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Tonga eruption depletes ozone in some areas of the southwest Pacific

Tonga eruption
Source: RNZ Pacific

Nuku'alofa, TONGA — New research has found the eruption of Tonga's Hunga Tonga-Hunga Ha'apai volcano in 2022 shot out an unprecedented amount of water vapor into the sky.

The vapor reached heights of up to 55 kilometres (about 34 miles) and depleted 5 percent of the ozone layer over the tropical southwestern Pacific and Indian Ocean regions in one week.

Increased humidity in the stratosphere led to a series of interactions between other components shot out from the volcano that ultimately broke down the layer over those regions, the authors say.

The National Institute of Water and Atmospheric Research Ltd (NIWA) principal scientist Atmosphere and Climate Olaf Morengstern said there were roughly four million water molecules per million in the stratosphere, and the volcanic plume from the Hunga Tonga-Hunga Ha'apai eruption contained up to 300.

"The authors show that this massive local enhancement of water caused substantial impacts on atmospheric chemistry, increased ozone loss, both due to gas-phase chemistry and in association with the enhanced volcanic aerosol.

"As a result, some highly unusual ozone depletion happened in the tropics in the aftermath of the eruption, especially given the generally small variability of ozone in that part of the world."

University of Canterbury atmospheric chemist Laura Revell told Morning Report it would have been a fairly short-lived ozone loss.

The vapor cooled the stratosphere quite rapidly and created the sorts of conditions that we might see over Antarctica over winter and spring when the ozone forms, she said.

"Normally we would see a bit of ozone depletion following an eruption in the months following.

"What we seem to, the scientists on this study, observed was a really rapid depletion that they observed from launching balloons carrying scientific instruments right in to that volcanic plume as it was carried away from the volcano."

Revell said the ozone layer shields us from harmful UVB radiation from the sun.

She said the data set confirms what was thought by scientists, she said.

The water in the stratosphere was expected to linger for four to five years, she said.