THE HUNGA-TONGA-HUNGA-HA'APAI VOLCANO, TONGA — The “once in 1,000 years” eruption of the Hunga-Tonga Hunga-Ha'apai[c] volcano on Saturday did not emerge from smaller volcanic cones as in previous eruptions in 2009 and across 2014 and 2015.
Rather, it blasted out of a five-kilometer-wide underwater caldera, according to Shane Cronin, Professor of Earth Sciences at the University of Auckland.
The power of the explosion is likely because magma rose up from the caldera so quickly there was no time for a film of steam to form and allow the magma’s surface to cool as it passed through the water.
Instead, hot magma came into direct contact with cold water, creating explosions which split the magma up and forced it into further contact with additional cold water, causing additional explosions.
The resulting blast reached supersonic speeds, sending out a sonic boom that reached New Zealand, according to The Associated Press.
Unusually high waves drowned two people in Peru and caused widespread tsunami alerts elsewhere.
Damage to internet connections meant that very little news of the volcano’s impact on Tonga was available initially, though The Associated Press reported tsunami waves crashing across the shore and people rushing to higher ground.
Two smaller eruptions occurred at the same volcano on December 20 and January 13, and previous 1,000-year major caldera eruption episodes involved many separate explosion events, meaning several weeks or even years of major volcanic unrest could be due, according to Professor Cronin’s article on The Conversation.
In line with this reasoning, CNN reported on Monday that the volcano had erupted again, for the third time in four days, though unlike Saturday’s eruption, which was likely the biggest recorded anywhere on the planet in more than 30 years, there were no additional tsunami alerts.
