Wet Snow Avalanche


    Out of the three types of avalanches wet snow avalanches produce the least amount of accidents. As such they are the least studied of the three. They differ from dry snow avalanches in how they are triggered, how they slide, and under what conditions they are formed.

Under what conditions do they form?

Wet snow avalanches are usually caused by decreased compression, tension, and shear strength of the snowpack due to prolonged melting and or rain.

How is the snowpack made unstable?

Wet snow avalanches differ from dry snow avalanches in how they become unstable. A dry snow avalanche occurs by overloading the weak layers in the snowpack, whereas a wet snow avalanche occurs by decreasing the overall strength of the snowpack. Under spring time conditions, such as snow with increased melting, corn snow can form. Corn snow is snow that has melted and liquid water has filled up the inner cavities of the snowpack. While the surface tension of water is enough to hold the remaining snow particles together if enough snow transforms to water it will dramatically decrease the internal strength of the snowpack causing it to slide.

    For example, think of a snowpack as a bag of gapes, where the internal bonds are the vines. When the bag of grapes is warmed up the vines begin to disappear. Thus when it is warm enough the grapes will cascade down the mountain.

                                        Wet snow avalanche

                                            Corn snow


How does a wet snow avalanche flow?

They consist of large boulder like chunks of icy snow, which have been compacted into very high densities, combined with slushy snow in between. One can think of this type of flow as a large mass of concrete slurry flowing down a mountain, with large rocks mixed in. As a result they are the slowest of all there avalanches attaining speeds of 10 to 40 miles per hour.