The Surprisingly Powerful Global Tsunamis Triggered by Underwater Volcanic Eruptions – USC Viterbi

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Interactive model of the global tsunami generated by the January 2022 eruption of the Hunga Tonga-Hunga Ha’apai volcano

In 1883 there was a volcanic eruption so large that it killed tens of thousands of people. It expelled so much ash into the sky that for a time it changed the colors of the sunsets the world would see and the palette with which Impressionist painters would paint. Historically, few volcanic eruptions have been so documented, until a recent underwater eruption occurred earlier this year off the island nation of Tonga.

The impact of the January 2022 Hunga Tonga-Hunga Ha’apai volcano was recorded by USC Viterbi professors Patrick Lynett, Costas Synolakis and their students, and their colleagues at eCoast Marine Consulting and Research in New Zealand , Tonga Meteorological Service, New Zealand National Water Institute and US Geological Survey. Their research represents the first time that a team of researchers has been able to simultaneously collect ocean, atmospheric and space data from a large underwater volcanic explosion. Their findings were shared in an article published in Nature.

The volcano’s underwater explosion boiled the ocean, creating a crater 300 feet deep and 5 miles wide on the surface of the ocean. You read that right: five miles wide. The tsunami from this explosion traveled away from the volcano towards the Tonga Islands moving at 250 miles per hour. Lynett of the USC Tsunami Research Center puts this explosion in perspective: Residents of the Tongan Islands 50 miles away could feel their ears popping from the change in pressure generated by the explosion. This tsunami reached Tonga in 10 minutes and inundated land up to an elevation of 60 feet, devastating resort communities.

The impact of this explosion and the tsunami it generated was not limited to Tonga and the South Pacific Ocean. Lynett says the eruption generated a overall tsunami, reaching California and even the Mediterranean Sea. Such a global tsunami was not generated directly by the explosion, but by a pressure pulse from the eruption that spread through the atmosphere – the same pressure pulse that caused residents’ ears to pop. This pressure pulse was remarkably stable, was recorded on weather stations around the world, and crossed the globe multiple times. As it crossed the oceans, the pulse pushed the ocean surface with it, continually creating tsunamis across the world. In California, as well as Hawaii and South America, the tsunami was similar in size to the Great Japanese Earthquake of 2011. (A screenshot of the interactive model of this tsunami is below, but the full interactive experience can be found here.)

It is obvious that tsunamis can cause considerable damage to coastal areas. But rising sea levels created by climate change can make the situation worse, says Lynett, who has continually worked with planners and policymakers to understand the dangers. This is particularly important in marinas and ports. When the height of the tsunami is greater than the height of the pilings, the docks and the ships connected to them float on the pilings and act like projectiles in the harbor. This situation, caused by the Tonga eruption, was narrowly avoided in some California ports. As the authors of the paper put it, “catastrophic damage in some ports…has been averted by only a few tens of centimeters, implying that a modest rise in sea level combined with a future event similar would result in a gradual increase in infrastructure impacts.”

Lynett also indicated that since this is the first time an explosion of this size has been documented, that doesn’t mean it hasn’t happened more frequently in the past. Indeed, there are underwater volcanoes all over the world, many of them in the Pacific, as well as in the Caribbean. Currently, contingency planning, mitigation efforts, and infrastructure design do not consider volcanic-source tsunamis. However, as the authors state: “Understanding the Hunga Tonga event has broad implications…for maritime and near-shore infrastructure under threat from sea-level rise, where global tsunamis from large volcanic eruptions are currently overlooked”.

Read the full article in Nature.

Posted on August 31, 2022

Last updated August 31, 2022


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