August 25, 2010

Trapped Lake Threatens To Flood Saint Gervais Valley

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

The lake was discovered last month during routine checks.  It is said to contain 2.3 million cubic ft of water.

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

Water from an underground lake flooded the same valley in 1892, killing 175 people.

The valley is a popular tourist area and is home to about 3,000 people.

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

"The town didn't want to wait for a catastrophe - we are taking action to prevent one," the mayor of the town of Saint-Gervais-les-Bains, Jean-Marc Peillex, told BBC News.

A system of alarms was put in place in July, but Peillex said that some people who did not trust the warning system had moved away from the area.

Nicolas Karr from France's National Forests Office told BBC that draining the lake was a delicate operation.

"They have to drill between 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 told BBC.

"We don't have much time to operate because after mid-October, we don't know if the weather will be OK to go on with our works."

Warmer temperatures may have melted the surface snow in order to create the lake, 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 an eight inch diameter hole in the ice to begin pumping a third of water from a pocket 656 feet below the surface.

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

Locals were briefed an on evacuation plan.

Peillex told The Associated Press that the operation was going smoothly so far.

"Once they take out the first few dozen cubic meters that doesn't mean there will be zero risk, but there won't be at all the same level of stress that there is today," he told AP.


Image Caption: The Mer de Glace glacier can be seen on the left side of the image. Courtesy Wikipedia