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Chapter 6Chapter 6

Cuffey & Paterson

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FIGURE 6.1

Some elements of the glacier water system: (A) Supraglacial lake. (B) Surface streams. (C) Swamp zones near the edge of the firn. (D) Moulins, draining into subglacial tunnels (for scale, white rabbit is about 10m tall). (E) Crevasses receiving water. (F) Water-filled fractures. (G) Subglacial tunnels, which coalesce and emerge at the front. (H) Runoff in the glacier foreland, originating from tunnels and also from upwelling groundwater. Though not depicted here, water is also widely distributed on the bed in cavities, films, and sediment layers. Sediment and bedrock beneath the glacier contain groundwater. (Refer to the insert for a color version of this figure)

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FIGURE 6.2

A meltwater lake on the surface of the Greenland Ice Sheet, 30 km from the western margin, August 2005. The lake’s diameter is 1.4 km on its long axis; the volume is about 30 × 106m3 (Box and Ski 2007). (Refer to the insert for a color version of this figure)

Photo by Nick Cobbing/Greenpeace

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FIGURE 6.3

A tunnel (R-channel) emerging at the terminus of Pastaruri, Peru. It formed during drainage of a lake. Photo courtesy of M. Hambrey. (Refer to the insert for a color version of this figure)

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FIGURE 6.4

Day-to-day variation of basal water pressure measured in three boreholes, Trapridge Glacier. The solid curve in both panelsshows the same borehole, repeated for comparison. Pressure variations in different boreholes may be correlated, anticorrelated, or uncorrelated. Horizontal dashed lines indicate overburden pressure. Adapted from Murray and Clarke (1995).

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FIGURE 6.5

Evolution of mean velocity and travel time for water entering a single moulin and appearing at the glacier front, Haut Glacier d’Arolla. Data acquired by tracer injection. Adapted from Nienow et al. (1998).

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FIGURE 6.6

Discharge from a glacierized basin near Zermatt, Switzerland, in four periods of fine weather in summer 1959 (dates indicated beside each curve). Adapted from Elliston (1973).

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FIGURE 6.7

Discharge from the same basin as in Figure 6.6 after summer snowfalls. (a) 29 June–2 July 1959, (b) 30 July–1 Aug. 1959, (c) 26–28 June 1960, (d) 4–8 Sept. 1960, (e) 17–19 Sept. 1960. Redrawn from Elliston (1973). Used with permission from the International Association of Hydrological Sciences, Elliston, G.R., Water movement through the Gornergletscher, IAHS Press, International Association of Scientific Hydrology Publications, vol. 95, Fig. 2/pp. 79–84.

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FIGURE 6.8

Variation of runoff from Haig Glacier (Canadian Rockies) over an entire summer season. The solid curve shows the center-weighted running mean over two days. The gray band shows the range of daily fluctuations. Two brief, exceptionally large discharge events occurred. The first peaked at 6.1m3 s−1, the second at 12.2m3 s−1. Adapted from Shea et al. (2005). Data courtesy of Shawn Marshall.

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FIGURE 6.9

Schematic diagram showing plausible variations of glacial runoff in two climate warming scenarios, on two landscapes. “Extensive glaciation” means that glaciers cover a large fraction of the land surface and a wide range of altitudes. “Minor glaciation” means that glaciers are present only in high basins. The value Qo indicates the relative scale of the vertical axes on the discharge plots.

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FIGURE 6.10

Schematic diagram of equipotential surfaces (broken lines) and related theoretical drainage pattern in a glacier. Small channels within the ice should tend to be perpendicular to the equipotential surfaces, but the inclination of a moulin is determined by that of the crevasse from which it formed. Water also flows along fractures of various orientations, in whichever direction the potential decreases. (See Figure 6.1 for a more complete depiction of features.)

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FIGURE 6.11

Variables for analysis of water flow in a tunnel surrounded by ice.

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FIGURE 6.12

Predicted variation of water pressure, velocity, and radius for a tunnel in steady state, beneath 250m of ice, with various discharges and one set of parameters (θ = 2.5°, A = 5 × 10−24, nm = 0.1).

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FIGURE 6.13

(a) Day-to-day variation of water level (a proxy for subglacial water pressure) in three sets of boreholes in Bench Glacier, Alaska. (b) A map showing the relative positions of boreholes belonging to each group. Adapted from Fudge et al. (2008).

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FIGURE 6.14

Schematic diagrams of linked cavities: (a) plan view, (b) cross-section. Panel (c) shows the idealization used in model formulation. Adapted from Fountain and Walder (1998) and Kamb (1987) and used with permission from the American Geophysical Union, Journal of Geophysical Research.

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FIGURE 6.15

Schematic depiction of water system elements on beds of sediment.

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FIGURE 6.16

The positive feedback mechanism responsible for catastrophic drainage in glacial floods. The feedback can fail to develop, however, if the volume of the reservoir is too small or the water too cold.

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FIGURE 6.17

Hydrograph of the 1954 jökulhlaup from Grimsvötn, Iceland. Redrawn from Rist (1955).