Abstract
AbstractThe 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.
Highlights
The experimental study of englacial and subglacial hydrological systems is inherently challenging due to the difficulty of accessing such systems
In the time period 8–21 August 2020, we performed a total of 70 tracer injections in the two artificial moulins AM15 and AM13
The results show that artificial moulins can provide insights into the hydraulics and evolution of an englacial R-channel
Summary
The experimental study of englacial and subglacial hydrological systems is inherently challenging due to the difficulty of accessing such systems. With the current understanding of englacial and subglacial drainage systems, physical models that aim at representing these systems still require a number of assumptions and involve poorly constrained model parameters, which motivates field experiments such as the one presented in this study. The validation of such models is difficult since measurements of subglacial water pressure, temperature, discharge and flow speed are usually sparse in space and time. Brinkerhoff and others (2021) arrived at largely the same conclusion as they coupled a subglacial drainage model (Werder and others, 2013) to an ice dynamics model enabling the use of surface velocity measurements to invert for subglacial drainage properties
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