Brennan Phillips and some colleagues were recently on an expedition to Kavachi volcano, an active underwater volcano near the Solomon Islands in the South Pacific. But they weren't prepared for what they saw deep inside the volcanic crater:

Sharks!

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Hammerheads and silky sharks, to be specific, contentedly swimming around despite the sizzling water temperatures and biting acidity.

Volcanic vents such as these can release fluids above 800 degrees Fahrenheit and have a similar acidity to vinegar, according to the Marine Education Society of Australasia.

"The idea of there being large animals like sharks hanging out and living inside the caldera of the volcano conflicts with what we know about Kavachi, which is that it erupts," Phillips, a biological oceanography Ph.D. student at the University of Rhode Island, says in a YouTube video.

This brings up some perplexing questions about what the animals do if the volcano decides to wake up:

"Do they leave?" Phillips asks. "Do they have some sign that it's about to erupt? Do they blow up sky-high in little bits?"

The volcano wasn't erupting when Phillips' team arrived, meaning it was safe to drop an 80-pound camera into the water to take a look around. After about an hour of recording, the team fished the camera out and watched the video.

First, the video showed some jellyfish, snappers, and small fish. Then, a hammerhead swam into view, and the scientists erupted in cheers. They also saw a cool-looking stingray.

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Why the sharks were hanging out inside an active volcano is a mystery, but one Phillips hopes to solve.

Check out the full video here:

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