A giant underwater volcano erupted in the South Pacific nation of Tonga in January this year. It produced massive pressure waves, some of which raced through the Earth’s atmosphere. In the audible range of frequencies, people 10,000 km away in the US state of Alaska reported hearing repeated booms. Two new studies have claimed it to be the biggest explosion in last 140 years. The Tonga event was comparable in terms of atmospheric intensity only to the Krakatau eruption, which took place in Indonesia in 1883. More than 30,000 people are believed to have died in that catastrophic event.

The Tonga explosion took place after several weeks of activity at the seamount. The global network of detectors set up to monitor Nuclear Test-Ban Treaty (CTBT) compliance picked up the infrasound signal, which has frequencies just below what humans are capable of hearing. The amount of energy produced was comparable to what might be generated by more than 100 Hiroshima-scale bombs detonating at once.

When the Tonga underwater volcano erupted, it sent up a plume of gas and particles to hit the mesosphere – the third layer of the atmosphere above Earth‘s surface. It was the largest volcanic plume satellite ever recorded.

The first set of researchers revealed in their study, published in the journal Science, that the January 15 event generated a broad range of atmospheric waves observed globally by various ground-based and space-borne instrumentation networks. They said the pressure pulse generated by the Tonga volcano was comparable in amplitude to that of the 1883 Krakatau eruption. In order of magnitude, it was greater than that of the 1980 Mount St. Helens eruption.

The second study said that this pressure pulse not only disturbed the atmosphere but also jiggled the ocean below. In fact, the atmospheric pulse triggered a series of fast-moving oceanic waves (meteotsunamis) which reached the shore hours before the conventional tsunamis generated by the volcano’s blast, the researchers said.

These small “forerunners” were observed all around the world, primarily in the Pacific Ocean.