Dynamic features of thinning and retreating Glaciar Upsala, a Lacustrine Calving Glacier in southern Patagonia

Glaciar Upsala, which calves into a lake on the eastern side of the Hielo Patagonico Sur, South America, has significantly retreated by 5 km during the last 20 yr. The glacier near the terminus has thinned by about 33 m from 1990 to 1993. Bathymetric surveys made in 1998 at the proglacial lake revealed the existence of bedrock rises spreading out from exposed islands in the western part of the lake. Between 1978 and 1990, the western half of the glacier terminus was located at the bedrock rises, which suggests that the front fluctuations were strongly controlled by the bed topography. During 1990-93, the glacier terminus was located upstream from the bedrock rises, and it is considered to have been floating after estimation of the buoyancy. Significantly large extending strain rate of 0.22 a(-1) was deduced from the continuity consideration in 1990-93. These results are discussed with those obtained at Columbia Glacier, Alaska.