The Hunga Tonga-Hunga Haʻapai volcanic eruption on January 15 produced the largest atmospheric explosion in recorded history. Credit: NASA / GOES / NOAA / NESDIS
Researchers are beginning to find out why the eruption of a submarine volcano in Tonga was so explosive and what happened next. Evidence gathered by two groups suggests that when the center of the volcano collapsed, it vomited a huge amount of magma that reacted violently with the water, feeding several large explosions and hundreds of much smaller explosions.
The Hunga Tonga – Hunga Haʻapai volcano erupted on January 15, 2022, causing the largest atmospheric explosion in recorded history. It sent shock waves around the world and a plume of ash into the upper atmosphere.
In May, Shane Cronin, a volcanologist at the University of Auckland, New Zealand, led a group that sailed over the volcano’s caldera, the central depression that forms when a volcano erupts, and used the sound to map its structure. They found that the four-kilometer-wide boiler had fallen from less than 200 meters below sea level to more than 850 meters.
“The volcano produced this huge new boiler,” Cronin says. He estimates that about 6.5 cubic miles of rock were thrown, roughly the equivalent of a sphere as wide as the Golden Gate Bridge in San Francisco, California. “It was an amazing find,” said Taaniela Kula, Tonga’s deputy secretary of land and natural resources in Nuku’alofa and a collaborator in the investigation. “Create a better picture of the mechanism of the volcano.” The work was presented at a meeting of the European Geosciences Union (EGU) in Vienna on 26 May.
After the eruption, researchers mapped the caldera, the central depression that forms when a volcano erupts. Credit: Shane Cronin / University of Auckland and Taaniela Kula Tonga Geological Services
The reason for this large explosion was probably the interaction between large amounts of magma and water when the eruption began, Cronin says. “You have 20-degree water and you have 1,110-degree magma that comes in direct contact,” he says. Such a large temperature difference meant that as the water was forced to come into contact with the magma by the eruption, it exploded. Each interaction pushed water deeper into the edges of the magma, Cronin says, increasing the contact surface and causing more explosions in a chain reaction.
The initial depth of the boiler was also small enough that the water pressure did not suppress the explosion, but deep enough for the magma to feed on large amounts of water to feed the interactions, resulting in several large explosions and hundreds of much smaller explosions each time. minute. Eyewitnesses on the day of the eruption reported “crackles and noises like artillery fire” up to 90 miles from the eruption, Cronin says. “These are not sounds you’ve heard before erupting volcanoes,” he says.
The ash grains recovered from Tonga after the eruption also suggest that there was a violent interaction between magma and water. When seawater came in contact with magma, it produced shock waves strong enough to fracture grains, said Joali Paredes-Mariño, a geological engineer at the University of Auckland, in a paper presented at the EGU. .
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A separate expedition from a team from New Zealand’s National Water and Atmospheric Research Institute (NIWA) to Auckland traveled to the volcano in April, but did not pass through the caldera. They took samples of ash from the seabed around the volcano, which showed that the eruption was probably followed by spectacular pyroclastic flows, hot streams of ash and lava that rained on the submerged sides of the caldera. The rapid hot ash turned the surrounding seabed into a white desert that “wiped it all out,” says voyage leader Kevin Mackay, a NIWA marine geologist.
These flows have spread underwater for thousands of square miles since the eruption, ripping off the seabed cables, including those providing access to Tonga’s Internet, which has not yet been fully restored, and feeding tsunamis that ravaged the nearby islands, reaching up to 18. meters in height. At the bottom of the sea, nothing seems to have survived, although samples are still being analyzed to determine the extent of the damage. “We don’t even think bacteria live there,” says Mackay. “That’s how toxic we think sediment is.”
Samples collected by the NIWA team are being used to study the potential impacts on ocean oxygen levels and ocean acidification, says Sarah Seabrook, NIWA’s biogeochemist.
Not everything was decimated, though. Satellite data showed a large bloom of phytoplankton in the ocean after the eruption, which fed on the nutrients released by the explosion, Seabrook says. And on the nearby hills that rose to the bottom of the sea just 15 miles from the eruption, life was flourishing, Mackay says. “We expected life to be universally destroyed.”
Water vapor pen
Other research presented at the EGU by Philippe Heinrich to the French Commission on Alternative Energy and Atomic Energy near Paris showed that the pressure wave of the eruption caused a tsunami to the French Mediterranean coast, 17,000 kilometers away, with several centimeters at sea level. recorded upload. Luis Millán of NASA’s Jet Propulsion Laboratory in Pasadena, California, also found that the eruption sent a plume of water vapor that reached a height of 53 kilometers to the stratosphere. This plume, which has now encircled the world, increased the water vapor content of the stratosphere by 146 teragrams (146 trillion grams), or 10%, and is likely to remain in the atmosphere for at least a year. “We haven’t seen anything like this before in the whole age of satellites,” says Millán.
Some research suggests there were clues as to what was to come. Thomas Walter, of the German Geosciences Research Center in Potsdam, says seismic readings point to a possible partial collapse of the boiler wall in the hours leading up to the event. “It’s a very weak track,” he says. “But it may indicate that we have a collapse first and then an explosion.”
Cronin agrees that there may have been some prior notice. Satellite images showed part of the northern edge protruding from the volcano falling into the sea the day before the eruption. “It could have indicated the early stages of the boiler collapse,” he says. This could be a crucial tool for predicting future underwater eruptions. “If we missed the big track that this big one would come up with, then this is obviously a lesson we’ll take forward,” Cronin says.