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A. Introduction
Image credit: Z. Strack. Used with permission. Franz Josef Glacier, New Zealand.

Importance

• flow rates

• debris removal & transport

Water sources

• surface (main source)

• englacial

• subglacial

Drainage network

• cold-based glaciers: supraglacial network

• warm-based & polythermal: 3-D network

B. Supraglacial Meltwater

Lakes & streams

• moulins & crevasses disrupt surface drainage pattern

• may be hidden beneath snow

Most well-developed in ablation zone

• low ice permeability

• melting

Image credit: Scott McGee (2006) The Crevasse Zone http://crevassezone.org/Photos/photos_frameset.htm

Image credit: Scott McGee (2006) The Crevasse Zone http://crevassezone.org/Photos/photos_frameset.htm

C. Englacial Meltwater

Occurrence

• warm or mixed thermal regime glaciers

Tunnels & small passageways (mm)

• fed by moulins & crevasses

  • moulin upper part straight & vertical

  • moulin lower part tilts down-glacier

• tunnel/passageway maintenance

  • glacier flow tends to close crevasses & tunnels

  • frictional heat from water flow helps keep them open

  • size changes depending on water flow

D. Subglacial Meltwater

Effective normal pressure
Image credit: Peter Knight http://www.physicalgeography.org.uk/photos/PhotosGlaciers.html Meltwater portal, Solheimajokul

• normal pressure: pressure perpendicular to bed

  • downward force

  • function of glacier thickness (& ice density, gravity, & slope)

• pore pressure: pressure perpendicular to bed

  • upward force

• effective normal pressure = normal pressure - pore pressure

  • effective downward force

  • factors affecting basal pressure:

    • ice thickness

    • rate of water supply

    • rate of meltwater discharge

• subglacial water flow

  • determined by pressure gradient in full tunnels

  • determined by underlying topography in partially full tunnels

Discrete subglacial meltwater systems

• meltwater occurs in discrete tunnels or channels

  • most common with hard substrate

  • number of channels decreases towards terminus

• channels may link subglacial cavities

  • cavity formation

• channels:

  • R-channels (Rothlisberger channels): cut up into ice

  • eskers: R-channels that have been filled with sediment

  • N-channels (Nye channels): cut down into underlying bedrock

Distributed subglacial meltwater systems

• glaciers with soft or porous substrates

• meltwater flow occurs over large portion of glacier bed

  • thin water film

  • braided flow network

  • porewater flow

E. Meltwater Discharge

• diurnal fluctuations

• seasonal fluctuations

• catastrophic outbursts: jokulhlaups

F. Summary