Investigation of subaerial landslide–tsunamis generated by different mass movement types using smoothed particle hydrodynamics

Subaerial landslide-tsunamis (SLTs) are generated by mass movements such as landslides, rockfalls, debris flows and iceberg calving impacting water bodies, posing significant hazards to humans and infrastructure. Events like the 2014 Lake Askja rockslide and the 2022 Capitólio toppling cases highlight their potential dangers. SLT characteristics depend on the mass movement type (MMT) such as sliding, falling or overturning (toppling). While most SLT studies have focused on sliding masses, the wave characteristics generated by other MMTs remain poorly understood. This study addresses this shortcoming, based on a Smoothed Particle Hydrodynamics (SPH), by examining how falling and overturning MMTs affect SLT properties through 26 tests in a numerical basin involving square and round blocks. The overturning MMT generates up to 5.58 larger maximum wave amplitudes a_M and 3.85 larger heights H_M than the falling MMT, aligned with theoretical predictions. Wave decay ratios for the overturning versus falling MMTs exceed 2 near the mass impact area, however, they generally decrease with the propagation distance r, as the steeper waves generated by the overturning MMT decay more rapidly. Empirical equations for the wave generation and propagation characteristics were derived in function of the Froude number, block geometry, r and the wave propagation angle. The same numerical framework was applied to the deadly 2022 Capitólio toppling case involving the case-specific slide geometry, bathymetry and topography. The numerical a_M and H_M deviated by 35.38% and 12.45%, respectively, from 2.52 and 8.93 m predicted by the new equations in this study. Furthermore, wave properties generated by the falling and overturning MMTs were compared with existing empirical predictions for sliding MMTs. This shows that sliding MMTs typically produce larger waves, except for smaller relative masses, for which they may generate smaller waves than both falling and overturning MMTs. These findings are aimed at improving the reliability of preliminary landslide-tsunami hazard assessment based on empirical equations.