there are three main causes that contribute to avalanche conditions. on the surface of a mountain is the snowpack. this is the snow that has fallen and accumulated over the past weeks and months. usually, there are several layers of snow on the mountain. the first layer of snow is called the "bed layer." some of this snow willmelt away, leaving a second thin layer of ice particles on top of the bed layer. it might take several weeks before another heavy snowfall. the danger comes when the third layer of snow falls. if it is made of light, loose or fluffy snow (not heavy wet snow), the danger starts. this third layer is called the "weak or slab layer." a weak layer of snow lying on top of ice and bed layers means that an avalanche is more likely to occur.