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A subglacial meltwater channel is a channel beneath an ice mass, like 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 kilometres 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 sub glacial melt water channels are commonly mentioned. The first type of channel is the R-channel (Röthlisberger, 1972)〔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. 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. 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== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Subglacial channel」の詳細全文を読む スポンサード リンク
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