Editing Snow (section)

===Avalanche===
{{Main|Avalanche}}
[[File:2007-02-15-CLB-Couloir2-1c.JPG|thumb|A powder snow avalanche]]
An avalanche (also called a snowslide or snowslip) is a rapid flow of snow down a sloping surface. Avalanches are typically triggered in a starting zone from a mechanical failure in the snowpack (slab avalanche) when the forces on the snow exceed its strength but sometimes only with gradually widening (loose snow avalanche). After initiation, avalanches usually accelerate rapidly and grow in mass and volume as they [[Entrainment (physical geography)|entrain]] more snow. If the avalanche moves fast enough some of the snow may mix with the air forming a powder snow avalanche, which is a type of [[gravity current]]. They occur in three major mechanisms:<ref name="McClung 2006">McClung, David and Shaerer, Peter: The Avalanche Handbook, The Mountaineers: 2006. {{ISBN|978-0-89886-809-8}}</ref>
* ''Slab avalanches'' occur in snow that has been deposited, or redeposited by wind. They have the characteristic appearance of a block (slab) of snow cut out from its surroundings by fractures. These account for most back-country fatalities.
* ''[[Powder snow avalanche]]s'' result from a deposition of fresh dry powder and generate a powder cloud, which overlies a dense avalanche. They can exceed speeds of {{convert|300|kph||abbr=|sp=us}}, and masses of {{convert|10000000|tonnes}}; their flows can travel long distances along flat valley bottoms and even uphill for short distances.
* ''Wet snow avalanches'' are a low-velocity suspension of snow and water, with the flow confined to the surface of the pathway.<ref name="McClung 2006"/> The low speed of travel is due to the friction between the sliding surface of the pathway and the water saturated flow. Despite the low speed of travel (~{{convert|10|to|40|km/h|0|abbr=|sp=us}}), wet snow avalanches are capable of generating powerful destructive forces, due to the large mass, and density.