It is hard to watch all of the ocean all of the time, especially the deep parts where undersea volcanoes go "boom." Submarines cannot be everywhere.
Listening devices can, pretty much, because sound travels a long way in the water. But scientists have not understood which noises are associated with different kinds of eruptions: One type created by the slow release and bursting of large lava bubbles, and aother type created by a quick explosion of gas bubbles. Lava can affect marine animals and ecosystems differently than gas can, so it is important to be able to distinguish the two.
In a new paper in Geophysical Research Letters, scientists have been able to connect sounds to sights in both types of eruptions. They took advantage of a rare moment in 2009, when a video camera and a hydrophone were floating 1,200 meters below sea level in the Pacific Ocean near Samoa, watching and listening as the West Mata Volcano blew up in several ways. Putting video and audio together let researchers learn the sounds made by slow lava bursting and the different noises made by hundreds of gas bubbles. In the recording above, you can watch and listen too. (Video is provided by the American Geophysical Union.)