Perito Moreno, world's first superstar glacier set to disappear

Glacier Perito Moreno was once considered a rarity: one of Patagonia's only stable glaciers. But scientists have found the glacier is now in sudden and probably irreversible retreat—and this collapse is a warning for the world's remaining ice.

- NEIL GLASSER

Perito Moreno is unusually accessible for such a large and spectacular glacier, with nearly 700,000 visitors a year. Fed by abundant snowfall high up in the Andes, the glacier descends through beech forest to end in Lago Argentino. From here, tourists can get up close and personal on a specially constructed observation deck to watch as icebergs break off the front of the glacier, a process called iceberg calving. Icebergs regularly crack off the ice front and tumble into the turquoise lake below. But now, it's on the verge of disappearing.

While 90 per cent of Patagonia's glaciers are shrinking, Perito Moreno has long been the exception thanks to its unique setting. The glacier flows into a narrow channel of Lago Argentino, where it sometimes advances far enough to block one arm of the lake entirely. This forms a natural ice dam, cutting off water flow and causing water to build up behind it. When the pressure becomes too much, the dam bursts.

These ruptures typically happen every few years, but timing can be unpredictable. The glacier has been stable up to now and has not been shrinking because it terminates in relatively shallow water where it bumps into the opposite shore.