Submarine Flank Collapses at Tagoro Volcano: Insights From Bathymetric Surveys and 3D Multiphase Simulations

Abstract

Volcanic islands are prone to flank instabilities that can generate tsunamis even when mobilized volumes are moderate. This study investigates submarine collapses during the 2011–2012 eruption south of El Hierro, which built the Tagoro submarine volcano. Repeated multibeam bathymetric surveys captured the rapid growth, collapse, and reconstruction of the edifice, providing an exceptional record of seafloor change during an active submarine eruption. This record is used to develop a hybrid survey‐modeling methodology that links observed collapse morphology to scenario‐based estimates of the near‐field wave response. First, two OpenFOAM‐based approaches are benchmarked against laboratory experiments of submerged landslide‐tsunami generation: a computationally efficient viscoplastic mixture model and a more detailed Eulerian‐Eulerian two‐phase model. The two‐phase model is included as a reference to help assess the simplified mixture approach in the laboratory benchmark. The mixture model is then applied at field scale to simulate the largest Tagoro collapse. In the absence of tide gauge records, the numerical parameter set for the field scale simulations is selected based on its agreement with the erosion and deposition patterns inferred from bathymetric differencing. The resulting simulations reproduce the main landslide pathway and predict a strongly directional near‐field wave field, with local amplification over the island shelf controlled by bathymetry. The results show that repeated bathymetric monitoring, combined with physics‐based 3D modeling, can bridge observed volcanic seafloor change and plausible landslide‐tsunami scenarios. This approach is not intended for real‐time warning, but provides a transferable framework for local hazard assessment during prolonged submarine eruptions.