Flood risk from lake under a glacier in the French Alps

A massive underground lake has been discovered in the French Alps.

The lake is trapped under a glacier on Mont Blanc, and contains enough water to flood the valley below in just 15 minutes.

Engineers are now trying to drain some of the water out of the lake to stop it flooding.

Parts of a special railway that takes tourists up the mountain have been closed and walkers have been told to stay away while the lake is drained.

Flooding

In 1892, a similar-sized underground lake killed around 200 people after it burst and flooded the valley.