France to Drain Glacial Lake That Threatens Thousands
August 25, 2010 8:15:31 PM
French engineers are prepping to drain a dangerous lake hidden underneath a glacier on Mont Blanc before the lake breaches its icy confines and floods the Saint Gervais valley, home to 3,000 people.
Valley residents are well acquainted with the raw power of glacial outbursts from Mont Blanc. In 1892, a lake broke through its frozen container, surged into the valley and killed 175 people.
To prevent a repeat of this catastrophe, French authorities are responding quickly to the threat. Scientists first noted a cavity of water below the mountain-top glacier in March, but the magnitude of the lake was only discovered in July.
Researchers believe the lake contains 2,275,000 cubic feet of water -- comparable to the amount of water released during the 1892 flood. If it bursts, it could inundate the valley in less than half an hour.
Melting of the overlying Tete-Rousse glacier, probably due to rising temperatures in the region, created this secret lethal lake. In other parts of the world, such as Iceland, glacial lakes often form due to volcanic activity.
In each case, the surrounding glacier acts as a temporary dam on the water. But it can easily crumble or, with enough water pressure, float up off the bedrock and release a torrent on the valley below. Icelanders are so used to these violent events that they've given them a name: "jokulhlaup."
This is the first attempt to defuse a jokulhlaup, and pumping the water out of the massive lake is a complicated, risky project. "They have to drill between 40-50 meters (131-164 feet) of ice before reaching the water cavity. We are about 3,200 meters (roughly 10,500 feet) high; there's no road, only helicopter access and it's also an area prone to avalanches," Nicolas Karr, a member of France's National Forests Office told the BBC in an interview.
It is unclear how much of the lake engineers plan to drain. Even pumping out a small fraction of it will significantly reduce the stress on the overlying glacial cap, and the chance of a flood. Authorities are still not sure where the drained water will go.
Image: girolame, Flickr