Environmental Engineering Reference
In-Depth Information
Figure 15.7 Glacier transport pathways and their
depositional environment: (a) and (b) numbered pathways, 1
subglacial, 2 englacial, 3 supraglacial, 4 glacier-marginal, 5
extraglacial, 6 glacio-lacustrine/marine; (c) principal
environments and processes typically found in environments
2, 4, 5 and 6.
sediment fluxes of the glacial environment. Meltwater processes may occur anywhere in
the glacial system but become increasingly important in the ablation zone below the
ELA, sourced primarily by surface melting and augmented by rainfall. Water proceeds
via a glacial plumbing system of surface channels, vertical moulins drawing water into
the englacial environment and subglacial channels which feed discharge portals at the
terminus (Plate 15.10). Water in englacial and subglacial domains is liable to be under
high pressure and capable of maintaining ice-walled phreatic channels below the glacier
water table. Where it incises bedrock, subglacial channels contain uphill segments cut
through bed irregularities.
Surface water is inhibited from entering the glacier during winter freezing of the
plumbing system in temperate glaciers and more general freezing in cold glaciers. It then
cuts lateral ice-marginal channels and becomes ponded in depressions at the glacier
margin, often developing overflow channels. Newtondale, for example, marks the
spillway of a former ice-marginal lake draining southward across the North York moors,
but the recognition of other former ice-dammed lakes from meltwater channels alone may
be spurious. Break-out in spring can be catastrophic if sufficient meltwater build-up
bursts through still frozen channels, and the resulting jökulhlaup is a powerful erosive
agent. Meltwater deposition is subject to normal fluvial 'rules'. It is restricted to ice-
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