Seventy percent of the volcanic activity on our planet happens underwater. Submarine volcanos cause tsunamis, kill fish, and even create islands. And there could be a million of them, largely invisible to us beneath the waves. But by virtue of being deep underwater, they are difficult to get to, which makes them difficult to study and observe.
Take the West Mata volcano for example. It's in the Pacific Ocean, over a hundred miles from land, and nearly three quarters of a mile below the surface. Though magma is still bright orange underwater, you can't exactly check out West Mata through a pair of swim goggles.
So, in 2009 scientists sent a remotely operated vehicle — a drone for the ocean, essentially — to check out West Mata in action, explains Nanci Bompey at GeoSpace, a blog of the American Geophysical Union. Fitted with a video camera, the vehicle witnessed two kinds of eruptions. From a vent called Hades, an explosion of large bursts of magma, as seen and heard in the video. From a vent called Prometheus, on of hundreds of tiny bubbles of gas.
Scientists have been studying the sounds of submarine volcanos for a while, but capturing such showy eruptions on video too was a big deal. Understanding what's happening in the video will make studying submarine volcanos by sound alone more fruitful.
With the footage in hand, a team of oceanographers went to work decoding the "acoustic signature" of the stuff coming out of West Mata's vents in the video. In a recent paper, they explain that the magma bursts produce short, low frequency noises, while the sounds from the bubble-releases are broadband in frequency and last a few minutes. These sound signatures could be useful in telling what kinds of submarine eruptions are happening — from afar.