A snow avalanche begins when an unstable mass of snow breaks away from a slope. The snow picks up speed as it moves downhill, producing a river of snow and a cloud of icy particles that rises high into the air. The moving mass picks up even more snow as it rushes downhill.

How are avalanches caused?

Avalanches can be triggered by wind, rain, warming temperatures, snow and earthquakes. They can also be triggered by skiers, snowmobiles, hikers, vibrations from machinery or construction.

How do humans trigger avalanches?

Human-triggered avalanches start when somebody walks or rides over a slab with an underlying weak layer. The weak layer collapses, causing the overlaying mass of snow to fracture and start to slide. Earthquakes can also trigger strong avalanches.