Seismic evidence of multi-stage volcanic flank collapse and refined deposit volume offshore Fogo, Cabo Verde

Abstract

Gravitational volcanic flank collapses are recurrent processes producing large-scale landslides, commonly associated with secondary instabilities and destructive tsunamis. Ocean island volcanoes are particularly prone to such failures, yet the dynamics, emplacement mechanisms, and tsunamigenic potential of gravitational collapses remain poorly constrained due to the scarcity of direct observations. The ~ 68 ka Monte Amarelo flank collapse at Fogo, Cabo Verde, is one of the prominent examples of tsunamigenic gravitational collapses globally. But key parameters, including the collapse volume and the number of collapse stages, remain debated. We identify an extensive (914 km 2 ) debris avalanche deposit associated with the Monte Amarelo volcanic flank collapse using high-resolution multibeam bathymetry and multichannel seismic reflection data. In addition, we find a smaller, previously unknown debris avalanche deposit superimposed on the northern half of the main deposit. Our results indicate that the Monte Amarelo collapse involved up to ~ 98 km 3 of material—the first volume estimate constrained by direct imaging of the submarine debris avalanche deposit through seismic data. The local morphology and internal structure of the main deposit suggest rapid emplacement and high tsunamigenic potential. The presence of a second deposit indicates multiple stages of collapse. Our results provide new constraints on the dynamics, volume, and sequence of events of one of the most recent gravitational collapses of a volcanic island in the Atlantic. These findings have important implications for tsunami generation and modelling and contribute to an improved understanding of hazards associated with gravitational collapses of volcanic islands.

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