Preprints
https://doi.org/10.5194/tc-2021-65
https://doi.org/10.5194/tc-2021-65

  17 Mar 2021

17 Mar 2021

Review status: this preprint is currently under review for the journal TC.

Development of a subglacial lake monitored with radio-echo sounding: Case study from the Eastern Skaftá Cauldron in the Vatnajökull ice cap, Iceland

Eyjólfur Magnússon1, Finnur Pálsson1, Magnús T. Gudmundsson1, Thórdís Högnadóttir1, Cristian Rossi2, Thorsteinn Thorsteinsson3, Benedikt G. Ófeigsson3, Erik Sturkell4, and Tómas Jóhannesson3 Eyjólfur Magnússon et al.
  • 1Institute of Earth Sciences, University of Iceland, Reykjavík, IS-102, Iceland
  • 2Remote Sensing Technology Institute, German Aerospace Center (DLR), Wessling, 82234, Germany
  • 3Icelandic Meteorological Office, Reykjavík, IS-105, Iceland
  • 4Department of Earth Sciences, University of Gothenburg, Gothenburg, Box 460, 405 30, Sweden

Abstract. We present repeated radio-echo sounding (RES, 5 MHz) on a profile grid over the Eastern Skaftá Cauldron (ESC) in Vatnajökull ice cap, Iceland. The ESC is ~3 km wide and 50–150 m deep ice cauldron created and maintained by subglacial geothermal activity of ~1 GW. Beneath the cauldron and 200–400 m thick ice, water accumulates in a lake and is released semi-regularly in jökulhlaups. The RES record consists of annual surveys with 200–400 m between profiles in early summers of 2014–2020. Comparison of the RES surveys (2D migrated profiles) reveals variable lake area (0.5–4.1 km2) and enables traced reflections from the lake roof to be distinguished from bedrock reflections. This allows construction of a digital elevation model (DEM) of the bedrock in the area, further constrained by two borehole measurements at the cauldron centre. It also allows creation of lake thickness maps and an estimate of lake volume at the time of each survey, which we compare with lowering patterns and released water volumes obtained from surface DEMs obtained before and after jökulhlaups. The estimated lake volume is 250 × 106 m3 in June 2015 but 320 ± 20 × 106 m3 drained from the cauldron in October 2015. In June 2018, RES profiles reveal a lake volume of 185 × 106 m3 while 220 ± 30 × 106 m3 was released in a jökulhlaup in August 2018. Considering the water accumulation over the periods between RES surveys and jökulhlaups, this indicates 10–20 % uncertainty in the RES-derived volumes at times when significant jökulhlaups may be expected.

Eyjólfur Magnússon et al.

Status: open (until 12 May 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Review of TC-2021-65', Anonymous Referee #1, 07 Apr 2021 reply
  • RC2: 'Comment on tc-2021-65', Anonymous Referee #2, 13 Apr 2021 reply

Eyjólfur Magnússon et al.

Eyjólfur Magnússon et al.

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Short summary
We present a unique insight into the shape and development of a subglacial lake over 7-year period, using repeated radar survey. The lake collects geothermal melt water, which is released in semi-regular floods, often referred to as jökulhlaups. The applicability of our survey approach to monitor the water stored in the lake for a better assessment of the potential hazard of jökulhlaups is demonstrated by comparison with independent measurements of released water volume during two jökulhlaups.