The Thurston Lava Tube stretches 500 feet through Hawai’i Volcanoes National Park, and walking through it feels like stepping into the intestines of the planet. Which, honestly, isn’t far from the truth.
These aren’t caves in the traditional sense—no patient water dripping over millennia, no stalactites hanging like geological icicles. Lava tubes form when the surface of a molten river cools and hardens while the liquid rock underneath keeps flowing, eventually draining away and leaving behind these hollow tunnels. It’s the difference between a frozen stream and a culvert, except the stream was 2,000 degrees Fahrenheit and could melt your face off.
Turns out Hawaii is basically Swiss cheese.
The Big Island alone harbors hundreds of these subterranean passages, some mapped, many not. Kazumura Cave—discovered in 1995—runs for 40.7 miles, making it the longest lava tube on Earth. That’s longer than a marathon. Underground. Through solidified magma. The cave drops 3,614 feet from entrance to end, which means you could fit the Burj Khalifa inside it vertically and still have room for a few extra floors.
When the Earth Decides to Plumb Its Own Depths Awkwardly
Here’s the thing about lava tubes: they’re shockingly common in volcanic regions, but we’re still finding new ones constantly. In 2018, researchers using ground-penetrating radar discovered a previously unknown tube system near Kīlauea that could potentially extend for miles. We’ve been to the moon, but we’re still mappping what’s literally beneath our feet on the Big Island.
The tubes form during pahoehoe flows—that’s the smooth, ropy lava that looks like someone froze chocolate fondue mid-pour. The aa flows, which are chunky and jagged, don’t create tubes because they’re too chaotic, too broken up. It’s weirdly specific. Lava has to be flowing steadily, not too fast, not too slow, with just the right viscosity and temperature. Goldilocks, but for molten rock.
What Lives in a 500-Year-Old Geological Leftover Nobody Thought About
Wait—maybe the wildest part isn’t the tubes themselves but what scientists found living in them. In 2016, researchers exploring lava tubes on Hawai’i discovered bacterial communities thriving in complete darkness, feeding on minerals in the rock walls. These extremophiles exist in conditions that would kill pretty much anything else, which has NASA extremely interested because similar tubes probably exist on Mars.
The Martian connection isn’t hypothetical. Lava tubes have been spotted in satellite imagery of the Moon and Mars, some potentially large enough to house entire lunar or Martian bases. The 2017 discovery of a Martian pit crater near Pavonis Mons—about 115 feet wide—likely opens into a much larger tube system below. Suddenly, Hawaii’s underworld becomes a testing ground for extraterrestrial architecture.
These Aren’t Tourist Attractions They’re Time Capsules Made of Basalt
The Thurston Tube (or Nāhuku, its proper Hawaiian name) formed around 500 years ago during one of Kīlauea’s eruptions. Five centuries. That’s nothing in geological time—a blink—yet here it is, accessible, walkable, lit with electric lights for tourists wearing flip-flops. Other tubes are far older. Some on the Big Island date back over 10,000 years, preserving evidence of ancient lava compositions and flow patterns that tell us how Hawaiian volcanism has changed over milennia.
The temperature inside stays around 65-70°F year-round, regardless of surface conditions. Natural climate control courtesy of thermal inertia.
During the 2018 Kīlauea eruption—which destroyed over 700 homes and created enough new land to add 875 acres to the island—new lava tubes were actively forming in real-time. Geologists watched as surface flows crusted over and drained, creating fresh tunnels that might survive for thousands of years. Or might collapse tomorrow. That’s the gamble with these structures: they’re simulataneously ancient and fragile, permanent and temporary.
