The Mechanism That Unleashed Tonga's Record-Breaking Tsunami Has Been Identified

0 Comments

The tsunami triggered by the Hunga Tonga–Hunga Ha'apai eruption in early 2022 wreaked havoc over Oceania, Asia, North America, and South America, with waves reaching up to 15 meters (49 feet) in some places - the deadly result of a volcanic shockwave that set new records.

A new research has uncovered the mechanism that scientists believe caused the tsunami to travel such a long distance and with such energy — a phenomenon known as acoustic-gravity waves (AGWs), a lengthy form of sound wave that can move extraordinarily swiftly across the water or the air.

When the volcano explosion progressed, these AGWs seemed to move through the water, up into the sky, and then out over the waves, giving the resultant tsunami even more energy as several waves merged.

As a result, the tsunami was larger, lasted longer, and went further and faster than it would have otherwise.

"The idea that tsunamis could be generated by atmospheric waves triggered by volcanic eruptions is not new, but this event was the first recorded by modern, worldwide dense instrumentation, allowing us to finally unravel the exact mechanism behind these unusual phenomena," says geologist Ricardo Ramalho of Cardiff University in the United Kingdom.

The presence of these waves was determined using a mix of data from sea level, the atmosphere, and satellite measurements, and there was a "direct correlation" between the first signals of air disturbance caused by AGWs and the start of the tsunami in multiple sites.

The Hunga Tonga–Hunga Ha'apai volcanic eruption was massive, although tsunamis of this magnitude are unusual for underwater eruptions. The way AGWs excite the ocean-atmosphere interface, according to the scientists, was important in causing such dramatic and devastating outcomes.

AGWs may be caused by a variety of violent events, and they are impacted by gravity, as the name implies. A single one of these waves can be hundreds of kilometers or miles long, travel thousands of meters or feet beneath the sea's surface, and reach speeds near to the speed of sound in water.

"The Tonga eruption was in an ideal location below the surface, in shallow water, which caused energy being released into the atmosphere in a mushroom-shape close to the water surface," explains Cardiff University applied mathematician Usama Kadri.

"Thus, the interaction of energetic AGWs with the water surface was inevitable." 

Nonlinear resonance occurs when AGWs interact with tsunamis they've previously caused, and the researchers believe this was a role in transmitting energy back into the ocean and boosting the tsunami's speed and ferocity even further.

The tsunami surged across the Pacific, Atlantic, and Indian oceans in less than 20 hours, the team believes, traveling 1.5–2.5 times faster than a normal volcano-triggered tsunami. It reached speeds of roughly 1,000 km/h (621 mph).

Furthermore, because the tsunami traveled partly through the sky, it was able to reach the Caribbean and Atlantic without first passing through South America. There appears to be a lot more science we can learn from this incredibly significant occurrence.

"Such a resonance at this scale allows us to move beyond proof of concept of the mechanism, and the development of more accurate forecasting models and real-time warning systems, into the potential of developing a new energy harnessing technology," adds Kadri.