Skip to content

Hazards of perched lava lakes -- high-volume subsurface spill and flow in the last phase of the 2021 Fagradalsfjall eruption, Iceland

Elisa Johanna Piispa 1, Gro Birkefeldt Moller Pedersen1,2, Kimberly Jean Hutchinson1,3, Jóhanna Malen Skúladóttir1,2, and Birgir Vilhelm Óskarsson4

  • Affiliations:  1Institute of Earth Sciences, University of Iceland, Reykjavik, Iceland; 2Icelandic Meteorological Office, Reykjavik, Iceland; 3National Tsunami Warning Center, National Oceanic and Atmospheric Administration, Alaska, USA; 4Natural Science Institute of Iceland, Garðabær, Iceland 

  • Presentation type: Poster

  • Presentation time: Tuesday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 46

  • Programme No: 6.5.15

  • Theme 6 > Session 5

Abstract

Perched lava lakes pose significant hazards due to their ability to suddenly release large volumes of molten lava during a breach or break through, often with effusion rates greatly exceeding those observed at the vent. During the final phase of the 2021 Fagradalsfjall eruption in Iceland, a perched lava lake formed, ponded and broke through. The resulting lava flowed through subsurface pathways into an upwelling zone and flooded the Geldingar valley with a large sheet flow with high effusion rate, endangering tourists and a hiking path downstream. Here, we evaluate the perched lava lake's size, volume loss during drainage, and effusion rates. These data are combined with post-eruption drone-based magnetic surveys to investigate the lava lake's evolution and subsurface lava transport pathways. Our results show that the perched lava lake acted as a temporary reservoir, with effusion rates 5-10 times the average vent effusion rate during the breakthrough. Although active for only three days during the six-month eruption, the upwelling zone discharged ~6 million m³ of lava. Magnetic surveys delineate possible locations of the hidden subsurface lava pathways, which facilitated the rapid flow of lava into the upwelling zone. This study highlights the hazards of perched lava lakes and their ability to drain via subsurface pathways, emerging downstream as large sheet flows with a sudden, drastic increase in local effusion rates. By integrating remote sensing data with geophysical surveys, this work provides new insights into lava transport processes and emphasizes the value of multidisciplinary approaches in hazard assessment.