New insights into the formation and distribution of Pleistocene tunnel valleys in northern Germany

Tunnel valleys are among the deepest erosional structures in formerly glaciated areas. Our project aims to provide a synoptic model of the distribution, dimensions and evolution of Pleistocene tunnel valleys and their infills in northern Germany. The results will be used to assess the potential for future tunnel valley formation, which may pose a threat to the long-term (i.e., the next 1 Ma) safety of a radioactive waste repository.

In the first phase of our project, we produced a new overview map of the Pleistocene tunnel-valley network. From this map, we extracted the tunnel-valley thalwegs and classified them into zones of similar maximum depths. Zones of deep erosion (>400m) follow the large-scale geometry of the North German Basin. The map of maximum depth zones can be used as a planning tool for long-term safety assessments.

The next phase of our project includes a regional analysis of the tunnel valley network and local case studies. The regional analysis will compare the trends observed in the tunnel-valley network with regional geological features such as faults, salt structures and basin-fill architecture. The correlation between tunnel-valley trends and faults is ambiguous. Parallel trends occur mainly where ice advance directions were parallel to fault trends.

As a first case study, we use high-resolution 3D seismic data from the German North Sea that image two intersecting tunnel valleys. Initial results show at least three distinct seismic units correlating with different sediment types and patterns, and possible multiple use of the tunnel valley.