Acoustic Ripples From Tonga Volcano

Graph from Brian McNoldy at the University of Miami.

In “Tonga faces daunting challenges after massive volcanic eruption,” University of Miami staff write:

The eruption was so powerful, it also generated acoustic waves in the atmosphere, with the explosion being heard as far away as Alaska, making it perhaps the loudest sound known. “Eventually it was too weak to be heard, but the wave is still going around the globe at the speed of sound, now on its third trip,” said McNoldy, adding that even Miami might have received a signal from the first wave’s third trip this morning.  

He noted that at the speed of sound, it takes about 35 to 36 hours for the acoustic wave to travel around the globe. “Barometers around the world have been detecting these little hiccups in surface pressure, too small to be noticed by people, but easily measured,” he said. 

…

The likely trigger was a submarine landslide. Once the overlying rock masses were removed, the volcano could explode. Powerful eruptions frequently start with a landslide. Another example is the 1980 eruption of Mt. St. Helens in Washington State. Emerging island volcanoes are particularly unstable and prone to land-sliding. An interesting fact is that there is geological evidence for a much larger mid-15th century tsunami in Tonga with 30-meter run-up height, likely caused by the collapse of an island volcano.

https://www.newswise.com/articles/tonga-faces-daunting-challenges-after-massive-volcanic-eruption

In “The eruption near Tonga was so powerful you could hear it in Alaska” (Alaska Public Media, 17 Jan 2022), Maggie Nelson (KUCB – Unalaska) and Rashah McChesney (KTOO – Juneau) write

Iris Caldentey and her kids were sleeping peacefully in their home early Saturday morning in Palmer when she woke up to loud, strange noises.

“How I would envision Pearl Harbor sounded — just constant, boom, boom, boom,” she said. “I mean, it was intense.”

Could it be avalanche control? A burglar? Maybe the kids bouncing off the walls? Like many people, Caldentey had no idea what she was hearing.

“I went outside to check the cars because then I was like, well, maybe there’s a burglar trying to get into our cars. And they’re opening, closing the door. Not a very good burglar,” she said.

In Unalaska, Laresa Syverson woke to similar sounds and vibrations.

“I thought for sure it was my cat — like, what’s my cat doing? So he got blamed for most of it,” she said.

First she thought her cat, then maybe fireworks, then she thought it could have just been bass coming from someone’s car.

While Syverson says she wasn’t immediately alarmed, neither she nor Caldentey would have guessed that the sounds were coming from an underwater volcano erupting near Tonga.

But that’s what it was — an eruption so massive it sent sound waves and a tsunami throughout the Pacific.

https://www.alaskapublic.org/2022/01/17/the-eruption-near-tonga-was-so-powerful-you-could-hear-it-in-alaska/

In “Tonga Volcano: A volcanologist explains what we know about this once-in-a-lifetime eruption” (Science Focus, 20 Jan 2022), Amy Barrett writes:

The volcano is said to have been responsible for nearly 400,000 lightning events in the hours following the explosion on Saturday, according to meteorologist Chris Vagasky.

Around 10 hours after the eruption, people in Miami, USA – over 7,000 miles away from the volcano – saw pressure ‘waves’ at speeds of 695 mph – acoustic ripples in the air which, according to atmospheric scientist Brian McNoldy on Twitter, were essentially traveling at the speed of sound through the atmosphere.

The shockwaves continued to travel around the globe, and were still being recorded on Tuesday 18 January. Seismology student Felix Eckel said readings made it “clearly visible that [the wave] has circled the planet twice at this time”.

The volcano’s activity has dropped since the eruption, however it continues to release gases into the atmosphere. These include sulfur dioxide and nitrogen oxide, which volcanologist Shane Cronin told Reuters news agency could interact with water and oxygen in the air to create acid rain over Tonga. Additionally, the amount of ash released at the time of the eruption could impact local waters, causing marine life to die or migrate to cleaner waters, and impacting the Tongan fishing industry.

https://www.sciencefocus.com/news/tonga-volcano/