Physical modeling of spikes during the volcanic tsunami generation.

This article focuses on large-scale physical experiments modeling tsunamis generated by underwater volcanic eruptions using a novel volcanic tsunami generator (VTG) in a three-dimensional wave basin. The VTG, a pneumatically driven telescopic column, produces controlled vertical motions that generate axisymmetric cylindrical N-wave tsunamis, allowing investigation of wave characteristics across eruption intensities and water depths. A key finding is the formation of a concentric vertical water spike during wave generation, which varies in pattern—classified as smooth, rough, or splash spikes—based on a dimensionless VTG motion parameter combining the spike Froude number and relative column diameter. The rough spike regime exhibits the greatest dimensionless spike height, reaching up to 30 times the submerged water depth, and its dynamics align with Worthington jet theory, while smooth and splash spikes show different dependencies on VTG parameters. The experimental data provide benchmark insights for validating and improving numerical models of volcanic tsunami generation and propagation.