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| Titel |
Fluvial incision in postglacial rivers: distribution, rates and controls |
| VerfasserIn |
K. Whitbread, J. Jansen, D. Fabel, P. Bishop |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250063990
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| Zusammenfassung |
| Following deglaciation, rivers take over from glaciers as the main geomorphic agents in
glaciated landscapes. Postglacial bedrock rivers rework glacial debris, incise bedrock and
reassert hydraulic scaling over the glacially-conditioned valley floor slopes, potentially
driving rapid topographic change and sediment transport. We assess the distribution,
timing and rate of postglacial fluvial incision in the post-orogenic, postglacial terrain
of the northwest Scottish Highlands using a combination of cosmogenic nuclide
surface exposure dating of strath terraces, field mapping and digital topographic
analysis.
Average Holocene fluvial incision rates of 0.4–1.3 ± 0.1 m/kyr, quantified from strath
terraces formed 1–4 kyr after deglaciation (14.0–11.7 kyr), are a function of stream power
and bedrock resistance. On the basis of these erosion rates, analysis of the distribution of
channel entrenchment in three mapped streams indicates that 63% of bedrock gorges
(1–12m depth) reflect postglacial fluvial incision. Fluvial incision is focused at
knickpoints formed where rivers have inherited glacially steepened reaches (riegels). Deep
gorges (12-22m depth), probably cut by sub-glacial meltwater, account for 37% of
bedrock reaches, mainly in steep valley-floor areas proximal to breached drainage
divides.
Erosion rates of ~0.1 m/kyr, derived from cosmogenic 10Be concentrations on active
channel beds, are significantly lower than the Holocene average, suggesting that declining
paraglacial sediment flux may control fluvial incision rates. The long-term reduction
in fluvial incision rates would prolong the timescale for fluvial adjustment and
thereby also the persistence of glacial landforms in the northwest Scottish Highlands. |
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