Pingo ruin

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Pingo ruin Frauenmeer near Timmel

The term pingo ruin (or fossil pingo ) denotes the remnant of a collapsed pingo . The name pingo comes from the Inuit and means "hill" or "pregnant woman". The melting of the ice core causes the pingo to collapse and form a circular to slightly oval depression in the ground, which is surrounded by a more or less large wall of earth. However, this wall can be destroyed by erosion or sinking into the hollow . Organic substances and mineral substances carried in by wind or groundwater are deposited in these hollows. Depending on the rising groundwater level, a bog then forms in the hollow shape , whereby all different forms of bogs can occur depending on the nutrient content.

Pingo

A pingo is a mound of earth that consists of an ice core inside. 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. The ice core is fed by groundwater or water in the Talik and in this way continues to grow, pushing the layer of earth above the ice core upwards. If this ice core melts, the pingo collapses and forms a circular hollow in the ground, which is surrounded by an earth wall made of sediment material that has slipped down.

Locations

Pingo ruins are typical soil forms in (former) permafrost areas . They can be found, for example, in the sub-Antarctic , in Greenland , in North America , in northern Siberia , on Svalbard and in northern Scandinavia. The world's highest density of pingo ruins per km 2 is found in Greenland, 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 Holland and East Frisia in Germany.

Identification and dating of pingo ruins

In the course of scientific research into pingo ruins, various researchers have established criteria that are still valid today for identifying pingo ruins:

  • The diameter of the pingo ruin is at least 25 meters and it is at least 1.5 meters deep.
  • The subsurface of the depression lies below the topography of the terrain and consists of material that is sufficiently permeable to groundwater.
  • Pingo ruins are oval to circular in shape.
  • A wall or at least part of a wall surrounds the pingo ruin.
  • Pingo ruins are found on slopes of up to 5% slopes or on flat floors.
  • Pingo ruins were formed in areas with permafrost phenomena.
  • The sides of the erosion form represent steep slopes.
  • The wells are filled with peat or other organic material.
  • Pingo ruins date from the alternation of permafrost.

Especially in densely populated areas that have not belonged to permafrost areas for a long time, the characteristic of the rim wall is not always observable. This can have been eroded over time by erosion or artificially by humans. In addition, additional technical procedures are used today to determine the age and identify pingo ruins. These are, for example, aerial photographs and satellite images, products such as ArcGIS , test drillings, pollen analyzes and age determinations of organic samples using the method of loss on ignition.

Formation of pingo ruins

There are basically several possibilities that can lead to the collapse of a pingo, regardless of the type.

Decline in permafrost

The decrease in permafrost and thus the ground temperatures of 0 ° C to −2 ° C required to maintain the pingo are exceeded, causing the ice core to slowly dissolve. The meltwater will then seep through cracks and openings in the pingo's mantle and possibly also downwards, and the pingo will slowly collapse. What remains is a depression in the ground, which is surrounded by a rim wall made up of sediment material that has slipped down. If the process of melting the earth wall takes place very quickly, it can happen that the pingo collapses very quickly and leaves no or only very little topographical traces.

Mechanical failure of the pingo

The ice core of the pingo 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 and dilation cracks form. As a result, the ice core is exposed to sunlight and begins to thaw. Such mechanical failure of the pingo can also occur in zones of permafrost. In addition, the ice core can deform. There are basically 3 variants of how mechanical failure can lead to the collapse of the pingo and thus to a pingo ruin.

Summit failure (summit dilatation)

The prerequisite for this is that the diameter of the pingo is fixed early and that most of the pingo's growth is at its height. At the summit, where the sediment material is thinnest due to the expansion upwards, there is a dilation jump (summit crack). If the pingo continues to grow, a so-called pingo crater can form. The cracks can also continue in the pingo's ice core.

Circumferential failure (radial dilatation cracks)

Usually these radial cracks appear after the summit cracks. They occur when the pingo's girth increases faster than its height. Many of these cracks running radially down the slope extend beyond the periphery of the pingo (in some cases as far as neighboring lake areas, where they form ice wedges). They, too, expose the pingo's ice core.

Hydrofractures and peripheral failure (hydrofracture and peripheral failure)

The formation depends on a large number of factors in the material surrounding the pingo, such as the ground temperature, the shape of the pingo or the material of the ground. They arise predominantly on the periphery of the duckweed. From there, the cracks spread into the surrounding area and up into the ice core of the pingo.

Cultural and historical significance

Various finds suggest that pingo ruins, in keeping with Gipskeuper's mardelles , were used by humans at different times and purposes. During investigations of various pingo ruins as part of a project supervised by the University of Utrecht, a hole in a pingo ruin in Mamburg near Esens found ceramics from the Roman Empire at a depth of 50 cm. It was also possible to prove in this project that the medieval village complex in Timmel (Aurich district) was essentially laid out on the edge of a pingo ruin. In places in the 19th and 20th centuries, peat was extracted from the pingo ruins . Numerous pingo ruins were made usable for agriculture by lowering the water table and adding a layer of sand, especially as grassland or hay meadows. In some cases also as arable land. Furthermore, artifacts from the Mesolithic were found in the edge of a pingo ruin. Corresponding pollen analyzes provide further indications of an early settlement history in the vicinity of pingo ruins.

Individual evidence

  1. ↑ 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 16, 2018
  2. ↑ RC Flemal: Pingos and pingo scars: Their characteristics, distribution, and utility in reconstructing former permafrost environments (PDF) . On: kundoc.com, Quaternary Research 6 (1), pp. 37-53, 1976 (English), accessed October 20, 2018
  3. ↑ a b Woolderink: Late Weichselian permafrost distribution and degradation: A pingo based reconstruction for the Netherlands (PDF download) . From: www.pingoruines.nl, page 1, Utrecht University, Faculty of Geosciences, Department of Physical Geography, 2014, accessed on October 16, 2018
  4. ↑ 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 16, 2018
  5. ↑ a b c d e f De Gans: Pingo scars and their identification . In: MJ Clark (editor): Advances in periglacial geomorphology , Publisher, John Wiley & Sons, Chichester, 1988, pp. 299-322
  6. ↑ a b c d e f g De Gans: Location, age and origin of pingo remnants in the Drentsche Aa valley area (The Netherlands) (page with a link to the article as PDF) . On: www.kngmg.nl, Netherlands Journal of Geosciences, Geologie en Mijnbouw, 1982, Volume 61 (2), pp. 147-158, accessed October 20, 2018
  7. ↑ a b c d e f 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 20, 2018
  8. ↑ a b Astrid Ruiter: Pingo ruins and permafrost . pingos-neu.kge-suss.de. Archived from the original on September 29, 2018. Retrieved January 12, 2020.
  9. ↑ 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, accessed on October 20, 2018
  10. ↑ a b J.R. Mackay: The Birth and Growth of Porsild Pingo, Tuktoyaktuk Peninsula, District of Mackenzie (PDF) . On: arctic.journalhosting.ucalgary.ca, Arctic Vol 41 No 4 (December 1988), pp. 267-274, The Arctic Institute of North America, University of Calgary, accessed October 20, 2018
  11. ↑ Axel Heinze, Wim Hoek, Martina Tammen: Pingo landscape in East Friesland (PDF download) . On: dspace.library.uu.nl, Settlement and Coastal Research in the Southern North Sea Area (SKN), Rahden / Westf. 2012, 36 111-999, accessed October 20, 2018
  12. ↑ Axel Heinze, Martina Tammen: Pingo ruins in NW Lower Saxony (geotope - biotope - soil monument) (PDF download) . From: www.pingoruines.nl, accessed October 20, 2018
  13. ↑ Holger Freund: Pollen analysis of the development of vegetation and settlements in the bog at the Upstalsboom, district of Aurich (Ostfriesland, Lower Saxony) . In: Problems of coastal research in the southern North Sea area . Volume 23, Oldenburg 1995.