And when an avalanche finally stops, the snow sets up like concrete, making rescue efforts extremely difficult, and chances for survival slim. An avalanche, or slide, is simply a mass of snow moving down a slope. But despite this apparent simplicity, avalanches can be surprisingly hard to predict. Changing weather conditions continually affect the strength of the layers within the snowpack, and the snowpack on every slope is different depending on what exposure that slope has to the wind and sun. In fact, layers within the snowpack are the first thing that avalanche forecasters look at to try to predict the stability of a slope and its potential to slide.
Different storms create distinct types and amounts of snow.
Once the snow settles onto the existing snowpack, it can quickly metamorphose into distinct crystal types, which are determined both by changes in temperature and whether or not the snow is exposed to the sun. As the season progresses, the snowpack becomes a multi-layered history of storms and weather. But even a deeply buried layer can continue to change, as changes in temperature slowly move through the snowpack, and heavier snow weighs down on lower layers. A weak layer is created whenever snow crystals are shaped in a way that prevents them from bonding tightly together. How much of a threat an avalanche may pose depends largely on how deeply buried a weak layer is.