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GLOF Types (1. Proglacial lakes (Collapse / GLOF may result from (Lake…
GLOF Types
1. Proglacial lakes
Dangerous
- moraine dam =
unstable
Collapse / GLOF may result from
Dam collapse
Lake overtopping moraine
i.e. Huarez, Peru 1941 - glacier ice fell into lake initiating a flood wave
Mitigation
monitoring & warning systems being developed
Difficult to predict
drainage occurs rapidly due to vast water volumes
Lakes 'impounded' / dammed behind proglacial moraine (lateral or terminal)
Himalayas
Currently 50 lakes threatening millions of lives
Villages downstream @ risk
Worsened by widespread retreat
Retreating glaciers form lakes
between ice front & terminal moraine
2. Ice marginal lakes
= Lake dammed along edge of glaciers
Dammed by
glacial ice
Water drains from ice surface --> impounded by marginal ice cliff
Can be v large -
up to 500 - 1000 cumecs melt water !
Drainage mechanisms
2. Drains under ice
If water pressure high enough due to
Decreasing ice thickness
Increasing lake level (filling)
Lake water floats ice ∴
forces pathway under ice
Channel enlarges via frictional melting
1. Could overtop topography
(if fills enough)
Gorner Glacier
Ice marginal lake drainage 1969
Characteristic flood hydrograph
Gradual rise melt volume
Reflects channel expanding as lake drains
Discharge drops off
Once lake has drained
Amount of filling required to drain
Depends on ice thickness
Thinner ice --> needs less water to float
Depth water required to float ice
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
Formation
Geoethermal heating and/or subglacial eruptions
Most dramatic GLOFs
Details Lake Grimsvötn
Subglacial lake beneath
Vatnajökull ice cap
in
Grimsvötn caldera
Periodic formation & drainage
Reversed hydraulic gradients
Due to geothermal heating in caldera
Subglacial channels drains lake