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| Titel |
Rivers under ice: fluvial erosion beneath decaying ice sheets |
| VerfasserIn |
John D. Jansen, Alexandru T. Codilean, Arjen P. Stroeven, Derek Fabel, Clas Hättestrand, Johan Kleman, Jon M. Harbor, Jakob Heyman, Peter W. Kubik, Sheng Xu |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250098042
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| Publikation (Nr.) |
 EGU/EGU2014-13681.pdf |
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| Zusammenfassung |
| The century-long debate over the origins of inner gorges cut within larger valleys that were
repeatedly covered by Quaternary glaciers hinges upon whether the gorges are fluvial forms
eroded by subaerial rivers, or subglacial forms cut beneath ice. We apply cosmogenic nuclide
exposure dating to seven inner gorges along ~500 km of the former Fennoscandia ice sheet
margin in combination with a new deglaciation isochron map. We show that the timing of
bedrock exposure matches the advent of ice-free conditions, strongly suggesting that inner
gorges were cut by channelised subglacial meltwater while simultaneously being
shielded from cosmic rays by overlying ice. Given the exceptional hydraulic efficiency
required for subglacial meltwater channels to erode bedrock and evacuate debris, we
deduce that inner gorges are the product of ice sheets undergoing intense surface
melting akin to that currently occurring on the Greenland ice sheet. The lack of
postglacial river erosion in our seven inner gorges leads us to propose that channelised
subglacial meltwater—boosted possibly by abrupt supraglacial lake drainage—may be a
key driver of valley deepening on the Baltic Shield over multiple glacial cycles. |
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