Digging Beneath the Ice: What Overdeepenings and Tunnel Valleys Reveal About Past Glaciations and Present-Day Subsurface Challenges (Gegg & Preusser, 2023)

by: Shiyu Zhan and Anna-Maria Dröge.

“These landforms lie hidden beneath the surface. Only drilling or geophysics can uncover them — and ideally, we need both.” — Prof. Dr. Frank Preusser

Similar Landforms from Contrasting Ice System

During the first phase of the DOVE project (Drilling Overdeepened Alpine Valleys, www.dove-icdp.eu) in 2023, Prof. Dr. Frank Preusser and his colleagues compared two types of buried subglacial landforms: overdeepenings in the northern Alpine foreland and tunnel valleys in northern Germany. While these features formed under very different glaciological conditions — valley glaciers in the Alps vs. continental ice sheets in the northern central Europe — their morphology is surprisingly similar. Both display sinuous forms, undulating longitudinal profiles, and cross-sectional diversity shaped by basal meltwater erosion. Recognition of commonalities and regional differences between the two structures enhances the interpretation of glacial erosion and geomorphic development.

Figure 1: Explanation of the location and differences between overdeepenings in Switzerland and tunnel valleys in northern Germany based on more precise localization (Gegg & Preusser , 2023)

Unseen Structures, Unmet Support

The study has real-world relevance beyond geoscience. Overdeepenings and tunnel valleys can act as groundwater reservoirs and potential geothermal sites. Understanding their structure is also vital for evaluating locations for radioactive waste storage, which requires stable and well-characterized subsurface conditions. However, while Alpine overdeepenings are well documented through drill cores, similar data for northern Germany’s tunnel valleys are lacking—often due to limited research funding. This data gap hinders systematic comparison and evaluation of their present-day hydrogeological roles. As Dr. Preusser noted in our interview, it's crucial to assess whether such structures could be reactivated by erosion. If located near future storage sites, renewed glacial activity or meltwater erosion could destabilize these buried features, threatening the long-term safety of underground facilities meant to isolate hazardous materials for millennia.

Unveiling the Subsurface, One Borehole at a Time

By combining geophysical imaging and deep sediment cores, researchers can reconstruct the shape, formation, and infill history of glacial basins. The authors advocate for more drill-based studies north of the low mountain ranges and broader interdisciplinary, transregional collaboration (e.g. DOVE project) to assess their evolution and future risks. The work represents an important impetus for greater networking of glacial morphological research between high mountains and lowlands and for integration across disciplinary boundaries.

Figure 2: left: Typical overdeepened valley landscape in the Alpine foreland – the target area of the DOVE drilling campaign; right: Drilling activity as part of the ICDP-DOVE project – sampling sediment cores from an overdeepened basin (DOVE-ICDP Team / dove-icdp.eu).

Reference

Gegg, L., & Preusser, F. 2023. Comparison of overdeepened structures in formerly glaciated areas of the northern Alpine foreland and northern central Europe. E&G Quaternary Sci. J., 72(1), 23-36. doi:10.5194/egqsj-72-23-2023.