1 Trigger.claim numerous lives every year when people get caught in a wall of snow. There are three main2. Causes that produce avalanches.The first is the3. snowpack.On top of the snowpack is the icy layer followed by a third layer called the4. slab layer .Having a weak layer of snow lying on top of the ice and bed layers means that an avalanche s more likely to occur.A 5. avalanches is needed for the slab layer of snow to6. slip off . Most avalanches occur on slopes that have angles of 25 to 60 7. Degrees.