Numerical simulations of tsunami generation in caldera lakes by subaqueous explosive volcanism

Caldera lakes are prominent volcanic features that can pose an additional hazard due to water presence, such as tsunamis, lahars, or flooding by lake breakout. Many of these lakes are populated and occupied by infrastructure on their shore, such as hydroelectric facilities. Volcanogenic tsunamis are a lesser modelled hazard compared to their seismogenic relatives, and the understanding of wave-making potential from subaqueous explosive eruptions is poor due to practical limitations of volcanic observation. Prior studies utilised models of surface waves produced from analogous chemical and nuclear explosions; however, these are derived from dated naval research and require reassessment.

This study verifies a non-hydrostatic, vertically-Lagrangian multilayer method from the open-source software Basilisk against a laboratory flume experiment to assess suitability for modelling waves produced by variable size disturbances. This is then used to evaluate free-surface initial condition models of shallow water explosions on a U.S. Army submerged explosive series on generating waves in Mono Lake, California. On establishing fitness of the underlying models, these are applied to simulate hypothetical scenarios of submarine eruptions at Lake Taupō, New Zealand. Event locations and disturbance sizes are chosen corresponding to vent sites and magnitudes of eruptions during the Holocene. The initial disturbance is fitted to a function of estimated eruption energy. Vulnerable areas include small settlements across the eastern shore, Taupō township and the lake outflow control gates. After the initial tsunami waves, a seiche of lower amplitude is established in the hour following the event. Such eruptions in lakes may pose multiple simultaneous hazards with minimal arrival times (< 15 minutes for tsunami waves at Taupō); therefore the modelling of eruptive scenarios is a primary approach to inform local area hazard maps of submarine volcanism and raise preparedness for surrounding facilities and communities.