By Stephanie Namahoe Launiu
Wherever there are volcanoes, there are lava tubes. Lava tubes are found all over the world. Here in Hawai‘i, each island has a maze of lava tubes running underground. There are also some well-known landmarks that actually formed from a lava tube.
So, what is a lava tube?
When a volcano erupts, the hot lava flows downward from the top slope of the volcano. The lava forms a lava field and hardens into a crust that eventually cools into solid rock. But underneath that top layer, the hot lava continues to flow and it forms tunnels of hot magma underground. After awhile, the hot magma breaks through and flows beyond the hardened upper crust that has formed a type of tube, and it leaves behind a network of caverns and tunnels resembling a subterranean subway system.
Hot flowing lava can reach temperatures above 2000° F as it rushes through an empty tube or tunnel of hardened lava. This intense heat generates fumes of gas that blast through the tube and liquid lava can travel long distances underneath the surface. When the lava supply finally stops at the end of an eruption, or the lava is diverted into another direction, it leaves behind an empty tunnel or cave.
In simple terms which isn’t exactly accurate but easier to imagine, a lava tube is like a big air bubble left behind by hot lava flowing through a tunnel of older crusted lava.
What is Inside of a Lava Tube?
These empty lava tubes left to themselves over centuries, become cold, dark homes to ecosystems of animals and microbes adapted to live in darkness. Species of insects, spiders, bats and other unseen creatures can make lava tubes their home.
Many times, a lava tube isn’t entirely underground. There’s usually a point of entry like an entrance to a cave. Bats and birds can fly in and out of these lava tubes.
It’s always risky to try to hike into or explore a lava tube that you are unfamiliar with. You could run out of light, your cell phone will most likely lose its signal, and you could fall down or get hurt. In Hawai‘i, especially if you’re near the ocean, the tide could enter a lava tube and trap you inside.
Did Native Hawaiians Know About Lava Tubes?
They sure did! Lava tubes—or nāhuku—are amazing relics of ancient lava flows.
To Native Hawaiians, lava tube caves held great cultural importance. And sometimes it held their most important secrets.
Lava tubes were used for shelter from the elements during dangerous storms and from human enemies in battle. The natives knew that food they stored in the cooler lava tubes would last longer. Excavation sites within lava tubes have uncovered remnants of edible sea foods, stone tools and other evidence of daily living.
Lava tubes were a valuable source of fresh water when rain was scarce. Droplets of water from the ceiling that had filtered down through the porous lava rock were collected into gourd bowls called ipu.
Lava tubes were also essential in some cultural ceremonies and burials. The bones of chiefs and important people were often secreted away into lava tube caves. Hawai‘i Volcanoes National Park on the Big Island protects sacred burial caves within their boundaries; no tours or entry is permitted. U.S. federal law protects native burial sites when found anywhere in Hawai‘i. Penalties for disrupting native burial sites include monetary fines and imprisonment.
What is a Lava Tube That the Public Can Enter?
Big Island Lava Tubes
Nāhuku, previously known as the Thurston Lava Tube, is located within Hawai‘i Volcanoes National Park. When the Park first opened, this lava tube was named for Lorrin Thurston, a local newspaper publisher and advocate for the national park, who found it in 1913. But in the 21st century, public sentiment changed towards Thurston who had been part of the overthrow of the Hawaiian monarchy in 1893 and the U.S. annexation of Hawai‘i in 1898. The Park renamed it Nāhuku, the indigenous Hawaiian word for lava tubes.
Back in 1913 when it was first revealed to the public, the interior ceiling of Nāhuku was covered with lava drippings. Those soon disappeared to insensitive souvenir collectors. Help protect this beautiful resource by not touching the walls or tree root systems that hang down.
When you enter Nāhuku, it feels like you’re entering a massive cave. And you are! The walk into the tube takes you through a tropical landscape with massive ferns. The tube is tall enough for an adult to walk upright, but there are areas with lower overhangs, so watch your head. Some parts of the tube have 20 ft high ceilings and are wide enough for several adults to walk side-by-side.
Believe it or not, Nāhuku is open to the public 24 hours a day. Yes, for real! The installed lights are turned on between 8am and 8pm. Outside of those hours, you’re on your own so be sure to bring a flashlight or headlamp.
Nahuku Lava Tube is a featured stop on the Volcano Adventure Tour!
Kaumana Caves in Hilo is above historic downtown Hilo in a residential area. It’s a big lava tube that was formed by the 1881 eruption of Mauna Loa. Entry is free and unsecured. You’re on your own. Parking is on Kaumana Drive.
To enter, you’ll walk down a set of steep stairs into a tropical ravine. Once you duck your head to enter the cave, the lights go out. Literally. No sunlight at all. It’s complete darkness. So even during the day, you need a headlamp or powerful flashlight. There are two sections of the cave— a left side and a right side. Both are tubes that you can follow completely to their ends. They wrap around back to the start so that you can explore the opposite side.
Privately Owned Lava Tubes
Kazumura Cave is the longest known lava tube system in the world! This 500-year-old cave system stretches 42.5 miles in length on the slopes of Kilauea Volcano. Part of the cave system is inside Hawai‘i Volcanoes National Park, but it also extends outside of park boundaries. No part of this long cave system is accessible to the public unless you reserve a spot on a licensed tour. This is to reduce human impact on the fragile environment of the caves, and to prevent injuries to adventurers unfamiliar with this ancient cavernous system.
Kula Kai Caverns is another large system of lava tubes that’s only accessible with a licensed tour operator. This underground network is near the community of Ocean View in the Ka‘ū district and is on private property. Many sections of this cavernous network are restricted to viewing because they contain Hawaiian artifacts and evidence of ancient human habitation. On some private tours, parts of the caverns can only be explored by crawling through them.
O‘ahu Lava Tubes
The island of O‘ahu is much older than the Big Island, and its volcanoes are dormant and unlikely to erupt again. Diamond Head. Punchbowl. Koko Crater. All are dormant (and hopefully extinct) volcanoes.
There are underground networks of lava tubes, but here are areas where lava tubes are most evident:
The Hālona Blowhole at Hālona Point off Hānauma Bay is a Hawaiian natural wonder. At high tide especially on windy days, it resembles a geyser when the ocean fills underwater lava tubes and seawater shoots up to 30 feet in the air through a ground hole. This is a favorite tourist spot for photos. It’s also one of the best places for whale-watching. The ancient Hawaiians seemed to know about the expansive ocean views here, because hālona means “lookout” in the Hawaiian language.
Sharks Cove at Pupukea Beach Park on the world-famous North Shore has an underwater series of lava caves. Because of their length, these caves are best explored with scuba gear. You won’t be able to (and you shouldn’t try) to hold your breath to swim through these caves. Sharks Cove is already known as a popular spot for snorkeling in the spring and summer. During winter months the surf gets rough and it’s no place for amateurs.
There are many other lava tubes and caves on O‘ahu. You may not even realize, when you see rock formations, that they were formed centuries ago by volcano eruptions. Lava tubes are truly natural wonders left behind by the creators of the Hawaiian Islands—volcanoes.