STOP PRESS: French speakers will find this recent item from French TV channel M6 of interest. Includes some great graphics.  Inhabitants of St Gervais are unlikely to miss the warning signals...

Tourists and residents have been warned there may only be a few minutes to evacuate if a giant water pocket under the Tete Rousse glacier on Mont Blanc bursts. 

Sirens will not give enough warning
Researchers at the National Centre for Scientific Research (CNRS) have claimed a substantial water pocket in the Tete Rousse glacier on the Mont Blanc could be a potential hazard if it were to burst.   Researchers say that Saint Gervais, a popular holiday spot and home to 3000 people, would be flooded in 15 minutes. Although sirens have been set up, the evacuation plan has been greeted with scepticism. "We'd have no chance," a holidaymaker said.

Mud slide as well as water
The water pocket is said to be some 65,000 cubic metres - the equivalent of 26 Olympic sized swimming pools.  If it burst, there would be "a brutal emptying of water which carries along everything in its path. You end up with a torrent of mud six to eight times bigger than the original volume of water".  The affects could be as devastating as in 1892, when a similar incident occurred on the Glacier Miage.   On that occasion 175 villagers were drowned.

Attempts to remove water have started
Researchers made the discovery whilst carrying out routine checks in the area, although such an occurance is rare the researchers knew what they were looking at and quickly drew conclusions.

Scientists will try to remove 25000m3 of water from one part of the pocket later this month.  Local authorities have started an operation to drain the water via the top of the glacier, drilling down through the top sheet ensuring the stability of the ice, whilst being able to pump the water out to drain away elsewhere.  The most likely reason for the formation of the pocket was a period of particularly cold temperatures within the glacier, freezing the water's escape routes. This may be a result of global warming, which has reduced the snow covering on the glacier and exposed it to the cold.

Tramway du Mont Blanc closed
It has since been confirmed that the highest section of the Tramway du Mont Blanc and the Refuge du Nid d'Aigle at 2360m will be closed for the rest of the summer.  

Many high mountain climbers, including those hoping to summit Mont Blanc, will have planned to stay at the Refuge, although the lower refuge at Mont Lachat will still be open.  

A similar pocket of water, if on a much smaller scale, was seen in Chamonix in 1996, when the centre of the town suffered severe flooding.

[Source: AFP, Dauphine Libere]