As big as it gets: Hunga volcano comparable to Krakatoa

Satellite image of the Hunga volcano on January 21, 2022. Image courtesy of the National Oceanic and Atmospheric Administration.

The January 2022 eruption of the Hunga volcano in Tonga was the largest volcanic eruption of the 21st century and the largest recorded since Mount Pinatubo erupted in 1991.

New research by an international team from 17 countries, including Lawrence Livermore National Laboratory (LLNL) scientist Keehoon Kim, demonstrates that, based on atmospheric pressure waves recorded by global barometers, the Hunga explosion was comparable in size to the eruption of Krakatoa in 1883. The research appears in the May 12 edition of Science.

Atmospheric wave data showed that the eruption spread through four passes around the Earth in six days. NASA determined that the eruption was “hundreds of times more powerful than the atomic bomb dropped on Hiroshima”.

The eruption began in December 2021 at Hunga Tonga-Hunga Ha’apai, an undersea volcano in the Tonga archipelago in the southern Pacific Ocean (undersea volcanoes are undersea vents or cracks in the Earth’s surface from which magma can erupt). The latest eruption in January caused tsunamis in Tonga, Fiji, American Samoa, Vanuatu and along the Pacific rim, including destructive tsunamis in New Zealand, Japan, the United States, the Russian Far East, Chile and Peru.

The 1883 eruption of Krakatoa began on May 20, 1883 and culminated in the late morning of August 27, 1883, when more than 70% of Krakatoa Island and its surrounding archipelago was destroyed as it collapsed in a caldera. The eruption killed more than 36,000 people, making it one of the most devastating volcanic eruptions in human history.

The new study indicates that the Hunga volcano produced an atmospheric explosion of a size that has not been documented in modern geophysical records. The event generated a wide range of atmospheric waves observed globally by various ground-based and space-based instrumentation networks. The eruption from a submerged vent delivered volcanic ash and gas primarily to the stratosphere. An umbrella cloud developed about 30 kilometers above sea level, with a much higher central transient overshoot.

Hunga is a largely submerged volcano located approximately 65 km north-northwest of Tonga. Eruption episodes consisting of relatively low-energy subterranean eruptions in 2009 and 2014-2015 had built a tephra cone that connected the established islands of Hunga Tonga and Hunga Ha’apai on the northwestern part of the volcano. These underground eruptions turned into violent and impulsive eruptions from December 19, 2021, as part of the most recent episode.

The January 15 culminating eruption produced a wide range of atmospheric waves observed globally by numerous ground and space-based instrumentation systems and weather satellites.

Kim specifically studied Lamb waves — acoustic gravity waves (AGWs) propagating along the Earth’s surface — with group velocities close to the average speed of sound in the lower atmosphere. They are also associated with the largest atmospheric explosions from volcanic eruptions and nuclear testing and have periods on the order of several to several hundred minutes.

Measurements of Lamb wave peak-to-peak pressure amplitudes as a function of distance indicated that the atmospheric pressure pulse generated by the Hunga event is comparable to that of the 1883 Krakatoa eruption. Hunga are an order of magnitude larger than those generated by the eruption of Mount St. Helens in 1980.

During the atmospheric nuclear test era of the 1950s to 1960s, theoretical and empirical relationships were generated relating AGW amplitudes and periods to explosive yield.

“We find that such relationships are inapplicable to Hunga-generated signals, as they result in non-physically significant equivalent returns,” Kim said. “This difference is likely due to the fact that, for a given energy release, the long-duration climatic eruption excites pressure disturbances of longer duration than the near-instantaneous nuclear reaction. The Hunga signals have peak-to-peak pressures comparable to those produced by the largest historical atmospheric nuclear test (55 mt), but the dominant flare signal periods are about four times longer than those of the nuclear explosion.

The LLNL portion of the work was funded by the National Nuclear Security Administration’s Office of Nuclear Nonproliferation Research and Development.

Other collaborators include the University of California, Santa Barbara; University of Alaska; Royal Netherlands Meteorological Institute; ADMIRATION; Royal Observatory of Belgium; NASA Jet Propulsion Laboratory; University of Toulouse; University of Tokyo; Brigham Young University; United States Geological Survey; NORSAR, Kjeller, Norway; University of the Côte d’Azur; Southern Methodist University; G-Time Laboratory; Nanyang Technological University; Massey University, Palmerston North; Organization of the Nuclear Test Ban Treaty; CEA, DAM, DIF, F-91297, France; BGR (Federal Institute for Geosciences and Natural Resources), Germany; Los Alamos National Laboratory; University of Mississippi; University of Liverpool; Embry-Riddle Aeronautical University; Wairakei Research Center; University of Florence; Universidad Nacional Autónoma de México; University of Paris, Institute of Physics of the Globe of Paris; Vanuatu Department of Meteorology and Geohazards; Korea Institute of Geosciences and Mineral Resources; Scripps Institution of Oceanography, University of California, San Diego; Volcanological Observatory of the Southern Andes, National Service of Geology and Mines (OVDAS, Sernageomin); Penn State University; Incorporated research institutions for seismology; University of Reading; NASA Goddard Spaceflight; Norwegian Geotechnical Institute; and Instituto Geofísico, Escuela Politécnica Nacional, Ecuador.

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