Hinterstein landslide

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Area of ​​the landslide in 2015 (mostly overgrown again)

The Hinterstein landslide created a geotope south of Hinterstein in the Oberallgäu district . On May 6, 1966, parts of the mountain slope on the eastern slope of the Breitenberg broke off over a length of 400 m and slipped into the Ostrach valley .

geology

The eastern slope of the Breitenberg is made up of dark Upper Triassic to Jurassic , thin-bank limestone , marl and clay stones from the Kössen and Allgäu Formations , which "spear" through a so-called tectonic window , the Hintersteiner window , younger rocks of the main dolomite of the Allgäu Nappe . The rhythmic alternation of limestone and marl stones is usually very susceptible to weathering. The limestones alternate with leafy to thick banked, dark gray, thin-leaved marl stones and clay marl stones and often have millimeter to centimeter-sized bioturbation spots.

Chronology of the landslide

Ground movements were observed years before the actual landslide in the area of ​​the later spoilage edge . The first major movements on the slope were recorded on September 3rd and 4th, 1964. After the slope movements had calmed down in the following months, after heavy rainfall on May 6, 1966 at 12.30 p.m., a section of rock was demolished over a length of 400 meters. Around 700,000 cubic meters of rubble slid down into the valley at a speed of one meter per minute, burying 14  hectares of forest and 11 hectares of grassland under them. The debris fell into the bed of the Ostrach stream and threatened to spill it or to dam the river. With the help of the local construction companies and bulldozers of the Bundeswehr , a barn and the Guferbrücke were demolished and an alternative bed was leveled for the Ostrach the following day in order to prevent uncontrolled build-up and flooding. The new Guferbrücke was built on May 28, 1966 .

The cause of the landslide must be seen as a reduction in static friction between the thin rock layers in the Hintersteiner window as a result of moisture penetration after the heavy rainfall. Because of the resulting reduced internal static friction , there was a loss of stability along a pre-drawn sliding joint , and the mountain flank slipped. On the now exposed mountain flank, the rocks of the Hintersteiner window and in the area of ​​the edge near the Älpe-Alpe the overlying moraine deposits of the last ice age became visible. The actual breaking edge was in the smeared area of ​​the allgäu layers of the Lias . This series of rocks is characterized by a very weather-prone, narrow alternating layer of clay, marl and limestone. Hidden by the debris cone , the Rätolias limestone and marl stones of the Kössen formation lie below the Allgäu formation .

Classification as a geotope

The mountain slide geotope south of Hinterstein has been classified by the Bavarian State Office for the Environment as a geoscientifically valuable geotope (geotope no. 780r016) with a suitability as an excursion and research object. On the occasion of the 50th anniversary of the landslide, an information board was set up in 2014 on a private initiative with the support of the market building office.

Bouldering

The bouldering in this area, which is also called a "landslide", is not without risk.

See also

Individual evidence

  1. ^ Dieter Richter: Allgäu Alps . In: Manfred P. Gwinner (ed.): Collection of geological guides . 3. Edition. Issue 77.Br.Bornraeger, Berlin and Stuttgart 1984, ISBN 3-443-15038-1 , p. 179 ff .
  2. ↑ Geotope data sheet of the Bavarian State Office for the Environment: Geotope no. 780R016 landslide south of Hinterstein , accessed on February 8, 2016
  3. ^ Mountain slide in Hinterstein 50 years ago. In: Gemeindeblatt Bad Hindelang 9/2014. Bad Hindelang market town, accessed on February 9, 2016 .
  4. ↑ Stephanie Eßer: Two tons of rock slab slips off and jams man (30). all-in.de, May 24, 2020, accessed on June 12, 2020 .

literature

  • H. Henrich & C. Hieke: Hintersteiner Valley. Geological and natural history hiking guide. Mountain slide in Hinterstein 50 years ago , Bad Hindelang, 2014
  • Dieter Richter : Allgäu Alps . In: Manfred P. Gwinner (Ed.): Collection of Geological Guides, 3rd edition. Issue 77, Gebr. Borntraeger, Berlin and Stuttgart 1984, ISBN 3-443-15038-1 , 253 pp.

Web links

Commons : Bergrutsch Hinterstein  - Collection of images, videos and audio files

Coordinates: 47 ° 28 ′ 19.5 ″  N , 10 ° 24 ′ 33.4 ″  E