Lava Tubes: The Hidden Underworld of Volcanoes

When we think of volcanoes, we usually imagine fire fountaining into the sky or rivers of red-hot rock flowing down a mountain. But some of the most spectacular volcanic creations are hidden from view, buried beneath the surface. These are lava tubes—natural conduits that once transported rivers of fire and now serve as dark, echoing cathedrals of stone.

From the tourist-friendly Thurston Lava Tube in Hawaii to the ice-filled caves of Mount Etna and the potential habitats on Mars, lava tubes are a key feature of basaltic volcanism.

How Do Lava Tubes Form?

Lava tubes are essentially the “veins” of a volcano. They form during long-duration eruptions of fluid basaltic lava (pahoehoe).

Channeling: The process begins with a lava channel—a river of open lava flowing downhill.
Crusting Over: As the lava flows, the surface is exposed to the cool air. It begins to solidify, forming a thin, dark crust of rock that floats on the molten stream.
Roofing: Eventually, this crust thickens and connects from the sides, creating a solid roof. The lava continues to flow beneath this insulating blanket.
Insulation: This is the key. Rock is an excellent insulator. Inside the tube, the lava can stay hot (around 1,200°C) and fluid for miles, losing very little heat. This allows volcanoes like Kilauea or Mauna Loa to transport lava huge distances from the vent to the ocean without cooling down.
Drainage: When the eruption stops, the source of the magma is cut off. The remaining lava drains out of the tube, leaving behind a hollow, tunnel-like void.

Anatomy of a Tube

Exploring a lava tube reveals geological features that mimic a limestone cave, but formed by fire instead of water.

Lavacicles: Like stalactites, these are drips of remelted rock that hung from the ceiling as the tube cooled.
Flow Lines: The walls often show horizontal ridges, marking the different levels of the lava stream as it drained away, similar to bathtub rings.
Skylights: Sections of the roof that were too thin may collapse, creating natural skylights. These are often the entry points for explorers and spots where sunlight pierces the darkness, allowing ferns and mosses to grow in a “green spotlight.”

Famous Lava Tubes of the World

1. Thurston Lava Tube (Nāhuku), Hawaii

Located in Hawaii Volcanoes National Park, this is perhaps the most visited lava tube in the world. It is a massive, cathedral-like tunnel surrounded by a lush fern forest. It formed about 500 years ago and is easily accessible, making it a perfect introduction to volcanic spelunking.

2. Cueva de los Verdes, Canary Islands

Part of the massive Atlantida Tunnel system on Lanzarote (one of the longest in the world at 7 km), this tube was once used by locals to hide from pirates. Today, one of its large chambers has been converted into a natural concert hall, famous for its incredible acoustics.

3. Kazumura Cave, Hawaii

This is the master system. Surveyed at over 65 kilometers (40 miles) long and over 1,000 meters deep, it is the longest and deepest known lava tube in the world. It challenges the notion that lava tubes are short features; Kazumura shows they can be complex, multi-level systems that transport lava across an entire island.

4. Manjanggul, South Korea

A UNESCO World Heritage site on Jeju Island, Manjanggul is famous for its sheer size. The tunnel is up to 30 meters high and 23 meters wide, housing the world’s largest lava column (7.6 meters high).

Life in the Dark: Troglobites

Once the lava cools, the tubes become habitats.

The Twilight Zone: Near the entrances, the cool, moist environment supports ferns, mosses, and nesting birds like the White-tailed Tropicbird.
The Dark Zone: Deep inside, in total darkness, live unique creatures called troglobites. These include specialized spiders, crickets, and millipedes that have lost their pigment and eyesight. They rely on tree roots penetrating the ceiling or bat guano for nutrients.
Microbial Mats: Scientists have discovered strange bacterial mats growing on the walls of lava tubes. These “snottites” (yes, that’s the scientific term) feed on minerals in the rock, showing us how life can survive in extreme, nutrient-poor environments.

Lava Tubes on Other Worlds

The study of lava tubes is not just about Earth; it is about the future of humanity in space.

The Moon: High-resolution images from lunar orbiters have revealed “skylights”—holes in the surface of the Moon that lead into vast underground voids. Because the Moon has lower gravity, these tubes could be hundreds of meters wide, large enough to house entire cities.
Mars: The giant volcanoes of Mars (like Arsia Mons) also have chains of pit craters suggesting massive tube systems.
The Ultimate Shelter: For future astronauts, lava tubes offer the perfect habitat. The thick rock roof provides natural shielding from cosmic radiation, micrometeorites, and the extreme temperature swings of the surface. Living inside a lava tube might be the safest way to colonize the solar system.

Hazards of Exploration

Exploring lava tubes (volca-speleology) carries unique risks.

Razor Rock: The floor is often covered in “aa” lava or sharp breakdown blocks that can shred boots and skin.
Instability: Unlike limestone caves which form over millions of years, lava tubes are geologically young and brittle. Roof collapses are a real danger, especially in seismically active areas.
Gases: In active volcanic areas (like during the 2018 eruption of Kilauea), tubes can accumulate CO2 or sulfur dioxide, making them deadly traps.

Conclusion

Lava tubes are the hidden arteries of the Earth. They remind us that a volcano is not just a mountain, but a plumbing system. Walking through one is a humbling experience—you are moving through the exact space where a river of liquid stone once roared at 1200 degrees, shaping the land we walk on today. Whether as a tourist attraction, a biological refuge, or a future lunar base, the dark world of the lava tube is one of geology’s greatest wonders.