What Are Lava Tubes? How Did Ancient Volcanoes Form These Natural Conduits?

Most people think of caves as underground worlds of stalactites and stalagmites. Unbeknownst to many, lava tubes are a common cave type and a fascinating feature of Earth's geography.

(Photo: Wikimedia Commons/ Z Thomas)

Molten-Molded Wonders

Lava tubes are underground caves formed from volcanic eruptions. They are natural conduits through which lava travels under the surface of a lava flow. Due to their proximity to the surface, they tend to have more entrances than any other type of cave.

Most people may not have heard of lava tubes, but there are actually quite a few of them. In California alone, up to 500 known lava tube caves are within the boundaries of Lava Beds National Monument. Some of the other famous lava tubes are Boyd Cave in Oregon, Leviathan Cave in Kenya, Thurston Lava Tube in Hawaii, and Manjanggul Cave in South Korea.

The longest lava tube on Earth is the Kazumura cave, located on the island of Hawaii. It is the record for being the longest and deepest known tube in the world, measuring 40 miles (64 kilometers) long and more than 3,000 feet (914 meters) down. It is estimated to be about 400 and 500 years old and resulted from an erupting vent on the east side of Kilauea Caldera.

Lava tubes are not limited to the creative forces on planet Earth alone; these features can also be observed in other members of the Solar System. There are lava tubes present below the surface of Mars and the Moon that could be 100 and 1,000 times wider than those found on Earth.

Astronomers have been interested in these underground formations on Mars and the Moon because they could provide relatively stable environments once cooled. As astronauts explore the harsh environments of the moon and Mars in the future, the lava tubes can be their natural shelter to protect themselves from unstable temperatures, radiation, and micrometeorites.

How are Lava Tubes Formed?

Most caves are created when softer rocks are dissolved in water over a long period. Meanwhile, lava tubes form through a far more volatile, sudden process.

The lava flow is thousands of degrees hot and moves like a river. The top part of this molten river is closer to the surface air, so it cools after exposure to cooler temperatures. As a result, the molten lava hardens into a rock and forms caves. As time passes, these rocks continue to cool until they thicken and widen enough to form a roof.

The disruption could either cease or move areas, so the lava tubes drain lava and leave behind the underground tunnel. As these tubes continue to cool, they become relatively stable in temperature. Over time, they also become significant niches within an ecosystem. For instance, owls, rodents, bats, and tree roots can be home in these spaces.

According to scientists, lava tubes can also be home to troglobites or animals specifically adapted to live in the dark. In some tubes, spider and cricket species have evolved to develop alongside microbial communities not found anywhere else on the planet. Today, these special kinds of volcanic caves serve as a record of the past, allowing visitors to travel back millions of years.