The impact of the structural framework of the North German Basin on Pleistocene tunnel‐valley formation

Tunnel valleys are impressive subglacial erosional landforms and may attain depths of almost 600 m. Climatic and glaciological factors exert the primary control on tunnel‐valley formation. Furthermore, regional geological features, e.g. faults and salt structures, have been suggested as controlling factors for tunnel‐valley formation. To improve the understanding of the impact of these geological factors on tunnel‐valley incision, we compare the distribution and orientations of buried Pleistocene tunnel valleys in the North German Basin with regional geological features, such as basin geometry and infill, faults and salt structures. Our analysis shows that deep tunnel valleys are restricted to areas with thick erodible Cenozoic deposits. The correlation between the trends of tunnel valleys, faults and salt structures varies between the analysed regions. The orientations of tunnel valleys commonly follow the trends of faults and salt structures in regions where the structural trend is NNW–SSE to east–west and ice‐flow directions were approximately parallel to this trend. However, correlations are rarely observed if the regional structural trend is NW–SE to WNW–ESE and ice advances occurred thus normal or oblique to the regional fault trend. Potential future tunnel‐valley incision is regarded as a major challenge for the long‐term safety of radioactive waste repositories because incision may reach depths under consideration for repositories. The presence and orientations of faults and salt structures, however, do not provide consistent indicators for future tunnel‐valley incision.