Analysing Pleistocene tunnel valleys to assess the impact of future glaciations on the long-term safety of radioactive waste repositories

Future glaciations are considered as a major challenge for the long-term safety of repositories for highly active radioactive waste, which has to be assessed for up to one million years. Especially the incision of subglacial tunnel valleys reaches depths of up to 600 m b.s.l., which is within the depth range considered for repositories.

Tunnel valleys are ubiquitous features of formerly glaciated sedimentary basins and are characterised by undulating basal profiles, abrupt terminations and steep flanks, all indicative of their subglacial formation by pressurised subglacial meltwater. To assess the potential of future tunnel-valley formation and its implications for long-term safety, we apply a multi-directional approach:

• By mapping the distribution and maximum depths of Pleistocene tunnel valleys in Germany a zonation map of the regional depth of erosion was generated. These depth zones may be used to define a regionally variable additional depth for a repository (Breuer et al., 2023).
• To understand the impact of pre-existing geological structures on tunnel-valley formation we compared the trends of Pleistocene tunnel valleys to faults, salt structures and the large-scale geometry of the North German Basin. A correlation between those features was only locally observed, presumably if ice-advance directions matched the major structural trends.
• High-resolution 3D seismic data from the central North Sea are analysed to gain insight into the morphology and depositional architecture of Pleistocene tunnel valleys. These insights may serve as analogue for other, less well-resolved tunnel valleys.

References:

Breuer et al. (2023), E&G Quat. Sci. J., 72, 113-125, DOI:10.5194/egqsj-72-113-2023