(lava tunnel (a) El Chato Reserve, Santa Cruz Highlands, Galápagos.JPG — David Adam Kess, CC BY-SA 4.0

Lava tunnels

Active

Santa Cruz0.676392° S, 90.333889° W

Underground lava tubes in the Santa Cruz highlands, some up to a kilometer long, open for walking. They formed when the surface of a lava flow hardened while the molten rock inside drained away, leaving hollow tunnels.