Ice dynamics and basal properties of Sofiyskiy glacier, Altai mountains, Russia, based on DGPS and radio-echo sounding surveys

Central Asian glaciers, compared to other glaciers in the world, should exhibit a different response to changing climate owing to (1) the extreme continentality that gives rise aridity and large seasonal temperature variations, and (ii) the coincidence of accumulation and ablation seasons in summer. A detailed 4 year field survey has been carried out on Sofiyskiy glacier in the south Chuya range (Altai mountains), Russia. Field observations reveal that this glacier retreated steadily during the 20th century at a rate of 18.3 in a(-1) considerably faster than Maliy Aktru glacier, 30 kin to the north. Based on radio echo sounding (RES), the subglacial topography of Sofiyskly glacier has been reconstructed, and stake and snow-pit measurements enable the determination of surface velocity and mass balance. Basal sliding plays an important role in Sofiyskiy glacier's behaviour, as is shown by a force-balance analysis. An analysis of RES measurements yields the bed reflection power (BRP). Using the three-layer reflectivity model of Born and Wolf (1986), the BRP is compared with the theoretical bed reflectivity for two contrasting layers of varying porosity and thickness. Results indicate that Sofiyskly glacier possibly exhibits a polythermal regime.