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Glacial ice formation (Firnification Stages (Settled snow (Layered…
Glacial ice formation
Firn
= material undergoing
conversion from snow to ice
aka snow that has survived one summer (melt season
--> without transforming into ice
Meltwater
Summer- percolates snow pack
Autumn - refreezes
requires that
snow = preserved through summer
Snow
= solid precipitation, has variety of forms
Ice
Distinguished from firn when
air becomes trapped
Firnification
= conversion of snow to glacial ice
Snow compressed + compacted
as progressively buried by further snowfall
eventually
metamorphoses into ice
Key ∆: Air passages sealed off
~ρ = 830 kg/m3
Firnification Stages
New snow
ρ ~ 50-70
Settled snow
Layered structure
ρ ~200-300
Wind-packed snow
Dune-like features possibly w bedding
ρ~350-400
Firn
ρ~400-830
If snow survives summer melt
Glacial ice
Air only present in bubbles
ρ~830-910
Firnification Complicating Factors
Density change snow/firn/ice
= f (burial depth) as result of compaction
HOWEVER
Meltwater complicates matters
Meltwater speeds up firnification
Meltwater interaction with snow/ice depends on
Thermal regime
Thermal zonation of glacier