ИСТИНА

The glaciers and ice caps in the Arctic are experiencing significant changes, manifested, in particular, in the intensification of their dynamic instability. Here we present data on a large-scale surge in the western basin of the Vavilov ice cap on Severnaya Zemlya. The ice cap is located at 79.30°N, 95.47°E, with total ice cap area 1781.4 km2 according the Randolph Glacier Inventory (Fig. 1a). The data were derived from satellite imagery (Landsat-1, 5, 7, 8, Terra ASTER, Sentinel-1 and Corona), goLIVE and Sentinrel-1 ice velocity data sets, and also from our airborne RES survey in 2014. Analysis of 28 space images from 1963 to 2017 showed that front advance has evolved during all this period (Fig. 1b). 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 a-1. In 2014 the volume of advanced snout was at least 4 km3. The rate of advance reached the maximum of 7 km a-1 in 2016. From 1963 to 2017 the glacier front moved forward by 11.7 km and its area increased by 134,1 km2 (by 47% relative to basin area in 1963), that was accompanied by spreading of crevasse zone up the glacier. Figure 1. Vavilov ice Cap, Severnaya Zemlya: a) ice cap location and outlines of its western basin; b) glacier front position from 1963 to 2017. 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. might be 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 debris-laden 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. Acknowledgements: This study is supported by the Russian Foundation for Basic Research, grant 16-35-00333, and by Russian National Foundation, grant 14-37-00038.