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

Abstract

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.

Natural Hazards in a Changing World: Methods for Analyzing Trends and Non‐Linear Changes

“…Monitoring processes may be interrupted in regions with disputed borders, for example, in High Mountain Asia, where data are confidential and physical access to those regions can be limited for nonresidents. Those regions often provide inconsistently filled and poorly annotated databases, and international recognition of natural hazards remains scant (Leinss et al, 2020). The Himalayas, for example, still have no permanently operating weather station above 5,000 m a.s.l., where climate-driven hazards such as flash floods, landslides, debris flows, or glacier detachments can develop (Salerno et al, 2015).…”