May 31, 2012
The Jorge Montt Glacier is one of the main tidewater glaciers of the Southern Patagonia Icefield. The glacier has been the focus of ongoing annual observations by the Laboratorio de Glaciologia at the Center for Scientific Studies, University of Chile. Two recent papers highlight the dramatic changes this glacier is undergoing. The glacier has retreated 19.5 km from 1898-2011 (Rivera et al, 2012a). A recent photograph of the terminus from Andrés Rivera indicates the extensive crevassing and calving of icebergs indicating the high very high velocities.. The velocities were determined from tracking of salient features for an 11 month period using time lapse photography and indicated a mean velocity of 13 meters/day, with maximum velocities of up to 33 meters/day, in the center of the glacier (Rivera et al, 2012b). These velocities rival the high velocities on the faster Greenland outlet glaciers and San Rafael Glacier, Chile. They did not observed seasonal velocity changes. This paper provides a nice visual of the velocity, top image. The velocity and retreat tend to increase when water depth increases. The mean water depth at the calving front has declined from over 260 m 1997-2003 to closer to 220 m 2003-2011, bottom image indicates the water depths from Rivera et al (2012a). . . A map of the long term retreat of the glacier is provided in both papers, here we examine a closeup view of the lower glacier from Landsat imagery in 1997, 2003 and 2011. The glacier retreat peaked during the 1990-2000 period with 8.5 km of retreat. The lake widened and deepened at the calving front for that period. The yellow arrow indicates the 1997 terminus, burgundy arrow 2003 and orange arrow 2011. The green arrows point the expansion of exposed bedrock areas on the east margin of the glacier from 1997-2011. Retreat from 1997-2003 was 2250 m, 375 m/year. Retreat from 2003-2011 was 2000 meters, 250 m/year. In 2011 an additional nunatak has emerged as the glacier has thinned. The 2011 terminus is near a point where the lake appears it will widen again, the potential depth is hard to assess. The map from Rivera et al (2012a) indicates at least a short term deepening at the ice front, this is at the same point as a modest lake width reduction. . Below is a closeup of the changes 12-14 km upglacier of the terminus indicating the rapid thinning from 2003 to 2011 expanding the bedrock exposed at point B and exposing the new nunatak at Point C. The retreat of this glacier follows the regional pattern observed by the Laboratorio de Glaciologia on other glaciers such as Gualas Glacier, Nef Glacier, Alemania Glacier, Tyndall Glacier and Colonia Glacier.