20 Jul 2022
20 Jul 2022
Status: this preprint is open for discussion.

Seismic Characteristics of the Largest Measured Subglacial Flood from the Eastern Skaftá cauldron, Iceland

Eva P. S. Eibl1, Kristin S. Vogfjörd2, Benedikt G. Ófeigsson2, Matthew J. Roberts2, Christopher J. Bean3, Morgan T. Jones4, and Bergur H. Bergsson2 Eva P. S. Eibl et al.
  • 1University of Potsdam, Institute of Geosciences, Karl-Liebknecht-Str. 24-25, 14476 Potsdam, Germany
  • 2Icelandic Meteorological Office, Bústaðavegi 7–9, 108 Reykjavík, Iceland
  • 3Geophysics Section, School of Cosmic Physics, Dublin Institute for Advanced Studies, 5 Merrion Square, Dublin 2, Ireland
  • 4Center for Earth Evolution and Dynamics (CEED), University of Oslo, PO Box 1028, Blindern 0315 Oslo, Norway

Abstract. Subglacial floods are hazardous events. Since seismic tremor accompanies them, the source can be located and tracked in space and time using a seismic array. However, understanding how these seismic signals are generated remains elusive. Here, we study the seismic characteristics of the largest measured flood from the Eastern Skaftá cauldron, Iceland. We track the propagation of the flood in 2015 using two seismic arrays and a local seismic network. Data from three GPS instruments above the cauldron lake and the subglacial flood path and from hydrological instruments in the Skaftá river aid the interpretation. We find that as the water drained from the lake, quakes were generated in the area around the cauldron and the glacier surface subsided by more than 100 m.We detected several-hours-long, non-harmonic tremor migrating downglacier following the subglacial flood front. We suggest that this tremor is composed of repeated, closely spaced icequakes generated as the glacier was being lifted, cracked and deformed enabling the subglacial water flow. When the lake had largely drained, we recorded minute-long tremor bursts with hour-long harmonic tails emanating from the cauldron area. Body waves compose the bursts. We interpret them as hydrothermal explosions in the geothermal system underlying the cauldron, followed by vigorous boiling due to the pressure drop within the hydrothermal system as a consequence of the lowering of the water level in the lake. We conclude that the three different tremor characteristics are associated with three different geophysical processes.

Eva P. S. Eibl et al.

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Eva P. S. Eibl et al.

Eva P. S. Eibl et al.


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Short summary
Floods draining beneath an ice cap are hazardous events. These floods are accompanied by seismic signals, but it is unclear how these signals are created. Here, we study the seismic signals of the largest measured flood of the Skafta lakes, Iceland in comparison to GPS, hydrological and geochemical data. We find three different seismic signals: Quakes mark the start of the flood, long-lasting signals track the flood front beneath the ice and bursts indicate the end of the water drainage.