The Perito Moreno Glacier in Los Glaciales National Park is rightly the best known and most visited of the many glacier tongues flowing down from the Patagonian Ice Sheet (cf. my book The Formation of Mountains). What makes it special is that it slides across into a side branch of Lago Argentino. When it reaches the opposite shore, it dams up the southern part of the lake by 10 or 20 metres. This is clearly visible on the shore of the upper part of the lake, which is bare and partly lined with dead trees. At some point, every few years (most recently a few months ago), the dam of ice breaks. At the moment, the glacier barely reaches the other bank, but the water flows out through two gates made of ice.
Few will experience such a bursting of the dam, but since the far bank is a perfect viewing pulpit, you can see the glacier from angles that are impossible on other glaciers. And the shimmering blue ice wall, broken into towers, is truly an impressive sight from any angle.
A veritable labyrinth has been built from steel and wood on the slope, which I walk through several times with many long stops over the course of a whole day.
I’ve often heard that the glacier is one of the few that advances rather than retreats. This is, of course, nonsense. Since the glacier front is always removed by damming and then bursting of the dam, it has always just made it to the other bank, and the glacier always stays about the same length. Of course it flows downwards, very quickly in fact, but even a glacier that retreats actually flows downwards, it is only the melting that is faster than the replenishment from above. How well the accumulation area of the glacier, i.e. the Southern Patagonian Ice Sheet, is doing is another question altogether. Overall, Patagonia’s glaciers are among the fastest melting in the world, and this will certainly affect the Perito Moreno Glacier at some point.