The rare underwater phenomenon found in Hawaii’s waters

The caves that exist in the Hawaiian Islands don’t stop at the surface. Underwater, there are lava tubes, or caves that formed when magma flowed beneath the surface of the earth. Some of these sites have turned into a playground for scuba divers, with tunnels, chambers and arches. 

A few of them, such as two dive sites off the island of Lanai, feature a rare phenomenon. A dive down into the large underwater lava tubes known as First Cathedral and Second Cathedral sees rays of sunlight streaming through holes, resulting in a lighting effect reminiscent of a cathedral.

“Lava tubes are not rare. Finding a lava tube underwater that is within scuba diving depths that has the ceiling broken out in a couple places to create windows for sunlight to come in, there just aren’t that many that are known of in Hawaii,” Chip Fletcher, interim dean for the School of Ocean and Earth Science and Technology at the University of Hawaii, told SFGATE.

Fletcher has been on both Cathedral dives and says he knows of just two others like them on Oahu.

First Cathedral is a five-minute boat ride from Manele Bay, near Puu Pehe (aka Sweetheart Rock), and at a depth of 55 to 70 feet. Kristin Belew, a scuba instructor for Lanai Ocean Sports, estimates First Cathedral to be very large, at about 100 feet long, 70 feet wide and 20 feet tall.

“It is more like one big chamber or room,” Belew told SFGATE. “You enter through this really beautiful archway. When you’re inside, the back wall has lots of little holes, and the light comes through these holes, giving it a stained-glass effect.”

Belew moved to Lanai in 2011 but got certified to scuba when she was 14 years old in 1994. She’s racked up over 1,000 dives at each Cathedral site. “The diving off of Lanai is some of the best diving in the state,” Belew says. “We’ve got really clear water, really healthy reefs and not very many people, too.”

At the center of First Cathedral is a large rock that has been nicknamed the “altar.” Depending on the time of day, light shines on this rock from the ceiling, illuminating it and the surrounding area. Belew says weddings do happen here, though not very often. Proposals are easier. Kneeling is possible, and the person proposing can use underwater slates for messaging.

When surf breaks over the rocks above, divers shoot out of the lava tube to exit the dive. “It generally gives you a little burst of speed as you pass through the smaller exit hole,” Belew says of what divers call the “shotgun.”

Second Cathedral is also at a depth of around 55 to 65 feet, and its lava cave is massive, at 80 feet in diameter. This dive site is farther down the southern Lanai coastline, closer to Kaunolu.

Belew describes it as a “big Swiss cheese” because there are about seven different ways to enter and exit. A rare black coral hangs from the ceiling, which divers refer to as the “chandelier.” 

Nocturnal fish are often found inside this lava tube, while the exterior is home to a large school of bluestripe snappers that swim together in a ball. “I think it’s really awesome to be down there,” Belew says. “You’re never going to see the same exact fish or eels. Sometimes we see an octopus now and then, a reef shark or a turtle. It’s always different.”

From a scientific point of view, Fletcher doesn’t believe these lava tubes were formed by lava falling into the ocean but rather that they were formed at a time it was on dry land. “Lava tubes that are underwater like this had to form when sea level was lower, and since they form from lava flows, they require that the volcano be active at the time,” Fletcher says. That means they’re very old.

The Cathedral lava tubes were created by the Lanai volcano. “The lavas are between 1.3 and 1 million years old,” Scott Rowland, undergraduate chair and specialist for the Department of Earth Science at the University of Hawaii, told SFGATE in an email. The island was created by the one volcano, with Lanaihale being the highest point. 

For Belew, even after diving into the Cathedral sites many times, she says it never gets old. “To me, they’re absolutely gorgeous,” she says. “It’s always a different experience.”