"Underwater volcano sharks" sounds like three random scary words strung together, but that's exactly what a team of National Geographic researchers recently discovered in the remote Solomon Islands while studying hydrothermal activity at Kavachi, a dangerous submarine volcano whose summit is 66 feet below the surface.

Although Kavachi is active, regularly spewing hot lava, ash, and steam out of the water and more than 500 feet into the air, on one recent day it was quiet, so the team was able to drop a deep-sea camera 147 feet into the crater. After an hour, they reeled the camera back up and reviewed the footage. In the hot, acidic, ash-filled water—full of carbon dioxide and methane gas bubbles—the scientists were surprised to see hammerheads and silky sharks.

"These large animals are living in what you have to assume is much hotter and much more acidic water, and they’re just hanging out,” expedition leader Brennan Phillips told National Geographic. “It makes you question what type of extreme environment these animals are adapted to. What sort of changes have they undergone? Are there only certain animals that can withstand it?”

The researchers are fascinated to learn more about what happens when the volcano does erupt—do the sharks know to leave or is their penchant for warmer water the source of their ultimate demise?