Tonga volcano triggered record-breaking lightning and a never-before-seen tsunami

The eruption of a large volcano in the South Pacific on January 15 has done significant damage to the island nation of Tonga. It also resulted in a number of exotic phenomena like super-intense lightning strikes and a rare "meteotsunami."

On the ground in Tonga, residents are dealing with the aftermath of the blast, and of the tsunami and ash-fall that has followed. Communications with Tonga have been seriously hampered by the explosion, which has contributed to delays in the arrival of aid. 

But as the world begins to respond to the humanitarian crisis, scientists have been trying to understand this powerful, explosive eruption better.

Eight centuries of volcanic activity

The volcano — familiar to locals but unknown to most outside of the remote island kingdom — is called Hunga Tonga-Hunga Ha'apai. The name refers to two islands that rise about 100 metres above the surface of the Pacific, roughly 65 kilometres north of Tonga's capital, Nuku'alofa.

The volcano has shown on-and-off activity over the years and even centuries with major eruptions recorded as far back as the twelfth century. In December 2021, it began rumbling once again, volcanologist and science writer Robin Andrews told Bob McDonald, host of CBC Radio's Quirks & Quarks.

There were "very gas-rich plumes, but without much material coming up," Andrews said, comparing it to "burping" or "volcanic indigestion." At that time, however, "it wasn't doing anything out of the ordinary."

Then, on January 15, it blew up. The energy released by the blast has been estimated as equivalent of 10 megatons of TNT. That makes it 25,000 times more powerful than the explosion that shook the port of Beirut, Lebanon, in August 2020, Andrews said. The Tonga explosion "was pretty cataclysmic. Even volcanologists who have studied all kinds of eruptions — their jaws dropped."

Though it was about half as powerful as the eruption of Mount St. Helen's in the northwestern U.S. in 1980, the Tonga eruption nonetheless "made the world stand up and take notice, just because of how violent it was," Andrews said.

The explosion was heard in New Zealand, 2,000 kilometres away, according to a report from the Smithsonian Institution's Global Volcanism Program, and its atmospheric shock wave was detected as far away as Europe, according to a tweet by the World Meteorological Organization.

WATCH | View satellite images of the eruption from the National Oceanic and Atmospheric Administration.

Tonga is located near the boundary between two tectonic plates, the Pacific plate and the Australian plate — a region known as a subduction zone. As a result, the area is home to many volcanoes. Andrews explained that as the Pacific plate slowly slides under the Australian plate, the water within it gets "baked out" and enters the mantle above. This, in turn, allows rocks closer to the surface to melt more readily.

The result is a massive amount of molten rock, known as magma, filled with gas — a potent recipe for a volcanic  explosion.

He compared the process to a pneumatic pump that "blasted the magma out of the way." This "sets off a chain reaction that leads, in a heartbeat, to a ten-megaton explosion."

 'Apocalyptic' lightning

This intense volcanic activity was also accompanied by record amounts of lightning.

As particles of ash within the plume bumped into each other, and into ice particles in the atmosphere, there was a build-up of electrical charge — similar to what happens when you rub a balloon against a wool sweater, Andrews said.

At one point, 200,000 lightning strikes were being recorded per hour — almost 60 per second, he said. Anyone unfortunate enough to have been close to the site would have seen the sky appearing to flicker almost continuously, accompanied by a deafening roar of thunder.

It would have looked apocalyptic, Andrews said. "It would have just been this constant roar of thunder and volcanic rumbling. It would have been an extraordinary thing to see."

The lightning was detected by arrays of radio antennas in various locations around the world, with each lightning strike creating a distinctive burst of radio waves.

A rare kind of tsunami

The tsunami waves triggered by the blast were large but not record-setting. However, as the shock wave rushed through the atmosphere and around the globe, the air pushed against the ocean, creating a smaller, secondary tsunamis.

This unusual phenomena was recorded thousands of kilometres away, in the Caribbean. Dr. Andrews says this is the first time this effect, known as a meteotsunami, has been recorded as a result of a volcanic eruption.

Written and produced by Dan Falk.