Subglacial System
Meltwater
@ ice-bed interface
Subglacial meltwater often under pressure
Basal water p influences:
Glacier sliding ∴ erosion
Sediment deformation
Basal water pressure = f (...
Volume of water in subglacial drainage system
Type of drainage system
- Supra --> Subglacial
- Water ponds in supraglacial channels
- Eventually enters moulins / crevasses
∴ Reaches glacier bed
- On reaching glacier bed
Meltwater encounters a
--> low efficiency drainage system
∴ Pressure builds up & ice may be 'buoyed' up
Composition supraglacial vs subglacial meltwater
Supraglacial meltwater
few solutes, purer than distilled water
Subglacial meltwater
high salts / solute / sed content
Subglacial drainage
structure importance
affects basal water pressure ∴ ice motion / dynamics
Subglacial water pressure effects
Greater subglacial water pressure
the more the water
supports weight of glacier
'floats' ice above it
Glaciers impose force vertically on their bed
~ effective normal pressure
Water @ bed reduces this force
by amount
= subglacial water pressure
Types Subglacial Drainage
Two types subglacial drainage system exist
B. Channelised system = FAST
A. Distributed system = SLOW
Both can exist under a single glacier
Transition A to B = Controlled by surface input peakedness & magnitude
Two modes drainage
= Characterised by hydraulic efficiency
Channels = hydraulically efficient
Hydraulically inefficient
Slow water flow is distributed
Fast water flow ( > 0.3 m/s)
Ice dynamics & subglacial water pressure
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