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Snowpack Metamorphism and Avalanche Conditions

The snowpack underneath the surface is constantly changing, and those changes can either improve or avalanche stability and sometime not. Slab vs Loose : There are two main types of Avalanches: Slab Avalanches and Loose Snow Avalanches. And it’s the Slab Avalanches that are our main concern. Metamorphism: The Snowpack is constantly changing and one reason for this change is the movement of vapour up out of the snowpack. This movement of vapour will change the crystals beneath the surface of the snow. Rounding: When temperatures are warmer and the snowpack is deeper we’ll get a metamorphism known as rounding. And rounded crystals are exactly as they sound. Nice round blobs of snow, with lots of surface area that do a great job of bonding and connecting with there neighbours. Faceting: And when temperatures are colder and the snowpack shallower we get the opposite, which is known as faceting. These are sugary, square-edged crystals that don’t like to bond and connect to neighbouring crystals or crusts and slabs above and below them. These facets can act as the weak layer in our slab avalanche problem. Buried Surface Hoar : Another weak layer that can persist and create a slab avalanche problem is buried surface hoar. This forms on the surface of the snow at night when it’s cold and clear, and it’s essentially the winter version of dew. These feathery crystals become a problem when they are buried by new snow. Melt-Freeze : Another type of metamorphism is melt-freeze crusts, and this one is fairly simple, the snow melts either through warmer air temperatures, strong sun or rain, and then this layer freezes creating a crust. That crust can then act as a bed surface for any new snow in the next storm. Common Trigger Points : In addition to snowpack considerations we also need to be aware of where likely trigger points might be. For example: on convex rolls, beneath cornices, around partially buried trees, rocky outcrops or where the snowpack is generally thin and more shallow. These are all areas that when in the start zone of an avalanche path we want to avoid.