PDA

查看完整版本 : Lake under Mont Blanc glacier drained to save Saint-Gervais-les-Bains


Mike
2010-08-26, 06:26
Reported in the BBC today:

French engineers have begun an operation to drain a lake under a glacier on Mont Blanc which threatens to flood the Saint Gervais valley.

The lake, which is said to contain 65,000 cubic metres (2.3m cubic ft) of water, was discovered last month during routine checks.

The engineers are drilling a hole into the ice to pump the water away.

In 1892, water from an underground lake flooded the same valley, killing 175 people.

The hidden lake, trapped beneath the Tete-Rousse glacier, holds enough water to form a torrent with mud, rocks and trees that would flood the valley in 15 minutes, potentially affecting 900 families.

Nicolas Karr from France's National Forests Office told the BBC's World Today that draining the lake was a delicate operation.
"They have to drill between 40m-50m (130ft-165ft) of ice before reaching the water cavity. We are about at 3,200m high, there's no road, only helicopter access, and it's also an area prone to avalanches," he said.

Warmer temperatures may have played a role in creating the lake, melting the surface snow, but it was a cold snap that was thought to have frozen the natural drainage routes.

The process of draining the lake is expected to take until October. The engineers will drill a 22cm diameter hole in the ice to begin pumping a third of the water from a pocket 200m below the surface.

They say they are not quite sure what will happen once the water is removed, but ahead of the operation local authorities closed the final section of the Mont Blanc tramway, which passes close to the glacier.