The lake was discovered earlier this summer whilst routine checks were being made on the Tete-Rousse glacier. The lake, trapped below the glacier holds 65,000 cubic metres water, enough to form a torrent with mud, rocks and trees that would flood the St Gervais valley in 15 minutes.
Engineers yesterday began work to drain the lake, which involves drilling through around 50m of ice to reach the lake in an area only accessible by helicopter.
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 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... 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."
Mr Peillex, St Gervais' mayor, told the Associated Press news agency that the operation was going smoothly so far. "Once they take out the first few dozen cubic metres 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,".
Written by Charlie Hamilton-Beaufort