Why the Tonga volcano generated a shock wave that was felt around the world
WASHINGTON.- The Southwest Pacific Hunga Tonga volcano erupted explosively on Saturday afternoon local time, sending ash 30,000 meters high and causing a atmospheric shock wave that traveled the planet. The eruption was heard more than 8,000 kilometers away in Alaska, and the column of smoke and ash covered an area of sky almost 200,000 square kilometers.
The volcano is located 65 kilometers north of Tongatapu, the main island of Tonga, very close to the international date line. The kingdom of Tonga has 105,000 inhabitants and is situated northeast of New Zealand and southeast of the Fiji Islands.
“It’s a nightmare situation: an isolated, island community suffering from the effects of a tsunami and a massive volcanic ash plume generating violent electrical storms,” tweeted Janine Krippner, a volcanologist with the Smithsonian Institution’s Global Volcanism Program. “I see that ash plume, that volcanic lightning bolt, and that tsunami, and it makes my heart clench to think of the people being impacted by this massive eruption.”
In addition to the more immediate and shocking atmospheric effects caused by the eruption, some speculate that the volcano could affect the planet’s climate. Experts don’t think so, but climatologists are still collecting data.
Hunga Tonga is a submarine volcano that erupted in 2009 and again in late 2014. New eruptions occurred on December 21, 2021, with occasional resurgence of activity during the following weeks. And on January 15 there was a particularly explosive eruption, which has probably resulted in the most remarkable and astonishing display of volcanic power ever captured by a weather satellite.
The volcanic plume, “plume” or eruptive column rose to about 30,000 meters, triple the height at which commercial airliners fly. Upon reaching the tropopause -the transition zone between the troposphere and the stratosphere-, thunderstorms flatten out, as a layer of warm air prevents them from continuing upwards indefinitely. The Hunga Tonga smoke plume, however, was so strong that it managed to pierce that layer and continue into the stratosphere before those “pockets” of air and ash fell again.
Satellite images captured the image of “gravity waves”, which, like the waves surrounding a stone thrown into a pond, spread out centrifugally from that point of penetration of the atmospheric layer.
Less than six hours after the initial explosion, Hunga Tonga’s ash plume already covered an area of 200,000 square kilometers. It was already night, but the plume was thick enough to have completely covered the sun. Static discharges inside the plume rose twice as high as the worst normal thunderstorm, with incessant volcanic lightning.
Lightning detection networks and satellites counted more than 60,000 discharges in the 15 minutes following the initial explosion, or nearly 70 lightning strikes per second. There is no conventional storm that comes close to those numbers.
Also notable is the bull’s-eye pattern that emerges in lightning images: it’s the result of the aforementioned gravity waves. As the waves pass, the upward motion increases locally, and that in turn increases the incidence of lightning. After its passage, the air sinks, reducing the electrical activity.
The blast was powerful enough to generate a multi-meter tsunami in Tonga and triggered tsunami warnings in Hawaii, Alaska, British Columbia and much of the West Coast of North America, including Washington, Oregon and California states.
A 1.2 meter rise in water levels was seen in Port St. Luis, California, and Arena Cove, California saw a 1 meter jump. In Crescent City, California, a peak of 80 centimeters was recorded and in King Cove, Alaska, the tsunami was almost one meter.
In addition to rising water levels, tsunamis can generate dangerous erratic currents, which move in waves across the oceans faster than commercial aircraft.
Experts from the National Weather Service in Anchorage and the University of Alaska Fairbanks confirmed that the rumbles heard in that state on Saturday morning came from the volcano: that means the sound traveled more than 5,000 miles.
“The dog and I suddenly woke up at 3:30am and now I understand why,” Shan Cole, an Anchorage-based writer, tweeted.
That means the sound traveled at almost 1300 kilometers per hour, and the instruments confirmed that much of the noise produced was within the audible spectrum, or what humans can hear.
In the first satellite images of the surroundings of the volcano, a white ring can be easily distinguished that radiates rapidly outwards, well in front of the volcanic plume: that is the atmospheric shock wave.
That shock wave traveled around the world, also faster than the speed of sound. In Florida, for example, it manifested itself as an air pressure disturbance shortly after 9 a.m. local time. This is because the wave briefly caused a jump in air pressure, meaning that for an instant when the shock wave passed, the atmosphere at the location was heavier.
Volcanic eruptions can release enormous amounts of sulfur dioxide and aerosols which, in large enough quantities, they can cool the planet and cancel the effects of the La Niña phenomenon. Although at first it was speculated that the material ejected by the Hunga Tonga could cause similar effects, some experts quickly came out to clarify that the ejected mass was comparatively small.
Simon Carn, a professor at Michigan Tech, tweeted that “So far, sulfur dioxide plumes don’t seem all that extreme.” To have a measurable climate impact, the volcanic plume would have had to be five to 10 times as dense.
Alan Robock, a professor in the Department of Environmental Sciences at Rutgers University, points out that in order to cool the Earth, the amount of sulfur dioxide released by a volcano would have to be immense.
“To have a climate impact, the eruption would have to inject a large amount of sulfur dioxide into the stratosphere, at least 1,000 kilotons or thousands of tons, or even more.” Robock points out.
Satellite measurements show that the amount of sulfur dioxide released in the last eruption was 400 kilotons. Still, experts warn that ongoing eruptions are something to monitor.
“Actually, we have no way of knowing whether or not this rash is going to continue”, Krippner said.
By Matthew Cappucci
Translation of Jaime Arrambide