Gabrielle Tepp/Alaska Volcano Observatory/U.S. Geological Survey

Underwater volcano belched explosive bubbles larger than a stadium

Two years ago, a barely submerged volcano in Alaska’s Aleutian Islands released giant bubbles of gas, some of which were broader than the world’s largest humanmade dome, the 310-meter-wide National Stadium in Singapore, researchers reported today in Nature Geoscience.

Known as Bogoslof, the volcano vents only 100 meters below sea level, with remnants of past eruptions forming a steaming lagoon at the ocean’s surface (above). Historically, at Bogoslof and other similar submarine volcanoes, passing ships have reported that before an explosive eruption, a giant, black dome emerges out of the ocean. But these exploding bubbles have remained poorly understood, as they make studying the volcanoes hazardous.

So researchers spied on Bogoslof from afar, using low-frequency microphones in the ocean 59 kilometers to the south. The volcano erupted more than 70 times over 9 months. And a distinctive, secondslong grumble preceded each eruption, scientists found. The vibration matched the song that eruptive bubbles would sing as they stretched, overexpanded, and collapsed, computer modeling shows.

The Bogoslof bubbles likely reached up to 440 meters in diameter and formed when lava hit seawater and chilled, creating a cap over the volcano’s vent. A bubble of volcanic water vapor, carbon dioxide, and sulfur dioxide then pushed the cap outward, until the encapsulating film of volcanic rock and liquid water collapsed to produce an eruptive plume.