The collapse of the Perito Moreno glacier near the city of El Calafate in the Patagonian province of Santa Cruz, southern Argentina, attracts thousands of tourists. This year, the leading edge of the glacier collapsed March 4.

The glacier, a massive tongue of ice in the Santa Cruz province that covers 250 square kilometres (97 square miles), advances every year 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 sheets come tumbling down. The phenomenon repeats itself at irregular intervals, with the last major ice falls occurring in 2008, Reuters reports.

Check out below some of the pictures of the glacier as tourists wait to see if it collapses.