Visitors to Hawai'i may not be aware that the 50^th US state holds a unique secret – it is home to the longest lava tube in the world.

What is a lava tube?

As a set of islands created by volcanic activity, Hawai'i is dotted with numerous lava tubes. These natural formations, sometimes referred to as pyroducts, are essentially underground conduits created by lava flows. When lava stops being propelled by an eruption, or if it ends up being diverted, the flow can leave behind these massive empty tunnels that form networks of caves.

The walls and ceilings of these tunnels can sometimes have incredible drip-like formations extending from them. These are created as the lava levels subside – like melted wax on a candle.

Generally speaking, it can take up to a year for the lava to cool to an extent that it can be approached by living organisms, but once it has the cave networks are quickly colonized by all sorts of unique troglobites – animals that live in caves. These subterranean beasties can include insects and spiders, as well as species of various microbes that cannot be found anywhere else.

Kazumura Cave

Although Hawai'i can boast plenty of lava tubes across its islands, the biggest by far is the Kazumura Cave, which is located around 19.3 kilometers (12 miles) south of Hilo, a town on what is commonly called the Big Island. This cave stretches over 65 km (40 miles) in length and reaches over half a mile (0.8 km) in depth. It is both the longest and deepest lava tube in the world.  

According to the Indigenous Polynesian people, some of the numerous entrances to the tube (there are estimated to be around 100) were entrances to a kind of underworld realm. These entrances were believed to be associated with the goddess of fire, Pele, and so were sacred. From time to time, people of importance were buried in them. However, it is clear that humans used the tunnels for other practical purposes too.

During hard times, the local people could use the caves to shelter from the weather or to evade their enemies. Archaeological excavation of middens found stone tools and other artifacts that attest to their use. Some of the chambers have also been turned into rudimentary living quarters, complete with hearths and areas for sleep.

The lava tubes were also a valuable site for collecting water, as there are few suitable standing lakes and streams on Hawai'i’s islands. As such, people can venture into the depths of the lava tubes where they can collect water that drips from the ceilings as it filters down through the porous volcanic rock from the surface.

As such, the Kazumura Caves represent a valuable link between Hawai'i's geological past and its cultural history. Beyond its awe-inspiring formations, this subterranean realm has been intertwined with the lives of generations of people who have lived on the islands.