Abstract
A submarine volcanic eruption has the potential to generate a dangerous local tsunami. To better understand the free surface disturbance generated by an underwater volcanic eruption, which will form the initial condition for any subsequent wave generation, we conducted a series of laboratory experiments. In these experiments, compressed air was injected into a tank filled with water to simulate an underwater eruption. The experiments were repeated over a range of different pressures and water depths. Each eruption can be divided into three phases: A momentum‐driven jet, a buoyancy‐driven plume, and a fountain‐generation regime. Our experiments exhibit two fountain regimes (a dome regime and a finger regime), with a transition between them. These fountain regimes have been observed in several real submarine volcanic eruptions. This paper proposes a Froude number criterion to combine the water depths and source conditions together with the aspect ratios of fountains to quantify different fountain regimes. This quantitative relationship holds for two real subaqueous volcanic eruption cases (Myojin‐Sho eruption in 1952 and 1996 eruption in Karymskoye Lake). The fountain of the Myojin‐Sho shallow submarine eruption on September 23,1952 appears to have been in the dome regime, which means it was a relatively weak eruption. Unlike other eruptions from this volcano, which did generate tsunamis, no tsunami waves were detected on September 23 . This study contributes to an enhanced understanding of the usually unseen mechanism of free surface disturbances by volcanic gas injection during submarine eruptions.
Plain Language Summary
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.
Key Points
We undertake novel experiments to quantify the evolution of an underwater gas eruption and its free surface response
Three types of fountain regimes observed in our experiments are consistent with field observations of underwater volcanic eruptions
Finger regimes occur at shallow depths or in the eruptions with strong source energy, while dome regimes occur under the opposite conditions