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Subglacial tunnel valleys in the Alpine foreland: an example from Bern, Switzerland

Dürst Stucki, Mirjam ; Reber, Regina ; Schlunegger, Fritz

In: Swiss Journal of Geosciences, 2010, vol. 103, no. 3, p. 363-374

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    Titel
    • Subglacial tunnel valleys in the Alpine foreland: an example from Bern, Switzerland
    Autor
    • Dürst Stucki, Mirjam. Institute of Geological Sciences, University of Bern, Baltzerstrasse 1+3, 3012, Bern, Switzerland
    • Reber, Regina. Institute of Geological Sciences, University of Bern, Baltzerstrasse 1+3, 3012, Bern, Switzerland
    • Schlunegger, Fritz. Institute of Geological Sciences, University of Bern, Baltzerstrasse 1+3, 3012, Bern, Switzerland
    Dokumententyp
    • Postprint
    Sprache
    • Englisch
    Veröffentlicht in
    • Swiss Journal of Geosciences, 2010, vol. 103, no. 3, p. 363-374. SP Birkhäuser Verlag Basel
    Andere elektronische Ausgabe
    OAI-PMH-ID
    • oai:doc.rero.ch:312101
    Summary
    The morphology of the Alpine and adjacent landscapes is directly related to glacial erosion and associated sediment transport. Here we report the effects of glacio-hydrologic erosion on bedrock topography in the Swiss Plateau. Specifically, we identify the presence of subsurface valleys beneath the city of Bern and discuss their genesis. Stratigraphic investigations of more than 4,000 borehole data within a 430km2-large area reveal the presence of a network of >200m-deep and 1,000m-wide valleys. They are flat floored with steep sided walls and are filled by Quaternary glacial deposits. The central valley beneath Bern is straight and oriented towards the NNW, with valley flanks more than 20° steep. The valley bottom has an irregular undulating profile along the thalweg, with differences between sills and hollows higher than 50-100m over a reach of 4km length. Approximately 500m high bedrock highlands flank the valley network. The highlands are dissected by up to 80m-deep and 500m-broad hanging valleys that currently drain away from the axis of the main valley. We interpret the valleys beneath the city of Bern to be a tunnel valley network which originated from subglacial erosion by melt water. The highland valleys served as proglacial meltwater paths and are hanging with respect to the trunk system, indicating that these incipient highland systems as well as the main gorge beneath Bern formed by glacial melt water under pressure