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Acoustic imaging of volcanic gas migration and degassing beneath Laacher See

Stijn Albers 1, Thomas Vandorpe2, Corentin Caudron3, Bernd Schmidt4, Joachim Ritter5, Klaus Reicherter6, Marc De Batist1

  • Affiliations: 1Renard Centre of Marine Geology (RCMG), Ghent University, Ghent, Belgium; 2Flanders Marine Institute (VLIZ), Ostend, Belgium; 3Université Libre de Bruxelles (ULB), Brussels, Belgium; 4Seismological Service, State Office for Geology and Mining of Rhineland-Palatinate, Mainz, Germany; 5Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany; 6Neotectonics and Natural Hazards Group, RWTH Aachen University, Aachen, Germany

  • Presentation type: Talk

  • Presentation time: Friday 14:15 - 14:30, Room S150

  • Programme No: 3.17.5

  • Theme 3 > Session 17

Abstract

Recent findings on deep magma-related seismicity and uplift in the Eifel (western Germany) has led to a renewed interest towards monitoring volcanic degassing, especially at the Laacher See volcanic lake, formed by a series of eruptions 13 ka BP. Present-day degassing activity is evidenced by several gas seeps in the lake and surrounding shore, emitting CO2 of magmatic origin. In this study, we used geophysical techniques during two surveys in 2019 and 2021 to image and monitor this CO2 seepage, both in the water column and in the sedimentary infill of the lake. A multibeam echosounder was used to locate gas bubbles rising through the water column, visible by their high backscatter intensity, as well as bathymetric gas escape features on the lake floor. Additionally, high-resolution seismic reflection profiles were acquired to identify and map gas accumulations in the subsurface, evidenced by enhanced reflections and acoustic blanking. Our results show that gas is present at different depths below the lake floor, making it possible to map out areas with subsurface gas accumulations. These often coincide with areas that have a high concentration of gas seeps in the water column. Furthermore, pockmarks can be identified on the lake floor bathymetry, linking upward gas migration in the subsurface to the water column seepage. Our data confirm that CO2 is actively migrating through the sediments and water column of Laacher See and illustrate the need for monitoring this degassing, which can contribute to a better volcanic hazard assessment in the Eifel region.