...The Perito Moreno glacier is seen after the rupture of a massive ice wall. The glacier, a massive tongue of ice in the Santa Cruz province that covers 250 square kilometres (97 square miles), advances yearly into a lake, known as Lago Argentino. As Perito Moreno moves forward, it cuts off a river feeding the lake. Water builds up pressure and slowly undermines the ice, forming a tunnel until ice comes tumbling down. The phenomenon repeats itself at irregular intervals, with the last major ice falls occurring in 2008