Tsunami Runup and Inundation in Tonga from the January 2022 Eruption of Hunga Volcano

Abstract

On January 15th, 2022, at approximately 4:47 pm local time (0347 UTC), several weeks of heightened activity at the Hunga volcano 65 km northwest of Tongatapu, culminated in an 11-h long violent eruption which generated a significant near-field tsunami. Although the Kingdom of Tonga lies astride a large and tsunamigenic subduction zone, it has relatively few records of significant tsunami. Assessment activities took place both remotely and locally. Between March and June 2022, a field team quantified tsunami runup and inundation on the main populated islands Tongatapu and Eua, along with several smaller islands to the north, including the Ha'apai Group. Peak tsunami heights were ~ 19 m in western Tongatapu, ~ 20 m on south-eastern Nomuka Iki island and ~ 20 m on southern Tofua, located ~ 65 km S and E and 90 km N from Hunga volcano, respectively. In western Tongatapu, the largest tsunami surge overtopped a 13-15 m-high ridge along the narrow Hihifo peninsula in several locations. Analysis of tide gauge records from Nukualofa (which lag western Tongatapu arrivals by ~ 18-20 min), suggest that initial tsunami surges were generated prior to the largest volcanic explosions at ~ 0415 UTC. Further waves were generated by ~ 0426 UTC explosions that were accompanied by air-pressure waves. Efforts to model this event are unable to reproduce the timing of the large tsunami wave that toppled a weather station and communication tower on a 13 m-high ridge on western Tongatapu after 0500 UTC. Smaller tsunami waves continued until ~ 0900, coincident with a second energetic phase of eruption, and noted by eyewitnesses on Tungua and Mango Islands. Despite an extreme level of destruction caused by this tsunami, the death toll was extraordinarily low (4 victims). Interviews with witnesses and analysis of videos posted on social media suggest that this can be attributed to the arrival of smaller 'pre tsunami' waves that prompted evacuations, heightened tsunami awareness due to tsunami activity and advisories on the day before, the absence of tourists and ongoing tsunami education efforts since the 2009 Niuatoputapu, Tonga tsunami. This event highlights an unexpectedly great hazard from volcanic tsunami worldwide, which in Tonga's case overprints an already extreme level of tectonic tsunami hazard. Education and outreach efforts should continue to emphasize the 'natural warning signs' of strong ground shaking and unusual wave and current action, and the importance of self-evacuation from coastal areas of low-lying islands. The stories of survival from this event can be used as global best practice for personal survival strategies from future tsunami.

Supplementary information: The online version contains supplementary material available at 10.1007/s00024-022-03215-5.

Keywords: Tsunamis; eyewitness; field survey; volcanic hazard and risk.

Fig. 1

The bathymetry surrounding the major islands of The Kingdom of Tonga. Red triangle shows the location of Hunga Volcano. Yellow dots are the location of the Tongan Navy vessel on January 15th. Inset shows the eruption rising to its climax at 5.24 pm (0424 UTC) January 15th as seen from ~ 5 km northeast of Nuku’alofa (Photo: Branko Sugar); the upper plume is already > 100 km wide

Fig.2

Locations of the nkfa and nkfa2 tide gauges along the Nuku’alofa waterfront

Fig. 3

Tide gauge water level data from Nuku’alofa. Panel a shows data from the month of January 2022, note the gap in the record commencing shortly after the tsunami arrival. Panel b shows an enlargement of the time span indicated with the red box in A. Small tsunami activity can be seen commencing at ~ 1800 h on from 13 January 2022. Red boxes indicate areas enlarged in Panels c and d. Panel c shows a close-up of this early tsunami activity with tsunami amplitudes of ± 15 cm. Panel d is a close-up of the main tsunami on 15 January with the data from nkfa2 included

Fig. 4

The detided (black) water level and the predicted tide (blue) at Neiafu (top) and Nuku’alofa (bottom). Vertical red line indicates the time of the large explosion from the erupting volcano (0415 UTC)

Fig. 5

Detail of the first 3.5 h of tsunami activity at Nuku’alofa. Vertical lines indicate key times; green (0347) the start of the surface eruption, pink (0406) eruption plume visible on satellite imagery, red (0415) the time of a large explosion and cyan (0441) the ~ 26-min tsunami arrival time for the large eruption from Hunga to Vuna Wharf

Fig. 6

Summary data plots of maximum measured tsunami heights

Fig. 7

a Locations surveyed along the western coast of Tongatapu. Yellow shaded area indicated extents of inundation. Green tringle indicates the location of the Tongan Meteorological Service weather station. The start and endpoints of each transect are indicated with the red dots. Left plot shows maximum tsunami trace height, maximum runup height and maximum inundation distance along each transect. b, c Detailed transects from Ha’atafu and Kanokupolu

Fig. 8

View to the north along the the Ha’atafu section of the Hihifo Peninsula. Yellow rectangle indicates the site of Ha’atafu Beach Resort. Blue ellipse is the location of the car videos mentioned in the Ha’atafu Timeline section. The red ellipse is the location of the ‘tsunami rock’, shown in the inset after the tsunami and covered with debris indicating that it had been overtopped by the waves

Fig. 9

Maximum tsunami trace elevation (red) and run up height (blue) along the north coast of Tongatapu

Fig. 10

Scenes from Nuku’alofa a tsunami surge coming ashore on the grounds of the Royal Palace at 17:47 local time b, c smaller vessels floated on to the wharf or across the street d inundation at the Tanoa Hotel along the waterfront

Fig. 11

Before and after images of Nomuka iki (top) Tonumea (middle) and Kelefesia (bottom) showing large scale morphological change due to tsunami over wash. (Imagery from Google Earth, Maxar Technologies)

Fig. 12

Tsunami damage on Tungua a Nomuka b, Nomuka Iki c and Mango d

Fig. 13

Timeline of events at Ha’atafu and other locations. Times given as UTC and Local (UTC + 13). Descriptions given in the figure and in the preceding text