Skip to content

Water column survey and structural analysis at the Öskjuvatn lake during a caldera unrest (Askja, central Iceland)

Robin Menu1, Nicolas Oestreicher1, 2, 3, Cesar Fernando Ordones Valdebenito4, Daniel Franck McGinnis4, Tom Sheldrake1, Angel Ruiz-Angulo5, Þorsteinn Sæmundsson5, 6, Ármann Höskuldsson5, Joël Ruch1

  • Affiliations: 1 Department of Earth Sciences, University of Geneva, Geneva, Switzerland; 2 WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland; 3 Climate Change, Extremes and Natural Hazards in Alpine Regions Research Centre CERC, Davos, Switzerland; 4 Department F.A Forel of Environmental Sciences University of Geneva; 5 Faculty of Earth Sciences School of Engineering and Natural Sciences University of Iceland; 6 Faculty of Life and Environmental Sciences School of Engineering and Natural Sciences University of Iceland

  • Presentation type: Poster

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

  • Poster Board Number: 67

  • Programme No: 3.11.27

  • Theme 3 > Session 11

Abstract

The lake Öskjuvatn is in the Askja caldera system (central Iceland). It originated from the Öskjuvatn caldera formation following the 1875 Plinian eruption. Since 2021, an uplift of over 80 cm has been observed. The deformation could cause overturning and massive CO2 degassing if the lake is saturated. There is thus an urgent need to analyse the lake's chemistry and morphology during this unresting phase of the caldera. We present results of a lake survey from August 2024, the chemical characteristics and sublacustrine geological structures. We performed water column profiles using seabird multi-factorial measurements distributed across the lake, which is slightly layered. To test dissolved CO2 concentration, we sampled spot analysis at different locations and depths. Results show a concentration of dissolved CO2 over 480 mmol/m3 at the bottom of the lake (220 m). We suggest that it originates from the emanation of CO2 from sublacustrine vents and fault zones located at the lake bottom, also observed with an underwater drone for the first time in 2024. The collected data suggests that the concentration of CO2 is far from saturation (<1%), and a catastrophic degassing event is unlikely in the current unrest phase. We further combined the high-resolution DEM from onshore drone flights in 2023 and 2024 with the 2012 and 2014 bathymetric data and obtained the first complete structural map of the Öskjuvatn caldera system. Together with the chemical analysis and underwater footage, it provides an important overview of the lake activity during an unresting phase of a caldera.