BBC News | SCI/TECH | Galt�r: Anatomy of an avalanche (original) (raw)

One key to understanding precisely what did occur on the afternoon of 23 February has come from a daring experiment in which scientists sat inside a concrete bunker as it was hit by a huge avalanche.

The bunker, which was filled with radar equipment, monitored the movement of the different snow layers inside the avalanche as the wall of powder went over the top and down the mountainside.

The data have allowed the researchers to build up a more realistic model of snow dynamics - one which explains how an avalanche can travel much further than previously thought possible and build in intensity as it goes.

This new thinking has been crucial to F�hn and Margreth's analysis of the Galt�r event.

Strong winds

Meteorological records show that relatively warm weather in January was immediately followed by record snowfalls and strong winds in February. This led to the build up of an exceptionally large and unstable slab of snow on one of the slopes above Galt�r.

When the slab eventually gave way, the avalanche came down on the village in a way only the latest computer models based on the bunker data could have forecast.

The scientists' calculations show that the block of snow that broke away on top of the mountain weighed some 170,000 tonnes. It moved at a speed of nearly 300 kph taking less than a minute to hit the valley floor. By this time, it had doubled in size. It was two minutes before the avalanche came to a stop. By then, the snow had covered what was thought to be some of the safest parts of the village.

The BBC's Horizon programme is broadcast on Thursdays on BBC Two at 2130 GMT