Ground-penetrating radar imaging reveals  glacier's drainage network in 3D

Church, Gregory; Bauder, Andreas; Grab, Melchior; Maurer, Hansruedi

doi:10.5194/tc-15-3975-2021

Cited by 17 publications

(15 citation statements)

References 69 publications

(86 reference statements)

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“…Theoretical calculations using Hooke (1984) (Section S3.1 in Supporting Information S1) suggest a closure rate of 0.18 m per year if we assume a 5-m-diameter semi-circular channel. One explanation for a higher closure rate than predicted by theory is the deviation of the channel from a semi-circular shape, as observed in boreholes made at the Glacier d'Otemma during the summer of 2021, and reported for the Rhonegletscher by Church et al (2021). An analysis using the theory for non-semi-circular conduits by Hooke et al (1990) produces closure rate estimates over a 16-day period of ∼0.03-0.13 m (Section S3.5 in Supporting Information S1), which is commensurate with our estimations.…”

Section: Discussionmentioning

confidence: 82%

Subglacial Channels, Climate Warming, and Increasing Frequency of Alpine Glacier Snout Collapse

Egli

Belotti

Ouvry

et al. 2021

Geophysical Research Letters

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Negative glacier mass balance can also be driven by reduced snow accumulation. Less considered is basal or internal ablation. This can involve the collapse of subglacial channels in the snout marginal zone, driven by thinning ice combined with slow creep closure. After the collapse, ice is removed via the channel to the glacier outlet. This mechanism of glacier retreat was first described some time ago as "subglacial stoping" or "block caving" (Loewe, 1957;Paige, 1956).

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Section: Discussionmentioning

confidence: 82%

Subglacial Channels, Climate Warming, and Increasing Frequency of Alpine Glacier Snout Collapse

Egli

Belotti

Ouvry

et al. 2021

Geophysical Research Letters

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“…Of special interest within glaciology is also the comparison of our method with the currently most commonly used method to localize glacial drainage systems: GPR. Most recently Church et al (2020) reconstructed an englacial channel on Rhonegletscher in Switzerland, both in 2D (Church et al, 2020) and in 3D (Church et al, 2021). In their 2020 study, Church et al (2020) reported a length error of 2.4 % (6 m) for a 250 m long englacial channel.…”

Section: Comparison With Gpr Perspectives and Limitationsmentioning

confidence: 99%

“…This indicates that the error in our method scales with the length of the investigated channel, thus resulting in a similar length error as reported for the GPR investigations by Church et al (2020) if scaled down to similar shorter channel length. However, our method only allows for reconstructing the actual water flow path and can currently not be used to infer information about channel width and height, as is possible with GPR (e.g., Stuart et al, 2003;Church et al, 2020Church et al, , 2021. The application of our drifter-based approach, in comparison to GPR, is further limited by a certain minimum needed discharge in combination with sufficient drainage system size for drifters to pass through, thus limiting the applicability to the main part of the melt season and channelized drainage systems.…”

Section: Comparison With Gpr Perspectives and Limitationsmentioning

confidence: 99%

“…Time-consuming geophysical investigation methods, utilizing ground-penetrating radar (GPR) (e.g., Stuart et al, 2003;Baelum and Benn, 2011;Hansen et al, 2020;Schaap et al, 2020;Church et al, 2020Church et al, , 2021 and seismic arrays (Nanni et al, 2021) are used to locate en-and subglacial channels. In wintertime, moulins and meltwater channels are accessible for direct speleological investigations and map-ping of water flow paths in shallow glaciers (e.g., Holmlund, 1988;Vatne, 2001;Gulley et al, 2009;Alexander et al, 2020b;Hansen et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

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Topology and spatial-pressure-distribution reconstruction of an englacial channel

2022

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Abstract. Information about glacier hydrology is important for understanding glacier and ice sheet dynamics. However, our knowledge about water pathways and pressure remains limited, as in situ observations are sparse and methods for direct area-wide observations are limited due to the extreme and hard-to-access nature of the environment. In this paper, we present a method that allows for in situ data collection in englacial channels using sensing drifters. Furthermore, we demonstrate a model that takes the collected data and reconstructs the planar subsurface water flow paths providing spatial reference to the continuous water pressure measurements. We showcase this method by reconstructing the 2D topology and the water pressure distribution of a free-flowing englacial channel in Austre Brøggerbreen (Svalbard). The approach uses inertial measurements from submersible sensing drifters and reconstructs the water flow path between given start and end coordinates. Validation of the method was done on a separate supraglacial channel, showing an average error of 3.9 m and the total channel length error of 29 m (6.5 %). At the englacial channel, the average error is 12.1 m; the length error is 107 m (11.6 %); and the water pressure standard deviation is 3.4 hPa (0.3 %). Our method allows for mapping of subsurface water flow paths and spatially referencing the pressure distribution within. Further, our method would be extendable to the reconstruction of other, previously underexplored subsurface fluid flow paths such as pipelines or karst caves.

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“…In addition to these in situ measurement techniques, remote geophysical methods have been used to infer properties of glacier drainage systems by radar and seismic imaging (e.g. Harper and others, 2010; Schroeder and others, 2013; Church and others, 2019, 2021; Egli and others, 2021) or by passively measuring seismic noise (e.g. Dalban Canassy and others, 2016; Gimbert and others, 2016; Röösli and others, 2016; Nanni and others, 2020).…”

Section: Introductionmentioning

confidence: 99%

Characterising englacial R-channels using artificial moulins

et al. 2022

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The englacial and subglacial drainage systems exert key controls on glacier dynamics. However, due to their inaccessibility, they are still only poorly understood and more detailed observations are important, particularly to validate and tune physical models describing their dynamics. By creating artificial glacier moulins – boreholes connected to the subglacial drainage system and supplied with water from surface streams – we present a novel method to monitor the evolution of an englacial hydrological system with high temporal resolution. Here, we use artificial moulins as representations for vertical, pressurised, englacial R-channels. From tracer and pressure measurements, we derive time series of the hydraulic gradient, discharge, flow speed and channel cross-sectional area. Using these, we compute the Darcy–Weisbach friction factor, obtaining values which increase from 0.1 to 13 within five days of channel evolution. Furthermore, we simulate the growth of the cross-sectional area using different temperature gradients. The comparison to our measurements largely supports the common assumption that the temperature follows the pressure melting point. The deviations from this behaviour are analysed using various heat transfer parameterisations to assess their applicability. Finally, we discuss how artificial moulins could be combined with glacier-wide tracer experiments to constrain parameters of subglacial drainage more precisely.

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Ground-penetrating radar imaging reveals glacier's drainage network in 3D

Cited by 17 publications

References 69 publications

Subglacial Channels, Climate Warming, and Increasing Frequency of Alpine Glacier Snout Collapse

Subglacial Channels, Climate Warming, and Increasing Frequency of Alpine Glacier Snout Collapse

Topology and spatial-pressure-distribution reconstruction of an englacial channel

Characterising englacial R-channels using artificial moulins

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