The topology at the toe of Perito Moreno provides for a spectacular vantage point. The glacier essentially gets split in two by a spit of land that separates a small section of Lago Argentino from the rest. As a result, the lake levels might start to differ as the glacier keeps water from passing between the two parts. And, most excitingly, every twenty years on average, the pressure exerted by the higher of the two lakes is enough to cause a catastrophic collapse of the ice dam. If you want to pick a day to see Perito Moreno at its finest, choose one of these days. However after an event in 2008 when the ice dam failed during winter, there is some debate whether it will ever form very strongly again, possibly because of global warming. Too bad.