If you're not familiar with the Missoula megafloods, the Geoblogosphere got an excellent summary with some excellent pictures from Anne Jefferson for last month's Accretionary Wedge. (BTW, shameless plug, this month's wedge, "Inspiration," is up over at Volcanista's.)
I was tipped off about this glacial lake and the periodic collapse of the dam by a post on the Google Sightseeing Blog. They have a link to a video of the most recent collapse event (last July), but it's not embeddable, nor does it appear to actually breach the ice dam and release the pent-up lake. However, a search at YouTube for "perito moreno ruptura" yields 39 results; a search for the English version, "perito moreno rupture" yields 14. The above is merely the first I watched that showed a full collapse and release. Wow!