Editing Snow (section)

==Metamorphism==
[[File:Sparkling-snow.crystals.jpg|thumb|Fresh snow beginning to metamorphose: The surface shows wind packing and [[sastrugi]]. In the foreground are [[hoar frost]] crystals, formed by refrozen water vapor emerging to the cold surface.]]
[[File:Svalbard-Sastrugi-Snow.jpg|thumb|Sastrugi formed during a blizzard just a few hours earlier.]]
According to the International Association of Cryospheric Sciences, ''snow metamorphism'' is "the transformation that the snow undergoes in the period from deposition to either melting or passage to glacial ice".<ref name="Classificationonground" /> Starting as a powdery deposition, snow becomes more granular when it begins to compact under its own weight, be blown by the wind, sinter particles together and commence the cycle of melting and refreezing. Water vapor plays a role as it deposits ice crystals, known as [[hoar frost]], during cold, still conditions.<ref>{{cite book|url=https://books.google.com/books?id=0Bpscs7Gqb8C&pg=PA71|title=The Avalanche Handbook|author1=David McClung  |author2=Peter Schaerer |name-list-style=amp |pages=49–51|isbn=978-0-89886-809-8|publisher=The Mountaineers Books|year=2006|access-date=July 7, 2009}}</ref> During this transition, snow "is a highly porous, sintered material made up of a continuous ice structure and a continuously connected pore space, forming together the snow microstructure". Almost always near its melting temperature, a snowpack is continually transforming these properties wherein all three phases of water may coexist, including liquid water partially filling the pore space. After deposition, snow progresses on one of two paths that determine its fate, either by ''ablation'' (mostly by melting) from a snowfall or seasonal snowpack, or by transitioning from [[firn]] (multi-year snow) into ''glacier ice''.<ref name = Classificationonground/>

===Seasonal===
{{Main|Snowpack|Névé}}
Over the course of time, a snowpack may settle under its own weight until its density is approximately 30% of water. Increases in density above this initial compression occur primarily by melting and refreezing, caused by temperatures above freezing or by direct solar radiation. In colder climates, snow lies on the ground all winter. By late spring, snow densities typically reach a maximum of 50% of water.<ref>{{cite web|url=http://cdec.water.ca.gov/snow/misc/density.html|author=California Data Exchange Center|publisher=Department of Water Resources California|title=Depth and Density|year=2007|access-date=July 8, 2009|url-status=live|archive-url=https://web.archive.org/web/20090713000814/http://cdec.water.ca.gov/snow/misc/density.html|archive-date=July 13, 2009|df=mdy-all}}</ref> Snow that persists into summer evolves into [[névé]], granular snow, which has been partially melted, refrozen and compacted. Névé has a minimum [[density]] of {{convert|500|kg/m3|lb/ft3}}, which is [[Density#Water|roughly half]] of the density of liquid water.<ref>{{cite web|author=Glossary of Meteorology|title=Firn|url=http://amsglossary.allenpress.com/glossary/search?id=firn1|year=2009|access-date=June 30, 2009|publisher=[[American Meteorological Society]]|url-status=dead|archive-url=https://web.archive.org/web/20070824054449/http://amsglossary.allenpress.com/glossary/search?id=firn1|archive-date=August 24, 2007|df=mdy-all}}</ref>

===Firn===
{{Main|Firn}}
[[File:Firn field on the top of Säuleck.jpg|thumb|right|[[Firn]]—metamorphosed multi-year snow]]
Firn is snow that has persisted for multiple years and has been [[Recrystallization (chemistry)|recrystallized]] into a substance denser than [[névé]], yet less dense and hard than glacial [[ice]]. Firn resembles caked sugar and is very resistant to shovelling. Its density generally ranges from {{convert|550|to|830|kg/m3|lb/ft3}}, and it can often be found underneath the snow that accumulates at the head of a [[glacier]]. The minimum altitude that firn accumulates on a glacier is called the ''firn limit'', ''firn line'' or ''snowline''.<ref name = Snowenclyclopedia/><ref name="Glacialprocess">
{{cite web|url=http://www.physicalgeography.net/fundamentals/10ae.html|title=CHAPTER 10: Introduction to the Lithosphere—Glacial Processes|last1=Pidwirny|first1=Michael|last2=Jones|first2=Scott|date=2014|website=PhysicalGeography.net|publisher=University of British Columbia, Okanagan|access-date=2018-12-20}}</ref>