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

人们早就认识到大型火山岛侧翼崩塌的潜在海啸，但与这些事件相关的风险规模及其频率仍然缺乏限制和激烈争论。最近在佛得角发现的海啸成因沉积物表明，福戈火山——世界上最活跃的海洋火山之一——在约73 ka发生了灾难性的崩塌，导致了一场近源海啸振幅超过250米的大海啸。然而，相应的碎屑雪崩沉积仅通过中分辨率水深数据绘制。基于这种知识短缺，2019年夏季实现了对侧翼崩塌沉积物的详细地质和地球物理特征的考察；在巡航期间收集了大量的数据集，包括水声和地震数据以及沉积物样本。本文将对新数据进行地球物理和地质综合分析，研究佛得角群岛南部块体搬运沉积物的两个主要方面：1)基于声波数据的整个火山碎屑带块体搬运沉积物的分布、大小和体积；2)在岩心沉积物上部10米范围内，块体搬运沉积物各自的成分变异性和物源。具体目标包括：1)重建佛得角南部的综合地层格架；2)建立事件层组成数据库，研究其在火山建筑物和/或斜坡的起源及其侧向和远端变异性；3)开发佛得角南部群岛外反复出现的体块搬运沉积的起源、侵位和触发因素的综合模型。以及它对海洋岛屿和海啸模型的影响。结合地质和地球物理参数的研究提供了一个独特的机会来重建海啸的产生和影响，直接联系到其触发机制的研究。这些结果将使我们处于一个关键时刻，在这个时刻，海啸模型的最新发展可以与海上和陆上的证据相结合，从而产生一个比目前任何可用的预测模型都更可靠的预测模型。鉴于最近福戈火山的动乱，这是特别及时和相关的。

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.