Integrated geophysical and geological investi-gations of volcanic flank collapses at the southern Cape Verdes archipelago: Origin, magnitude and tsunami potential

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The tsunamigenic potential of large volcanic island flank collapses has long been recognized, yet the scale of risks associated with these events as well as their frequency are still poorly constrained and heavily debated. The recent discovery of tsunamigenic deposits in the Cape Verdes showed that Fogo - one of the most active oceanic volcanoes in the world - collapsed catastrophically at ~73 ka, resulting in a megatsunami with a near-source tsunami amplitude in excess of 250 m. The corresponding debris avalanche deposits, however, had only been mapped by medium resolution bathymetric data. Based on this shortage in knowledge, a cruise for a detailed geological and geophysical characterization of the flank collapse deposits was realized in summer 2019; an extensive data set consisting of hydroacoustic and seismic data as well as sediment samples was collected during the cruise. The combined geophysical and geological analysis of the new data in this proposal will address two major aspects of mass transport deposits from the southern Cape Verdes archipelago: i) the distribution, size and volume of mass transport deposits in the entire volcaniclastic apron based on acoustic data, and ii) their respective compositional variability and provenance within the upper 10 meters of cored sediments. Specific objectives include i) the reconstruction of a comprehensive stratigraphic framework for the southern Cape Verdes, ii) the development of a compositional database for event layers with respect to their origin at the volcanic edifices and/or the slope as well as their lateral and distal variability, and iii) the development of an integrated model for origin, emplacement, and triggers of recurrent mass transport deposits off the southern Cape Verde archipelago, and its implications for oceanic islands and tsunami modelling in general. The study of combined geological and geophysical parameters provides a unique opportunity to reconstruct the generation and impact of a megatsunami, directly linked to a study of its trigger mechanism. The results will put us at a critical juncture where the latest developments in tsunami modelling can be integrated with both offshore and onshore evidence, to produce a forecast model more robust than any currently available. This is particularly timely and relevant given the recent unrest at Fogo volcano.