ИСТИНА

We use satellite imagery (1963- 2015) and airborne radar data (September 2014) to document rapid acceleration and surge of western sector of the Vavilov ice cap, Severnaya Zemlya. In the 1960s-70s, the ice margin there was stable and followed the general smooth outline. Only slight advance by 80 meters in average occurred in this decade. Thereat the margin was land-terminated and separated from sea by ram- part of "dead" sediment-laden ice up to 0.5 km width. In 1980s- 2000s the margin began to bulge towards the sea with mean rate 70 m a1, so that in 2012 the outlet lobe of 2.4 km length, 8 km width, and 12.36 km2 area was formed. When advancing it pushed forward the "dead" ice belt that framed the front. In 2012, the protrusion of front dramatically accelerated: rate of advance in- creased from 180 to 1540 m a1 (maximum up to 2.4 km a1). In September 2014 the area enlargement rate reached 37 000 m2 d1.The surg- ing lobe with 3.142 km3 of ice occupied an area of 30.14 km2, and embossed into the sea by 4.5 km. Its thickness reached 178 m (104 m mean), with bedrock at average depth -40 m (minimum -67 m) below sea level. The framing rampart almost completely collapsed; the margin spread and spitted into fingers, but, nev- ertheless, it advanced further by February 2015. Only shallows waters seems to prevent the major eruption of icebergs and front destruction. Radarograms show no large barriers or overdeepenings on bedrock, but reveal a feature that might be remains of marginal structure of 1963, also traceable through ice on imagery. Possibly, it is the roots of the cold-based plugging belt that was in most part cut off and pushed to the sea, where ice movement accelerated on soft unfrozen marine sediments.