Wool sack weathering
The weathering of wool sacks (more rarely also called "mattress weathering ") is a special form of weathering of rocks . Due to the interaction of physical and chemical processes, the weathering of wool sacks results in rock blocks with rounded edges, which are stacked on top of one another like pillows, mattresses or wool sacks. The figurative term “wool sack” is derived from coarse sacks filled with wool, which were historically used both as sleeping pads and for transporting wool.
Weathering processes
Primarily in coarse crystalline, massive rocks such as granite , granodiorite , diorite and corresponding gneisses , this weathering phenomenon can also be observed worldwide in thick, banky sandstone . The “wool sacks” often form largely vegetation-free rock castles , such as on the Externsteine and in many places in the Harz Mountains, in the Black Forest on Karlstein near Hornberg and the Günterfelsen near Furtwangen , in Myanmar ( Goldener Fels ), in the Teufelsküche in the Upper Palatinate Forest or in large areas from Felsenmeeren , in the Luisenburg rock labyrinth in the Fichtelgebirge, in the Blockheide (Waldviertel, Lower Austria) or in the Felsenmeer in the Odenwald . In the Saxon Erzgebirge is the " Hefekloßfelsen " near Breitenbrunn / Erzgeb. a popular destination. The striking granite cliffs in southern England, known as “ Tors ”, are also known .
The cause of the wool sack is caused by weathering processes occurring on or near the surface of the terrain. An important prerequisite is the existence of a network of more or less perpendicularly oriented dividing surfaces that divide the rock into blocks. These can be fissures or stratified surfaces (for example with sandstone). For the emergence or accentuation of the fractures can frost damage play a significant role. Particularly in the case of plutonites such as granite, the pressure relief due to the ascent from their formation depth (see → lithostatic pressure ) plays an essential role in the formation of the fracture network.
At layer contacts and crevices, chemically aggressive solutions (rainwater or soil water enriched with humic acids ) can penetrate the rock and begin to decompose the correspondingly vulnerable minerals . This happens particularly quickly at the corners and edges of the individual blocks, because there the ratio of attack surface to rock volume is significantly greater than in the other places. The decomposition leads to a fundamental loosening of the rock structure. The thus formed fine-grained loose material is used as crus and the formation process is as Abgrusung or Vergrusung designated. In the case of exposed rock, there is also desquamation of coherent thin rock flakes . The chemical dissolution processes are favored by warm and alternately humid climates in the tropics and subtropics.
As the weathering progresses, the typically rounded shapes finally emerge, whereby rock that has weathered in the subsurface near the surface must first be exposed through erosion so that the weathering residues (grus) are carried away. In the advanced stage, rocking stones can form due to wool sack weathering . On larger areas, the blocks that remain after the fine material has been removed can form block seas .
See also
- Rock needle , a partly similar stone formation
- Karlu Karlu (Devil's Marbles) in Central Australia, a special form of wool sack weathering, partly from underground tower formation (diameter approx. 2 meters)
Individual evidence
- ↑ Geographisch-Kartographisches Institut Meyer (Ed., Head Adolf Hanle): Meyers Naturführer: Erzgebirge. Meyers Lexikonverlag, Mannheim, Leipzig, Vienna, Zurich 1992, ISBN 3-411-07151-6 , p. 158
- ↑ a b Rudolf Hohl (ed.): The history of the development of the earth. 7th edition, VEB FA Brockhaus Verlag, Leipzig 1981, p. 102
- ↑ Keyword “Wollsackverwitterung” in: Hans Murawski: Geological Dictionary. 9th edition, Enke, Stuttgart 1992, ISBN 3-432-84109-4 , p. 222
- ↑ vdf.ethz.ch - Wool sack weathering ( Memento from October 3, 2011 in the Internet Archive )
- ↑ Wool sack weathering. In: Lexicon of Geography. Spektrum Akademischer Verlag, accessed on January 3, 2018 .
