Kavachi is one of the most active underwater volcanoes in the southwest Pacific Ocean. It's surrounded by hot, acidic seawater that can make it too dangerous for human divers — and that's when it's not erupting explosively.

But when a team of scientists recently sent down camera-equipped robots, they not only found animals surviving in and around the volcano; they found a surprising amount of biodiversity, including silky sharks, hammerhead sharks and the rarely seen Pacific sleeper shark, which had previously been caught on video just twice.

It's like "Sharknado," but with a volcano instead of tornadoes. Plus it's real.

The sharkcano is located south of Vangunu in the Solomon Islands, where researchers funded by the National Geographic Society recently embarked on a risky trip to explore Kavachi. The volcano is very active, having experienced a minor eruption in 2014 as well as more explosive outbursts in 2007 and 2004.

Kavachi seamountSteam rises from the Kavachi seamount during a 2000 eruption. (Photo: Brent McInnes/CSIRO/NOAA)

"Nobody actually knows how often Kavachi erupts," team member Brennan Phillips tells National Geographic. And even when it's not launching lava, ash and steam above the surface, he adds, it can be too extreme for divers to explore. "Divers who have gotten close to the outer edge of the volcano have had to back away because of how hot it is or because they were getting mild skin burns from the acid water."

To avoid that risk, Phillips and his colleagues sent down submersible robots with underwater cameras to explore Kavachi's inhospitable environment. Despite the extreme conditions, the robots spotted a variety of wildlife living around Kavachi, including jellyfish, crabs, stingrays and the aforementioned sharks.

On top of the volcano-dwelling silky and hammerhead sharks, the team was also psyched to see a Pacific sleeper shark swimming near Kavachi. These enigmatic fish are normally found in the North Atlantic, the North Pacific and around Antarctica, but they've never been seen near the Solomon Islands before. Phillips says this is only the third time the species has been caught on video anywhere, and his HD footage may represent the highest-quality glimpse in history. Check it out below:

Even though Kavachi wasn't erupting at the time, the team still saw bubbles of carbon dioxide and methane rising from seafloor vents, notes National Geographic's Carolyn Barnwell. It's unclear how the sharks and other animals deal with the extremes of this habitat, but given the growing threat of ocean acidification around the world, any animals that are adapted to conditions like these are worth a closer look.

"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," Phillips says. "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?"

Phillips is also curious what all these animals do when Kavachi erupts. "Do they get an early warning and escape the caldera before it gets explosive," he wonders, "or do they get trapped and perish in steam and lava?" He hopes to deploy longer-term cameras and set up a seismic observatory to answer those questions.

In the meantime, given the disproportionate danger sharks face from humans, it's nice to know these ancient fish have at least a few places they can hide from us.



Sharks found living inside an active volcano
Despite its hot, acidic water and looming risk of eruption, Kavachi is home to a surprising abundance of sharks.