Volcanoes are not restricted to the land, there are many undersea versions. One such undersea volcano known as Hunga Tonga-Hunga Ha’apai off the coast of Tonga. On 15th January 2022, it underwent an eruption which was one of the most powerful in recent memory. A recent paper shows that seismic waves were released 15 minutes before the eruption and before any visible disruption at the surface. The waves had been detected by a seismic station 750km away. This is the first time a precursor signal has been detected.
Undersea volcanoes are openings in the Earth’s crust beneath the ocean, where magma from the mantle escapes, triggering eruptions. They are surprisingly common, with most of Earth’s volcanic activity occurring underwater, particularly along mid-ocean ridges and subduction zones. They play a vital role in creating new seafloor through seafloor spreading, as magma cools and solidifies into basaltic crust. Some grow so tall that they rise above the ocean’s surface, forming volcanic islands such as Iceland and Hawaii. Their eruptions release significant amounts of gas, heat, and minerals into the surrounding water, shaping marine ecosystems.
An erupting undersea volcano forms a new island off the coast of Nishinoshima, a small unihabited island in the southern Ogasawara chain of islands. The image was taken on November 21, 2013 by the Japanese Coast Guard. The Hunga Tonga-Hunga Ha’apai volcano is an undersea volcano located in the South Pacific. It became well known after its massive eruption in January 2022. The eruption was one of the most powerful volcanic events of the 21st century, triggering tsunamis that affected coastlines as far away as Japan and the Americas. The explosion released a plume of ash, gas, and water vapour, reaching over 50 kilometres into the atmosphere, making it the highest plume ever recorded. It impacted global weather patterns and temporarily increased water vapour in the stratosphere.
The eruption of January 2022 formed a caldera on Hunga Tonga-Hunga Ha’apai. There were disturbances that were recorded by many surface stations and satellites in orbit. The data which had been captured revealed that the eruptions began just after 04:00 UTC on 15 January. There were a number of reports of seismic waves from around 15 minutes before the onset of eruption. In a paper published recently by lead author Takuro Horiuchi and a team from the University of Tokyo, they explore the wave detection and mechanics of the eruption.
Volcanic eruptions at Mt. Etna from orbiting NASA Terra Satellite. Acquired on January 11, 2011. NASA Earth Observatory Image of the Day on January 15, 2011. Credit: NASA Terra SatelliteThe team aim to confirm that the event actually occurred just before the 04:00 published timestamp. If they can confirm this, it will help understand the processes that led to the violent eruption. At the time of the eruption, no seismic stations had been working on Tonga but data had been recorded as far away as Fiji and Futuna, both of which around 750km away from the volcano.
The study concluded that the waves which had been detected were Rayleigh waves – a type of seismic waves which are a combination of compression (longitudinal) and shearing (vertical) movements. The waves started around 03:45 on the 15th January 15 minutes before the onset of the eruption. This is the first time significant seismic activity has been seen before the eruption event. It demonstrates that seismic stations hundreds of kilometres away can be positively used to detect signals as precursors to eruptions.
