According to newly published research, the massive January 2022 eruption of the Hunga volcano in the Kingdom of Tonga generated its most destructive tsunami not from an initial explosion, but from the sudden collapse of the volcano’s caldera. Investigators found that this underwater collapse produced a hydro-acoustic sound wave detectable thousands of kilometres away, potentially offering a new method for early detection of deadly volcanic tsunamis.
Listening to Submarine Volcanoes via T-Waves
Monitoring submarine volcanoes remains a challenge across the Pacific Ring of Fire due to sparse instrumentation. According to the study, the closest conventional seismometer during the 2022 eruption was located in Fiji, approximately 750km away, where seismic signals from volcanic processes are often poorly transmitted through the Earth.
To overcome this, researchers re-analyzed records from 14 seismic stations across the southwest Pacific, examining hydro-acoustic signals known as tertiary waves, or T-waves. Because underwater sound travels efficiently over long distances, isolated volcanoes acting like an ocean-floor bell can radiate violent underwater processes. During the first hour of the eruption, data detected submarine landslide flows racing down the volcano’s flanks, capable of destroying submarine communications cables hundreds of kilometres away, according to the findings.
The Caldera Collapse and Telecom Tower Evidence
At approximately 6:28 pm Tonga time, the centre of the Hunga volcano began collapsing inward, ultimately forming a caldera about 4km wide and more than 850 metres deep, according to the research team. This massive displacement of rock and seawater generated the eruption’s largest local tsunami, which reached run-up heights of 18 to 40 metres on islands within 100km.
While the collapse was only weakly detected by conventional seismic monitoring, it generated a powerful T-wave detected at 14 stations up to 2,600km away. To pinpoint when the tsunami struck land, researchers examined data traffic from a telecommunications tower at Kanokupolu on the western side of Tongatapu. According to the Tonga Communications Corporation, the weather station’s weather data transmission stopped precisely at 6:45:24 pm as the wave tore the 180-metre-inland structure apart, aligning with the travel time for a tsunami triggered by the 6:28 pm collapse.
Did you know? Sound waves travel through ocean water at roughly 1.5km per second—more than seven times faster than a tsunami wave moves across the sea floor.
Frequently Asked Questions
What caused the most destructive tsunami during the Hunga eruption?
According to researchers, the largest local tsunami was generated by the sudden collapse of the volcano’s caldera rather than the initial explosions.
How do scientists detect underwater volcanic collapses?
Researchers listen for hydro-acoustic T-waves, which are efficient underwater sound signals that radiate across the ocean and can be picked up by distant seismic stations.
Why are conventional seismometers limited for undersea volcanoes?
Conventional seismometers are often too far away—such as the closest sensor in Fiji being 750km from Hunga—meaning seismic signals are poorly transmitted through the Earth.
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