The Kingdom of Tonga doesn’t usually appeal to world consideration, however a violent eruption of an underwater volcano on January 15 has unfold shock waves, fairly actually, round half the world.
The volcano is normally not a lot to have a look at. It consists of two small uninhabited islands, Hunga-Ha’apai and Hunga-Tonga, poking about 100m above sea stage 65km north of Tonga’s capital Nuku‘alofa. However hiding under the waves is an enormous volcano, round 1800m excessive and 20km vast.
A large underwater volcano lies subsequent to the Hunga-Ha’apai and Hunga-Tonga islands.
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The Hunga-Tonga-Hunga-Ha’apai volcano has erupted recurrently over the previous few a long time. Throughout occasions in 2009 and 2014/15 sizzling jets of magma and steam exploded via the waves. However these eruptions have been small, dwarfed in scale by the January 2022 occasions.
Our analysis into these earlier eruptions suggests this is without doubt one of the huge explosions the volcano is able to producing roughly each thousand years.
Why are the volcano’s eruptions so extremely explosive, provided that sea water ought to cool the magma down?
If magma rises into sea water slowly, even at temperatures of about 1200℃, a skinny movie of steam kinds between the magma and water. This offers a layer of insulation to permit the outer floor of the magma to chill.
However this course of doesn’t work when magma is blasted out of the bottom filled with volcanic gasoline. When magma enters the water quickly, any steam layers are shortly disrupted, bringing sizzling magma in direct contact with chilly water.
Volcano researchers name this “fuel-coolant interplay” and it’s akin to weapons-grade chemical explosions. Extraordinarily violent blasts tear the magma aside. A series response begins, with new magma fragments exposing contemporary sizzling inside surfaces to water, and the explosions repeat, finally jetting out volcanic particles and inflicting blasts with supersonic speeds.
Learn extra:
The ‘pulse’ of a volcano can be utilized to assist predict its subsequent eruption
Two scales of Hunga eruptions
The 2014/15 eruption created a volcanic cone, becoming a member of the 2 outdated Hunga islands to create a mixed island about 5km lengthy. We visited in 2016, and found these historic eruptions have been merely curtain raisers to the principle occasion.
Mapping the ocean ground, we found a hidden “caldera” 150m under the waves.
A map of the seafloor exhibits the volcanic cones and large caldera.
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The caldera is a crater-like melancholy round 5km throughout. Small eruptions (corresponding to in 2009 and 2014/15) happen primarily on the fringe of the caldera, however very large ones come from the caldera itself. These large eruptions are so giant the highest of the erupting magma collapses inward, deepening the caldera.
Wanting on the chemistry of previous eruptions, we now assume the small eruptions symbolize the magma system slowly recharging itself to organize for an enormous occasion.
We discovered proof of two large previous eruptions from the Hunga caldera in deposits on the outdated islands. We matched these chemically to volcanic ash deposits on the biggest inhabited island of Tongatapu, 65km away, after which used radiocarbon dates to indicate that large caldera eruptions happen about ever 1000 years, with the final one at AD1100.
With this information, the eruption on January 15 appears to be proper on schedule for a “large one”.
Learn extra:
Why White Island erupted and why there was no warning
What we will anticipate to occur now
We’re nonetheless in the midst of this main eruptive sequence and lots of features stay unclear, partly as a result of the island is at the moment obscured by ash clouds.
The 2 earlier eruptions on December 20 2021 and January 13 2022 have been of reasonable dimension. They produced clouds of as much as 17km elevation and added new land to the 2014/15 mixed island.
The newest eruption has stepped up the size by way of violence. The ash plume is already about 20km excessive. Most remarkably, it unfold out virtually concentrically over a distance of about 130km from the volcano, making a plume with a 260km diameter, earlier than it was distorted by the wind.
This demonstrates an enormous explosive energy – one that can’t be defined by magma-water interplay alone. It exhibits as an alternative that enormous quantities of contemporary, gas-charged magma have erupted from the caldera.
The eruption additionally produced a tsunami all through Tonga and neighbouring Fiji and Samoa. Shock waves traversed many hundreds of kilometres, have been seen from area, and recorded in New Zealand some 2000km away. Quickly after the eruption began, the sky was blocked out on Tongatapu, with ash starting to fall.
All these indicators recommend the big Hunga caldera has awoken. Tsunami are generated by coupled atmospheric and ocean shock waves throughout an explosions, however they’re additionally readily brought on by submarine landslides and caldera collapses.
It stays unclear if that is the climax of the eruption. It represents a significant magma strain launch, which can settle the system.
A warning, nevertheless, lies in geological deposits from the volcano’s earlier eruptions. These complicated sequences present every of the 1000-year main caldera eruption episodes concerned many separate explosion occasions.
Therefore we could possibly be in for a number of weeks and even years of main volcanic unrest from the Hunga-Tonga-Hunga-Ha’apai volcano. For the sake of the individuals of Tonga I hope not.
