The undersea volcano that erupted near Tonga, causing a massive surge in the Pacific Ocean, could erupt again in days, but Saturday’s explosion was likely the largest we’ll experience, an expert says.
- Scientists say there is evidence of regular large eruptions, occurring roughly every 1,000 years
- During the 2015 eruptions, two small uninhabited islands joined and a new cone formed
- A scientist who camped on the volcano in 2015 discovered that it was 1,800 meters high and 20 kilometers wide
Shane Cronin, professor of earth sciences at the University of Auckland, spent six nights camping on the Hunga Tonga-Hunga Ha’apai volcano after its last round of eruptions in 2015.
As part of a team of experts, Dr. Cronin conducted tests across the region to study volcanic behavior taking place below the ocean surface and determine the likelihood of future eruptions.
The team found evidence of “large” regulars occurring roughly every 1,000 years.
With the last occurring around 1100 AD, it seemed likely that the area was heading for another large-scale eruptive sequence.
This week, a streak that started with smaller eruptions throwing smoke and ash into the air culminated in a massive surge that was captured by satellite imagery on Saturday.
Additional and larger eruptions possible
“When I looked at the past deposits of this volcano…there was evidence of very many eruptions during each episode,” Dr Cronin said.
While this latest eruption could very well be “the big one”, Dr Cronin said it was possible that “larger and larger” eruptions could follow.
Over the weekend, tsunami warnings were issued across much of the Pacific, including New Zealand, Canada and the United States.
Little information on the extent of damage or injuries has been received from Tonga – home to around 105,000 people – as internet access was cut after the eruption.
Tonga’s internet goes through an undersea cable from Suva in Fiji.
Dr Cronin said the cable itself could have been damaged or the outage could have been due to power cuts on the island caused by heavy ashfall which also blackened the sky.
Video posted to social media showed large waves crashing into Pacific coastal areas, swirling around homes, a church and other buildings.
Satellite images showed a huge eruption, with a plume of ash, steam and gas rising like a mushroom above the blue waters of the Pacific.
Sleep on an active volcano
The volcano consists of two small uninhabited islands, Hunga Ha’apai and Hunga Tonga, located 100 meters above sea level, 65 kilometers north of Tonga’s capital, Nuku’alofa.
The 2015 eruptions created a new cone – made up largely of lava and ash – which united the islands into a single mass.
This volcanic platform is where Dr. Cronin and the team camped.
“We went to measure the bathymetry, or the depth of the ocean around the islands, and that’s when we found the very large caldera sitting on top of the volcano,” Dr Cronin said.
Their tests revealed that hiding beneath the waves was a massive volcano, about 1,800 meters high and 20 kilometers wide.
After Saturday’s explosion, the site was difficult to monitor due to thick clouds of smoke and ash, but new satellite data has revealed the immense size of the blast.
Dr Cronin said the entire crater had been destroyed and “just tiny little shards” of the two original islands remained intact.
“The generation of this very large eruption, as well as the tsunami, indicates that the upper part of this volcano has collapsed,” he said.
“So that probably means now that, well, first of all, we have less gas-rich magma left – most of it is erupting.”
It also means that the volcano is deeper than before.
But the Hunga Tonga-Hunga Ha’apai is not the only volcano, nor the largest, to threaten Tonga and the Pacific.
“The Tongan part of the Pacific Ring of Fire is a part that we don’t see a lot because a lot of the volcanoes are undersea,” he said.
“But they are huge and basically every 100 kilometers along this chain is another massive volcano.”