20 Jul 2022
 | 20 Jul 2022

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

Eva P. S. Eibl, Kristin S. Vogfjörd, Benedikt G. Ófeigsson, Matthew J. Roberts, Christopher J. Bean, Morgan T. Jones, and Bergur H. Bergsson

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.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-644', Anonymous Referee #1, 22 Aug 2022
    • AC1: 'Reply on RC1', Eva Eibl, 30 Nov 2022
  • RC2: 'Comment on egusphere-2022-644', Anonymous Referee #2, 02 Sep 2022
    • AC2: 'Reply on RC2', Eva Eibl, 30 Nov 2022
  • RC3: 'Comment on egusphere-2022-644', Anonymous Referee #3, 22 Sep 2022
    • AC3: 'Reply on RC3', Eva Eibl, 30 Nov 2022

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.