Buried Quaternary valleys - a geophysical approach

Buried Quaternary valleys, incising several hundred metres in Tertiary sediments, are of a glacial origin and demonstrate the immense forces acting below the glaciers by the pressurised melted water. Aside from their fascinating genesis, these valleys have a practical value because the sedimentary filling can be very permeable and can act as important aquifers for the water supply. Sustainable water management requires a detailed knowledge of the subsurface structures. Geophysical tools for the investigation and characterisation of aquifers in unconsolidated sediments are tested in six different study areas. Valleys with a width of more than 1 km and a depth of more than 200 m differ in their sedimentary environment and filling. This can be detected by gravity anomalies. Using seismic profiles, shape, internal structure and embedding in the surroundings are revealed. Airborne electromagnetic surveys map the distribution of electrical resistivity down to a depth of 300 m. In most cases the valley is clearly distinguishable from the surrounding material. The quality of the covering layers is quantified by the electrical resistivity. A reliable interpretation can be attained by combining the various methods with borehole information and expert geological knowledge.