Last Thursday, a professional snowboarder was killed in the Italian Alps when an avalanche carried him down the slopes of Mont Blanc. Read about a tragic avalanche in Galtur, Austria, that killed 31 people last year. In a dry slab avalanche, a large mass of snow on a slope suddenly slides as a slab-like unit on top of a weaker layer of snow underneath. Adding weight to the top layer, either by new snowfall or rain, can cause an avalanche if the buried weak layer can't adjust to the increased weight load fast enough. Left to its own natural processes, the snowpack might not break loose.
Friction can help keep a slab of snow from sliding downslope.
Samuel Colbeck of the Cold Regions Research and Engineering Laboratory has been researching what happens where frozen water molecules come together. Colbeck's research has changed the way people look at the snowpack when trying to predict avalanche conditions. Interestingly enough, Colbeck also sees other ways humans might be causing an increase in the number and severity of avalanches. Increased development and pollution in mountain regions can destroy trees, decreasing the natural buffers to avalanches. Friction actually helps skis move over the snow.