Fractures as the main pathways of water flow in temperate glaciers

Abstract

Understanding the flow of water through the body of a glacier is important, because the spatial distribution of water and the rate of infiltration to the glacier bottom is one control on water storage and pressure, glacier sliding and surging, and the release of glacial outburst floods. According to the prevailing hypothesis, this water flow takes place in a network of tubular conduits. Here we analyse video images from 48 boreholes drilled into the small Swedish glacier Storglaciären, showing that the glacier's hydrological system is instead dominated by fractures that convey water at slow speeds. We detected hydraulically connected fractures at all depths, including near the glacier bottom. Our observations indicate that fractures provide the main pathways for surface water to reach deep within the glacier, whereas tubular conduits probably form only in special circumstances. A network of hydraulically linked fractures offers a simple explanation for the origin and evolution of the englacial water flow system and its seasonal regeneration. Such a fracture network also explains radar observations that reveal a complex pattern of echoes rather than a system of conduits. Our findings may be important in understanding the catastrophic collapse of ice shelves and rapid hydraulic connection between the surface and bed of an ice sheet.

Moment Tensor Inversions of Icequakes on Gornergletscher, Switzerland

“…Such fractures have also been observed in other studies (Harper and Humphrey, 1995;Fountain et al, 2005;Meierbachtol et al, 2006) and may have a significant influence on water flow inside temperate glaciers.…”

Dynamic perennial firn aquifer on an Arctic glacier

“…In our survey area, the lack of large local deviations in the PFA suggests that there are no large local recharge sources or discharge sinks from crevasses, moulins, or other features [e.g., Fountain et al, 2005], and that the base of the PFA is relatively impermeable. Instead, our data suggest that summertime meltwater percolates downward into the firn and that water, if not refrozen, then flows along the PFA roughly parallel to the glacier surface toward the firn limit.…”

“…There is some evidence that these aquifers respond dynamically to surface forcing, rising and lowering in response to diurnal meltwater input variation [Ambach et al, 1978;Fountain, 1989]. Primary aquifer discharge is probably through the englacial crevasse network into the englacial and subglacial hydrologic system [Fountain, 1989;Fountain et al, 2005], possibly affecting glacier dynamics. Especially vigorous drainage can occur when a new connection to a crevasse is established, perturbing the firn water table, so that it no longer follows the surface topography [Fountain, 1989].…”

The physics of premelted ice and its geophysical consequences

“…Theoretical models for water flow through the veins of temperate glacial ice ͑Lłi-boutry, 1971; Shreve, 1972;Fowler, 1984͒ suggest that this mode of englacial transport typically represents only a minor contribution to the total fluid flux, which is dominated by flow through moulins, channels, and fractures ͑Röthlisberger, 1972; Paterson, 1994;Fountain et al, 2005͒. Nevertheless, phase equilibrium conditions along vein walls are thought to represent an important buffer in controlling the temperature within glacial ice ͑Harrison, 1972͒.…”