Summary
Analysis of seismic data from Tonga’s 2022 Hunga eruption found that distant sensors detected T-waves linked to the collapse that produced the eruption’s largest tsunami. Because these signals travel at least seven times faster than tsunamis, they could support earlier warnings after underwater volcanic eruptions.
Seismic signals recorded hundreds to thousands of kilometres from Tonga’s Hunga Tonga–Hunga Ha‘apai volcano have revealed a possible way to detect tsunamis generated by underwater eruptions before the waves arrive.
The finding comes from an analysis of the volcano’s January 2022 eruption, which lasted 11 hours and sent tsunamis towards nearby islands with little warning. Some waves reached more than 40 metres in height. Underwater volcanoes are difficult to monitor because the eruptions and structural changes occur beneath the ocean surface.
How the distant signal tracked the eruption
Shane Cronin of the University of Auckland and colleagues examined records from seismic sensors located hundreds to thousands of kilometres from Hunga. They identified high-frequency, slow-moving seismic signals called T-waves, produced as energy from the eruption travelled into the ocean.
The strength of those signals changed during the eruption. They were strongest about an hour after the eruption began, when the top of the underwater volcano fractured and collapsed. The timing and characteristics of the T-waves linked that collapse to the largest and most destructive tsunami in the event.
This gives researchers a way to use instruments far from a hidden submarine volcano to identify a major change occurring at the eruption site. The sensors did not need to be positioned directly above the volcano to record the signal.
Why the timing could matter for warnings
Tsunamis move as long-period waves through the ocean. The T-waves identified in the seismic records travel at least seven times faster than the resulting tsunamis. That difference creates a potential window in which a monitoring system could detect the volcanic signal and issue an alert before the tsunami reaches a coastline.
The result is especially relevant to eruptions that occur far from established monitoring stations. A remote seismic network could provide information about an underwater eruption’s progression even when direct observation is impossible. In the Hunga event, the signal associated with the volcanic collapse—the stage that produced the largest tsunami—was visible in data collected at great distances.
The study is a reconstruction of one eruption, and the proposed use of T-waves is presented as a possible early-warning approach rather than an operating warning service. How consistently the signal can identify tsunami-generating collapses in other underwater eruptions will determine its wider value. For now, the Hunga records show that the ocean can carry a detectable seismic announcement of a dangerous volcanic collapse well ahead of the tsunami itself.