Tsunami models underestimated shockwave from Tonga eruption

• Atmospheric shockwave amplified waves across Pacific
• Models unable to factor in shockwave's boost
• Calls to reassess tsunami risk from other volcanoes

The volcanic eruption in Tonga this month unleashed an atmospheric shockwave that radiated out at close to the speed of sound, pushing large waves across the Pacific to the shores of Japan and Peru, thousands of kilometres away.

Forecasting models and warning systems, designed primarily to assess earthquake-triggered waves, did not account for the boosting effects of the shockwave. It was a critical flaw in these systems, scientists said, leaving them unable to predict exactly when the waves would hit land.

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Volcano-triggered tsunamis have been rare in modern history, and the shockwave from Tonga's volcano was among the largest ever recorded, similar to the one produced by the 1883 eruption of Krakatoa.

Prior to the 2018 tsunami that followed the eruption of Anak Krakatau, a tsunami set off by a volcano had not happened in the ocean in more than a century. Rather, 90 percent of tsunamis are triggered by earthquakes.

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Tsunami waves, driven by gravity, travel at around 200 metres (660 feet) per second - roughly the speed of a jetliner. But the shockwave from Tonga's volcano had moved at more than 300 metres per second and was so powerful, scientists said, that it caused the atmosphere to ring like a bell.

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