structural, e.g. B. by a differently close gap .
Inselbergs can also arise in areas with strong pediment formation according to a different morphodynamic sequence, namely through lateral erosion of the water that runs off the pediments during the rainy season. By retreating this erosion, individual island mountains can be separated from a mountain complex in this way. If an extended trunk step is cut up from the lower level by regressive demolition with strong pedimentation, rows of separated island mountains can form; they are called zonal island mountains in contrast to the azonal shield island mountains .
Due to global climatic fluctuations and as a result of continental drift , the island mountains created in the tropical climate can reach climatic areas in which either there is extensive rest in shape or in which they are further shaped with different morphodynamics. Examples of the first case are the island mountains in the fully arid area in central Australia. In the area of the moderate climate and - in the meantime during the Pleistocene - the glacial and periglacial climates are the island mountains that can be detected in today's Central Europe, for example the Zobten with its secondary peaks in the Silesian plain. The Tors in Northern Canada and the Tunturi in Lapland are also considered to be further developed island mountains created under tropical conditions .
vegetation
Due to their climate and soil conditions, Inselbergs can differ significantly from their surroundings. Plants adapted to water or nutrient deficiencies such as carnivorous plants of the sundew and water hose family or plants resistant to dehydration such as Afrotrilepis pilosa find their habitat here, as well as water-storing leaf and stem succulents , in South America often bromeliads . On the other hand, there are also aquatic plants in temporary small bodies of water on the surface of island mountains. Larger and higher island mountains are also called sky islands in ecology .
Surname
The term "Inselberg", which Wilhelm Bornhardt coined in his research in East Africa in 1898, has also established itself in the Anglo-Saxon and Francophone-speaking areas. Steep, dome-shaped island mountains, also called Dom , Glocken or Helmberg in the German-speaking world , are called Bornhardts in Anglo-Saxon countries .
See also
- Großer Inselsberg , Thuringia
- Mount Island , Antarctica
literature
- Frank Ahnert : Introduction to Geomorphology. 5th edition, Verlag Eugen Ulmer, Stuttgart 2015.
- Herbert Louis , Klaus Fischer: General Geomorphology . Walter de Gruyter 1979, ISBN 3110071037 , p. 144ff ( limited online version (Google Books) )
- Lexicon of Geosciences. Second volume. Spectrum Academic Publishing House, Heidelberg, Berlin 2000.
Web links
Individual evidence
- ↑ a b c Frank Ahnert: Introduction to Geomorphology , p. 266 f.
- ^ Herbert Wilhelmy : Climate geomorphology in key words. Verlag Ferdinand Hirt, 1974, p. 18.
- ^ Lexicon of Geography. Volume 2, p. 505.
- ^ Frank Ahnert: Introduction to Geomorphology , pp. 267–268.
- ↑ Frank Ahnert: Introduction to Geomorphology , pp. 269–271.
- ^ Herbert Wilhelmy: Climate geomorphology in key words. Verlag Ferdinand Hirt, 1974, p. 109.
- ^ Herbert Wilhelmy: Climate geomorphology in key words. Verlag Ferdinand Hirt, 1974, p. 98.
- ↑ Hans Murawski: Geological Dictionary. 6th edition, Stuttgart 1972, p. 100.