Tongan volcano eruption 'largest ever recorded,' New Zealand scientists say

A New Zealand-led team of marine geologists investigating an underwater volcano that erupted on Jan. 15 in the Tongan archipelago in the South Pacific Ocean have found that it was the “largest ever recorded” with modern equipment.

The Hunga Tonga-Hunga Ha’apai volcano, which triggered a tsunami and a sonic boom that twice-circled the globe, was captured in dramatic satellite imagery which showed huge cloud of ash and steam thrust into the atmosphere.

A team of oceanographers, scientists and marine geologists headed by the New Zealand National Institute for Water and Atmospheric Research (NIWA), with assistance from a robot boat remotely operated in the UK by Sea-Kit International, have conducted the “fullest investigation yet” into the underwater Tongan volcano. They discovered that almost 10 cubic kilometres of seafloor was displaced -- the equivalent of 2.6 million Olympic-sized pools.

“The eruption reached record heights, being the first we’ve ever seen to break through into the mesosphere,” said Kevin Mackay, NWA marine geologist. “It was like a shotgun blast directly into the sky.”

“While this eruption was large, one of the biggest since Krakatoa in 1883, there have been others of similar magnitude since then that didn’t behave in the same way. The difference here is that it’s an underwater volcano and its also part of the reason we got such big tsunami waves,” added Mackay.

The team of scientists also unravelled new information into the volcano’s underwater pyroclastic flows -- a mixture of hot, dense volcanic ash, lava fragments and gas ejected from the volcano -- through examining sediment debris found 80 km away.

“The sheer force of the flows is astonishing -- we saw deposits in valleys beyond the volcano, which is where the international cable lies, meaning they had enough power to flow uphill over huge ridges and then back down again,” said Dr Emily Lane, Principal NIWA scientist.

The volcano was also found to have injected an immense plume of water vapour into the Earth’s stratosphere. According to NASA, only the 2015 Calbuco eruption in Chile and the 2008 Kasatochi Island eruption in Alaska released significant amounts of high-altitude water vapour.

“We’ve never seen anything like it,” Luis Millán, atmospheric scientist at NASA’s Jet Propulsion Laboratory, said in a statement in August.

The Hunga Tonga-Hunga Ha’apai volcano’s crater was also found to be 700 meters deeper than before the eruption.