What Conditions Make for a Violent Volcanic Eruption

What Conditions Make for a Violent Volcanic Eruption

The Kingdom of Tonga doesn’t often attract global attention, merely a violent eruption of an underwater volcano on January xv has spread shock waves, quite literally, around one-half the globe.

The volcano is unremarkably not much to await at. It consists of two small uninhabited islands, Hunga-Ha’apai and Hunga-Tonga, poking about 100m higher up body of water level 65km north of Tonga’s uppercase Nuku‘alofa. Merely hiding below the waves is a massive volcano, effectually 1800m high and 20km broad.

A massive underwater volcano lies side by side to the Hunga-Ha’apai and Hunga-Tonga islands.

Author provided

The Hunga-Tonga-Hunga-Ha’apai volcano has erupted regularly over the past few decades. During events in 2009 and 2014/15 hot jets of magma and steam exploded through the waves. But these eruptions were pocket-sized, dwarfed in scale by the Jan 2022 events.

Our research into these before eruptions suggests this is one of the massive explosions the volcano is capable of producing roughly every k years.

Why are the volcano’s eruptions and so highly explosive, given that sea water should cool the magma down?

If magma rises into sea water slowly, even at temperatures of about 1200℃, a thin picture of steam forms between the magma and water. This provides a layer of insulation to allow the outer surface of the magma to cool.

But this process doesn’t work when magma is blasted out of the basis full of volcanic gas. When magma enters the water apace, whatsoever steam layers are quickly disrupted, bringing hot magma in direct contact with cold water.

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Volcano researchers call this “fuel-coolant interaction” and it is akin to weapons-class chemical explosions. Extremely violent blasts tear the magma apart. A chain reaction begins, with new magma fragments exposing fresh hot interior surfaces to h2o, and the explosions repeat, ultimately jetting out volcanic particles and causing blasts with supersonic speeds.




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2 scales of Hunga eruptions

The 2014/15 eruption created a volcanic cone, joining the two former Hunga islands to create a combined island about 5km long. Nosotros visited in 2016, and discovered these historical eruptions were merely drapery raisers to the master event.

Mapping the bounding main floor, we discovered a hidden “caldera” 150m below the waves.

A map of the seafloor shows the volcanic cones and caldera.

A map of the seafloor shows the volcanic cones and massive caldera.

Author provided

The caldera is a crater-similar depression around 5km across. Small eruptions (such as in 2009 and 2014/15) occur mainly at the edge of the caldera, simply very big ones come from the caldera itself. These large eruptions are and then large the top of the erupting magma collapses inward, deepening the caldera.

Looking at the chemistry of past eruptions, nosotros now think the small-scale eruptions represent the magma system slowly recharging itself to prepare for a large effect.

We institute evidence of two huge by eruptions from the Hunga caldera in deposits on the old islands. Nosotros matched these chemically to volcanic ash deposits on the largest inhabited island of Tongatapu, 65km away, and then used radiocarbon dates to show that big caldera eruptions occur about ever 1000 years, with the last one at AD1100.

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With this knowledge, the eruption on January 15 seems to exist right on schedule for a “large one”.




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What we can expect to happen at present

We’re withal in the eye of this major eruptive sequence and many aspects remain unclear, partly because the island is currently obscured by ash clouds.

The two before eruptions on December 20 2021 and January 13 2022 were of moderate size. They produced clouds of up to 17km elevation and added new country to the 2014/15 combined island.

The latest eruption has stepped up the scale in terms of violence. The ash plume is already nearly 20km high. Nigh remarkably, it spread out almost concentrically over a distance of almost 130km from the volcano, creating a plume with a 260km diameter, before it was distorted past the current of air.

This demonstrates a huge explosive power – ane that cannot be explained past magma-water interaction solitary. It shows instead that large amounts of fresh, gas-charged magma have erupted from the caldera.

The eruption also produced a tsunami throughout Tonga and neighbouring Fiji and Samoa. Daze waves traversed many thousands of kilometres, were seen from space, and recorded in New Zealand some 2000km away. Soon after the eruption started, the sky was blocked out on Tongatapu, with ash beginning to autumn.

All these signs suggest the large Hunga caldera has awoken. Tsunami are generated by coupled atmospheric and ocean shock waves during an explosions, simply they are also readily caused by submarine landslides and caldera collapses.

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It remains unclear if this is the climax of the eruption. It represents a major magma pressure release, which may settle the arrangement.

A warning, however, lies in geological deposits from the volcano’s previous eruptions. These circuitous sequences evidence each of the 1000-yr major caldera eruption episodes involved many separate explosion events.

Hence we could be in for several weeks or even years of major volcanic unrest from the Hunga-Tonga-Hunga-Ha’apai volcano. For the sake of the people of Tonga I hope not.

What Conditions Make for a Violent Volcanic Eruption

Source: https://theconversation.com/why-the-volcanic-eruption-in-tonga-was-so-violent-and-what-to-expect-next-175035

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