Subglacial channel

A subglacial meltwater channel is a channel beneath an ice mass, such as ice sheets and valley glaciers, 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 wall closure rates (governed by the ice thickness) and squeezing of fluidized sediment.[1] 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.[2] 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. 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. [3]

H-channels

The second type mentioned are H-channels, after Roger Hooke.[4] 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 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.[5]

gollark: Also gravitational field strength.
gollark: I suppose the air pressure is slightly lower higher up, but I'm not sure why that would be relevant.
gollark: What? Why's that a bad thing?
gollark: I live in a house, not an apartment, and while it actually has advanced 3D stacking technology for better land utilization, I am on the ground floor.
gollark: No.

References
  1. van der Meer, Jaap JM, John Menzies, and James Rose. 2003. "Subglacial till: the deforming glacier bed." Review of. Quaternary Science Reviews 22 (15):1659-85.
  2. Röthlisberger, H. 1972, Water pressure in intra- and subglacial channels. Journal of Glaciology, Vol. 11, No. 62, p. 177-203.
  3. Walder, J S. 2010. Röthlisberger channel theory: its origins and consequences, US Geological Survey, Cascades Volcano Observatory, https://www.cambridge.org/core/services/aop-cambridge-core/content/view/39BCA503939401F57BB79A5B0044528D/S0022143000213282a.pdf/rothlisberger_channel_theory_its_origins_and_consequences.pdf.
  4. Hooke, Roger LeB, T. Laumann, and J. Kohler. 1990. "Sub glacial water pressures and the shape of subglacial conduits." Journal of Glaciology 36 (122):67-71.
  5. 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.


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