The Physics of Avalanches
Cornices
Slabs

Formation
Triggering

Bibliography

Slabs are a little easier to explain because no wind is necesserily needed for them to form. Slabs form when snow falls on a mountain and then is transformed into different layers by the sun. The sun causes the snow to melt small amounts and transform into different types of snow. Generally it makes the snow layer less dense. Then when more snow falls on top of this layer it forms the slab that will ultimately do the most damage in the avalanche. Here is a diagram of the snow layers.

http://www.fsavalanche.com/uploads/images/snow.layers2-2.jpg