1 Trigger claim numerous lives every year when people get caught in a wall of snow. There are three main 2.Causes that produce avalanches.The first is the 3.slab layer.On top of the snowpack is the icy layer followed by a third layer called the4.snowpack.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.