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| Titel |
How fast do landscapes respond to active faulting? |
| VerfasserIn |
Alex Whittaker, Sarah Boulton |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250048541
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| Zusammenfassung |
| Understanding the rate at which landscapes respond to tectonic perturbation remains a key
challenge in the Earth Sciences. Central to solving this problem is the behaviour of transient
knickpoints in bedrock rivers draining areas of high relief, because they transmit the signal of
boundary condition change to the landscape. Consequently, the rate at which they propagate
upstream fundamentally controls geomorphic response times to tectonics. Here we present
knickpoint retreat rates upstream of active normal faults for bedrock catchments in Turkey
and Italy where we have excellent constraints on both the magnitude and history of fault
throw rates, and where climate histories are well documented. We show that the
knickpoints have average retreat rates of between 0.2 and 2 mm/yr for catchments with
drainage areas between 6 and 65 km2 and we test whether differences in rock mass
strength and catchment size are sufficient to explain this range in retreat rates. Our
analysis suggests that even accounting for these two variables, knickpoint propagation
velocities differ markedly, and we show that channels crossing faults with higher
throw rates have knickpoints that are retreating faster. Importantly, the dependence
of knickpoint retreat velocity and throw rate is at least as important as catchment
drainage area. The link between the knickpoint propagation velocity and throw rate
is best explained by dynamic channel adjustment, because rivers crossing high
throw rate faults are both narrower and steeper for the same drainage area than
those crossing slower moving faults. These results indicate, counter-intuitively, that
landscapes forced by large amplitude tectonic perturbations will have shorter response
times than those perturbed by smaller amplitude changes. Our results also highlight
that dynamic adjustment of channel widths and slopes, in response to a tectonic
perturbation, makes a significant difference to fluvial response times, and we argue
that this effect must be incorporated routinely within landscape evolution models. |
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