Looks! The eruption of the extreme Tonga volcano leaves a telltale fingerprint in space

Displacing air, land and water, volcanic eruptions also tickle the atmosphere, according to a new study. A group of Japanese researchers have found that this high-altitude signature can warn people several hours in advance of tsunamis coming their way.

On January 15, the Hunga Tonga-Hunga Haʻapai volcano in the Pacific Ocean in the Kingdom of Tonga unleashed a violent eruption as powerful as up to 18 megatons of TNT. This explosion triggered an acoustic shockwave that spread across the Earth, creating a worrying tsunami that spread faster than those caused directly by the eruption.

In a new study published in the journal Earth, Planets and SpaceAtmospheric scientist Atsuki Shinbori explains how a vertical shock wave left an imprint on ions floating more than 50 miles above the Earth’s surface, sending out ahead of the first tsunami wave triggered by the largest atmospheric explosion in human history, an early warning to some instruments in Japan.

Shinbori – who works at the Institute for Space-Earth Environmental Research at Nagoya University in Japan – tells Vice versa that if his findings lead to a detection approach, “it might be possible to estimate the size [a] tsunami, such as B. Altitude…several hours before it arrives.”

The enigmatic waves of the eruption

“The Tonga tsunami was characterized by a uniformly small main wave that arrived earlier than theoretically expected for a tsunami wave propagating freely away from the volcano,” writes Matías Carvajal, associate professor at the Department of Geography at the Pontifical Catholic University of Valparaíso Chile in a March 2022 study.

This first was followed by the biggest waves, which were up to three meters high. According to a model developed by the USGeological Survey (USGS) of how waves propagate north from the volcano, there are roughly three types of waves: the first two are generated by the atmospheric explosion, and the last are the product of the eruption’s vibrations in the sea . The US National Oceanic and Atmospheric Administration (NOAA) acknowledges that these types of air-generated waves, called meteotsunami, are not very well understood. That’s a problem when the catalyst for these ominous crests is sonic pressure surges.

But fortunately something is faster than sound: the speed of light.

It appeared out of nowhere

“Volcanic tsunamis of this magnitude are very rare,” says Carvajal Vice versa. “The last one that seems similar occurred in the 19th century, in 1883, in Indonesia.”

The catastrophic eruption of 1883 was Krakatoa, killing 36,000 people, destroying hundreds of villages and creating a thick blanket of ash and pumice that plunged the planet into darkness. According to NOAA, it took five years for things to get back to normal. Its descendant, the volcano Anak Krakatau, also left a horrific trail when it erupted in December 2018. He killed at least 430 people. The tsunami it triggered left thousands injured or missing.

These disasters were difficult to predict because they are rare. Carvajal admits the power of the January 15 atmospheric shock wave came as a surprise.

“Up until January, it was thought that the main sources or mechanisms of tsunami generation associated with a volcanic eruption had to do with processes happening right there in the volcano,” he says.

“For example, we thought that the sudden collapse of the volcano’s caldera or the submarine explosion were the main mechanisms behind the formation of a volcanic tsunami, since both processes are theoretically capable of displacing large amounts of water.” Here’s what happened in 2018: A Flank of Anak Krakatau caldera plunged into the sea, creating an initial 43-meter wave.

The danger of an eruption’s atmospheric waves is not unknown, but Carvajal believes it hasn’t received much attention. He says Tonga’s 2022 eruption “showed once again that our knowledge of how tsunamis form is far from complete.”

Atmospheric mechanics aside, the eruption itself came out of nowhere. Even a 38-year veteran, says Jim Garvin, a senior earth and planetary scientist at NASA Vice versa that Hunga Tonga-Hunga Haʻapai was not to erupt for centuries.

What is faster than sound?

Shinbori made a potentially life-saving discovery.

When the Hunga Tonga-Hunga Haʻapai volcano erupted, it produced sound waves. Some of these waves shot straight up, reaching space and leaving an imprint on the sunlit charged particles of the ionosphere. This imprint then traveled along Earth’s magnetic field lines, running south to north. Shinbori describes these as the conductor wires of an electrical generator that transports electricity at about the speed of light.

Instruments in Japan detected this ionospheric imprint — an electric field — before their other instruments detected the tsunami’s air shock and before other instruments detected tsunami water waves. The magnitude of the electric field corresponds to the strength of the shock wave, so it can also give scientists an estimate of the magnitude of the incoming tsunami wave.

What’s coming in the future

Scientists may not get these types of early ionospheric signals during a nighttime flare.

“Sunlight affects the signals of ionospheric disturbances,” he says Vice versa, which explains that their amplitude decreases when ions are in the shadow. At night, “there’s a chance we won’t be able to tell the origin of a tsunami from other sources,” he says.

Shinbori wants to analyze more data in the future to see how this technique could be refined. He hopes to one day set up an ionospheric warning system that can reveal ominous volcanic tsunamis at any time of the day, ahead of what deep-water buoys and satellites can currently report.