Shockwave from Tonga volcanic eruption sent atmosphere ringing like a bell

The volcanic eruption in Tonga this month triggered an atmospheric shock wave that radiated at near the speed of sound, pushing large waves across the Pacific to the coasts of Japan and Peru, at thousands of kilometers.

Forecasting models and warning systems, designed primarily to assess the waves triggered by earthquakes, did not take into account the amplifying effects of the shock wave. It was a critical flaw in these systems, the scientists said, leaving them unable to predict exactly when the waves would hit land.

“The trans-Pacific and global waves came in earlier than expected, which (was) terrible for distant shores,” said civil engineer Hermann Fritz of Georgia Tech University, who studies tsunamis.

The eruption of the Hunga Tonga-Hunga Ha’apai volcano triggered a tsunami that destroyed villages and resorts and cut communications for the South Pacific nation of around 105,000 people. Three people were reportedly killed.

However, the Tongans were well equipped to deal with the tsunami. The small island nation is considered one of the best prepared for natural disasters, with years of tsunami drills under its belt, and many people evacuating to higher ground.

But for distant Peru, for example, the lack of accurate information may have contributed to the deaths of two people who drowned in unusually high waves, as well as the catastrophic oil spill from a ship near the refinery. of La Pampilla.

“We need to reassess the tsunami risks for other volcanoes around the world,” Fritz said.

For example, the underwater volcano known as Kick’em Jenny is thought to pose only a regional tsunami hazard to the neighboring Caribbean island of Grenada. But in fact, “it could very well excite the whole of the Caribbean and the Gulf of Mexico, and possibly even the Atlantic and world oceans, if a Tonga-like event were to occur,” he said.

Volcano-triggered tsunamis have been rare in modern history, and Tonga’s volcano shock wave was among the largest on record, similar to that produced by the 1883 eruption of Krakatoa.

Prior to the 2018 tsunami that followed the eruption of Anak Krakatau, a volcano-triggered tsunami had not occurred in the ocean for over a century. On the contrary, 90% of tsunamis are triggered by earthquakes.

As such, tsunami warning systems are programmed to prioritize seismic events, with scientists grading risk based on whether an earthquake’s magnitude is high enough above 7.5 on the Richter scale to cause a destructive tsunami.

The shock wave from the Tonga volcano had traveled at more than 300 meters per second and was so powerful, scientists say, it caused the atmosphere to ring like a bell. (Photo: AP)

Seafloor instruments also monitor irregular changes in wave height, sending information by surface buoy and then by satellite to a warning center for evaluation.

The Pacific Tsunami Warning Center in Hawaii initially warned of dangerous waves within 1,000 km of the Tonga eruption. However, their bulletin noted that “due to the source of the volcano, we cannot predict the magnitude of tsunamis or how far the tsunami hazard may extend.” About 10 hours later, the warning was updated to include a possible threat to Peru – a surprising development given that the tsunami near Tonga was relatively weak.

Tsunami waves, driven by gravity, travel at about 200 meters (660 feet) per second, about the speed of an airliner. But the shock wave from the Tonga volcano had traveled at more than 300 meters per second and was so powerful, scientists say, that it rang the atmosphere like a bell.

Thanks to the transfer of this energy from the atmosphere to the ocean, the shock wave amplified ocean waves around the world, pushing them further and accelerating their travel time – what tsunami warning centers were not equipped to handle.

Now, Fritz said, the possibility of atmospheric pressure waves must “be added to the suite of modeling and forecasting tools from tsunami warning centers.”

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