Perito Moreno Glacier lays in the southern Andes Mountains, near Santa Cruz, Argentina, and it is one of nearly 50 glaciers fed by the Southern Patagonia Ice Field. It drives thousands of tourists every year.
Periodically the glacier advances over the L-shaped lake Lago Argentino forming a natural dam which separates the two halves of the lake when it reaches the opposite shore. The water-level on the Brazo Rico side of the lake can rise by up to 30 meters above the level of the main lake. The enormous pressure produced by the height of the dammed water finally breaks the ice barrier holding it back, in a spectacular rupture event.