WHOI assistant scientist Wenbo Wu, who has not been involved in studying this particular volcano, reinforces the idea that these types of features can interfere with sound travel in the ocean. “Since the volcano is surrounded by underwater features, the acoustic waves coupled directly from the volcano were blocked, and did not travel far.” said Averbuch. The Lau Basin, where the volcano sits, is a relatively shallow, yet geologically-complex environment of steep underwater cliffs and seamounts. Averbuch says it's one of “many open questions” that he and more than 70 other scientists around the world have been grappling with since the “once in a lifetime event,” as he refers to it.Īverbuch believes that underwater geology may have played a role in blocking sound waves as they traveled through the ocean. The question of why the ocean remained so quiet during the Tonga eruption is a complicated one. The network is run by the Comprehensive Nuclear-Test-Ban Treaty Organization ( CTBTO) for the purpose of detecting nuclear explosions around the world, but they have no trouble picking up soundwaves from other sources. Once those seismic waves interact with the water column via geological/bathymetric features in the ocean, they turn into acoustic waves (aka, sound waves).Ī global network of underwater microphones, known as hydrophones, record and measure these waves, giving scientists like Averbuch a read on the ruckus they cause in the ocean. Submarine volcanic eruptions, like the Hunga-Tonga, cause earthquakes that transmit seismic energy below the seafloor. “We were expecting to see much more prominent signals.” “We detected very weak acoustic signals in the hydrophone data, which was really surprising given the intensity of the eruption,” said Gil Averbuch, a postdoctoral scholar at WHOI who studies how acoustic waves propagate in the ocean. It turns out that while the explosion was loud enough to reach Alaska, things stayed pretty quiet in the ocean.

But for scientists studying how sound travels through the ocean, it was downright baffling. Hurricane-force winds blew at the edge of space, while atmospheric pressure waves injected so much energy into the ocean below that meteotsunamis formed around the world.įor volcanologists, the Tonga eruption was a case study beyond their wildest dreams. It not only sent atmospheric waves that circled the globe several times, but thrust more than a trillion grams of water vapor into the stratosphere and sent an ash cloud 35 miles into the mesosphere. This resulted in one of the most intense volcanic eruption ever recorded, with some estimates suggesting that the explosion was hundreds of times stronger than Hiroshima. Finally, magma rose up from the depths of the volcano and collided with the seawater at more than 1,000 degrees Celsius. Then, seawater percolated through its exposed cracks and faults. The volcano, known as the Hunga Tonga–Hunga Haʻapai, had been restless for about a month before a perfect storm of events occurred: First, the volcano’s 150-meter-deep caldera collapsed. “I never thought something from Tonga would be heard on my deck,” she said. Later the next day, she saw the news report on TV: a massive submarine volcano 10,000 miles away in the South Pacific had erupted and sent audible shockwaves all the way to Alaska. She had no idea what the boom was, so she shrugged it off and went back to bed. This sound was clearly different-it was like unlike any I had ever heard.” “But I’m from a family of hunters and very familiar with gunshots. “When we hear noises like that, it’s typically gunshots since there’s a lot of hunting in the area,” Willoya said. It was a beautiful, quiet night, she recalls, until suddenly, a thunderous explosion echoed through the dimly-lit sky. She hopped out of bed, made tea, and stepped out onto her back deck for some fresh air.

It was January 15, 2022, and the resident of Wasilla, Alaska had been having bouts of insomnia.

Ocean noises for sleep