"A spectacle unseen for 16 years occurred in Patagonia this week: a natural dam of blue ice gave way to crushing lake waters trapped behind it, finally breaking apart.
Watching tourists applauded as a section of the 60-metre high Perito Moreno glacier collapsed and the waters of the dammed southern arm of Lago Argentino surged through it. Since last October this section – known as Brazo Sur - had been blocked off from the rest of the lake by the glacier's flowing ice tongue, which extended a solid wall of ice across the narrow water channel.
The 30-km-long Perito Moreno glacier is the most famous part of the Parque Nacional Los Glaciares in Argentina, a UNESCO World Heritage Site. It is the subject of a long-term study by the University of Innsbruck's Institute for Meteorology and Geophysics, with in-situ observations supplemented by ESA satellite data.
EDIT
"What makes Perito Moreno so interesting to us is that it is one of the few Patagonian glaciers that has advanced during recent days. It dams the Brazo Sur on a periodic basis, the previous time being 1988, then some 20 times before that. It first occurred in 1917, and we know it was the first time because a several-hundred-year old forest was submerged as a result." Once the glacier blocks the channel between the Brazo Sur, water and the main section of Lago Argentino, water and ice commence a kind of duel. Water from melting glaciers and running down from mountain drains into the trapped section of lake: its height rose by eight metres in the last five months; at the time of the fracture the rate of increase was ten centimetres a day."
EDIT
http://www.sciencedaily.com/releases/2004/03/040322080132.htmIncidentally, MSNBC has a video clip of the collapse on their website - it's pretty impressive!
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