Why was the explosion of the volcano in Tonga so strong and what to expect now?

(ORDO NEWS) — The Kingdom of Tonga doesn’t often attract attention, but the massive eruption of an underwater volcano on January 15 affected literally half of the world.

The volcano consists of two small uninhabited islands, Hunga Ha’apai and Hunga Tonga, rising about 100 meters above sea level, 65 kilometers north of Nuku’alofa, the capital of Tonga.

But beneath the waves lies a massive volcano about 1,800 meters high and 20 kilometers wide.

The Hunga-Tonga-Hunga-Ha’apai Volcano has erupted regularly over the past few decades. During the events of 2009 and 2014/15, hot jets of magma and steam burst through the waves.

But these eruptions were small, compared to the events of January 2022, their scale seemed dwarfed.

Our study of these earlier eruptions suggests that this is one of the most powerful eruptions that a volcano is capable of producing about once every thousand years.

Why is a volcanic eruption so explosive, given that seawater must cool the magma?

If magma slowly rises into sea water, even at temperatures around 1200 degrees Celsius, a thin film of vapor forms between the magma and the water.

This provides a layer of insulation to allow the outer surface of the magma to cool.

But this process does not work when magma filled with volcanic gas is ejected from underground. When magma hits the water quickly, any layers of vapor quickly break down, bringing the hot magma into direct contact with the cold water.

Volcanologists call this “fuel-coolant interaction,” and it’s like weapon-grade chemical explosions. Extremely strong explosions tear the magma apart.

A chain reaction begins as new magma fragments expose fresh hot interior surfaces to water, and the explosions repeat, eventually ejecting volcanic particles at supersonic speeds.

What to expect next.

We are still in the middle of this major eruption sequence and many aspects remain unclear, in part because the island is currently obscured by ash clouds.

The two previous eruptions on December 20, 2021 and January 13, 2022 were of medium size. They produced clouds up to 17 kilometers high and added new land to the combined 2014/15 island.

The latest eruption has increased the scale. The ash plume has already reached a height of about 20 kilometers.

The most remarkable thing is that it spread almost concentrically at a distance of about 130 kilometers from the volcano, creating a plume with a diameter of 260 kilometers.


This demonstrates a tremendous explosive force that cannot be explained by the interaction of magma and water alone. This means that a large amount of fresh, gas-rich magma is erupting from the caldera.

The eruption also generated tsunamis across Tonga and neighboring Fiji and Samoa. The shock waves traveled many thousands of kilometers, were seen from space and recorded in New Zealand at a distance of about 2000 kilometers.

All of these signs indicate that the large Hunga caldera has awakened. Tsunamis are generated by coupled atmospheric and oceanic shock waves during explosions, but they are also easily triggered by underwater landslides and caldera collapses.

It remains unclear whether this is the climax of the eruption.

Therefore, we can expect several weeks or even years of major volcanic unrest due to the Hunga-Tonga-Hunga-Haapai volcano.

Shane Cronin, professor at the University of Auckland.


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