(Forbes) – Back in 2015, a video of hammerheads and silky sharks swimming around in an underwater volcano, in sizzling water temperatures and elevated acidity levels, went viral. Dubbed “sharkcano,” people wondered if there were any places sharks couldn’t survive. (Spoiler alert: there are a few, like Mount Everest and your backyard pool.)

The sharks (and a sixgill stingray!) were first found inside the volcano caldera by Brennan Phillips five years ago following the eruption of submarine volcano Kavachi, which has built itself above sea level at least nine times since 1950. Located in the Solomon Islands (south of Gatokae and Vangunu islands), it is known as one of the most active underwater volcanoes in the Pacific Ocean even though it has rarely been observed.

Also known as Rejo te Kvachi, or “Kavachi’s Oven,” it is said to be named after a local sea god. Seems fitting that sharks, that are also revered as sea gods in some parts of the world, were found to be living here all those years ago. But what were they doing there? And how long could they feasibly survive here?

“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, said in a YouTube video.

According to Dr. Michael Heithaus of Florida International University, the discovery shed a spotlight on how important underwater volcanoes are in the marine ecosystem. “Seeing that got me thinking about just how important volcanoes are to life in the ocean,” Heithaus told Newsweek. “And it isn’t just about active volcanoes. It’s about the habitat they create out in the middle of the ocean.”

More than 70 percent of all volcanic eruptions occur underwater but researchers know very little when it comes to understanding underwater volcano behaviour. While volcanic eruptions cause significant geologic hazards, submarine volcanoes like Kavachi play an integral role in the way our planet works. “If there hadn’t been volcanoes in certain areas there would be no reefs or no land,” Heithaus continued. “That would mean that the species of sharks that need those habitats couldn’t live in those areas without the presence of a volcano.”

The 2015 shark video has resurfaced again in a National Geographic documentary as part of “Sharkfest,” the three-week-long program dedicated to shark science and discoveries from around the world. The episode will focus on the extraordinary relationship between these predators and underwater volcanoes with Heithaus traveling to various locations worldwide looking at how different species of shark co-exist with the unique conditions submarine volcanoes provide. One of his stops is off the coast of Réunion Island, a French overseas territory in the Indian Ocean which is renowned for its volcanoes, rainforests, coral reefs and beaches. Here, he found bull sharks taking advantage of the turbulent water caused by the submarine volcano, using it like a cloak of invisibility to better ambush prey.

Up North in Guadalupe Island, a volcanic island located off the western coast of Mexico’s Baja California Peninsula, the researchers found seals taking advantage of the island’s resources – and baby seals are an easy meal for sharks. According to Heithaus, volcanic islands like Guadalupe are appealing to sharks due to the abundance of nutrients that flows into the surrounding water, which helps boost the environmental food chain from the bottom up. “And where you have lots of food you tend to have lots of sharks, if there isn’t too much fishing to reduce their populations,” he said. According to the scientist, active underwater volcanoes like Kavachi also help supply nutrients into the surrounding area, attracting large predators like sharks. But what happens if it erupts? Well, Heithaus says the warm water can be utilized by pregnant females as a nursery area.

It was not previously known how vital this habitat was to some species of sharks. But, it makes sense according to the scientist. “Most of the open ocean is a place without a ton of food,” Heithaus explained. “In the open ocean, it’s volcanoes that have created most of the land out there. So, at the base level, many sharks depend on volcanoes in ways most people wouldn’t think about.” Since this expedition, Heithaus has continued to study shark behavior in relation to this habitat.

“A big part of that work is understanding what determines where sharks naturally occur. The types of islands they associate with—including volcanoes—is part of that puzzle. Ultimately, what I really want to know is when, where and why are sharks important to the health and function of ecosystems so we can start to restore their populations and functions in the many places their populations have crashed.”