Tourists look at the Perito Moreno glacier after the rupture of a massive ice wall near the city of El Calafate in the Patagonian province of Santa Cruz, southern Argentina, Mar 4, 2012.  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. [Photo/Agencies]

Tourists pose for a picture as they await to see the rupture of the leading edge of the Perito Moreno glacier near the city of El Calafate in the Patagonian province of Santa Cruz, southern Argentina, Mar 2, 2012. [Photo/Agencies]