Hi, I’m Ali Sealander with UTD Geonews and I’d like to tell you about a violent
volcanic eruption and tsunami that happened in the southwest Pacific island kingdom of Tonga.
Residents in the capital city of Nuku’alofa were not terribly surprised on Friday Jan. 14
when a volcano 40 miles away erupted violently, sending a plume of ash high into the sky.
They knew that the volcano had been waking up and had already erupted 5 times since
1912. This is just one of many volcanoes in what geologists call the Tonga-Kermadec island arc,
formed as a result of subduction of the Pacific Plate westward beneath the Australian plate.
The Tonga-Kermadec arc is part of the Circum-Pacific Ring of Fire and can be
traced for almost 2000 miles northwards from New Zealand through the island kingdom of Tonga almost
to Samoa. The southernmost part of the arc is the spectacular Taupo Volcanic Zone of New Zealand and
the arc continues north with the first volcanic island, White Island near of the city of Auckland.
A small eruption of White Island volcano in December 2019 killed 22 tourists, showing just
how active and dangerous these volcanoes can be.
The arc continues north through the Kermadec arc,
which has 30 or so volcanoes, only a few of which are tall enough to rise above sealevel as islands.
North of these is the Tonga arc, with many more submarine and island volcanoes. Some of these
are where people of the Kingdom of Tonga live. The Kingdom extends for almost 500 miles along
the northern part of the Tonga-Kermadec arc but the Kingdom is mostly Pacific Ocean, not land.
It consists of 169 small islands where about 100,000 people live on 36 of them.
The erupting volcano in the news is called Hunga
Tonga-Hunga Ha’apai after the two islands that mark its summit.
Volcanoes can erupt quietly, like those now going on in Hawai’I or violently,
and arc volcanoes like White Island and Hunga Tonga-Hunga Ha’apai are the most violent.
This is because arc magmas contain a lot of water, which expands rapidly as the magma rises to cause
violent eruptions, like what happens with Mentos and Diet Coke, only unimaginably hotter.
Hunga Tonga-Hunga Ha’apai volcano is about 40 miles north of Nuku’alofa
where most Tongans live.
It was no surprise that it erupted but the violence of the eruption and the tsunami it caused were surprising.
The eruption sent a huge mushroom cloud of ash 12 miles high into the sky, twice as high as jet airliners fly.
A lot of ash rained down on Nuku’alofa. Satellite images provide amazing views of how this ash cloud
quickly mushroomed.
But this eruption also caused a tsunami, how did that happen?
Tsunamis are created when large amounts of water — in the ocean, a bay or even a lake — are quickly
displaced, usually by earthquakes.
That’s what caused the 2011 tsunami in Japan that killed
20,000 people.
But explosive underwater eruptions can also move a lot of water and make a tsunami.
That’s what happened in 1883 when Krakataoa in Indonesia erupted so violently
that it collapsed into the sea, creating a 37m tsunami, as tall as a 6 story building.
The Krakatoa tsunami destroyed 300 coastal villages and towns, killing an estimated 86,000 people.
Fortunately for the people of Nuku’alofa, the tsunami created by the Tongan eruption was only about 4 feet high.
This damaged a lot of houses and shops in Nuku’alofa though
and also spread damage all around the Pacific, causing small tsunamis and damage along coastal regions.
I hope you enjoyed learning more about the Hunga Tonga-Hunga Ha’apai
eruption and tsunami.
I’m Ali Sealander with UTD Geonews and I’ll see you next time!