Editing Snow (section)

==Movement==
There are four main mechanisms for movement of deposited snow: ''drifting'' of unsintered snow, ''avalanches'' of accumulated snow on steep slopes, ''snowmelt'' during thaw conditions, and the ''movement of glaciers'' after snow has persisted for multiple years and metamorphosed into glacier ice.

===Drifting===
[[File:Long Mynd snowdrift.jpeg|thumb|right|Snow drifts forming around downwind obstructions]]
When powdery snow drifts with the [[wind]] from the location where it originally fell,<ref>{{cite web|url=http://www.cocorahs.org/media/docs/KS/CoCoRaHS%20Snow.PDF|title=CoCoRaHS in the Cold – Measuring in Snowy Weather|publisher=Colorado Climate Center|author=Joy Haden|date=February 8, 2005|access-date=July 12, 2009|url-status=live|archive-url=https://web.archive.org/web/20110718172302/http://www.cocorahs.org/media/docs/KS/CoCoRaHS%20Snow.PDF|archive-date=July 18, 2011|df=mdy-all}}</ref> forming deposits with a depth of several meters in isolated locations.<ref>{{cite news|url=https://www.telegraph.co.uk/topics/weather/4434935/Snow-Britain-Snow-drifts-and-blizzards-of-the-past.html|title=Snow Britain: Snow drifts and blizzards of the past|author=Caroline Gammel|date=February 2, 2009|access-date=July 12, 2009|publisher=Telegraph Media Group|url-status=dead|archive-url=https://web.archive.org/web/20090205075802/http://www.telegraph.co.uk/topics/weather/4434935/Snow-Britain-Snow-drifts-and-blizzards-of-the-past.html|archive-date=February 5, 2009|df=mdy-all}}</ref> After attaching to hillsides, blown snow can evolve into a snow slab, which is an avalanche hazard on steep slopes.<ref name="McClung 2006"/>

===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.

===Melting===
[[File:1997 Red River Flood Grand Forks.jpg|thumb|right|Snowmelt-induced flooding of the [[Red River of the North]] in [[1997 Red River flood|1997]]]]
Many rivers originating in mountainous or high-latitude regions receive a significant portion of their flow from snowmelt. This often makes the river's flow highly seasonal resulting in periodic [[flooding]]<ref name="Howard Perlman">{{cite web|url=http://ga.water.usgs.gov/edu/watercyclesnowmelt.html|title=The Water Cycle: Snowmelt Runoff|author=Howard Perlman|publisher=[[United States Geological Survey]]|date=May 13, 2009|access-date=July 7, 2009|url-status=dead|archive-url=https://web.archive.org/web/20090813020946/http://ga.water.usgs.gov/edu/watercyclesnowmelt.html|archive-date=August 13, 2009|df=mdy-all}}</ref> during the spring months and at least in dry mountainous regions like the mountain West of the US or most of [[Iran]] and [[Afghanistan]], very low flow for the rest of the year. In contrast, if much of the melt is from [[glaciated]] or nearly glaciated areas, the melt continues through the warm season, with peak flows occurring in mid to late summer.<ref>{{cite web|url=http://watershed.ucdavis.edu/copper_river/background/data/BowersoxCopper.pdf|title=Hydrology of a Glacial Dominated System, Copper River, Alaska|author=Randy Bowersox|page=2|access-date=July 8, 2009|date=June 20, 2002|publisher=[[University of California]]-Davis|url-status=live|archive-url=https://web.archive.org/web/20100612005951/http://watershed.ucdavis.edu/copper_river/background/data/BowersoxCopper.pdf|archive-date=June 12, 2010|df=mdy-all}}</ref>

===Glaciers===
{{Main|Glacier}}
Glaciers form where the accumulation of snow and ice exceeds ablation. The area in which an alpine glacier forms is called a cirque (corrie or cwm), a typically armchair-shaped geological feature, which collects snow and where the snowpack compacts under the weight of successive layers of accumulating snow, forming névé. Further crushing of the individual snow crystals and reduction of entrapped air in the snow turns it into glacial ice. This glacial ice will fill the cirque until it overflows through a geological weakness or an escape route, such as the gap between two mountains. When the mass of snow and ice is sufficiently thick, it begins to move due to a combination of surface slope, gravity and pressure. On steeper slopes, this can occur with as little as {{convert|15|m|ft|abbr=on}} of snow-ice.<ref name = Snowenclyclopedia/>