Pakistan, May 16 -- Once a stable wonder of nature, Argentina's Perito Moreno Glacier is showing signs of alarming change. Local guides and glaciologists are concerned about the glacier's recent sharp increase in the size of the icebergs breaking off from its face. The glacier is well-known for its breathtaking calving events, in which enormous chunks of ice break off and fall into the waters of Lake Argentina.

The glacier, which stands in Los Glaciares National Park in southern Patagonia, had long been a draw for tourists, many of whom gather on viewing platforms to witness the dramatic cracking sounds that signal the collapse of ice blocks up to 70 metres (230 feet) tall - equivalent to a 20-storey building. However, this natural spect...