Glacier hydrology and glacier flow are strongly interlinked. Glacier flow transfers ice from accumulation areas to ablation areas and as the melting of ice occurs in these ablation areas, the hydrological cycle is strongly affected by the processes of glacier motion. A greater amount of ice melt in ablation areas due to increases to glacier flow speed may lead to a changes in the water content within the glacier, hence impacting the glacier hydrology. Likewise, changes to the production, storage and transport of water within the glacier influences its motion, through a number of processes. These links are particularly important for warm or temperate glaciers because they generally contain much more water (Meier and Post, 1991).
Glacier motion occurs by strain within the ice or the bed (ice creep deformation), or by sliding at the interface between the ice and bed. It is driven by the force exerted by the ice and balanced by the drag at the glacier boundaries and by ice viscosity. Ice creep is strongly influenced by the intergranular water content within the ice. At low water contents, surface tension pulls surfaces together, increasing the effective pressure and causing a rise in frictional strength.
A greater impact on glacier flow by glacier hydrology is from water stored within and at the base of the glacier. Warm or temperate glaciers have strong diurnal and seasonal variations in their hydrology (Knight, 1999), which leads to varying quantities of water descending crevasses into the bed of the glacier. Wallace (1871) was the one of the first to note the affect these variations have on the rate of glacier motion. Pressure builds when water accumulates at the base of the glacier, which offsets the weight of the glacier. This causes the basal resistance between wet ice and the smooth surface to be very low and hence allows the glacier to slide forward at an increasing rate. Bartholomaus (2008) found that this mechanism occurs when englacial, as well as subglacial, water storage increases.
Figure 1 shows how changes in water storage are well correlated with glacier velocities. The study suggested that when water inputs exceed the ability of the existing conduits to transmit water, the conduits pressurize and drive water back into the extensive linked cavity system, which in turn promotes basal motion. The mechanism of basal sliding is suggested to account for up to 90% of the movement of thin ice on steep slopes and 20-50% of the movement in valley glaciers (Sharp, 1954).
The flow of meltwater associated with regelation sliding occurs through a thin film between the ice and its bed (Weertman, 1964; Hallet, 1979), but can also flow through a vein network within a basal ice layer (Lliboutry,1993), particularly in temperate glaciers.
Glacier motion occurs by strain within the ice or the bed (ice creep deformation), or by sliding at the interface between the ice and bed. It is driven by the force exerted by the ice and balanced by the drag at the glacier boundaries and by ice viscosity. Ice creep is strongly influenced by the intergranular water content within the ice. At low water contents, surface tension pulls surfaces together, increasing the effective pressure and causing a rise in frictional strength.
A greater impact on glacier flow by glacier hydrology is from water stored within and at the base of the glacier. Warm or temperate glaciers have strong diurnal and seasonal variations in their hydrology (Knight, 1999), which leads to varying quantities of water descending crevasses into the bed of the glacier. Wallace (1871) was the one of the first to note the affect these variations have on the rate of glacier motion. Pressure builds when water accumulates at the base of the glacier, which offsets the weight of the glacier. This causes the basal resistance between wet ice and the smooth surface to be very low and hence allows the glacier to slide forward at an increasing rate. Bartholomaus (2008) found that this mechanism occurs when englacial, as well as subglacial, water storage increases.
Figure 1 shows how changes in water storage are well correlated with glacier velocities. The study suggested that when water inputs exceed the ability of the existing conduits to transmit water, the conduits pressurize and drive water back into the extensive linked cavity system, which in turn promotes basal motion. The mechanism of basal sliding is suggested to account for up to 90% of the movement of thin ice on steep slopes and 20-50% of the movement in valley glaciers (Sharp, 1954).
The flow of meltwater associated with regelation sliding occurs through a thin film between the ice and its bed (Weertman, 1964; Hallet, 1979), but can also flow through a vein network within a basal ice layer (Lliboutry,1993), particularly in temperate glaciers.
Fig.1 Taken from Bartholomaus (2008) showing the rate of
change of water storage and ice speed, for (a) diurnal, (b) seasonal and (c)
outburst-flood timescales. At each timescale, sliding coincides with times of
increasing water storage.
References
Barry, R.G. and Gan, T.Y. (2011). The global cryosphere: past, present and future. Cambridge University Press, Cambridge.
Bartholomaus, T. C., Anderson, R. S., & Anderson, S. P. 2008. Response of glacier basal motion to transient water storage. Nature Geoscience, 1, 33−37.
Benn, D.I. and Evans, D.J.A. (1998). Glaciers and Glaciation. London, Wiley.
Hallet, B. (1979). Subglacial regelation water film. Journal of Glaciology 23, 321-34.
Knight, P.G. (1999) Glaciers. London: Routledge. 261pp.
Lliboutry, L. (1993). Internal melting and ice accretion at the bottom of temperate glaciers. Journal of Glaciology 39, 50-64.
Meier, M.F. and Post, A. (1991) Glaciers: a Water Resources. United States Department of the Interior, US Geological Survey, Denver.
Sharp, R.P. (1954). Glacier flow: A review. Bull. Geol. Soc. Amer., 65: 821-38.
Wallace, A.R. (1871). The theory of glacier motion. Nature, 3:309-10.
Weertman, J. (1964). The theory of glacier sliding. Journal of Glaciology 5, 287-303.
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