Upsala Glacier Retreat, Patagonia Icefield (NASA, International Space Station, 10/02/13)
Upsala Glacier Retreat and Patagonia Icefield are featured in this image photographed by an Expedition 37 crew member on the International Space Station. This photograph highlights the snout of the Upsala Glacier (49.88S 73.3W) on the Argentine side of the North Patagonian Icefield. Ice flow in this glacier (white mass, left) is from the north (left). Dark lines of rocky moraine within the ice give a sense of the slow ice flow from left to right. A smaller side glacier joins Upsala at the present-day ice front -- the wall from which masses of ice periodically collapse into Lake Argentino. In this image the 2.75-kilometer-long wall casts a thin, dark shadow. The surface of Lake Argentino is whitened by a mass of ice debris from a recent collapse of the ice wall. Larger icebergs that have calved appear as white dots on the lake surface at right.
Remotely sensed data, including detailed astronaut images such as this, have recorded the position of the ice front over the years. Even though the ice actually flows slowly southward, comparison of this October 2013 image with older data (not shown) indicates that the ice wall of the glacier has moved backwards -- upstream -- an average of 3.6 kilometers since early 2002. This so-called "retreat" is believed by scientists to indicate local climatic warming in this part of South America. The warming not only causes the ice front to retreat but more importantly, causes overall thinning of the glacier ice mass, as a study of 63 glaciers in Patagonia has shown is now a general trend (Rignot et al. 2003). Ice-front retreat is now known to be related to volumetric loss due to melting. Water color is related to glacier flow. Lake Argentino receives most of the ice from the glacier and thus also receives most of the "rock flour" (rocks ground to white powder by the ice scraping against the rock floor of the valley) from underneath the glacier. Glacial flour turns the lake water a gray-green hue in this image. The darker blue of the smaller lakes (top) indicates that they are receiving much less rock flour.
Image credit: NASA
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