Tsunamis generated by subaerial mass flows

TLDR

Tsunamis generated in lakes and reservoirs by subaerial mass flows pose distinctive hazards assessment challenges because the near‑field domain is close enough to the source that wave propagation effects are not predominant. Scaling analysis of water‑wave equations shows that near‑field wave amplitude and wavelength depend on measures of mass‑flow dynamics and volume. The authors demonstrate that near‑field tsunami amplitude and wavelength scale with dimensionless wave‑maker travel time and volume, with experimental data from solid, rigid, and deformable wave‑makers collapsing onto a single trend, and that applying these relations to historical events yields predicted amplitudes that agree with observations, providing essential inputs for wave‑propagation modeling and hazard assessment.

Abstract

Tsunamis generated in lakes and reservoirs by subaerial mass flows pose distinctive problems for hazards assessment because the domain of interest is commonly the “near field,” beyond the zone of complex splashing but close enough to the source that wave propagation effects are not predominant. Scaling analysis of the equations governing water wave propagation shows that near‐field wave amplitude and wavelength should depend on certain measures of mass flow dynamics and volume. The scaling analysis motivates a successful collapse (in dimensionless space) of data from two distinct sets of experiments with solid block “wave makers.” To first order, wave amplitude/water depth is a simple function of the ratio of dimensionless wave maker travel time to dimensionless wave maker volume per unit width. Wave amplitude data from previous laboratory investigations with both rigid and deformable wave makers follow the same trend in dimensionless parameter space as our own data. The characteristic wavelength/water depth for all our experiments is simply proportional to dimensionless wave maker travel time, which is itself given approximately by a simple function of wave maker length/water depth. Wave maker shape and rigidity do not otherwise influence wave features. Application of the amplitude scaling relation to several historical events yields “predicted” near‐field wave amplitudes in reasonable agreement with measurements and observations. Together, the scaling relations for near‐field amplitude, wavelength, and submerged travel time provide key inputs necessary for computational wave propagation and hazards assessment.