An ice dam at Argentina's Perito Moreno glacier has collapsed, creating an impressive spectacle not seen since July 2008, although few tourists were awake to experience the moment.
Several tonnes of ice fell off the 60-metre ice dam into Lago Argentina at the national park in southern Santa Cruz province.
About 5000 tourists had been in the park on Saturday awaiting the ice show, park rangers said.
But the slight movement of ice that began on Wednesday turned into an avalanche only about 4am, leaving visitors disappointed.
Only a group of rangers saw the collapse, which created a crash heard several kilometres away, accelerated by heavy rainfall overnight.
"The noise was very great, it was coming down in buckets," park ranger Carlos Corvalan said.
Perito Moreno, one of the biggest tourist attractions in Argentina, is one of the largest glaciers on the Patagonian ice cap.
The glacier has a travel speed of 1.7 metres a day in its central part and periodically creates an ice dam which collapses from the pressure of the advancing glacier.
The glacier was named after one of the first explorers in Argentine Patagonia.