ИСТИНА

Here we present data on a large-scale surge in the western basin of the Vavilov ice cap on Severnaya Zemlya, derived from satellite imagery (Landsat-1, 5, 7, 8, Terra ASTER, Sentinel-1 and Corona), and supported by airborne RES-2014. Analysis of 28 space images from 1963 to 2018 showed that front advance has evolved during all this period. In the first decade from 1963 to 1973 the advance was very slow from 2-5 to 12 m a-1. Since the 1980s, the advance began to accelerate from the first tens of m a-1 to the first of hundreds m-1 in the 2000s, the turning point came in 2012, when the front was advancing with a velocity about 0.5 km/year. In 2014 the volume of advanced snout was at least 4 km3. The rate of advance reached the maximum of 9.2 km a-1 in 2016. From 1963 to 2017 the glacier margin moved forward by 11.7 km and its area increased by 134,1 km2 (by 47 % relative to basin area in1963), that was accompanied by spreading of crevasse zone up the glacier. Ice surface velocity reached a maximum of 25.4 m d-1 in 2016, and in 2017 reduced to 6.8 m d-1. We assume that the initial activation of the southern and western margins of the ice cap in second half of XX c. was a response to the climate signal occurred possibly several centuries ago. As a result, the ice crevassing accompanied with cryo-hydrologic warming and reinforced by positive feedback, led to the instability of the glacier and displacement of the marginal stagnant belt of debrisladen ice frozen to the bed. The surge was facilitated by change of bedrock conditions as the ice lobe progressed offshore from permafrost coastal zone to the area of soft marine bottom sediments with low shear strength. The surge seems to be also stimulated by anomalously warm summer of 2012. This study is supported by the Russian Foundation for Basic Research, grant 16-35- 00333, by Russian National Foundation, grant 14-37-00038 and grant № 01201352474. Europe's largest ice-covered volcanic massif of Elbrus (5642 m) is a unique object for studying the reaction of mountain glaciers to modern climate changes. The feeding areas of the Elbrus glaciers are in conditions of almost free atmosphere, while their languages descend to heights of about 3000 m, covering the maximum diversity of conditions in the entire glacial zone of the Central Caucasus. One of the most important indicators characterizing the regime and dynamics of its glaciers are changes in the speed of ice movement. The estimation of this indicator becomes especially actual in conditions of negative mass balance, observed annually during the last 11 years (2006-2017). In this paper, the data of the radar satellites (Sentinel-1 A and B) and digital terrain models are used to solve this problem. Selected Sentinel interferometric pairs on the Elbrus glaciation area were obtained during the ablation period of 2017. Evaluation of the movement of the glacial surface between the images of each pair was performed using the displacement tracking function in the SNAP 5.0 toolkit. The spatial resolution of the radar data varies from 5 to 20 m. The obtained surface velocities of the Elbrus glaciers range from 0 to 0.6 m/day. The paper analyzes the spatial and temporal variability of this indicator on the basis of comparison with the data of existing ground and remote measurements and gives an assessment of the possibility of using the results obtained in calculations of the mass balance of glaciers in Elbrus. This study is supported by the Russian Foundation for Basic Research, grant 18-05- 00838.