Laboratory Experiments on Tsunamigenic Discrete Subaqueous Volcanic Eruptions. Part 1: Free Surface Disturbances

Abstract

Underwater volcanic eruptions inject hot magma into cold ambient water. The interaction between magma and water creates steam explosions which can displace a large amount of water. An eruption occurring in shallow enough water and with sufficiently strong energy will be able to disturb the water surface and even initiate a tsunami. As these eruptions are hidden beneath water, their direct observation near their vents is difficult and dangerous, while the water surface disturbances are much easier and safer to measure. In order to understand the relationship between different kinds of eruptions and their disturbance of the water surface, we model underwater volcanic eruptions in the laboratory by injecting compressed air into water. We observe three main shapes of fountains on the water surface in our experiments: a) finger-like; b) dome-like; c) shapes intermediate between them. A finger-shaped fountain accompanied by a large number of splashes normally occurs at shallow-water depths and/or in an eruption with intense source strength, while a dome-shaped fountain occurs under the opposite conditions. We find a good consistency between our experimental results and field observations, which means that we are able to estimate the unseen source conditions from the observed free surface disturbances.