Diurnal fluctuations in borehole water levels: configuration of the drainage system beneath Bench Glacier, Alaska, USA

Fudge, T. J.; Humphrey, N. F.; Harper, Joel T.; Pfeffer, W. T.

doi:10.3189/002214308784886072

Cited by 43 publications

(63 citation statements)

References 42 publications

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“…Specifically, we assume each weakly connected patch is a circle of radius 10 m (based on observations of differing connectivity on that scale in GrIS and elsewhere4343552) and set Δ s =10 m. For the chosen values of the fractional area of the weakly connected system ( f w =0.67) and grid spacing (Δ x =Δ y =200 m) we can calculate P w ≈5,355 m from basic geometry. While other choices could be made here, these details are not important from a practical standpoint without detailed knowledge of the bed, as these parameters, along with k 0w , are free variables in equation (6).…”

Section: Methodsmentioning

confidence: 99%

Greenland subglacial drainage evolution regulated by weakly connected regions of the bed

et al. 2016

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Penetration of surface meltwater to the bed of the Greenland Ice Sheet each summer causes an initial increase in ice speed due to elevated basal water pressure, followed by slowdown in late summer that continues into fall and winter. While this seasonal pattern is commonly explained by an evolution of the subglacial drainage system from an inefficient distributed to efficient channelized configuration, mounting evidence indicates that subglacial channels are unable to explain important aspects of hydrodynamic coupling in late summer and fall. Here we use numerical models of subglacial drainage and ice flow to show that limited, gradual leakage of water and lowering of water pressure in weakly connected regions of the bed can explain the dominant features in late and post melt season ice dynamics. These results suggest that a third weakly connected drainage component should be included in the conceptual model of subglacial hydrology.

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Section: Methodsmentioning

confidence: 99%

Greenland subglacial drainage evolution regulated by weakly connected regions of the bed

et al. 2016

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“…Measurements of subglacial water pressure [94][95][96][97][98][99], along with the less common measurements of borehole turbidity, electrical properties and geochemistry [100][101][102][103], have also been used to study drainage-system structure and dynamics [103][104][105][106]. Direct visual observations are rare, though borehole imagery [107,108] and exploration of englacial/subglacial tunnels [109,110] and cavities [111] have furnished some important and surprising information [112].…”

Section: Elements Of the Basal Drainage Systemmentioning

confidence: 99%

Modelling water flow under glaciers and ice sheets

2015

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Recent observations of dynamic water systems beneath the Greenland and Antarctic ice sheets have sparked renewed interest in modelling subglacial drainage. The foundations of today's models were laid decades ago, inspired by measurements from mountain glaciers, discovery of the modern ice streams and the study of landscapes evacuated by former ice sheets. Models have progressed from strict adherence to the principles of groundwater flow, to the incorporation of flow 'elements' specific to the subglacial environment, to sophisticated twodimensional representations of interacting distributed and channelized drainage. Although presently in a state of rapid development, subglacial drainage models, when coupled to models of ice flow, are now able to reproduce many of the canonical phenomena that characterize this coupled system. Model calibration remains generally out of reach, whereas widespread application of these models to large problems and real geometries awaits the next level of development.

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“…11, also Harper et al (2002)). Different parts of bed still exhibit diurnal oscillations but cease to be mutually well-connected, as also observed by Fudge et al (2008). We will refer to the parts of the bed that remain internally well-connected as hydraulic subsystems ( over an increasing fraction of the bed.…”

Section: Discussionmentioning

confidence: 96%

“…We label this as the start of stage 3 in Figs. 4 and 8, 10;in Fudge et al (2008), this is referred to as the "fall event" (though their data makes connections with snow fall less easy to establish).…”

Section: Discussionmentioning

confidence: 99%

Subglacial drainage characterization from eight years of continuous borehole data on a small glacier in the Yukon Territory, Canada

Rada

Schoof

2018

Preprint

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Abstract. The subglacial drainage system is one of the main controls on basal sliding, but remains only partially understood.Here we use an eight-year data set of borehole observations on a small, alpine polythermal valley glacier in the Yukon Territory to assess qualitatively how well the established understanding of drainage physics explains the observed temporal evolution and spatial configuration of the drainage system. We find that the standard picture of a channelizing drainage system that evolves towards higher effective pressure explains many features of the data set. However, our data set underlines the importance of 5 hydraulic isolation of parts of the bed. We observe how isolated portions of the bed systematically grow towards the end of the summer season, causing the drainage system to fragment into progressively more distinct subsystems. We conclude with an adaptation of existing drainage models that aims to capture the ability of parts of the bed to become hydraulically isolated due to basal cavities of finite size becoming disconnected from each other as they shrink.

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Diurnal fluctuations in borehole water levels: configuration of the drainage system beneath Bench Glacier, Alaska, USA

Cited by 43 publications

References 42 publications

Greenland subglacial drainage evolution regulated by weakly connected regions of the bed

Greenland subglacial drainage evolution regulated by weakly connected regions of the bed

Modelling water flow under glaciers and ice sheets

Subglacial drainage characterization from eight years of continuous borehole data on a small glacier in the Yukon Territory, Canada

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