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Subglacial Lakes (Lake Grimsvötn Periodicity (Drainage largely = f (…
Subglacial Lakes
Lake Grimsvötn Periodicity
Drainage largely =
f ( geothermal heating )
Geothermal heat melts ice & fill lake
∴ Eruptions make lake fill faster
Drains when water level = sufficient to float ice
Caldera water level monitored
Revealed periodic formation & drainage
Period drainage
As hydraulic gradients = reversed
Flotation criteria = main factor
,
but not only
Subglacial lakes
Distribution
V common beneath Antarctica
Some found beneath Greenland
Hazard
Ice sheets
Drainage not normally hazardous
Iceland
Poses signif danger
Significance
Microbial life @ lake bed e.g. Lake Vostok
Extreme envmts & aphotic
Details Lake Grimsvötn
Subglacial lake beneath
Vatnajökull ice cap
in
Grimsvötn caldera
Periodic formation & drainage
Due to geothermal heating in caldera
Reversed hydraulic gradients
Subglacial channels drains lake
Jokulhlaup Grimsvotn 1996
Subglacial fissure eruption
lasted 2 weeks
Meltwater
Stored in subglacial caldera
Initially -
floated ice dam
Later -
enlarged a subglacial conduit
in margin
Water flooded
into outwash plain
Flooding reached Q ~ Ganges in 11 hours!
Damage = $10-15 million
Antarctic subglacial lakes
Radar profiles
reveal
flat bottomed surfaces
Visible dome in surface elevations
- Lake Vostok
Discovered from radar study
Hydraulic Potential
Combine: ice thickness + bed topography
Infer likely
drainage routes
of water
e.g. the Labyrinth
= Geomorphic evidence for massive GLOF in past
Canyons evince vast volumes of water flow
Formation
Geoethermal heating and/or subglacial eruptions
Produce most dramatic GLOFs