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Titel |
Export of earthquake-triggered landslides in active mountain ranges: insights from 2D morphodynamic modelling. |
VerfasserIn |
Thomas Croissant, Dimitri Lague, Philippe Davy, Philippe Steer |
Konferenz |
EGU General Assembly 2016
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Medientyp |
Artikel
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Sprache |
en
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 18 (2016) |
Datensatznummer |
250132657
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Publikation (Nr.) |
EGU/EGU2016-13184.pdf |
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Zusammenfassung |
In active mountain ranges, large earthquakes (Mw > 5-6) trigger numerous landslides that
impact river dynamics. These landslides bring local and sudden sediment piles that will be
eroded and transported along the river network causing downstream changes in river
geometry, transport capacity and erosion efficiency. The progressive removal of
landslide materials has implications for downstream hazards management and also for
understanding landscape dynamics at the timescale of the seismic cycle. The export time of
landslide-derived sediments after large-magnitude earthquakes has been studied from
suspended load measurements but a full understanding of the total process, including the
coupling between sediment transfer and channel geometry change, still remains an issue.
Note that the transport of small sediment pulses has been studied in the context of river
restoration, but the magnitude of sediment pulses generated by landslides may make the
problem different. Here, we study the export of large volumes (>106 m3) of sediments with
the 2D hydro-morphodynamic model, Eros. This model uses a new hydrodynamic module
that resolves a reduced form of the Saint-Venant equations with a particle method. It is
coupled with a sediment transport and lateral and vertical erosion model. Eros accounts for
the complex retroactions between sediment transport and fluvial geometry, with a
stochastic description of the floods experienced by the river. Moreover, it is able
to reproduce several features deemed necessary to study the evacuation of large
sediment pulses, such as river regime modification (single-thread to multi-thread), river
avulsion and aggradation, floods and bank erosion. Using a synthetic and simple
topography we first present how granulometry, landslide volume and geometry,
channel slope and flood frequency influence 1) the dominance of pulse advection
vs. diffusion during its evacuation, 2) the pulse export time and 3) the remaining
volume of sediment in the catchment. The model is then applied to a high resolution
(5-10 m) digital elevation model of the Poerua catchment in New Zealand which
has been impacted by the effect of a large landslide during the last 15 years. We
investigate several plausible Alpine Faults earthquake scenarios to study the propagation
of the sediment along a complex river network. We characterize and quantify the
sediment pulse export time and mechanism for this river configuration and show its
impact on the alluvial plain evolution. Our findings have strong implications for
the understanding of aggradation rates and the temporal persistence of induced
hazards in the alluvial plain as well as of sediment transfers in active mountain
belts. |
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