Avalanche Science 101
With the heavy dump of snow we had on Monday, there has been much talk of avalanches and many resorts this season in the Western Alps have had deadly slides. In some places in Austria, 3.5m of snow are reported to have fallen in the space of a week. Although Val d’Isere might not have been hit by nearly as much snow, we thought we would take a look at what actually happens when an avalanche occurs.
So what causes a slope to slide or not? Essentially the stability of the snowpack and a trigger. The snowpack is made up of different layers, each of which represents an individual snowfall. Each of these layers has different properties due to the conditions present when the snow fell. Things like the structure of the ice crystals and the surrounding temperature and humidity when they fell impact how well the layer bonds to the one above or below. If the individual snow molecules are 6 branched crystals, i.e what we envisage when we think of a snowflake, they interlock well, creating a more stable layer. On the other hand, when needles form, they don’t gel so well. Similarly, if super-cooled water comes into contact with snow crystals in the air, it creates what is known as rime. Heavy rime deposits can cause pellet-like snow called graupel, which creates a very unstable layer.
6 point snowflake Depth hoar crystal Snowflakes with rime