Bombs, grenades & dynamite - the inside story on controlling avalanches

The dull thuds can be heard in the early mornings after a big snowfall across Val d'Isere. We've all heard them but what are they? I got behind the scenes with the 'L Catex' tour to find out how controlled avalanches work.

I'll admit that I didn't really know what to expect from this freely available tour. It started well enough: Five minutes late only to realise that the other tour-goers were fully skied up. Compared to my jeans and boots I felt somewhat under prepared. Turns out this was a blessing in disguise as my wonderful guide for the tour Thibault gave me a lift down to the Catex building on the back of his skidoo! After that small adrenaline rush I was ready for whatever this tour had in store for me and it was far from disappointing.

Thibault led us under the ominously signposted ropes on the side of the piste into the small Catex building. It's hard from looking at it to imagine how such explosive results can occur from what is essentially a glorified shed on the side of the mountain but I was keen to find out and obediently followed Thibault through the Val d'Isere snow.

I didn't know what I thought the procedure for the controlled avalanches would be but as Thibault began to explain the system it became quickly apparent that the vague ideas I had couldn't have been much further from the truth.

While you're sipping tea...

At 7.30 in the morning as the rest of the resort is still sleeping or taking their first sip of tea, a small team of ski patrollers are preparing bundles of dynamite, each two kilograms in weight, to drop at any number of the twenty points that the Catex system can reach. It begins as one patroller clears the platform of snow and ice whilst the others attach the fuses to the dynamite. The dynamite is then attached to hooks hanging from the wire that spans across the mountain face. At this point everything is ready to go and it's just waiting on the controls to be set into the huge computer inside the Catex building. This is where the placement of the dynamite is controlled. When everything is ready to go the fuses are lit and the winch creaks into motion pulling the dynamite along until they are suspended above their desired position to be dropped down into the snow.

All of this was simulated, albeit with fake dynamite, by Thibault as part of the tour and it was a real treat seeing this intricate but yet routine procedure unfold before me by the actual person whose job it was. After the demonstration Thibault went on to explain the two other methods of causing controlled avalanches. These are used for points on the mountain which the Catex building cannot send dynamite to and given the size of the mountain range these points are extensive.

1. Gas bombs

One of these methods involves gas pipes running up the mountain faces which contain supplies of oxygen and propane. These gasses ignite at the end of these pipes resulting in an explosion under the snow which sends a shockwave in the surrounding area which hopefully causes the desired avalanche. However what was perhaps a slightly worrying detail was that sometimes the shock waves only result in cracks or a loosening of the snow. At this point the danger of the avalanche has not been overcome but actually heightened by the explosion. Thibault explained how they could never know if the explosions would create the desired effect or result in a dud. I made a mental reminder to myself at that point to take extreme care when attempting off-piste. One thing this tour did do was bring the reality of the danger of avalanches home for me.

2. Hand grenades

The final method for causing controlled avalanches was a hand-drop-off of dynamite. This is as basic as it sounds as a ski patroller would have to ski to wherever they want a detonation and throw the dynamite in the desired position. This method does have some vital intricacies though as the explosion is set off via an electrically controlled fuse so that it can be stopped at any point. This makes sure the patrollers can get far enough away but also allows them to stop the explosion if any skiers turn up whilst the fuse is lit!

3. The fly by

As Bondesque as this sounds the patrollers can go one better: If the explosion is wanted in an extremely difficult to reach spot then they bring in the helicopter. The helicopter drops pipes containing oxygen and propane which are then detonated remotely by one of the patrollers. Thibault did stress that this was extremely rare as the aforementioned methods cover almost all scenarios however it did sound like an extremely exciting part of his day job.

By the end of the tour I was in awe of this aspect of Thibault's job that is so important but yet so routine for all of the ski patrollers. This tour is free to book onto at the Office du Tourisme and is definitely worth the effort even if I didn't manage to get a skidoo ride back down the mountain.