Rock glacier

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Block glacier on the Bettmerhorn

Rock glaciers are masses of rubble and ice that move slowly down the valley or slope when they are active.

They consist of frozen loose material such as debris or moraine . Since the rock-ice mixture is hidden under the surface rubble of the thawing layer, rock glaciers are often difficult to see for laypeople. They are considered a typical landscape element of the alpine permafrost ( permafrost ) and occur in many high mountain regionsthe earth. Optimal educational conditions for rock glaciers prevail in mountains and mountain areas under wintry, continental climates. A non-existent or only slight snow cover and long-lasting temperatures well below freezing point lead to intensive deep-reaching cooling and freezing of the substrate. If a sufficiently thick snow cover> 80 cm has only developed at the beginning of the ablation phase in spring, this has a conserving effect on the frozen ground. In the Alps, rock glaciers can therefore be found primarily in the inner-alpine dry valleys of the Engadine (e.g. the Murtél rock glacier) and the Eastern Alps (e.g. the rock glacier oil pit in Kaunertal; Schober group). Much larger rock glaciers can be found in the continental Tien Shan Mountains(Kazakhstan / Kyrgyzstan). The geomorphological lower limit of the rock glaciers is generally regarded as the lower limit of the zone of discontinuous permafrost. An exception are very fast flowing rock glaciers, which can penetrate up to the montane altitude.

Block glacier 'Gorodetsky' in northern Tien Shan (August 2005), block glacier lower limit at approx. 3150 m, coordinates: 42.997 ° N, 77.032 ° E
Very fast flowing rock glacier 'Ordshonikidze' in northern Tien Shan (August 2006) penetrates up to the montane height level. Coordinates: 43.069 ° N, 77.161 ° E

Block glacier types

Block glacier tongue on the Hangerer in Ötztal , Austria

In contrast to glaciers in the true sense of the word, rock glaciers are not superficial ice bodies. There are two types of education:

  • Block glaciers are typical phenomena of alpine or high mountain permafrost, in which erosion debris is glued to frozen ground water, i.e. a form of ground ice
  • But they can also arise from melting back, debris-covered kar glaciers , in which the rock content takes over

Depending on the level of activity, there are three types of rock glaciers:

  • Active rock glaciers are mass movements that, like pure ice glaciers, crawl or flow like a lava flow or mur . They typically move at 0.10 to 1 m / year.
  • Inactive rock glaciers no longer move, but still contain frozen material. One speaks of climatic inactivation when the rock glacier has moved into non-permafrost areas or when the ice has melted, for example due to global warming. Dynamic inactivity occurs when the rock glacier has moved too far from its rubble slope so that it is cut off from its supply of rubble and ice.
  • Fossil rock glaciers are ice-free debris deposits, since the ice has melted through a long stay in non-permafrost areas. The fine-grained silt and clay fractions were washed out with the meltwater, which together with the ice formed the ice cement, which is also responsible for the flowing or sliding of the rock glacier. A fossil rock glacier can no longer become active even if the permafrost limit, the permafrost depression (PFD), is lowered.

Recently, a distinction has been made between two types in the literature based on the geological properties of the material of a rock glacier:

  • Pebbly rock glaciers : They consist of 15–20 cm large boulder material ( pebble , gravel ) and are usually shorter than rocky rock glaciers with a length of less than 200 meters. They are nourished by a rock face, usually less than 50 meters high, made of less resistant rock.
  • Rocky rock glaciers (bouldery rock Glacier) : They are (from larger debris material boulder , rock '), which they receive from a higher, mostly over 100 meters high cliff from resistenterem rock. They are regularly over 200 m long and, in contrast to the pebbly rock glaciers, form a steeper frontal forehead and a bulging surface.

Structure and flow of rock glaciers

Natural outcrop on the Manschuk-Mametowa glacier in northern Tien Shan, Kazakhstan in August 2010 (43.0774 ° N; 77.093 ° E, altitude: 3450 m). The rubble-ice mixture is located under a 1.5 m thick thaw layer

Block glaciers show - regardless of the level of activity - similar geomorphology to other glaciers, they can form large plateaus as ground ice bodies of various sizes , ice lenses embedded in the terrain, up to lobed to tongue-shaped ice bodies on slopes and in valleys that clearly stand out from their surroundings ( tongue-shaped: length> width, praise-shaped: length <width) as well as complex shapes. The latter occurs when several rock glaciers converge to form a single tongue, when a rock glacier splits into several tongues, with rock material from different times and with different rock sources. They are typically a few hundred meters long and 100-200 meters wide, but can also reach lengths of several kilometers. Their thickness is usually in the range of 30-50 meters.

Usually it is a mixture of rubble and ice with a volumetric ice content of 40–70% on average, which flows down the slope or valley - but slower than a glacier in the real sense. The frontal forehead and superficial bulges that are characteristic of active rock glaciers are formed . The forehead is a typically steep slope made of unfrozen rubble with a slope angle of approx. 40 °.

Inactive rock glaciers generally have a flatter frontal forehead and a softer transition between the forehead and the top. Due to the lack of movement, vegetation up to the size of shrubs and even smaller trees can settle on them. Relic forms are characterized by irregular structures and a collapsed upper side due to the completely melted ice in this status.

Many rock glaciers are quite old . The boulders of the near-surface layers act as insulation and protect the ice from melting .

Research history and investigation

The exact dynamics of alpine rock glaciers was first researched in more detail in the 1970s. The associated investigations were initiated by Professor Adrian Scheidegger , who was Professor of Geophysics at the Vienna University of Technology until around 1995 . The German geomorphologist Professor Dietrich Barsch and the Swiss cryosphere researcher Professor Wilfried Haeberli have made a decisive contribution to the scientific knowledge of rock glaciers.

Actually, they are not the subject of glaciology or hydrology , but geomorphology and hydrogeology . In contrast to glaciers in the strict sense of the word, they form underground , while the latter is caused by the accumulation of snow on the surface.

The rock glaciers aroused the interest of science relatively late, mainly for four reasons:

  • Their importance as water - resources , particularly in arid (- semi-arid ) areas such as the Chilean Andes save hardly larger where mountain lakes and glacier water quantities. At the same time they are there (because of the climate and the special rock - erosion ) is very prevalent and after the (ice) -Gletschern the second most important water resources are.
  • Conversely, they also make a contribution to summer meltwater discharge in mountain regions that has not been taken into account so far, and must therefore be taken into account as a hydrological factor in flood models.
  • They are climate indicators . The lowest occurrences of active rock glaciers correspond to the lower limit of the permafrost in the high mountains, which is around the −1 ° C isotherm . Therefore, they are indicators of today's temperature conditions . Fossil rock glaciers that (almost) no longer contain ice are indicators of lower layers of permafrost and therefore of colder climatic phases (see the Little Ice Age in Europe around 1850).
  • You can stabilize the high alpine soils. As phenomena of permafrost, they replace the effect of vegetation in arid areas - which, for example, in Santiago de Chile only exists up to an altitude of 3000 meters. In the Andes, the rock glaciers are often the only factors that give the scree slopes a certain strength. Without permafrost, soils would slide faster and devastating processes such as mudslides and large-scale landslides could occur and threaten numerous high-altitude settlements .

The dynamics of movement is an interesting challenge for several geoscientific disciplines such as soil mechanics or pedology , geodesy , geology , geophysics , hydrology and geotechnics , and their modeling for geoscientific informatics. In fact, it can only be successful in interdisciplinary cooperation.

literature

General:

  • D. Barsch: Rock glacier studies, summary and open problems. In: H. Poser, E. Schunke (Ed.): Mesoforms of the relief in today's periglacial space. Vandenhoeck & Ruprecht, Göttingen 1983, pp. 133-150.
  • D. Persch : Rockglaciers . Springer, Berlin 1996 (English).
  • D. Barsch: Active rock glaciers. Movement and process understanding. In: Yearbook of the Geographical Society of Bern. Vol. 59, 1996. pp. 263-270.
  • KC Burger, JJ Degenhardt, JR Giardino: Engineering geomorphology of rock glaciers . In: Geomorphology . No. 31 , 1999, p. 93-132 (English).
  • W. Haeberli, B. Hallet, L. Arenson, R. Elconin, O. Humlum, A. Kääb, V. Kaufmann, B. Ladanyi, N. Matsuoka, S. Springman, D. Vonder Mühll: Permafrost creep and rock glacier dynamics . In: Permafrost and Periglacial Processes . No. 17 , 2006, p. 189-214 (English).
  • P. Höllermann: Rock glacier studies in European and North American mountains. In: H. Poser, E. Schunke (Ed.): Mesoforms of the relief in today's periglacial space. Vandenhoeck & Ruprecht, Göttingen 1983, pp. 116-119.
  • M. Kuhle: Glacial Geomorphology. Wissenschaftliche Buchgesellschaft, Darmstadt 1991, pp. 81–84.
  • F. Wilhelm: Snow and glacier science. De Gruyter, Berlin / New York 1975, pp. 153–156.
  • OR way: the periglacial. Geomorphology and climate in glacier-free, cold regions. Borntraeger, Berlin / Stuttgart 1983.

Discourse:

  • P. Höllermann: Problems of rock glacier research. Presentation of the contributions to the discussion. In: H. Poser, E. Schunke (Ed.): Mesoforms of the relief in today's periglacial space. Vandenhoeck & Ruprecht, Göttingen 1983, pp. 151–159.
  • Atsushi Ikeda, Norikazu Matsuoka: Pebbly versus bouldery rock glaciers: Morphology, structure and processes. In: Geomorphology 73, 2006, pp. 279-296.
  • W. Klaer: The rock glacier question, a terminological problem? In: H. Poser, E. Schunke (Ed.): Mesoforms of the relief in today's periglacial space. Vandenhoeck & Ruprecht, Göttingen 1983, pp. 120-132.

Special and regional topics:

  • D. Persch: Studies and measurements on rock glaciers in Macun, Lower Engadine. In: Journal of Geomorphology. Supplement volume 8, 1969, pp. 11-13.
  • D. Persch: A permafrost profile from Graubünden, Swiss Alps. In: Journal of Geomorphology. New series Volume 21. 1977, pp. 79-86.
  • D. Barsch, W. Zwick: The movements of the Macun I rock glacier from 1965–1988 (Lower Engadine, Graubünden, Switzerland). In: Journal of Geomorphology. New episode Volume 35, 1991, pp. 1-14.
  • D. Persch: The relationship of the snow line and the lower limit of the active rock glaciers. In: C. Jentsch, H. Liedtke: Height limits in high mountains. Work from the geographical institute of Saarland University 29, 1992, pp. 119-133.
  • SRJr. Capps: Rock Glaciers in Alaska. In: J. Geol. 18, 1910, pp. 359-375.
  • G. Chesi, S. Geissler, K. Krainer, W. Mostler, T. Weinhold: 5 years of movement measurements on the active rock glacier Inneres Reichenkar (western Stubai Alps) with the GPS method. In: G. Chesi, T. Weinhold (Ed.): 12th International Geodetic Week Obergurgl 2003. Wichmann, Heidelberg, pp. 201–205.
  • H. Hausmann, K. Krainer, E. Brückl, W. Mostler: Internal structure and ice content of Reichenkar rock glacier (Stubai Alps, Austria) . Assessed by geophysical investigations. In: Permafrost and Periglacial Processes . tape 18 , no. 4 , October 2007, ISSN  1099-1530 , p. 351-367 , doi : 10.1002 / ppp.601 .
  • Aldar P. Gorbunov, Sergei N. Titkov, Victor G. Polyakov: Dynamics of rock glaciers of the Northern Tien Shan and the Djungar Ala Tau, Kazakhstan . In: Permafrost and Periglacial Processes . tape 3 , no. 1 , 1992, ISSN  1099-1530 , pp. 29-39 , doi : 10.1002 / ppp.3430030105 .

Web links

Commons : Block Glacier  - Collection of images, videos and audio files

Individual evidence

  1. ↑ a b c d Lit. Persch : Rockglaciers . 1996.
  2. ↑ a b c Lit. Burger, Degenhardt, Giardino: Geomorphology . 1999.
  3. ^ A b c Karl Krainer, Markus Ribis: Rock glaciers and their hydrological significance in the high mountains . In: Gabriele Müller, Federal Ministry of Agriculture, Forestry, Environment and Water Management, Dept. VII 3 Water Management (Ed.): Communications from the Hydrographic Service in Austria (=  information sheet of the Hydrographic Service in Austria . No. 86 ). No. 86 . Vienna 2009, 2. What are rock glaciers? , S. 65–78 , p. 66, PDF, p. 72 ( bmlfuw.gv.at [PDF] with numerous photos).
  4. ↑ Lit. Ikeda, Matsuoka 2006
  5. ↑ Lit. Haeberli et al .: Permafrost and Periglacial Processes . No. 17 , 2006.
  6. ↑ a b G.F. Azócar, A. Brenning: Hydrological and geomorphological significance of rock glaciers in the dry Andes, Chile (27 ° -33 ° S) . In: Permafrost and Periglacial Processes . No. 21 , 2010, p. 42-53 .
  7. ↑ Krainer, Ribis: rock glaciers and their hydrological importance in the high mountains . 2009, 3. Significance of rock glaciers , p. 67 f ., PDF p. 73 .
  8. ↑ Andreas Kellerer-Pirklbauer: How old are rock glaciers in the Austrian Alps? The example of the rock glaciers in the Dösener valley, Ankogel group, dates with the help of the Schmidt-Hammer method . In: Institute for Geography and Spatial Research, Karl-Franzens-University Graz (Ed.): Alpine space - man & environment . tape 6 : Climate change in Austria . iup • innsbruck university press, Innsbruck 2009, ISBN 978-3-902571-89-2 ( uibk.ac.at [PDF]).