In 2010, a dark cloud descended over Europe. Iceland’s Eyjafjallajökull had erupted, sending plumes of volcanic ash more than 60,000 feet in the air. Across Europe, air traffic came to a halt for a week—the largest disruption to air travel on the continent since World War II. President Barack Obama, in Ireland at the time, was forced to cut his European trip short, but he may have left feeling a little vindicated.
The previous year, his administration announced a plan to spend $15 million to modernize volcano monitoring equipment, something his political opponents seized on as an example of wasteful spending. Eyjafjallajökull’s violent eruption had just demonstrated why the project was necessary. Fast forward to today, and the U.S. Geological Survey (USGS) has revealed one of their new techniques to predict eruptions—listening to the ocean.
As waves from the Pacific crash on the shores of the island of Hawaii, the sounds travel through the rocks. Seismometers littered around the island, typically used for listening to volcanic activity, can also pick up these gentle sounds. By measuring how quickly they travel through different parts of the island, geologists can glean useful data about how imminent a volcanic eruption is.
Read more: “Iceland Is Going to Erupt Again Very Soon”
Here’s how it works: Before an eruption, magma accumulates beneath the surface, forcing rocky material outward and forming subterranean cracks. These cracks slow down the sounds of ocean waves. As the magma moves into the caldera (the bowl-shaped portion), the opposite effect occurs—molten rock fills fissures in the volcanic rim which speeds up the sound of ocean waves. That means comparing the velocity of ocean sounds measured by seismometers positioned at both the base and rim of the volcano may offer important clues to whether an eruption is imminent.
USGS researchers applied this technique (called “ambient noise interferometry”) to data gathered prior eruptions of Kīlauea. Sounds from the ocean waves measured by seismometers close to where subterranean cracks form started slowing two months before the volcano blew its top in 2020, reaching their lowest speed right before eruption. A seismometer located on the rim, on the other hand, recorded the fastest ocean noise sounds four days prior to a 2025 fountaining event.
“While the ambient noise interferometry technique is still being tested and evaluated with every new fountaining episode, scientists at the USGS Hawaiian Volcano Observatory see promising results,” officials from the observatory wrote in a post detailing the technique. “Looking at ocean noise could be another useful tool for forecasting when eruptive activity will begin at Kīlauea volcano.”
So much for ambient ocean sounds being soothing. 
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Lead image: Hawaii Volcanoes National Park / Wikimedia Commons
