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Natural Hazards and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/nhess-2020-285
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/nhess-2020-285
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  08 Oct 2020

08 Oct 2020

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This preprint is currently under review for the journal NHESS.

Glacier detachments and rock-ice avalanches in the Petra Pervogo range, Tajikistan (1973–2019)

Silvan Leinss1, Enrico Bernardini1, Mylène Jacquemart2, and Mikhail Dokukin3 Silvan Leinss et al.
  • 1Institute of Environmental Engineering, ETH Zürich, Switzerland
  • 2Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, United States
  • 3High-Mountain Geophysical Institute, Nalchik, 360030, Russia

Abstract. Glacier detachments are a rare phenomenon of glacier instability, whereof only a handful have been documented to date. Common to all known cases are the large detached volumes of many million cubic meters of ice and long runout distances. Recently, two detachments of smaller size were observed in the Petra Pervogo range, north west of the Pamir mountains, Tajikistan. Using a variety of satellite images, we identified in total 9 detachments and several ice and rock avalanches which occurred in four different catchments between 1973 and 2019. The avalanche run out distances vary between 2 and 19 km and detached volumes range between 2 and [8.8 × 106] m3. Seven out of nine detachments occurred between July and September in years with temperature above the past 46-years trend. No active glacier surge was observed immediately before detachment, but elevation model (DEM) differences indicate a surge-like behavior about 10 years before the two largest detachments. Instead, one glacier retreated before detachment while the other remained stagnant before increased sliding pronounced the impending detachment. To put results into a regional context, we analyzed DEM differences over the entire Pamir range and found 237 surging glaciers, predominantly in the north-western part where soft and fine-grained rock-types are common. We are confident that no major events were missed due to lack of satellite data, because destroyed vegetation remains visible in the normalized difference vegetation index (NDVI), several years after large mass flows, e.g. about 10 years for the Kolka–Karmadon rock-ice avalanche. From the large number of detachments which occurred under very similar conditions we conclude that rising temperatures combined with soft, fine-grained sediments are very critical components favouring the detachment of entire valley glaciers.

Silvan Leinss et al.

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Silvan Leinss et al.

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Short summary
We document a cluster of glacier detachments in the Petra Pervogo range, Tajikistan, between 1973 and 2019. In four glaciated catchment areas, we identified 13 mass flows of up to 19 km length. Though globally extremely rare, nine events represent large-scale glacier detachments and seven of them occurred between July and September in years with temperatures above the past 46-years trend. Similar to other detachments the detached glaciers are relatively short and rest on soft erodible sediments.
We document a cluster of glacier detachments in the Petra Pervogo range, Tajikistan, between...
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