%0 Conference Proceedings %T Export of earthquake-triggered landslides in active mountain ranges: insights from 2D morphodynamic modelling. %+ Géosciences Rennes (GR) %A Croissant, Thomas %A Lague, Dimitri %A Davy, Philippe %A Steer, Philippe %< avec comité de lecture %( Geophysical Research Abstracts %B European Geosciences Union General Assembly 2016 %C Vienne, Austria %V 18 %P EGU2016-13184 %8 2016-04-12 %D 2016 %Z Sciences of the Universe [physics]/Earth Sciences/GeomorphologyConference papers %X 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 networkcausing downstream changes in river geometry, transport capacity and erosion efficiency. The progressiveremoval of landslide materials has implications for downstream hazards management and also for understandinglandscape dynamics at the timescale of the seismic cycle. The export time of landslide-derived sediments afterlarge-magnitude earthquakes has been studied from suspended load measurements but a full understanding of thetotal process, including the coupling between sediment transfer and channel geometry change, still remains anissue. Note that the transport of small sediment pulses has been studied in the context of river restoration, but themagnitude of sediment pulses generated by landslides may make the problem different. Here, we study the exportof large volumes (>106 m3) of sediments with the 2D hydro-morphodynamic model, Eros. This model uses a newhydrodynamic module that resolves a reduced form of the Saint-Venant equations with a particle method. It is coupledwith a sediment transport and lateral and vertical erosion model. Eros accounts for the complex retroactionsbetween sediment transport and fluvial geometry, with a stochastic description of the floods experienced by theriver. Moreover, it is able to reproduce several features deemed necessary to study the evacuation of large sedimentpulses, such as river regime modification (single-thread to multi-thread), river avulsion and aggradation, floods andbank erosion. Using a synthetic and simple topography we first present how granulometry, landslide volume andgeometry, channel slope and flood frequency influence 1) the dominance of pulse advection vs. diffusion during itsevacuation, 2) the pulse export time and 3) the remaining volume of sediment in the catchment. The model is thenapplied to a high resolution (5-10 m) digital elevation model of the Poerua catchment in New Zealand which hasbeen impacted by the effect of a large landslide during the last 15 years. We investigate several plausible AlpineFaults earthquake scenarios to study the propagation of the sediment along a complex river network.We characterizeand quantify the sediment pulse export time and mechanism for this river configuration and show its impact onthe alluvial plain evolution. Our findings have strong implications for the understanding of aggradation rates andthe temporal persistence of induced hazards in the alluvial plain as well as of sediment transfers in active mountainbelts. %G English %L insu-01308943 %U https://insu.hal.science/insu-01308943 %~ INSU %~ UNIV-RENNES1 %~ UR2-HB %~ CNRS %~ GR %~ OSUR %~ GIP-BE %~ UR1-HAL %~ UR1-SDLM %~ UR1-SDLMJONCH %~ GR-DIMENV %~ UNIV-RENNES2 %~ OSUR-OSU %~ TEST-UNIV-RENNES %~ TEST-UR-CSS %~ UNIV-RENNES %~ INRAE %~ UR1-ENV %~ GR-R %~ GR-DEMO