On January 15, the cataclysmic eruption of a submerged volcano in the South Pacific devastated the archipelagic nation of Tonga, unleashed tsunamis around the world, and created a sonic boom heard as far away as Alaska.
The blast was captured using a variety of sensors in land, sky, and sea. Two groups of scientists published their analyses of this data on May 12 in the journal Science.
One team concluded that pressure waves from the event were comparable in scale to those from the massive 1883 Krakatau eruption in Indonesia, which unleashed clouds of ash that reached 50 miles high and explosions that could be heard 2,200 miles away at its peak. The second group investigated how pressure waves caused tsunamis that arrived on distant shores several hours earlier than anticipated. These findings will help scientists to better understand tsunami-warning systems and the mechanisms that underlie eruptions, they say.
” There’s nothing like it in the digital age,” said Robin Matoza, a geophysicist from the University of California Santa Barbara, and coauthor of one of these papers. It’s an extraordinary event .”
Randy Cerveny is a meteorologist from Arizona State University. He was also the United Nations’s rapporteur on climate extremes and weather for the World Meteorological Organization.
“The more information we have now–and continued analyses of that available information–hopefully will make us better prepared for future eruptions of such incredible magnitude,” he said in an email.
The volcano responsible for all this turmoil lies 40 miles from Tongatapu, the largest island of Tonga. It’s roughly 12 miles across and topped by 3-mile-wide caldera with two “lips” that protrude above the water. The Hunga volcano experienced several minor eruptions from 2009 to 2015. A series of more violent outbursts began last December, climaxing with the massive January 15 eruption, which sent a cloud of ash more than 20 miles into the sky.
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Matoza’s team, which included researchers from 17 countries, investigated the pressure waves emitted by the powerful eruption. They collected measurements from seismometers and buoy-based pressure sensors as well as hydrophones and weather satellites. These instruments record the bend of radio waves in the Earth’s atmosphere.
The researchers were particularly interested in Lamb waves, low-frequency perturbations which travel at approximately the speed of sound along the Earth’s surface. Cerveny compares the phenomenon with the behavior of a jiggly desert.
“Think about an explosion at the bottom of a large container of Jell-O. The pressure ripples from compressed jello would spread horizontally from the explosion location,” he stated.
Lamb wave typically cover the entire depth of the atmosphere. This allows researchers to track them using a variety sensors both on ground and in satellites. He said that the amplitude of the Lamb waves we saw here was not high enough to cause damage but it did help us understand wave propagation and the characteristics of the eruption.
He observed with his collaborators that the Lamb wave produced by the Hunga volcano was so strong that it traveled multiple times around the Earth over six days. The team concluded that the wave was on par with that of the infamous Krakatau eruption of 1883 in size and distance traveled, and more than 10 times larger than the one produced by the 1980 Mount St. Helens eruption.
“It shows just how extreme the January 2022 eruption of Hunga volcano actually was,” Cerveny said. “If the Hunga eruption had been primarily above sea-level (like the Krakatau eruption), the effects would have been something not witnessed in nearly 150 years.”