Seismic reconstruction of seafloor sediment deformation during volcanic debris avalanche emplacement offshore Sakar, Papua New Guinea.

Kühn, Michel , Karstens, Jens , Berndt, Christian and Watt, S. (2021) Seismic reconstruction of seafloor sediment deformation during volcanic debris avalanche emplacement offshore Sakar, Papua New Guinea. [Poster] In: 81. Jahrestagung der Deutschen Geophysikalischen Gesellschaft (DGG). , 01.03.-05.03.2021, Kiel (online) .

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Volcanic island sector-collapses have produced some of the most voluminous mass movements on Earth and have the potential to trigger devastating tsunamis. In the marine environment, volcanic landslide deposits often consist of a mixture of volcanic material and incorporated seafloor sediments. The interaction of the initial volcanic failure and the seafloor is highly complex and has an impact on both the total landslide deposit volume and its emplacement velocity, which are important parameters during tsunami generation and need to be correctly attributed during numerical landslide-tsunami simulations. Here, we present a 2D seismic analysis of two previously unknown volcanic landslide deposits north-west of the island of Sakar (Papua New Guinea) in the Bismarck Sea. The younger deposit directly overlies the older one and both are separated by a package of well-stratified sediment. Despite both originating from the same source, with the same broad failure direction, and having similar deposit volumes (~15.5-26 km3), the interaction of these landslides with the seafloor is markedly different. High-resolution seismic reflection data show that the lower deposit comprises a proximal, chaotic, volcanic debris avalanche component and a distal, frontally confined seafloor-sediment failure component. Deformation of this sediment unit was probably caused by interaction of the debris avalanche component with the substrata. The unit shows various compressional structures, including thrusting and folding, over a downslope distance of more than 20 km, generating a shortening by >27 % in the deposit’s toe. The volume of the deformed sediments is almost the same as the driving debris avalanche deposit. In contrast, the younger landslide deposit does not show evidence for similar seafloor sediment incorporation and is a relatively simpler block-rich volcanic debris avalanche deposit. Our observations show that the nature of the slide plane, i.e., the geological characteristics of the underlying material, control the amount ofseafloor incorporation and secondary seafloor failures far more than the nature of the original slide material or other characteristics of the source region. Our results indicate that estimating the volume of volcanic sector collapses based solely on the surface morphology and extent of their deposits may overestimate the primary volcanic component, which is much more important for tsunami generation than secondary sediment failure, by a factor of 2

Document Type: Conference or Workshop Item (Poster)
Research affiliation: OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-GDY Marine Geodynamics
Date Deposited: 09 Jul 2021 12:21
Last Modified: 09 Jul 2021 12:21

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