Köfelsit

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A Köfelsit sample - on the right in the picture is a euro coin as a scale.
This satellite image shows the area of ​​the Köfels landslide. Approx. three cubic kilometers of material fell down there a good 9,800 years ago.
Another example of a Köfelsit - the sample is approx. 4.1 cm wide.

Köfelsit describes a rock glazing caused by a landslide , similar to pumice stone. Köfelsite mainly consists of silicon dioxide and is petrographically referred to as frictionite . It is named after the village of Köfels in the municipality of Umhausen in the Ötztal (Tyrol / Austria).

Köfelsit has been used by locals as a cleaning and emery material for centuries. Scientific processing began around 1860, when the special position of the rock was recognized. Köfelsite is chemically similar to the eye gneiss widespread at the site , which indicates that it emerged from it. The fact that Köfelsite occurs in small dykes within a very extensive and mighty scree slope proves a causal connection with the Köfels landslide around 9000 years ago .

After it was long doubted that a landslide would release enough energy to melt silicate, and volcanic activity or a meteorite impact were assumed to be the primary event , recent calculations suggest that landslides are sufficient to trigger such glazing. The energy converted during the Köfels landslide event is estimated at an equivalent of 4.5 megatons TNT (about 19 petajoules ), the temperature on the rock friction surfaces at 1700 ° C.

Analogous sites

Large-scale glazing on rock friction surfaces that cannot be explained by an impact has also been described in connection with the prehistoric Tsergo-Ri landslide ( Langtang region , Nepal ).

literature

  • Th. Erismann, H. Heuberger, Ekkehard Preuss : The pumice stone from Köfels (Tyrol), a landslide “frictionite” . In: Mineralogy and Petrology . tape 24 , no. 1-2 . Springer, March 1977, ISSN  0930-0708 , p. 67-119 , doi : 10.1007 / BF01081746 .
  • G. Kurat, W. Richter: Impactites from Köfels, Tyrol . In: Mineralogy and Petrology . tape 17 , no. 1 . Springer, March 1972, ISSN  0930-0708 , p. 23-45 , doi : 10.1007 / BF01082919 .
  • S. Simon: Pumice between rubble rubble in the Ötztal . In: The opening . 24. Special publication, 1974.
  • R. Sureniam: Köfelsite deposits in Ötztal, Tyrol . In: Mineralogical Review . No. 1 , 1994.
  • E. Brückl, J. Brückl, H. Heuberger: Present structure and prefailure topography of the giant rockslide of Köfels . In: Journal of Glacier Science and Glacial Geology . tape 37 , no. 1 . Universitätsverlag Wagner, Innsbruck 2001, p. 49–79 ( info.tuwien.ac.at [PDF; accessed on July 10, 2010]).