RV SONNE 252 Cruise Report / Fahrtbericht, Yokohama : 05.11.2016 - Nouméa : 18.12.2016. SO252 : RITTER ISLAND Tsunami potential of volcanic flank collapses

Abstract

Large volcanic debris flows associated with volcanic island flank collapses may cause devastating tsunamis as they enter the ocean. Computer simulations show that the largest of these volcanic debris flows on oceanic islands such as Hawaii or the Canaries can cause ocean-wide tsunamis (Løvholt et al., 2008; Waythomas et al., 2009). However, the magnitude of these tsunamis is subject to on-going debate as it depends particularly on landslide transport and emplacement processes (Harbitz et al. 2013). A robust understanding of these factors is thus essential in order to assess the hazard of volcanic flank collapses. Recent studies have shown that emplacement processes are far more complex than assumed previously. With a collapsed volume of about 5 km3 the 1888 Ritter Island flank collapse is the largest in historic times and represents an ideal natural laboratory for several reasons: (I) The collapse is comparatively young and the marine deposits are clearly visible, (II) the pre-collapse shape of the island is historically documented and (III) eyewitness reports documenting tsunami arrival times, run-up heights and inundation levels on neighboring islands are available. We propose to collect bathymetric, high resolution 2D and 3D seismic data as well as seafloor samples from the submarine deposits off Ritter Island to learn about the mobility and emplacement dynamics of the 1888 flank collapse landslide. A comparison to similar studies from other volcanic islands will provide an improved understanding of emplacement processes of volcanic island landslides and their overall tsunamigenic potential. In addition, a detailed knowledge of the 1888 landslide processes in combination with tsunami constraints from eyewitness reports provides a unique possibility to determine the landslide velocity, which can then be used in subsequent hazard analyses for ocean islands.