Abstract
Submarine volcanic eruptions have the potential to generate tsunamis, which can cause destruction well beyond the range of the eruption itself. Here, we present a series of underwater eruption experiments in which a non-condensing gas was injected into a water tank with a range of water depths and applied pressures. This study proposes an effective scaled water depth and categorizes underwater eruptions into three types: deep-water eruptions, intermediate-water eruptions, and shallow-water eruptions. In deep-water eruptions, most of the energy is dissipated within the water column before the plume reaches the surface, and negligible waves are generated. In intermediate-water eruptions, reductions in water depth reduce the loss of energy to the water column, leaving more energy available for wave generation. This causes an increase in wave heights as water shallows, up to a point. In sufficiently shallow-water cases, the water depth is so small that almost all of the energy from the eruptive jet or plume passes through the water and is dissipated into the air, so there is only small wave-making potential, even with relatively intense source strength. Therefore, there exists a critical water depth at which an eruption with a given source intensity will generate the largest waves. That depth lies at the boundary between the intermediate- and shallow-depth regimes, where the energy available for wave generation is at a maximum. This research reveals fundamental wave generation mechanisms related to underwater gas eruptions, thereby extending our understanding of submarine volcanic tsunami generation and providing a foundation for future hazard assessment.