This study investigates the tsunamigenesis of a shallow-water submarine landslide, recently mapped at the mouth of the Tagus delta River, off Lisbon, Portugal——submarine landslides can be a major source of tsunamis, with waves highly dependent of the properties of both the landslide and the marine domain. This work propose two scenarios that account for the morphological changes in the region under long-term (i.e., ~ 8 ky) sedimentation processes and sea level rise: a paleo-scenario built by reconstructing pre-failure conditions and the paleo-bathymetry model from the time the event occurred, and a future-scenario projection assuming similar pre-failure conditions and using present-day bathymetric model. These two scenarios present differences in the seafloor morphology and the pre-failure mass distribution that significantly influenced the tsunami generation, propagation, energy channelling and coastal height.
Simulation results show that both scenarios posed important tsunami coastal impacts with wave heights up to ~ 2 m (paleo-scenario) and ranging from 3 to 5.5 m (future-scenario). This coastal hazard significantly increased with the relative sea level rise, as demonstrated by the distribution of the simulated tsunami wave height from both scenarios. Findings suggest considering climate change (i.e., relative sea level rise) in the assessment of tsunami hazard, particularly when projecting the occurrence of future events in the region. The results of this work, along with recent information from the mapped database of submarine landslides in the SW Portuguese margins, shows the need to enhance our understanding of the potential hazards posed by significant mass-wasting events: to include these small, but frequent, events and their induced tsunamis in marine geo-hazard assessments of the region.
