The Tsunamis Generated by the Hunga Tonga-Hunga Ha'apai Volcano on January 15, 2022

Abstract

Abstract On the evening of January 15th, 2022 at approximately 5:15 pm local time (4:15 am Greenwich Mean Time), the Hunga Tonga-Hunga Ha'apai volcano unleashed a violent underwater eruption, blanketing the surrounding land masses in ash and debris (1). The eruption generated tsunamis observed throughout the globe. The last time such an event occurred was the 1883 Krakatau eruption (2), and thus here we have the first observations of a tsunami from a large emergent volcanic eruption captured with modern instrumentation. The mechanisms of tsunami generation here are rare and complex, but a wealth of observations permit a forensic analysis. With the use of oceanographic and meteorological data, post-event field survey observations, and high-order hydrodynamic modeling, we show that the event generated tsunamis at different times and from distinct mechanisms. There is evidence of a relatively small wave generated through a pre-cursor source approximately 10 minutes before the primary eruption; due to lack of observational data, it is difficult to specify the source of these waves, but a submarine landslide associated with an early eruption is possible. The main eruption appears to have generated waves through multiple mechanisms, including: 1) air-sea coupling with the initial and powerful shockwave radiating out from the explosion in the immediate vicinity of the eruption, 2) the collapse of the water-crater created by the underwater explosion, and 3) air-sea coupling with the air-pressure wave that circled the earth multiple times, leading to a global tsunami. In the nearfield, the tsunami impacts are strongly controlled by the shockwave and water-crater source, while the far-field tsunami, which was uncommonly persistent, can be largely described by the air-pressure wave mechanism. Catastrophic damage in some harbors in the far-field was averted by just 10’s of cm, implying that a modest sea level rise combined with a future, similar event would lead to a step-function increase in infrastructure impacts. Piecing together the complexity of this event has broad implications to the hazard in similar geophysical