• Greatly affects glacial flow, both creep and basal sliding
• Responsible for a variety of meltwater features
• Important to understanding processes of glacial quarrying, debris entrainment, and abrasion
• Responsible for the deposition of economically important glacial fluvial sediments

• temperature
• pressure melting

• Frictional heat produced by flow
• Geothermal heat flux
• Atmospheric heat exchange
  • Latent heat
    • Meltwater can transfer heat from the surface. Latent heat is the heat, usually measured in calories/g, release or absorb by a substance, under conditions of constant pressure and temperature, while undergoing a phase change.
  • When water freezes heat is released: latent heat of crystallization
  • When ice melts heat is absorbed: latent heat of fusion
• Ice thickness

Phase diagram of H20

Pressure melting is possible because as pressure increases the melting point of ice decreases. According to Benn and Evens (1998) the melting temperature decreases .072°C/MPa. The melting poing of a 200m thick glacier (Epi=17.6 MPa) would be -1.27°C.

• Subglacial pressure changes that cause freezing or melting may be caused by:
  • Epi (Effective pressure) = pgh - wp
    • Ice thickening can induce melting. Thinning can induce freezing.
  • Obstacle related pressure changes:
  • Increased pressure on stoss-side of obstacles and decreased pressure on lee side: results in pressure melting and regelation.
  • Changes in water pressure and its effect on Epi:
  • Increased basal meltwater decreases Epi. Pressure melting point increases at points of contact causing freezing.
  • Decreased water pressure increases Epi. Pressure melting point decreases causing melting. Latent heat is remove if meltwater escapes causing the formation of a cold patch and freezing down ice (Robin's Heat Pump effect)
  • Changes in pressure on super-cooled water beneath a glacier.
    • Water flowing beneath a glacier under pressure is cooled below its normal freezing point. A slight decrease in pressure can therefore cause freezing.

These processes greatly affect quarrying and plucking beneath a glacier.

• seasonal melting and freezing (surface water drains towards glacial bed)
• spatial variations in geothermal heat flux
• changes in ice thickness and velocity
• pressure changes
  • changes in ice thickness
  • obstacle related pressure melting
  • fluctuations in water pressure

• Meltwater may drain through a series of supraglacial (surface), englacial (interior), or subglacial (basal) channels.
  • The formation of these channels varies seasonally and with the thermal regime of the glacier. Supraglacial meltwater often flows into the glacier through crevasses or near vertical shafts called moulins.
• Cold-based glaciers typically lack subglacial drainage systems.
• The direction of meltwater flow is govern by the pressure gradient which is largely determined by variations in ice thickness. The direction of meltwater flow is therefore roughly parallel to the direction of ice flow.
• Meltwater can also drain through permeable subglacial rock and sediment
• Meltwater flow in the Greenland Ice Sheet

Jokulhlaups: Catastrophic released of glacial meltwater

• Can be volcanically induced such as those produced in Iceland
• May also be caused by the catastrophic draining of a glacial lake cause by failure of a sediment or ice dam

Features carve by outbursts of glacial meltwater (jokulhlaups)

• Channel Scablands: Carved by the sudden release of water from glacial lake Missoula, an ice-dammed lake.
  • Geomorphology from Space/Montana Natural History
• Channel Formed by the draining of Glacial Lake Agassiz in Manitoba [Canadian Landscapes]
• Icelandic Jokulhlaups created by subglacial volcanism
  • Icelandic Jokulhlaup (BBC)
  • 1996 eruption beneath the Vatnajokull ice cap:Lowell and Huff/Larry Smith
    

• solution (corrosion)
  • dissolution of soluble rock
• cavitation
  • microchipping induced by changes in pressure
• traction
  • removal of loose grains by the shear force exerted by the flow
• abrasion (corrasion)
  • scouring and removal of material by particles carried by the flow

• Subglacial forms
  • Nye or N-Channels (bedrock)
    • Anatomizing channels caved in bedrock
    • aligned parallel to glacial flow
  • Rothlisberger or R-Channel (ice)
  • Tunnel valleys
    • Large channels carved in bedrock or sediment
    • Typically have steep sides and wide flat floors
    • May be formed by catastrophic subglacial floods (e.g. Jokulhlaups)
  • P-forms (formed by meltwater or ice?)
• Marginal Channels
  • Typically formed along the margins of locally cold-based glaciers
• Erosional proglacial Meltwater features
  • Spillways: carved overflow channel of a glacial lake
    • bedrock channels
    • channels with boulder pavements

• Meltwater Channels in bedrock: 1, 2, 3 Melville Peninsula, Nunavut [Canadian Landscapes]
• Modern ice-marginal channel, Bylot Island [Canadian Landscapes]
• Moraines and channels at a glacier margin, Bylot Island [Canadian Landscapes]
• Erosional subglacial meltwater features
  • Subglacial features, Ste-Marguerite, Quebec. [Canadian Landscapes]
  • Meltwater channels cut in gravel (bedrock) , Prince Patrick Island, Northwest Territories [Canadian Landscapes]
  • Nye channel Switzerland [Adam Bothy]

[Glacial and Quaternary Geology] [extended GeoIndex][QkRef][Geological Sciences] [Degree Programs] [Salem State College]
Lindley Hanson (email) Last Modified 3/27/03