Lava tubes are natural conduits through which lava travels beneath the surface of a lava flow. The Thurston Lava Tube formed about 350-500 years ago. At that time a large vent was erupting on the east side of Kilauea’s summit. When the eruption stopped the lava drained from the tube, leaving it an open chamber. Visitors can now walk through this chamber, which is about 400 feet long.