Volcanic island sector collapses can produce extremely voluminous debris avalanches, which have the potential to trigger devastating tsunamis. Deposits of these events found on the Cap Verdes, the Canaries and Hawaii indicate that large-scale (> 100 km³) volcanic landslides can trigger ocean-wide tsunamis that may reach run-up heights of more than 100 m on neighboring islands. Such large-scale events have long recurrence intervals, while less voluminous (< 5km³) volcanic island flank collapses occur far more frequent and still have the potential to trigger hazardous tsunamis (e.g.Osima-Oshima in 1741, Mt. Unzen in 1792, Ritter Island in 1888). Tsunamis from historic volcanic sector collapses have caused more than 15,000 casualties.

The tsunami genesis of volcanic landslides is mainly controlled by the slide volume and velocity, but also by the interaction with seafloor sediments. To establish a robust tsunami hazard assessment for volcanic debris avalanches, it is necessary to understand the emplacement dynamics and slide parameters and feed them into numerical tsunami simulations. On March 13 1888, a large sector of the subaerial and submarine edifice of Ritter Island (Papua New Guinea) collapsed and slid into the Bismarck Sea, triggering a tsunami with a run-up height of more than 25 m on the neighboring islands. The tsunami traveled for more than 600 km and caused destruction in several settlements. The young and fresh deposits are clearly recognizable in geophysical surface data, the subaerial collapsed volume is well known and the timing of the flank collapse as well as tsunami arrival and wave heights are well documented by contemporary colonists. Therefore, Ritter Island represent one of the best-suited case studies for investigating the genesis of volcanic landslide tsunamis.

During research cruise SO252 onboard RV Sonne, we collected a comprehensive set of multibeam and sediment echosounder data, seafloor video footage, rock samples, 2D seismic profiles, and a 60 km2 high-resolution Pcable 3D seismic cube. This dataset, combined with the historic eyewitness accounts, allows detailed reconstruction of the large-scale volcanic sector collapse and the associated tsunami genesis, which can be tested with numerical tsunami simulations.

SO252: Ritter Island cruise Report