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.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.

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.Röthlisberger, H. 1972, Water pressure in intra- and subglacial channels. Journal of Glaciology, Vol. 11, No. 62, p. 177-203. 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

: $\frac{dp_w}{dx}=const\cdot Q^{-2/11}\Big(\frac{p_i-p_w}{nA}\Big)^{8n/11}$

where $Q$ is the discharge, $A$ and $n$ the same as in Glen's flow law, $p_w$ is the steady state pressure, $p_i$ is the initial pressure, and $x$ is the distance upstream. 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.

H-channels

The second type mentioned are H-channels, after Roger Hooke.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. 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.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

Category:Glaciology