D. Petrakov

Glacial geomorphology of the Altai and Western Sayan Mountains, Central Asia

In this article, we present a map of the glacial geomorphology of the Altai and Western Sayan Mountains, covering an area of almost 600,000 km2. Although numerous studies provide evidence for restricted Pleistocene glaciations in this area, others have hypothesized the past existence of an extensive ice sheet. To provide a framework for accurate glacial reconstructions of the Altai and Western Sayan Mountains, we present a map at a scale of 1:1,000,000 based on a mapping from 30 m resolution ASTER DEM and 15 m/30 m resolution Landsat ETM+ satellite imagery. Four landform classes have been mapped: marginal moraines, glacial lineations, hummocky terrain, and glacial valleys. Our mapping reveals an abundance of glacial erosional and depositional landforms. The distribution of these glacial landforms indicates that the Altai and Western Sayan Mountains have experienced predominantly alpine-style glaciations, with some small ice caps centred on the higher mountain peaks. Large marginal moraine complexes mark glacial advances in intermontane basins. By tracing the outer limits of present-day glaciers, glacial valleys, and moraines, we estimate that the past glacier coverage have totalled to 65,000 km2 (10.9% of the mapped area), whereas present-day glacier coverage totals only 1300 km2 (0.2% of the mapped area). This demonstrates the usefulness of remote sensing techniques for mapping the glacial geomorphology in remote mountain areas and for quantifying the past glacier dimensions. The glacial geomorphological map presented here will be used for further detailed reconstructions of the paleoglaciology and paleoclimate of the region.

Monitoring of Bashkara Glacier lakes (Central Caucasus, Russia) and modelling of their potential outburst

Glacier lakes pose threat to downstream settlements and infrastructure. In recent decades the number and area of lakes have been growing at an accelerating rate due to worldwide glacier shrinkage. In the Russian Caucasus this process is understudied. We present results obtained during a 12-year (1999–2010) continuous field monitoring of the Bashkara proglacial lakes group, which we identified as the place with the highest GLOF risk in the region. Recession of the parent Bashkara Glacier was the main driver of the rapid expansion of the lower Lake Lapa. The upper Lake Bashkara has not been enlarging, but its water level has shown significant inter- and intra-annual fluctuations. The lake outburst probability has increased in recent years, and in 2008 we observed surface overflow over the moraine dam. Taking into account that in the late 1950s lake outbursts at this site led to large-scale glacial debris flows, we have simulated a potential outburst using River and FLO-2D software and carried out hazard zonation. An early warning system has been designed and established at Lake Bashkara, and measures to mitigate risk have been proposed. Rapid change of proglacial lakes requires regular monitoring in ‘hot spot’ areas where the GLOF hazard is high and is dynamically changing.

Mass-balance reconstruction for Glacier No. 354, Tien Shan, from 2003 to 2014

Abstract This study presents a reconstruction of the seasonal mass balance of Glacier No. 354, located in the Akshiirak range, Kyrgyzstan, from 2003 to 2014. We use a distributed accumulation and temperature-index melt model driven by daily air temperature and precipitation from a nearby meteorological station. The model is calibrated with in situ measurements of the annual mass balance collected from 2011 to 2014. The snow-cover depletion pattern observed using satellite imagery provides additional information on the dynamics of mass change throughout the melting season. Two digital elevation models derived from high-resolution satellite stereo images acquired in 2003 and 2012 are used to calculate glacier volume change for the corresponding period. The geodetic mass change thus derived is used to validate the modelled cumulative glacier-wide balance. For the period 2003–12 we find a cumulative mass balance of –0.40±10mw.e.a-1. This result agrees well with the geodetic balance of –0.48±0.07mw.e.a-1over the same period.

Accelerated glacier shrinkage in the Ak-Shyirak massif, Inner Tien Shan, during 2003–2013

The observed increase in summer temperatures and the related glacier downwasting has led to a noticeable decrease of frozen water resources in Central Asia, with possible future impacts on the economy of all downstream countries in the region. Glaciers in the Ak-Shyirak massif, located in the Inner Tien Shan, are not only affected by climate change, but also impacted by the open pit gold mining of the Kumtor Gold Company. In this study, glacier inventories referring to the years 2003 and 2013 were created for the Ak-Shyirak massif based on satellite imagery. The 193 glaciers had a total area of 351.2±5.6km(2) in 2013. Compared to 2003, the total glacier area decreased by 5.9±3.4%. During 2003-2013, the shrinkage rate of Ak-Shyirak glaciers was twice than that in 1977-2003 and similar to shrinkage rates in Tien Shan frontier ranges. We assessed glacier volume in 2013 using volume-area (VA) scaling and GlabTop modelling approaches. Resulting values for the whole massif differ strongly, the VA scaling derived volume is 30.0-26.4km(3) whereas the GlabTop derived volume accounts for 18.8-13.2km(3). Ice losses obtained from both approaches were compared to geodetically-derived volume change. VA scaling underestimates ice losses between 1943 and 2003 whereas GlabTop reveals a good match for eight glaciers for the period 2003-2012. In comparison to radio-echo soundings from three glaciers, the GlabTop model reveals a systematic underestimation of glacier thickness with a mean deviation of 16%. GlabTop tends to significantly underestimate ice thickness in accumulation areas, but tends to overestimate ice thickness in the lowermost parts of glacier snouts. Direct technogenic impact is responsible for about 7% of area and 5% of mass loss for glaciers in the Ak-Shyirak massif during 2003-2013. Therefore the increase of summer temperature seems to be the main driver of accelerated glacier shrinkage in the area.

Geophysics in Glacial-hazard Initiation Zones, Russian Caucasus

Numerous glacier lakes have formed in recent decades due to worldwide glacier retreat induced by climate change. These lakes, dammed by glaciers and moraine ridges, are hazardous because of potential glacial lake outburst flows (GLOF). The GLOF probability is increasing in the Russian Central Caucasus, like at the Bashkara glacier which has been extensively studied, but detailed information about the ground is missing. A pilot geophysical campaign carried out during summer 2009 tested GPR and resistivity profiling at this site, using towed-systems to facilitate acquisition. The GPR measurements were successful with penetration depth down to 70 m on icy ground, though the acquisition was difficult due to rough ground terrain. The results show that GPR measurements would greatly improve the knowledge of the internal structure of that complex zone, thus helping for hazard assessments, but more field work is needed, including CMP measurements. The resistivity measurements were not that successful, the towed system requiring repeating each profile with increasing offset, the progression on the ground being heavy. Only the very first meters of the ground were retrieved, i.e, not really providing useful information. Results and experience gathered in 2009 are now analysed to plan another campaign summer 2011.

Modeling potential scenarios of the Tangjiashan Lake outburst and risk assessment in the downstream valley

This research is devoted to Tangjiashan Lake, a quake landslide-dammed lake, situated in Sichuan Province, China, which was formed by a landslide triggered by the Wenchuan Earthquake on 12 May 2008. A STREAM_2D two-dimensional hydrodynamic model of Russia was applied to simulate the process of two flood scenarios: 1, lake dam outbreak, and 2, dam overtopping. An artificial dam outbreak was made after the earthquake to lower the water level of the lake in 2008, which led to a great flood with a maximum water discharge of more than 6400 m3/s. The negative impact of the flood was reduced by a timely evacuation of the population. Flood hazards still remain in the event of new landslides into the lake and lake dam overtopping (Scenario 2), in which case a maximum water discharge at the dam crest would reach 5000 m3/s, placing the population of Shabacun and Shilingzi villages in the zone of flood impact.

Geophysical Investigations of Unstable Mountain Slopes in Jotunheimen, Norway

Studying glacial and mountain hazards is necessary as the world seems to face major climate changes, which may increase the frequency of catastrophic events, e.g., debris flows. The latter processes are well understood, but changes in their frequency and relationships to climatic variability are not. In the present study, aiming at imaging an entire debris-flow system from the release area to the depositional area, correlations of lake sediments to specific slope deposits on land are looked for by using a combined approach including geology, sediment-core analysis and geophysical surveys (ERT, GPR and seismic). Our overall goal is to create a chronology of debris-flow events from lake Leirvatnet in order to be able to compare debris-flow records with existing paleo-climatic data and evaluate the climatic impact on debris-flow frequency in a long-term perspective. Following the mapping and thickness estimate of the sediment cover on the lake bottom obtained from GPR, we are evaluating the spatial continuity of reflectors associated with sections of high debris-flow activity to relate them to debris-flow deposits on land (imaged by ERT, GPR and seismic), having a complete Holocene sedimentological history from the lake. Actual results indicate a large temporal variability in debris flows.