Among the premier attractions of Hawaii Volcanoes National Park, Nahuku is also the most easily accessible and visitor-friendly lava tube on the Big Island. Also known as Thurston Lava Tube, this cave is electrically lit daily along a roughly 300-yard loop, offering a memorable subterranean walk-through.
Located at about 3,900 feet on the eastern flank of Kilauea Volcano, Nahuku was formed fairly recently, by geological standards. It was one of the numerous lava tubes created in the main flow field of Kilauea’s Ailaau eruption, which began in the early 1400s and is thought to have lasted more than a half-century.
Lava tubes are created when the exterior of a lava flow cools and crusts over, while insulating the still-hot, still-streaming interior. When, eventually, the molten flow within drains away, you’re left with a hardened lava flow with a linear hollow inside.
Nahuku is not far from the main vent of the Ailaau eruption. Some 600 feet long, it’s certainly an impressive lava tube, but far from the biggest in the Ailaau flow field. The Kazumura—which runs some 25 miles from near the Kilauea summit almost to the Pacific coast—is the longest known lava tube in the world.
A designated parking area serves the Thurston Lava Tube as well as the Kilauea Iki pit crater. From this parking area, the hike through the lava tube is 1.5 miles round-trip and rated as moderate.
If you’re physically able and have the time, you might consider making a six-mile round-trip trek from the Devastation Trailhead. That allows you to hike the Devastation Trail, the Byron Ledge, and the Kilauea Iki Loop in addition to Nahuku: an awesome ramble through spectacular geology and scenery. (Add an extra mile to that circuit if you decide to start instead from the Puu Puai Overlook, yet another option.)
Part of the magic of the short Nahuku hike itself is the contrast between the above-ground rainforest and the mysterious underworld of the lava tube. Tree ferns and other luxuriant vegetation, plus ringing birdsong, mark the start and end of your journey into the depths.
The portion of the Nahuku lava tube traversed by the loop is illuminated by electric lights from 8 AM till 8 PM. Outside of that morning-to-evening window, you’ll need flashlights and/or headlamps to do the walk. (The lava tube’s open 24 hours a day, so nighttime exploration is a possibility for the prepared and stout-hearted.)
This is a popular hike, to say the least. You can ditch some of the crowds by timing your visit before 9 AM or after 4 PM. (That’s explicitly advertised by Hawaii Volcanoes National Park, so don’t expect to be the only person avoiding the peak visitation window for the day.) The Thurston Lava Tube parking lot is very often full. In that event, you can park at the Kilauea Iki Overlook about a half-mile northwest and hike the Crater Rim Trail to the Nahuku parking area. The parking lot has restrooms and drinking water available.
The loop proceeds along the spacious portal of the lava tube. The floor is quite flat and smooth. The ceiling is pretty smooth, too, but at one point it came festooned with stalactites. Indeed, Nahuku—the Native Hawaiian name for the lava tube—means “the protuberances,” quite possibly a reference to those features, which likely formed as the lava tube drained off. Unfortunately, following its official “discovery” in 1913, rockhounds and souvenir hunters chipped off these drippings.
Be sensitive to the fragile cave environment existing within the lava tube, which supports subterranean organisms and a unique ecology. Avoid touching the walls of the lava tube, and resist the temptation to feel the tree roots that hang in places. Such touch can damage the micro-ecosystems active here.
At the end of the loop, steps lead back out of the cave into the rainforest realm above. If you have a flashlight or headlamp and feel up for a more challenging exploration, you can proceed past the exit a short ways into an unlit, less-visited reach of Thurston Lava Tube with trickier footing.
Though you may find it very crowded during the day, Nahuku is absolutely worth checking out as a rarely lit, easily walked, self-guided lava tube. It’s quite amazing to walk in comfort where 2000-degree (Fahrenheit) lava rushed along a few centuries ago!
If you’re exploring Nahuku outside of when it’s lit up or going into the unimproved section beyond the loop, take a backup flashlight or headlamp as well as extra batteries. You want to be prepared in case your main light dies, after all!