Preprints
https://doi.org/10.5194/egusphere-2022-566
https://doi.org/10.5194/egusphere-2022-566
 
03 Aug 2022
03 Aug 2022
Status: this preprint is open for discussion.

Recent changes in drainage route and outburst magnitude of Russell Glacier ice-dammed lake, West Greenland

Mads Dømgaard1, Kristian Kjellerup Kjeldsen2, Flora Huiban1, Jonathan Lee Carrivick3, Shfaqat Abbas Khan4, and Anders Anker Bjørk1 Mads Dømgaard et al.
  • 1Department of Geoscience and Natural Resource Management, University of Copenhagen, 1350 Copenhagen K, Denmark
  • 2Geological Survey of Denmark and Greenland (GEUS), 1350, Copenhagen K, Denmark
  • 3School of Geography and water@leeds, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, UK
  • 4DTU Space – National Space Institute, Technical University of Denmark, Kgs. Lyngby, Denmark

Abstract. Glacial lake outburst floods (GLOFs) or ‘jökulhlaups’ from ice-dammed lakes are frequent in Greenland and can influence local ice dynamics, bedrock displacement, geomorphological changes and flooding hazards. Multidecadal time series of lake drainage dates, drainage volumes and flood outlets are rare but essential for understanding the impact on and interaction with the surroundings, identifying drainage mechanisms, and for mitigating downstream flood effects. In this study, we use ultra-high-resolution structure-from-motion (SfM) digital elevation models (DEM) and orthophotos from unmanned aerial vehicle field surveys in combination with optical satellite imagery to reconstruct robust lake volume changes associated with 14 GLOFs between 2007 and 2021 at Russell Glacier, West Greenland. This makes it, one of the most comprehensive and longest records of ice-dammed lake drainages in Greenland. We find a mean difference of 10 % between the lake drainage volumes compared with estimates derived from a gauged hydrograph 27 km downstream. Due to ice dam thinning, the potential maximum drainage volume in 2021 is c. 60 % smaller than that estimated to have drained in 2007. Our time series reveals variations in the drainage dates ranging from late May to mid-September and moreover that drained volumes range between 0.9–37.7 M m3. We attribute these fluctuations between short periods of relatively high and low drainage volumes to a weakening of the ice dam and an incomplete sealing of the englacial tunnel following the large GLOFs. The syphoning drainage mechanism is triggered by a reduction in englacial meltwater, likely driven by late seasonal drainages and sudden temperature reductions, as well as annual variations in the glacial drainage system. Furthermore, we provide geomorphological evidence of an additional drainage route first observed following the 2021 GLOF with a sub- or englacial and supraglacial water flow across the ice margin. It seems probable that the new drainage route will become dominant in the future which will drive changes in the downstream geomorphology and raise the risk of flooding-related hazards as the existing buffering outlet lakes will be bypassed.

Mads Dømgaard et al.

Status: open (until 28 Sep 2022)

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  • RC1: 'Comment on egusphere-2022-566', Nathaniel Baurley, 12 Aug 2022 reply

Mads Dømgaard et al.

Mads Dømgaard et al.

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Short summary
Sudden releases of meltwater from glacier-dammed lakes can influence ice flow, cause flooding hazards and landscape changes. This study presents a record of 14 drainages from 2007–2021 from a lake in West Greenland. The time series reveals how the lake fluctuates between releasing large and small amounts of drainage water which is caused by a weakening of the damming glacier following the large events. We also find a shift in the water drainage route which increases the risk of flooding hazards.