Geoheritage and geodiversity aspects of catastrophic volcanic eruptions: Lessons from the 15th of January 2022 Hunga Tonga - Hunga Ha'apai eruption, SW Pacific

On the 15th of January 2022, a massive hydrovolcanic eruption at Hunga Tonga-Hunga Ha'apai in Tonga (SW Pacific) sent shockwaves in the near-field regime, close to the volcano. The far-field disturbances that encircled the globe were of a slower velocity. The most prominent disturbance was the Lamb wave, with the rest of the disturbances being a variety of gravity waves travelled around the globe and instantly became an international headline story. The eruption generated atmospheric pressure waves recorded multiple times across the globe, triggered a tsunami, and injected highly fragmented pyroclasts up to 55 km into the atmosphere. Enduring several hours, a series of individual large blasts generated an unprecedented lightning “show” recorded by the lightning detection networks, such as Vaisala. Consequences were devastating to the local community and the tsunami was felt across the Pacific and beyond. The impact of the eruption was truly global and comparable to the Krakatau 1883 eruption. A question we pose here is which geoheritage elements were created and preserved after the eruption. First reports confirmed that while fine ash was reported on land about 100 km from the source, most deposits were thin (mm-cm thick). This indicates that it is unlikely that any major section will be preserved, especially in the years following the event given the tropical setting. In addition, most of the ash fell into the Pacific Ocean, leaving no visible mark of this catastrophe. Unfortunately, the proximal region (e.g., the vent site) has also been destroyed, leaving only limited in-situ geoheritage elements likely to be accessible in the future. This poses a problem for human societal memory, as major catastrophic events in the collective memory of a community may only persist for a few decades, even when significant eruptive features may be preserved. Without “visible” geoheritage elements, this time will likely be much shorter. Geocultural elements (oral traditions or cultural activities) are likely to preserve and transmit information within the local communities for a longer period, but their accessibility and decoding may face difficulties in the absence of physically preserved evidence. Therefore, we consider it is important to trace and explore these geocultural elements through a mix of traditional and western approaches of community engaged activities. For example, the Pacific region has experienced several similar large-scale eruptions in historic times, and a few of them resulted in preserved geoheritage elements such as superb sections of the 1452–53 CE Kuwae eruption in Vanuatu. While these sites are locally known, their appearance and their geological context are not evidently and immediately considered as part of a major volcanic system, as they do not fit the common human perception of volcanoes as large conical mountains. Such visual perceptions do not align with the common near-sea level/shallow subaqueous caldera-dominated systems such as the location of the recent Tonga event. In achieving a better understanding in local communities of this type of geohazard, the geoheritage and geoeducation values of those rare geosites will increase significantly over time