Agustin Magall  /  AP
Perito Moreno's ice tunnel collapses Wednesday into Lake Argentino.
updated 7/8/2008 3:49:11 PM ET 2008-07-08T19:49:11

After several days of pieces calving off, a famous glacier on Wednesday saw the collapse of an enormous ice tunnel that forms every four to five years.

The spectacular crash of ice into Lake Argentino usually occurs during the Southern Hemisphere's summer, September through May.

The tunnel collapsed before a scattering of people visiting the Perito Moreno glacier during the winter off-season.

The glacier cuts the lake in two. Water flows beneath the ice when the level on one side of the lake rises higher than the other. The rushing water erodes the ice and sometimes causes it to collapse.

Scientists debate whether global warming is responsible. Some say the winter melting phenomenon also happened in 1917 and 1951.

Climate change is causing roughly 90 percent of the world's mountain glaciers to shrink, said Lonnie Thompson, a glacier expert at Ohio State University who this year received a National Medal of Science from President Bush.

"The picture points unfortunately (to) massive loss of ice on land, which has huge implications for future sea level rise," he said.

Agustin Magall  /  AP
Perito Moreno's tunnel before it collapsed.
The U.N. Intergovernmental Panel on Climate Change says global temperatures are likely to warm from 2 degrees to 11.5 degrees Fahrenheit by the end of the century if no major efforts are undertaken to reduce greenhouse gas emissions.

In Bolivia, north of Argentina, the capital La Paz gets a third of its water from a tropical Andes glacier that's nearly vanished.

Scientists predict that all the glaciers in the tropical Andes will disappear by mid-century. The implications are dire not just for La Paz but also for Quito, Ecuador, and Bogota, Colombia. More than 11 million people now live in those burgeoning cities.

Copyright 2008 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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