Multidisciplinary constraints of hydrothermal explosions based on the 2013 Gengissig lake events, Kverkfjöll volcano, Iceland

• Published in: Earth and Planetary Science Letters
• Main Authors: Montanaro, Cristian, Scheu, Bettina, Gudmundsson, Magnus Tumi, Vogfjörd, Kristin, Reynolds, Hannah Iona, Dürig, Tobias, Strehlow, Karen, Rott, Stefanie, Reuschle, Thierry, Dingwell, Donald Bruce
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2016
• Subjects: hydrothermal explosions; lake drainage; multidisciplinary; deposits volume; energy partitioning; Dammed Lake; Kverkfjöll; Vatnajökull; Iceland
• Online Access: https://hdl.handle.net/1983/7b7fffca-1143-48d8-98ea-a2cf3bf43f77; https://research-information.bris.ac.uk/en/publications/7b7fffca-1143-48d8-98ea-a2cf3bf43f77; https://doi.org/10.1016/j.epsl.2015.11.043; https://research-information.bris.ac.uk/ws/files/75923705/1_s2.0_S0012821X15007475_main.pdf

Hydrothermal explosions frequently occur in geothermal areas showing various mechanisms and energies of explosivity. Their deposits, though generally hardly recognised or badly preserved, provide important insights to quantify the dynamics and energy of these poorly understood explosive events. Furthermore the host rock lithology of the geothermal system adds a control on the efficiency in the energy release during an explosion. We present results from a detailed study of recent hydrothermal explosion deposits within an active geothermal area at Kverkfjöll, a central volcano at the northern edge of Vatnajökull. On August 15th 2013, a small jökulhlaup occurred when the Gengissig ice-dammed lake drained at Kverkfjöll. The lake level dropped by approximately 30 m, decreasing pressure on the lake bed and triggering several hydrothermal explosions on the 16th. Here, a multidisciplinary approach combining detailed field work, laboratory studies, and models of the energetics of explosions with information on duration and amplitudes of seismic signals, has been used to analyse the mechanisms and characteristics of these hydrothermal explosions. Field and laboratory studies were also carried out to help constrain the sedimentary sequence involved in the event. The explosions lasted for 40–50 s and involved the surficial part of an unconsolidated and hydrothermally altered glacio-lacustrine deposit composed of pyroclasts, lavas, scoriaceous fragments, and fine-grained welded or loosely consolidated aggregates, interbedded with clay-rich levels. Several small fans of ejecta were formed, reaching a distance of 1 km north of the lake and covering an area of approximately 0.3 km 2 , with a maximum thickness of 40 cm at the crater walls. The material (volume of approximately 10 4 m 3 ) has been ejected by the expanding boiling fluid, generated by a pressure failure affecting the surficial geothermal reservoir. The maximum thermal, craterisation and ejection energies, calculated for the explosion areas, are on the order of 10 ...