The eruption of an underwater volcano off Tonga, which triggered a tsunami warning for several South Pacific island nations, is seen in an image from the NOAA GOES-West satellite taken at 05:00 GMT January 15, 2022. CIRA/NOAA/Handout via
The eruption of an underwater volcano off Tonga, which triggered a tsunami warning for several South Pacific island nations, is seen in an image from the NOAA GOES-West satellite taken at 05:00 GMT January 15, 2022. CIRA/NOAA/Handout via Reuters / CIRA/NOAA

When an underwater volcano off Tonga erupted last month, it was accompanied by one of the largest volcanic lightning events ever recorded.

The Hunga Tonga-Hunga Ha'apai volcanic island, about 65 km (40 miles) north of Nuku'alofa, the capital of Tonga, had been puffing away for about a month before a series of blasts began on Jan. 13.

Two days later, rising magma, superheated to around 1,000 degrees Celsius (1,832 Fahrenheit), met with 20 degree Celsius seawater, causing an instantaneous and massive explosion. Almost 400,000 lightning strikes were recorded in six hours that evening.

"I can't imagine what the people on the islands would have been going through, with a huge ash cloud overhead, a tsunami flooding everything they own, and cloud-to-ground lightning coming down around them. It must have felt apocalyptic," said Chris Vagasky, a meteorologist at Vaisala.

The Finland-based environmental technology company has been studying the wave pattern created as the eruption plume hit the stratosphere and spread outward.

(For an interactive graphic on the lightning storm around Tonga, open https://tmsnrt.rs/3HQ81Bq in an external browser.)

According to data from a ground-based global lightning detection network owned and operated by Vaisala, dubbed GLD360, there was a total of almost 590,000 lightning strikes over the three-day period, dwarfing the next largest event on Vaisala's records, the 2018 eruption of Anak Krakatau in Indonesia, when a large chunk of a flank of the volcanic island slipped into the ocean, triggering a tsunami.

"In the December 2018 Anak Krakatau eruption, we detected about 340,000 events over a one-week period, so to detect nearly 400,000 in just a few hours is extraordinary," Vagasky said.

The highly explosive nature of the eruption in Tonga could be a reason for the large number of lightning strikes. Another factor is the presence of seawater. Lava breaks into smaller pieces when it comes into contact with water, thus increasing the number of charged particles available for collision, causing lightning.

"Lots of research will be coming in the months and years ahead to understand it," Vagasky said.