A subglacial meltwater channel is a channel beneath an ice mass, such as
ice sheet
In glaciology, an ice sheet, also known as a continental glacier, is a mass of glacial ice that covers surrounding terrain and is greater than . The only current ice sheets are in Antarctica and Greenland; during the Last Glacial Period at Las ...
s and
valley glacier
A valley is an elongated low area often running between hills or mountains, which will typically contain a river or stream running from one end to the other. Most valleys are formed by erosion of the land surface by rivers or streams ove ...
s, roughly parallel to the main ice flow direction. These meltwater channels can have different sizes, ranging from very small channels of a metre deep and wide to big valleys which can be up to a kilometre wide. The dimensions of these channels are regulated by several factors: water temperature, meltwater volume, debris content in the water,
ice
Ice is water frozen into a solid state, typically forming at or below temperatures of 0 degrees Celsius or Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaq ...
wall closure rates (governed by the ice thickness) and squeezing of fluidized sediment.
In the
glaciological literature three forms of subglacial meltwater channels are commonly mentioned.
R-channels
The first type of channel is the ''R-channel'' after
Hans Röthlisberger who initiated work on water pressures in tubes under glaciers. These are semi-circular channels cut upward into the ice. The balance between channel enlargement by viscous heating and closure by ice deformation when the channels are water-filled reflects their size and
water pressure
Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...
. He stated the equation
:
where
is the discharge,
and
the same as in Glens's Flow Law,
is the steady state pressure,
is the initial pressure, and
is the distance upstream.
H-channels
The second type mentioned are H-channels, after Roger Hooke. These channels are similar to R channels, cut upward into the ice that tends to follow the local bed slope but are broad and flatter than R channels. Such channels form where water flows at
atmospheric pressure
Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equivalent to 1013.25 millibars, 7 ...
beneath thin ice and on steep downglacier bedslopes.
N-channels
The final type, the N-channel (after
John Nye), are those incised into bedrock, perhaps suggesting long-term channel stability under some glaciers.
[Gray, H H. 2001. ''Subglacial meltwater channels (Nye channels or N-channels) in sandstone at Hindostan Falls, Martin County, Indiana'', Proceedings of the Indiana Academy of Science, 110, 1-8.]
References
Glaciology
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