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Hydraulic impacts of glacier advance over a sediment bed

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Abstract:

A sedimentary sequence of till overlying a gravel aquifer was instrumented with water-pressure transducers prior to a small, anticipated surge of the margin of the glacier Breiðamerkurjökull in Iceland. The records of water pressure at each transducer site show a well-defined temporal sequence of hydraulic regimes that reflect the changing recharge of surface-derived meltwater, the pressure drop along the drainage pathway and the pattern of ice loading. The poroelastic and water-pressure response of glacially overridden sediments to the recharge rate is determined in the frequency domain through an analytic solution. This permits the in situ conductivity, compressibility and consolidation states of subglacial sediments to be derived, and reveals aquifer-scale compressibility that produces an important water-pressure wave associated with the advancing glacier. The model is then used to explore how varying conductivity/compressibility, largely determined by granulometry, can determine drainage states and instabilities that may have a large impact on glacier/ice-sheet dynamics, and how the drainage time of surface water to the bed can determine the frequency response of subglacial groundwater regimes and their influence on subglacial sediment stability. Mismatches between model predictions and specific events in water-pressure records are used to infer processes that are not incorporated in the model: hydrofracturing that changes the hydraulic properties of subglacial sediments; the impact on groundwater pressure of subglacial channel formation; upwelling beyond the glacier margin; and rapid variations in the state of consolidation. The poroelastic model also suggests how seismic methods can be developed further to monitor hydraulic conditions at the base of an ice sheet or glacier.

Document Type: Research Article

DOI: https://doi.org/10.3189/172756506781828403

Publication date: 2006-12-01

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  • The Journal of Glaciology is published six times per year. It accepts submissions from any discipline related to the study of snow and ice. All articles are peer reviewed. The Journal is included in the ISI Science Citation Index.

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