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

• Main Authors: Magnússon, Eyjólfur, Pálsson, Finnur, Gudmundsson, Magnús T., Högnadóttir, Thórdís, Rossi, Cristian, Thorsteinsson, Thorsteinn, Ófeigsson, Benedikt G., Sturkell, Erik, Jóhannesson, Tómas
• Format: Text
• Language: English
• Published: 2021
• Subjects: Skaftá; The Cauldron; Vatnajökull; Ice cap; Iceland
• Online Access: https://doi.org/10.5194/tc-2021-65; https://tc.copernicus.org/preprints/tc-2021-65/

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 km 2 ) 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 × 10 6 m 3 in June 2015 but 320 ± 20 × 10 6 m 3 drained from the cauldron in October 2015. In June 2018, RES profiles reveal a lake volume of 185 × 10 6 m 3 while 220 ± 30 × 10 6 m 3 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.