GEORADAR MONITORING OF THE PERETOLCHIN GLACIER (EASTERN SAYAN)
For the first time, a monitoring was carried out for assessing the volume of the ice of the Peretolchin Glacier in the Munku-Sardyk mountain range (Eastern Sayan) using georadar profiling both directly to measure the thickness of the ice and to refine the parameters of mathematical models for determining the volume of the glacier. Based on results of the area radar survey, the volume of the various structures of the glacier (firn, the main icy body, and bottom moraines) was assessed. 3D models of these components of the glacier have been constructed. It was found that, in comparison with results of georadar profiling for other glaciers, the modern bed of the Peretolchin Glacier consists of deposits of the previous glaciation which ended 11 ka. Measurements of the ice thickness on the northern Peretolchin Glacier were made in June 2014, and in May 2016 and 2017, with a constant increase in the study area using the Oko-2 radar with the ABDL Triton antenna unit at 100 MHz. Maps of the ice thickness of the Peretolchin Glacier were updated, and its volume was determined, equal to 0,007 ± 0,0001 km <sup> 3 </sup> . The section of the glacier of direct study (the lower open part) measures 0,00297 km <sup> 3 </sup> . The method of sections, taking into account the relief of the glacier from additional profiles, proved to be the most accurate. In the surveyed portion, the proportion of firn, the ice and the bottom moraine makes up 25 %, 29 and 46 %, respectively. On the other hand, the proportion of the clean ice reduces from the middle part of the glacier to its bottom. Over more than 100 years, the Peretolchin Glacier (northern) has decreased in length, area and volume by factors of 1,75, 2,9 and 3,71, respectively. It has been established that the rate of reduction of the Peretolchin Glacier has been increasing since 2009.