PHOTO: SUPPLIED
SCIENTISTS studying the after-effects of the Hunga Tonga-Hunga Ha’apai volcano eruption in Tonga on January 15 last year believe it is a major contributing factor to the deluge that struck the upper North Island on Anniversary Weekend.
The reason is because of the large amounts of water the eruption carried into the mesosphere 57km above the ocean.
It’s not just the New Zealand floods the volcano gets the blame for, devastating one in 100-year flooding in New South Wales and Queensland in 2022 are also now thought to be an effect of the HTHH eruption.
The plume from the HTHH eruption was higher than any other recorded volcanic eruption, as was the amount of water carried into the upper atmosphere.
It’s now estimated the underwater eruption of HTHH in the South Pacific Ocean ejected about 145 million tonnes of water vapour into the stratosphere.
Scientists originally thought HTHH would have a similar effect on the weather as the 1991 Mt Pinatubo eruption in the Philippines.
That eruption blasted vast amounts of dust as high as 45km, which cooled the weather over the next couple of years. But the HTHH plume had only 2% of the dust of the Pinatubo event.
The Oxford University scientist who led the study, using weather satellites to measure the height of HTHH’s plume, believes the HTHH plume will have a warming effect.
“The eruption was so big that we couldn’t use our normal ways to figure out how high it went.
“Usually, we use satellites to measure the temperature of the volcanic cloud, and because the atmosphere gets colder as you get higher you can work out the altitude. But not here,” Simon Proud posted on Twitter.
“Hunga-Tonga’s plume went so high that it got warmer again. So, we found another way.
We used images from weather satellites in three different places to triangulate the plume height, much like our eyes work together to help our brain figure out how far away something is.
“Our research shows that previous eruptions, like Pinatubo in 1991, that weren’t seen by these advanced eyes in space, probably went higher than we previously thought. Scientists couldn’t see the volcano from multiple angles and didn’t have frequent enough images.”
The sheer volume of water altered the weather pattern, which was already experiencing a La Nina event. La Nina pushes warm ocean water across to the western Pacific – the origin of the cyclone remnants that eventually arrive in New Zealand.
The HTHH eruption raised the water vapour in the mesosphere by 10%. Fifty km above the earth, water reflects solar radiation back into space while reflecting earth’s heat back to the surface – warming the surface while cooling the stratosphere.
NASA atmospheric scientist Luis Millan said the water injection was unprecedented in both height and volume in the 17 years they had been collecting the data.
“It may take several years for the H2O plume to dissipate. This eruption could impact climate not through surface cooling due to sulfate aerosols, but rather through surface warming due to the radiative forcing from the excess stratospheric H2O,” he said.
The reason the eruption was able to move such a volume of water more than 50km into the sky is another unique marker for what is proving to be a highly unusual event.
The January 15 eruption took place in the volcano’s caldera, a bowl-shaped depression formed by previous eruptions.
If it was any deeper than about 150m, the eruption would have been smothered by the weight of sea water.
Any shallower, and there would not have been enough sea water flashed to steam to account for the volume observed.
