By Pacific Island Times News Staff
The 2022 eruption of a submarine volcano in Tonga was more powerful than the largest U.S. nuclear explosion and the subsequent tsunami was similar in size to the one caused by the eruption of Krakatoa in 1883, making it the largest natural explosion in over a century, according to a new study.
Scientists at the University of Miami Rosenstiel School of Marine, Atmospheric, and Earth Science and the Khaled bin Sultan Living Oceans Foundation, said the 15-megaton volcanic explosion from Hunga Tonga-Hunga Ha'apai generated a mega-tsunami with waves up to 148 feet along the coast of Tonga’s Tofua Island and waves up to 56 feet on Tongatapu, the country’s most populated island.
Despite their immense magnitude, the twin disasters left only three dead, which was considered a wonder considering that whole communities were left under a blanket of volcanic ash and mud from the tsunami that followed the eruption.
Sam Purkis, chief scientist at the foundation, attributed the low death toll mainly to "the quirk of the location, the Covid-19 pandemic, and increased evaluation drills and awareness efforts carried out in Tonga in the years prior to the eruption."
The submarine volcanic eruption of Hunga Tonga-Hunga Ha'apai, which forms the island chain of Tonga and is a result of the convergence of the Pacific and Indo-Australian tectonic plates, rivaled the 1883 eruption of Krakatoa that killed over 36,000 people.
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“While 2022 may have been a lucky escape, other submarine volcanoes possess the capacity to spawn a future tsunami at the same scale," said Purkis, professor and chair of the Department of Marine Geosciences at the Rosenstiel School.
Purkis is one of the authors of "The 2022 Hunga-Tonga Megatsunami: Near-Field Simulation of a Once-in-a-Century Event,” which was published in the April issue of Science Advances.
He noted that Tonga's volcanic event holds important lessons for both past and future tsunamis.
"The eruption was an excellent natural laboratory to test hypotheses and models that can be deployed elsewhere to improve future disaster preparations, and better understand similar eruptions and subsequent tsunami as preserved in antiquity and in the geologic record," Purkis added.
In a new analysis in Science Advances, researchers used a combination of before-and-after satellite imagery, drone mapping, field observations collected by scientists at the University of Auckland, and high-resolution bathymetric maps from the Khaled bin Sultan Living Oceans Foundation’s Global Reef Expedition, to produce a tsunami simulation of the Tongan archipelago.
The results showed how the complex shallow bathymetry in the region acted as a low-velocity wave trap, capturing a more than hour-long tsunami with waves up to 85 meters (279 feet) high one minute after the initial explosion.
The simulation also suggested that the eruption location relative to urban centers saved Tonga from a worse outcome.
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The data that made this modeling possible came from an unexpected source.
In 2013, scientists from the foundation came to Tonga to map and survey their coral reefs as part of the Global Reef Expedition, a 10-year research mission to assess the state of coral reefs around the world.
As part of this research mission, scientists created ultra-high-resolution bathymetry maps of the Tongan Archipelago, which were needed to build detailed habitat maps of Tonga’s coral reefs.
These bathymetry maps, which were generated from satellite imagery and acoustic measurements recorded in the field, were integral in creating the tsunami simulation.
“It is fantastic to see the Global Reef Expedition data being used not only for coral reef ecology and conservation studies in the classic sense but that these data are important for understanding the complexity of seismically active regions in the ocean,” said Alexandra Dempsey, director of Science Management at the Living Oceans Foundation and one of the paper’s authors.
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“Time and again, the high quality of the data from the GRE is proving to pay off in dividends with new and exciting results," she added.
Dempsey said although the data was originally collected to support coral reef conservation, this is one of the many ways data from the Global Reef Expedition is being used to advance ocean science.
As for the reefs in Tonga, Dempsey said more surveying and reconnaissance fieldwork is needed to truly see how the tsunami has impacted the reefs around Tonga.
Having the baseline data of the state of the reefs prior to the tsunami, such as the coral reef surveys the Foundation collected on GRE, will be critical for determining those impacts as well.
The study is also co-authored by Nathan Fitzpatrick from the University of Miami Rosenstiel School, James Garvin and Dan Slayback from the NASA Goddard Space Flight Center, and Shane J. Cronin from the University of Auckland and Monica Palaseanu-Lovejoy from the U.S. Geological Survey.
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