What Is a Lava Tube?
A lava tube is a natural conduit — a tunnel — through which lava once flowed underground. It only happens with a very specific ingredient: hot, runny, low-viscosity basaltic lava, the kind that flows like syrup rather than piling up like paste. That's why lava tubes are a signature of shield volcanoes and basaltic lava fields, not steep, sticky stratovolcanoes. Of the 1,740 volcanoes in our database, 182 are shield-type and 1,025 have basaltic dominant rock— the exact settings that build tubes. Hawaii, Iceland, the Canary Islands and the volcanic fields of the western US are the classic tube country because that's where fluid basalt erupts in volume.
How a Lava Tube Forms
The process is beautifully simple. When fluid pāhoehoe lava pours downhill, the surface in contact with the air cools fastest and crusts over into a solid roof. Insulated underneath that crust, the lava inside stays molten and keeps flowing — sometimes at over 1,100 °C, barely losing heat over many kilometers. When the eruption wanes and the supply cuts off, the still-liquid lava drains downslope and out the end, leaving an empty tunnel behind.
That insulation is the whole point of why tubes matter to volcanologists, not just tourists: a tube lets a lava flow travel muchfarther than an open channel would. Kīlauea's 2018 flows and countless Hawaiian eruptions have used tube systems to carry lava 10+ km from the vent all the way to the sea with minimal cooling. The tube is basically a natural pipeline — and it's why a single fluid eruption can bury land far beyond the mountain itself.
The expert's tell: the ceiling of a lava tube often has stubby lava stalactites— not dripping mineral water like a limestone cave, but re-melted rock that dripped from the hot roof and froze mid-drip. Horizontal ledges on the walls ("lava benches" or high-lava marks) show you exactly how deep the molten river ran before it drained. If a cave has those, it's a lava tube, full stop.
Lava Tubes You Can Actually Visit
Most of the internet's lava-tube pages either explain the science or cover one specific cave. Here's the part that's hard to find in one place — a worldwide shortlist of tubes you can walk into, sorted from easiest to most adventurous, with what each one asks of you:
| Lava Tube | Where | Length | Access | Why It's Notable |
|---|---|---|---|---|
| Kazumura Cave | Kīlauea, Hawaii | 65.5 km | Guided tour only | Longest & deepest lava tube on Earth |
| Thurston Lava Tube (Nāhuku) | Hawaiʻi Volcanoes NP | ~600 m | Free, lit, self-guided | Easiest famous tube to walk |
| Kaumana Caves | Hilo, Hawaii | Multi-km | Free, self-guided | Formed by the 1881 Mauna Loa flow |
| Ape Cave | Mount St. Helens, WA | 4.0 km (2.5 mi) | Timed permit | Longest lava tube in the continental US |
| Lava River Cave | Bend, Oregon | ~1.6 km | Lantern rental, self-guided | Fed by a Newberry Volcano flow |
| Lava Beds National Monument | Northern California | 800+ caves | Free, self-guided | Built by the Medicine Lake volcano |
| Raufarhólshellir | Reykjanes, Iceland | ~1.4 km | Guided tour | One of Iceland's longest, near Reykjavik |
| Cueva del Viento | Tenerife, Spain | 18.5 km mapped | Guided tour | Largest lava tube in Europe, 6th on Earth |
Volcano links go to that system's full page in our database. Lengths per NPS, USDA Forest Service and published cave surveys.
Hawaii — the world capital of lava tubes
If you only visit one, make it Thurston Lava Tube (Nāhuku) in Hawaiʻi Volcanoes National Park — a lit, paved ~600 m walk-through that takes about 20 minutes and costs nothing beyond park entry. For the real thing, Kazumura Cave on the eastern flank of Kīlauea is the longest and deepest lava tube on Earth at 65.5 km long and 1,102 m deep; it's on private land and only accessible on a guided tour. Near Hilo, the free Kaumana Caves were formed by the 1881 Mauna Loa flow — bring your own light for that one.
The Pacific Northwest — an unexpected tube
Ape Cave at Mount St. Helens is the longest lava tube in the continental US at 4 km (2.5 mi) — and it's a genuine geological oddity. St. Helens is a stratovolcano that normally erupts sticky, explosive lava, but roughly 2,000 years ago it produced one rare, fluid basaltic flow, and that single anomaly carved Ape Cave. It now runs on a timed-entry permit. Down in Oregon, Lava River Cave near Bend is a self-guided ~1.6 km tube fed by the Newberry Volcano, with lantern rentals at the entrance. And Lava Beds National Monument in northern California packs more than 800 caves into the flanks of the Medicine Lake volcano — the densest concentration of lava tubes in North America.
Iceland, Tenerife & beyond
Raufarhólshellir, one of Iceland's longest tubes at ~1.4 km, sits 30 minutes from Reykjavik and runs guided tours year-round — a good pairing with a trip to see the ongoing Reykjanes eruptions. On Tenerife, Cueva del Viento is the largest lava tube in Europe and sixth largest on Earth, with 18.5 km mapped through the flanks of an ocean-island volcano. South Korea's Manjanggulon Jeju Island is part of a UNESCO World Heritage lava-tube system, and Australia's Undara tubes in Queensland were left by one of the longest lava flows from a single volcano anywhere on the planet.
Booking a lava-tube tour
Kazumura, Raufarhólshellir and Cueva del Viento are guided-only and book out in peak season. The free walk-throughs (Thurston, Kaumana, Lava River Cave) need no reservation but do need your own lights. See our roundup of volcano tours and how to book them before you go.
Lava Tubes on the Moon and Mars
Lava tubes aren't only an Earth phenomenon. Because the Moon and Mars both had extensive basaltic volcanism and have weaker gravity, their tubes can be vastly larger — orbital images show collapsed tube segments and "skylights" (roof-collapse pits) hundreds of meters across, far bigger than anything on Earth. NASA and ESA study them seriously as future habitats: a lunar or Martian lava tube offers natural shielding from radiation, micrometeorites, and wild surface temperature swings — a ready-made shelter that astronauts wouldn't have to build. The same physics that carved Ape Cave could, one day, house a Moon base.
Lava-Tube Safety
Before you go underground
- Carry two or more light sources. Undeveloped tubes are absolute dark — a single dead headlamp is a real emergency.
- Dress for cold. Tubes hold a steady ~7–13 °C year-round even in Hawaii or Tenerife; floors are wet and uneven.
- Wear a helmet and sturdy shoes. Low ceilings and sharp, ankle-turning ʻaʻā rubble are the usual injuries, not lava.
- Never enter a closed or unmapped tube. Roof collapse and getting lost are the genuine hazards; respect gate closures and bat-protection rules.
Frequently Asked Questions
What is a lava tube?
A lava tube is a natural underground tunnel formed by flowing lava. As a river of fluid basaltic lava moves downhill, its outer surface cools and hardens into a roof and walls while the molten interior keeps flowing. When the eruption stops, the last of the lava drains out and leaves a hollow tube behind. They range from crawl-spaces to cathedral-sized passages — Hawaii's Kazumura Cave is 65.5 km long.
Where can you visit a lava tube?
Many are open to the public. The easiest is Thurston Lava Tube (Nāhuku) in Hawaiʻi Volcanoes National Park — lit, paved and free. Others worth the trip include Ape Cave near Mount St. Helens (the longest in the continental US), Lava River Cave near Bend, Oregon, Lava Beds National Monument in California (800+ caves), Raufarhólshellir near Reykjavik, and Cueva del Viento on Tenerife — the largest lava tube in Europe.
What is the longest lava tube in the world?
Kazumura Cave on the eastern slope of Kīlauea, Hawaii, is the longest and deepest lava tube on Earth — surveyed at 65.5 km (40.7 miles) long and 1,102 m (3,614 ft) deep. It formed roughly 500 years ago from a single sustained eruption of fluid pāhoehoe lava. Guided tours cover a small section of it.
Are lava tubes safe to explore?
The developed ones (Thurston, Ape Cave, Lava River Cave) are safe with basic preparation: bring two or more light sources, wear sturdy shoes and a warm layer — caves stay cold and damp year-round — and never enter a closed or unmapped tube. The real hazards are the dark, uneven floors, low ceilings, and getting lost in undeveloped systems, not the volcano itself (these tubes are long extinct).
Can you see lava inside a lava tube?
Not in the tubes you can visit — they are cold, drained conduits from eruptions that ended centuries or millennia ago. Active lava tubes do exist during eruptions (Kīlauea builds them regularly), carrying molten lava for kilometers beneath a hardened crust, but they are far too hot and dangerous to enter. What you'll see instead are lava stalactites, benches, and 'high-lava marks' frozen onto the walls.
Continue Exploring
Shield Volcanoes
The fluid-basalt volcanoes that build lava tubes.
Kīlauea Eruption
Hawaii's tube-building volcano, live status.
Types of Lava
Pāhoehoe vs ʻaʻā — why only one makes tubes.
Volcano Tours
Lava caves, craters and how to book them.
Lava Flows
How lava travels — and why tubes extend its reach.
Mount Etna Hike
Etna's lava caves and guided ascents.
Planning a trip? Every volcano linked above has a full data page — eruption history, elevation, alert status and nearby tours.