“Should we go see the sharks?” Terry Kerby asked, treading water beneath the Makai Research Pier. This was a rhetorical question. Of course we were going to see the sharks. Before I could answer he was gone in a hail of bubbles, weaving through wooden pilings and arrowing 20 feet down to the seafloor. I adjusted my goggles, took a deep breath and followed him. Kerby was close to 70 years old, but to watch him free dive you’d never guess it.

We popped up about 50 yards away, clear of the gauntlet of fishing lines hanging from the pier. To our left, volcanic cliffs framed Oahu’s eastern shore. To our right, the Pacific Ocean ran uninterrupted to Baja California. By Hawaiian standards it was a drab day, with stern clouds overhead and a brisk wind giving the water a bouncy chop. I knew that didn’t matter much to Kerby. Rain or shine, in perfect calm conditions or in the face of approaching hurricanes, he swam the same two-mile circuit every day at lunchtime—a routine he’d observed for the past 40 years. To commute from his desk to the ocean, all he had to do was climb down a ladder: Kerby’s workplace, the Hawaii Undersea Research Lab (HURL), occupied most of the pier. While other people stepped out for sandwiches, Kerby was traversing Waimanalo Bay, clad in a black shorty wet suit, scuba mask and fins. “It’s a spiritual thing,” he told me.

It’s also unsurprising: Kerby is one of the most aquatic souls I’ve ever met. In his role as operations director and chief pilot of the Pisces IV and Pisces V, HURL’s two deep-sea submersibles, he had spent thousands of hours roving the Pacific depths. On Kerby’s résumé there were no stints in an office building, no gigs that involved clock punching, nothing that remotely resembled an average job. In fact, throughout his career, none of his employment had even occurred on land.

After our swim, Kerby gave me a tour of HURL’s headquarters, a weatherworn building that resembled a small airplane hangar. The front of the structure was open, and I could see the two Pisces hunkered inside, 13-ton sea creatures temporarily stuck on land. They were 20 feet long, roughly the size of a minibus, set atop skids that enabled them to land on any type of seabed terrain. Their front and back ends were rounded; their tops were flat, with a fire-engine-red hatch tower poking up. The passenger compartment, known as the pressure hull, was a white sphere positioned up front. A viewport gazed from the center of each sphere like the pupil of a Cyclopean eyeball.

On the outside the subs bristled with high-definition cameras and sonars, lights, altimeters, laser-measuring devices, acoustic tracking systems, long banks of batteries. On their front bumpers they carried plastic crates stocked with sampling containers for water, gases, rocks, sediment and marine life. “We have two hydraulic manipulators on each sub,” Kerby explained. He pointed to one of them, a robotic appendage with multiple joints and a clawlike hand: “This is like an extension of your arm, it’s so fluid.” Working the manipulators in concert, a skilled pilot could pluck even the most delicate organisms and secure them in a jar.

Under their hoods, the Pisces contain ballast tanks that can take in or pump out air and water as the pilot adjusts buoyancy throughout the dive. The goal, as with scuba, is to be able to rise and fall as needed through the water column, but to be neutrally buoyant on the bottom so it’s easy to cruise around. Thrusters positioned on both sides of the pressure hull can propel the subs in any direction; the Pisces glide gracefully underwater despite their size and weight. Most of their bulk comes from blocks of syntactic foam—a buoyant, crush-resistant material made of glass microspheres in epoxy resin—that are padded around the frame. Each sub also carries 400 pounds of steel shot. This ballast weight aids the descent; on the bottom, half of it is dropped. The remainder is released at the end of the dive. (The steel oxidizes on the seafloor, helped along by metal-eating bacteria.) In an emergency, the pilot can jettison all the weight to rise to the surface more quickly.

Kerby and I left the Pisces V and walked through the hangar to his office in a loft above the subs. HURL’s décor could be described as man-cave chic, minus the chic. It was the ultimate garage—thousands of square feet of machinery, tools, workbenches, diving equipment, spare parts and men in surf shorts tinkering with gear. Zodiac inflatable boats were stacked on trailers. Dog-eared manuals were piled on shelves. An outboard motor hung from the ceiling. Ocean posters and magazine articles featuring the Pisces were thumbtacked to plywood walls. A fridge was plastered in stickers with a distinct undersea theme: the Deep Submersible Pilots Association, the Schmidt Ocean Institute, Poseidon USA, Micronesia Aquatics of Truk Lagoon. One bumper sticker of a rampaging shark boasted: “I’ve Been Seen by the Great White.”

Kerby ushered me into his office, a well-loved space that was lined with mementos: pictures, awards, battered leather chests, scraps of coral and driftwood. He went to the kitchen to get us some coffee, and I settled in on a couch that was actually the torn-out bench seat of a car. I had about a million questions, and I wanted to spend the rest of the day talking. Or rather, what I hoped was that Kerby would talk and I would listen, because I wanted to hear every last detail about his deep-sea experiences. To ask Kerby what he has seen in the abyss is to unleash a torrent of recollections, historical accounts, names of remote seamounts, GPS coordinates, facts, figures, dates, locations. He seemed to have total recall of every dive he had ever made. On top of that, he had thousands of photos taken from the subs, hours of video and logbooks dating back to the ’80s. Kerby, a talented artist, had even made paintings of his favorite undersea spots.

One site he knew intimately was Loihi, the submarine volcano that is currently building itself into Hawaii’s next island. It rises about 13,000 feet from its base to its summit, which lies nearly a mile beneath the ocean’s surface. Like the other Hawaiian Islands, Loihi was created by a hot spot: a plume of magma welling beneath the seafloor and eventually bursting through. (In July 2021, the Hawaiian Board on Geographic Names officially renamed the volcano Kamaʻehuakanaloa.) It’s the handiwork of Pele, goddess of volcanoes and fire, one of the fiercest and most revered deities in the Hawaiian culture. At 400,000 years old, Loihi is her youngest child, a little sister sitting at the feet of Mauna Loa, the world’s largest volcano; Kilauea, one of the world’s most active volcanoes; and Mauna Kea, another mammoth volcano that ranks as the world’s tallest mountain (if you measure it from the seafloor). Scientists don’t know exactly when Loihi will grow tall enough to poke its head above the waves. Maybe a hundred thousand years from now—maybe more, maybe less.

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“I did my first dive on Loihi in 1987,” Kerby said, handing me a mug and sitting down in his desk chair. “And I’m dropping down there in Pisces V going, What am I doing diving on an active submarine volcano?” No one knew if this was a good idea. There was no map to follow, no best practices to avoid getting buried by eruption debris or crushed beneath unstable lava shelves. Live undersea volcanoes are uneasy places, and Kerby was aware that he needed to approach this one with caution.

The submersible sank into the darkness on its white-knuckle reconnaissance, drifting down and down until it reached Loihi’s highest point, which would later become known as Pisces Peak. Trimming the sub, Kerby began to orient himself. He could see mounds of black pillow lava, and rust-colored mineral deposits that signaled the presence of iron, and strands of bacteria waving lazily in the current. Jumbles of rocks glistened with volcanic glass. It was a landscape of stark Plutonian beauty.

Suddenly, an immense pinnacle reared up in his viewport. It had to be a hundred feet tall. Chimneys sprouted from its sides, pumping translucent fluid. Kerby knew what to call the strange formation—a hydrothermal vent system—but vents had been discovered only a decade earlier, on the Galápagos’s deep seafloor. Scientists were just beginning to study them and marvel at their weirdness. Like hot springs on land, hydrothermal vents pop up in volcanically active areas, roiling out a mix of seawater, minerals, gases and microbes from the earth’s superheated plumbing. When this brew hits the cold, deep water, it precipitates minerals that form chimneys of various heights. Kerby named the giant looming before him “Pele’s Vent.” At that moment it seemed prudent to pay her some respect.

After that first dive scientists kept clamoring to return, and Kerby became familiar with Loihi’s twisted gray-green chimneys and spooky ochre-yellow rocks, its rubble-strewn craters streaked with something that looked like dried blood. There were uncommon animals down there, too. Kerby regularly ran into a toad-like fish called Sladenia remiger that squatted on the rocks with fins that resembled feet. It’s a member of the anglerfish family, and so awful-looking that it’s cute. Steel-blue eels would zip by the viewports: these were synaphobranchids, nicknamed “cutthroat eels” because their gill slits are slashed across their necks.

Kerby also encountered chimaeras, or ghost sharks, primitive cartilaginous fish with big heads, pointy snouts, fins like airplane wings, long trailing tails and shiny silver-dollar eyes. A sensory network of lateral lines curve around the chimaeras’ bodies, making them look as though they’ve been stitched together, or assembled from jigsaw puzzle pieces. Sometimes a false catshark would swish by like a runway model, sporting the elongated eyes of a gray alien and a wide jack-o’-lantern grin. It’s one of the many deep-sea shark species that we barely know, because they wisely spend their lives as far from us as they can possibly get.

On one memorable dive, the Pisces subs were greeted by a Pacific sleeper shark—a thick-bodied deep-dweller with mottled skin and a buzz-saw mouth. It’s closely related to the Greenland shark, the earth’s longest-lived vertebrate, with a life span that can top 400 years. (Researchers once thought they were the same species.) Pacific sleeper sharks are covert creatures, hefty as great whites and the only predators besides sperm whales that are known to hunt giant squid.

Kerby showed me a video of the sleeper gliding by in dramatic chiaroscuro and closely approaching both subs, one after the other, while excited scientists shouted in the background. The shark had an oddly gentle vibe, a body as brindled as old granite, and blind-white eyes thanks to a parasite that eats its corneas. It wasn’t like any shark I had ever seen. It seemed to have come from deep time rather than the deep ocean, like a visitor from a vanished era. “Look at her,” Kerby said, gesturing to the screen. “If ever there was an ancient Hawaiian spirit wandering Loihi, that was it.”

In 1996, the seafloor around Loihi rattled with a swarm of 4,000 earthquakes, the largest seismic event ever recorded in Hawaii. “Nobody had any idea what was happening,” Kerby recalled, raising his eyebrows for emphasis. “It just sounded like something major was going on.” A Pisces expedition was quickly mounted. Descending into a deep-sea eruption is not on the average person’s to-do list, but this was an event scientists couldn’t afford to miss. That didn’t mean it wasn’t wildly dangerous.

Submarine volcanoes don’t always present themselves politely. During one notorious tantrum in September 1952, the U.S. Navy’s deep-sea hydrophones detected a series of loud explosions in the Pacific Ocean, 230 miles south of Tokyo. It was a known spot for frisky tectonics, part of a longer arc at the seam where two oceanic plates collide. Active volcanoes had been charted on the nearby seafloor.

Over the next week, the blasts continued, becoming so convulsive they generated multiple tsunamis. Often these outbursts were accompanied by thunder and lightning that lasted for hours. “Great sparks rose into the sky,” one fisherman noted. Someone else called in a “pillar of fire.” Marine observers watched a 200-foot dome of water swell up on the surface like a colossal bubble, its edges running with waterfalls. They heard roaring and moaning noises that seemed to come from the ocean itself, which had turned a sickly green color and was puking up dead fish. When U.S. Air Force pilots flew over the site, they saw spiky black rocks emerge in a boil of whitewater and then sink back into the depths.

For marine geologists this was blockbuster stuff, so when the explosions stopped—momentarily, as it turned out—a group of 31 Japanese scientists and crew motored out on a research ship, the Kaiyo Maru 5, to document the action firsthand. We’ll never know what they witnessed that day, for the ship was never seen again. A few days later, scraps of it were found floating nearby. The wreckage was shot through with lava shrapnel.

It’s hard to imagine the force that’s needed to propel hundreds of tons of volcanic mayhem upward through a mile of water, but it’s safe to say that you don’t want to be near it in a submersible. And the Hawaiian Islands have hosted a lot of turbulent rocks. On a wall outside Kerby’s office, I’d noticed a bathymetric map of Hawaii that revealed vast debris fields on the seafloor. Rocks the size of bungalows, buildings and city blocks had, at some point, careened across 38,000 square miles of submarine real estate, an area five times larger than the combined landmass of the islands.

I felt humbled by the sight of the map because I knew what it meant: Monumental violence had occurred here in the past, when the volcanoes rose to a point where they shuddered and partially collapsed, generating mighty submarine landslides. (Some of the slides would have caused mega-tsunamis, which explains why coral fragments have been found high on the slopes of the Big Island.) During a massive earthquake swarm, anyone familiar with this submerged carnage would’ve instantly wondered: Was Loihi shifting and sliding and shedding its skin in that same way now?

“It was nerve-racking,” Kerby confirmed. “We got out to the site and there was still activity coming off the bottom. The ship was getting hit with these shock waves, just—BANG! I was supposed to go down there to see what was going on.” He laughed. “I never would have done a dive like that if I hadn’t been exploring that volcano for nine years already.”

Kerby descended in the Pisces V, easing the sub down warily. The water in the depths was turbid, and it gave off an unsettling, almost electric, vibe. Visibility worsened. “I worked my way up to where Pele’s Vent should’ve been. We came to the edge of this huge drop, and we just sat there staring at it.” It took a moment to grasp what had happened. Pele’s Vent was gone: In its place was a thousand-foot-deep crater. The volcano’s magma reservoir, its molten heart, had drained, flowing down the rift zone and causing the peak to implode. Later, scientists would discover vent fluids emitting from the new pit crater at temperatures up to 392 degrees Fahrenheit.

Creeping forward, Kerby dropped into the maw: “It got to the point where I couldn’t see anything.” Orange bacterial floc and white flecks of sediment whirled around the sub like a blizzard. On his sonar, Kerby saw that the Pisces had flown perilously close to the crater’s wall. He reversed with one of the thrusters, triggering an avalanche of loose rock. “The thruster started all this stuff moving, so I got out of there,” Kerby said with a grin. “After that I was completely addicted to volcano diving.”

From The Underworld: Journeys to the Depths of the Ocean by Susan Casey. Reprinted by permission of Doubleday, an imprint of the Knopf Doubleday Publishing Group, a division of Penguin Random House LLC. Copyright © 2023 by Susan Casey.

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