From repeated seafloor mapping to 3D multiphase simulations: reconstructing submarine landslides and predicting near-field waves in the Canary Islands

Submarine landslides at volcanic islands can generate tsunamis that pose a threat to coastal communities. Identifying potential landslides is therefore essential to estimate the tsunami impact. Among possible triggering mechanisms, submarine eruptions are an important source of instability because rapid cone growth can steepen and destabilize volcanic flanks. However, the evolution of submarine volcanoes is rarely monitored. An exception is the 2011-2012 submarine eruption south of El Hierro (Canary Islands), where repeated multibeam surveys captured rapid cone growth alternating with multiple collapse episodes. This survey time series provides a unique opportunity to quantify failure volumes and geometries and to evaluate 3D numerical simulations of slide deformation and the associated near-field ocean response.

First, we estimate collapse volumes and map erosion/deposition patterns by differencing successive bathymetric digital elevation models. Then, in order to simulate slide deformation and mobility, we use a 3D viscoplastic mixture approach implemented in OpenFOAM. The modeling strategy is validated against a laboratory benchmark of tsunami generation by a submerged granular collapse, including slide kinematics and free-surface time series.

At field scale, the numerical simulation of the largest collapse is initialized from the mapped failure geometry. In the absence of nearshore wave gauge data, the rheological parameters of the slide are calibrated to reproduce the observed erosion/deposition pattern. After matching the landslide runout and deposits, we use the numerical simulations to study the resulting free-surface response, focusing on wave generation, directionality, and nearshore amplification. Overall, we show how repeated seafloor mapping and 3D modeling can be combined to reconstruct submarine landslide dynamics and assess nearshore tsunami hazards at volcanic islands.