Hawaii Volcanoes National Park reopens popular lava tube after 'unusual' rock movement

HONOLULU – Hawaii Volcanoes National Park visitors are able to once again explore one of the park's most popular destinations, the Nahuku lava tube, after an inspection of an "unusual" fracture movement in the tallest part of the tube's ceiling.

Park management closed the 500-year-old tube down for 18 days, starting July 30, for "data monitoring and inspection" after a crackmeter found the fracture to have narrowed by 2.47 millimeters over the course of a few hours.

The movement meant other fractures were possibly moving, making the large rock slab "unstable and dangerous," Jessica Ferracane, a spokesperson for Hawaii Volcanoes National Park said.

Typically, rock movements had stayed under one millimeter since November 2019. Two crackmeters were installed in the tube after the 2018 eruption and summit collapse of the Kilauea volcano dislodged large rocks inside.

During the monitoring period, park scientists kept a "close watch" on the crack's movement and also did a visual inspection earlier this week, a Hawaii Volcanoes National Park spokesperson said. They found that no rocks fell and there were no new cracks observed. When movement returned to normal, the park determined the lava tube could reopen.

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People can drive to the parking area, which is very limited in space, for easy access to the tube. Those wanting more of an adventure can reach the tube via the Devastation Trail, considered a moderate hike.

The Nāhuku lava tube is one of the few accessible lava tubes in the park and is considered to be the most popular destination in the park, besides the summit of Kilauea, Ferracane said.

"Walking through a tall tunnel formed by a 500-year-old river of lava is an incredible and memorable experience for many people," she said. "To think that the vacant space was once a fast-moving torrent of molten rock from Kilauea volcano can be hard to fathom. Equally astonishing is that Nahuku is accessed by a gorgeous, easy trail surrounded (by a) verdant native rainforest. Towering tree ferns, ohia trees, and rare Hawaiian plants thrive where this massive flow once dominated the landscape."

What travelers should know before visiting the Nāhuku lava tube

The tube is open 24 hours a day, and it's recommended visitors go before 9 a.m. or after 4 p.m. to avoid crowds. The tube is lit starting from 8 a.m. to 8 p.m. After that, you will need a flashlight or headlight.

Molten lava flow carved the tube into the mountain nearly five centuries ago, and was discovered in 1913. Formerly known as the Thurston lava tube, the Nahuku tube was renamed as part of the park's initiative to return to Native Hawaiian or indigenous place names. Nahuku means "the protuberances" in Hawaiian, likely referring to the lava drippings that used to cover the ceiling of the tube but were removed by souvenir collectors.

Park officials urge visitors to leave no trace, and not touch the walls or hanging tree roots. They also warn people to be careful.

"Volcanic landscapes are constantly changing," Ferracane said. "Entering any lava tube or cave is not without risk. Potential hazards include rockfall, low ceilings, standing water, tripping hazards, low light or no light."

Park visitors should always plan ahead, check the park website for any closures or safety alerts, and stay out of closed areas.

This article originally appeared on USA TODAY: The popular Nahuku lava tube reopens in Hawaii Volcanoes National Park