A natural ice dam in southern Argentina broke open spectacularly on Wednesday the first time it has burst in winter, prompting experts to say climate change was the reason.
The 60m high wall of ice from the Perito Moreno glacier that usually divides Lake Argentina in Patagonia bursts from time to time under the built-up pressure of the held-back water.
The event is one of the prime tourist attractions of Argentina.
But until now it has occurred in the warmer seasons.
This year's breaking of the dam was forecast well in advance, though the exact day was unknown, so relatively few visitors about 300 were on hand to photograph the phenomenon.
Scientific experts' predictions that the rupture could still be days away meant Argentine television stations were caught unprepared and were forced to air images of the last collapse.
An internet broadcast, however, caught this year's rupture live for an estimated 150,000 viewers.
One unidentified female witness said, ''It was like an explosion. Everything shook.
''It was stirring, rousing. I was overjoyed.
'' I didn't know what to do.
''I screamed and clapped like a crazy person, and I think I even cried.''
The glacier's ice dam does not break with any regularity, on average just once every four to six years. It remained intact for 16 years until the last time it broke, on March 14, 2006, when 10,000 visitors and millions of television viewers watched the awesome show put on by nature.
Los Glaciares National Park director Carlos Corvalan said of Wednesday's breaking of the dam, ''This is the first time the glacier has broken up in winter.
''It could be related to global warming as rising temperatures affects ice friction.''
A geographer and glaciology professor at the University of Chile, Francisco Ferrando, said global warming was probably causing the ice dam to become thinner.
''There is also increased loss of mass in the front of the glacier,'' Professor Ferrando said.
''This would result in fewer and shorter periods in which the ice is in contact with the basin of the lake,'' he said.
The spectacular blue-white Perito Moreno glacier is the largest of 356 rivers of ice in Los Glaciares National Park, and each year is visited by thousands of tourists from South America and elsewhere around the world.
It is one of the largest glaciers in the world, measuring 275sqkm and 5km wide at its mouth.
It is 2800km south-east of Buenos Aires. AFP