Scientists were at first puzzled out how a glacial lake like this one could abruptly disappear. Photographer: George Wood / Agency: Dreamstime.com

Sometime in May 2007, a glacial lake in southern Chile disappeared. Chilean surveyors reported in March that the lake was its usual siz­e, 100 feet deep and covering an area around five acres. Located in Bernardo O'Higgins Park, in the southern Andes mountains, the lake is (was) rarely visited and didn't even have a name. When Chilean forestry officials arrived, they were surprised to find nothing more than "chunks of ice on the dry lake-bed and an enormous fissure" where the unnamed lake had once been [Source: The Guardian]. Five miles away, a river that was once more than 130 feet wide barely flowed. What could cause such a massive disturbance to make an entire lake and much of a river disappear?

Global warming seems to be the knee-jerk response lately whenever a dramatic environmental change is observed. Indeed, global warming is a big concern for lakes, as many bodies of water are experiencing receding water levels due to a combination of low rainfall and high temperatures. In the Magallanes province, where the lake is located, the Tempano and Bernardo glaciers are shrinking, and both of those glaciers contributed water to the lake. Experts like Gino Casassa and Andres Rivera, both glaciologists, point to global warming as the cause of the glaciers' melting. So global warming was immediately considered as a possible cause, but when investigating the lake, scientists considered several other possibilities.



One theory scientists considered was that an earthquake in the area opened a fissure in the earth, which sucked down the lake. Southern Chile experiences hundreds of small earthquakes a year, and a fairly large tremor was detected on April 21. The fissure observed in the empty lake bed could have provided an outlet for the lake water to escape, much like a stopper being pulled from a sink.

A second possibility draws in part on global warming and the melting of glaciers. Glacial lakes often develop behind natural dams, which are made of ice or a pile of rock and earth debris a glacier leaves behind (called a moraine). Once the dam is broken, whether by an avalanche, earthquake, warming or other event, water bursts through and the lake sometimes drains.

It took scientists several weeks before they were able to discover the answer because the site is very remote -- about 4,900 feet above sea level and 1,250 miles south of Chile's capital, Santiago. But in early July 2007, scientists got their answer.

An investigation has revealed that too much water was the problem. The melting Tempano and Bernardo glaciers filled the lake beyond the crater's capacity. The increased pressure broke the lake's moraine through which water flowed out, later ending up in the ocean. The lake is refilling as the chunks of ice on the lake bed melt, though Chilean scientists pointed out that global warming did have a serious effect. Glaciers naturally melt and reform, but warming is causing the Tempano and Bernardo glaciers to melt more than they should.

For some lakes, rapidly appearing or disappearing is part of a natural process. The lake in Chile did not exist 30 years ago, though, again, global warming is likely affecting the process. Some lakes, including many in Alaska and Florida's Lake Jackson, go through a similar process regularly, disappearing and reappearing during certain seasons, or from year-to-year or decade-to-decade.