On the role of geothermal feedback mechanisms on tunnel valley genesis above salt domes

• Main Author: Bodenburg, Sascha Barbara
• Other Authors: Kowalski, Julia, Hübscher, Christian
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: RWTH Aachen University 2023
• Subjects: info:eu-repo/classification/ddc/550; Gorleben salt dome; apparent heat capacity methods; heat conduction and hydrothermal flow; southern North Sea; subglacial feedback mechanisms; tunnel valley genesis; Ice Sheet
• Online Access: https://publications.rwth-aachen.de/record/969814; https://publications.rwth-aachen.de/search?p=id:%22RWTH-2023-09361%22

Physical feedback mechanisms between the subsurface and an overlying ice sheet are manifold. They lead to the development of special landforms, e.g. tunnel valleys. Tunnel valleys are widespread in (formerly) glaciated areas. They are eroded by subglacially flowing water. To investigate their genesis, it is necessary to model feedback mechanisms between the ice sheet and the subsurface. In the North German Basin, a possible spatial correlation between tunnel valleys and underlying salt domes was often observed. Partly, this was explained mechanically with the presence of faults. We want to investigate a different hypothesis for tunnel valley genesis based on the following geothermal argumentation: As salt better conducts heat than the surrounding rocks, the geothermal heat flux is augmented above. Hydrothermal groundwater flows through crestal faults enhance this effect. The resulting subglacial melting leads to subglacial rivers eroding the tunnel valleys. In order to determine the subglacial melting rate, a holistic computational model is needed. Usually, the different regimes of the overlying ice sheet and the underlying subsurface are investigated separately. The other domain is only included by a boundary condition. In this study, we developed a coupled computational model comprising both the heterogeneous subsurface and the dynamic ice sheet including subglacial phase change processes to allow for feedback mechanisms. The basing physical assumptions are the following: The subsurface is influenced by heat conduction and advection due to groundwater flow through the different rocks. The ice sheet melts at its base, while ice is accumulated at its surface. Therefore, it moves as a whole ice sheet. In our approach, we attached great value on the energy balance at the ice sheet's base. First, very simplified models show that the subglacial temperature should be increased at locations of increased geothermal heat fluxes as above salt domes. However, the temperature at the glacier's base must be assumed to be the ...