This summer , the 235-foot research vessel Marcus G. Langseth set out into the ocean off the Pacific Northwest. Trailing the ship were four electronic serpents, each five miles in length. These cables were adorned with scientific instruments able to peer into the beating heart of a monster a mile below the waves: Axial Seamount, a volcanic mountain.

The ship’s crew had one overriding imperative: Do not let the cables get tangled.

If they did , “it’s game over,” said Sam Mitchell, a submarine volcanologist who joined the voyage.

The ship belongs to the National Science Foundation, and is operated by Columbia University’s Lamont-Doherty Earth Observatory. Scientists aboard spent 33 days in July and August hoping to create 3D maps of the magmatic ponds and pathways in an individual, active submarine volcano for the very first time. If the researchers succeeded, they would provide a view of a hyperactive volcano that had never been seen.

Charting Axial’s internal anatomy also would improve scientists’ understanding of underwater volcanoes all over the world, most of which still lie waiting to be discovered in the gloomy depths.