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| Titel |
Long-term fluvial adaptation to post-glacial landscapes of the Ladakh Himalaya: processes, rates and timescales |
| VerfasserIn |
D. E. J. Hobley, H. D. Sinclair, P. A. Cowie |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250028451
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| Zusammenfassung |
| Both glacial and fluvial processes are well recognised as key elements in moulding
landscapes in high mountain environments – rivers transmit baselevel change signals through
such landscapes and flush sediment out of mountain belts and into basins, while glaciers are
highly efficient erosional agents and producers of sediment, capping relief production and
directly coupling landscape erosion to climatic change. However, little research has focussed
on the manner in which these two agents of landscape change interact, especially on longer
timescales.
We use a suite of catchments draining the previously glaciated Ladakh batholith in the
northwest Indian Himalaya, which preserves the oldest known moraine succession in this
mountain chain, to describe and quantify for the first time the rates, processes and timescales
of postglacial recovery of a fluvial system across an unprecedented time interval of 105 –
106 years. Catchments which show significant modification by glacial scouring
share a common long profile form, with a flattened headwater reach creating a
broad convexity in the middle section of the channel, downstream of which the
channel has a concave up geometry and flows entirely on loose sediment. However,
channel concavities downstream of such convexities in the channel long profile are
systematically and nonlinearly elevated above the expected value range of 0.3 –
0.6. The measured concavity increases with increasing glacial influence on the
catchment, as measured by relative position of the long profile convexity in the long
profile. This result constitutes the first direct evidence that glacial modification of
the upper reaches of a catchment in the form of subglacial abrasion by glaciers
can have profound first order influence on the hydraulic scaling of the channel
downstream.
The exceptional age of this post-glacial landscape also allows us to show that the response
time of these systems as they recover must exceed 500 ka, longer than any previously
reported estimate for recovery times from glaciation, but comparable with estimates from
many tectonically perturbed landscapes. Similarly, maximum rates of river incision in this
landscape are c. 1 mm/y, comparable with rates derived from many tectonically perturbed
settings. |
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