Pingo
A pingo (plural: pingos; Inuktitut for hill , pregnant woman ) is a mound of earth formed in permafrost. The inside of the hill consists of an ice core, injection ice or segregation ice . Pingos have a circular or oval shape and can reach a diameter of up to 600 meters and a height of up to 60 meters. Above the ice core is a layer of earth that is covered with vegetation. Occasionally the diameter can also be considerably larger, as with the Ibyuk Pingo , the largest pingo in Canada, which has a diameter of approx. 1000 meters at its base. When the ice core melts, the pingo collapses and forms a depression in the ground. One then speaks of a fossil pingo ( pingo ruin ). In Siberia , pingos are known under the Yakut term Bulganniakh .
Locations
Pingos and fossil pingos (pingo ruins) are typical soil forms in (former) permafrost areas . You can z. B. be found in the Subantarctic , Greenland , North America , Northern Siberia , Spitsbergen and Northern Scandinavia. In Germany and Holland only fossil pingos are preserved due to the lack of permafrost. Greenland has the highest density of pingos and fossil pingos per km 2 worldwide , followed by the Mackenzie Delta and the Yukon region in Canada, the Interior Alaska region in Alaska and, in Central Europe, the regions of Drenthe in the Netherlands and East Frisia in Germany.
genesis
The basic requirement for the formation of a pingo is the presence of permafrost, a source of water from which the pingo's ice core can be fed, and a pressure gradient that provides the supply. In addition, the layer of soil above the ice core must be thick enough to cover the ice core as it grows. If this is not the case, if it is exposed, it can melt away from sunlight. Even if the formation of a pingo depends on various factors, such as its growth and the environment, pingos can be divided into two main groups: pingos of the open hydraulic system and pingos of the closed hydrostatic system.
Pingo of the closed (hydrostatic) system
These pingos usually arise under silted up thermal karst lakes. The prerequisite is correspondingly strong permafrost and the presence of water-containing talik in the ground. This talik is surrounded by strong permafrost. As the permafrost layer above is only thin, the water now begins to freeze over from above. The resulting ice then exerts cryostatic pressure on the water underneath, which, since it cannot expand downwards or to the sides, is pressed upwards and thus enlarges the ice core. If there is enough water in the talik, the ice core can grow so that it lifts the soil above and forms a pingo. The pingo growth stagnates as soon as no more water can be squeezed from the ice core. This is the case at the latest when the previously unfrozen soil is completely frozen again. Under certain circumstances, the taliks of different lakes can also combine to form a talik. Especially if they are close together.
Pingos of the closed system are mainly found in flat areas, for example in river deltas, where there is a corresponding supply of water. For example in the Mackenzie Delta in Canada, which has the second highest density of pingos per km 2 after Greenland . This is why closed system pingos are also known as Mackenzie-type pingos.
Open (hydraulic) system pingos
Open system pingos were first discovered in East Greenland. This is why open system pingos are also known as East Greenland-type or East-Greenland-type pingos. They feed themselves from groundwater. The prerequisite for formation is that the permafrost soil is thin, non-existent or interrupted at one point above the groundwater. Artesian pressure forces the groundwater close to the surface, where it freezes and forms an ice core. The pingo grows as long as water can reach the ice core through hydraulic rise. Such groundwater-flooded soils with only weak permafrost occur mostly on slopes and at the bottom of valleys as well as in the transitions between slope sediments and valley filling sites. This is the reason why open system pingos are mostly found in areas with different elevation profiles. Although the pingos grow differently, they often form small groups or rows with pingo ruins, unlike the Mackenzie-type pingos. This can be attributed to changes in the groundwater that feeds the pingos. Greenland-type pingos can also be found in flat areas. There the water is supplied by springs or, for example, by melt water from glaciers.
Formation of fossil pingos (pingo ruins)
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There are basically several possibilities that can lead to the collapse of a pingo of any type. This creates pingo ruins . The two most common causes are:
Decline in permafrost
As the permafrost has receded, the pingo's ice core slowly melts and the hill collapses and a depression forms. The edge wall is created by sediment material that has slipped down.
Breaking up of the sediment layer above the ice core
The ice core continues to grow due to the constant supply of water. At a certain point it is so powerful that the layer of sediment covering it tears open or slips off the flanks. As a result, the ice core is exposed to sunlight and begins to thaw. Even at the end of this process, a depression in the ground remains with an edge wall.
See also
Individual evidence
- ↑ Parriaux, A .: Géologie - bases pour l'ingénieur , Lausanne, 2006, p. 330
- ↑ a b www.spektrum.de Lexicon of Geosciences On: www.spektrum.de, accessed on October 4, 2018
- ↑ a b c d Woolderink: Late Weichselian permafrost distribution and degradation: A pingo based reconstruction for the Netherlands (PDF download) . On: www.pingoruines.nl, page 1, Utrecht University, Faculty of Geosciences, Department of Physical Geography, 2014, (English), accessed on October 3, 2018
- ↑ Ronald C. Flemal: Pingos and Pingo Scars: Their Characteristics, Distribution, and Utility in Reconstructing Former Permafrost Environments , Quaternary research 6, pp. 37-53, University of Washington, 1976
- ↑ Eike Rachor: Pingos, special formations in permafrost areas and their traces in Northern Germany (PDF) . At: www.klima-warnsignale.uni-hamburg.de, accessed on October 3, 2018
- ↑ Carsten Smidt, Steffen Wolters, Bernd Zolitschka: Pingo ruins: evidence and extensive distribution of periglacial relics south of Friedeburg (East Frisia) . From: www.researchgate.net, Nachrichten des Marschenrat 54/2017, page 46, accessed on October 3, 2018
- ↑ a b c d e f g h Astrid Ruiter: Pingo ruins and permafrost . pingos-neu.kge-suss.de. Archived from the original on September 29, 2018. Retrieved January 12, 2020.
- ↑ a b Frank Ahnert: Introduction to Geomorphology (limited preview) On: books.google.de, 5th completely revised and expanded edition, Verlag Eugen Ulmer, Stuttgart, 2015, ISBN 3-8252-8627-4 , page 117
- ↑ JR Mackay: The Birth and Growth of Porsild Pingo, Tuktoyaktuk Peninsula, District of Mackenzie (PDF) . From: arctic.journalhosting.ucalgary.ca, Arctic Vol 41 No 4 (December 1988) P. 267-274, The Arctic Institute of North America, University of Calgary, (English), accessed October 15, 2018
- ↑ a b c J.R. Mackay: Pingo Growth and Collapse, Tuktoyaktuk Peninsula Area, Western Arctic Coast, Canada: a long-term field study (PDF) . From: www.erudit.org, Department of Geography, University of British Columbia, Vancouver, British Columbia, V6T 1Z2, 1998, accessed October 15, 2018