Indian Tunnel
Indian Tunnel looks like a cave, but it is a lava tube. When a pahoehoe lava flow is exposed to the air, its surface begins to cool and harden. A crust or skin develops. As the flow moves away from its source, the crust thickens and forms an insulating barrier between cool air and molten material in the flow’s interior. A rigid roof now exists over the stream of lava whose molten core moves forward at a steady pace. As the flow of lava from the source vent is depleted, the level of lava within the molten core gradually begins to drop. The flowing interior then pulls away from the hardening roof above and slowly drains away and out. The roof and last remnants of the lava river inside it cool and harden, leaving a tube.
Lava tube
Great horned owl
Many lava tubes make up the Indian Tunnel Lava Tube System. These tubes formed during the same eruption within a single lava flow whose source was a fissure or crack in the Big Craters/Spatter Cones area. A tremendous amount of lava was pumped out here, forming the Blue Dragon Flows. (Hundreds of tiny crystals on its surface produce the color blue when light strikes them.) Lava forced through the roof of the tube system formed huge ponds whose surfaces cooled and began to harden. Later these ponds collapsed as lava drained back into the lava tubes. Big Sink is the largest of these collapses. Blue Dragon Flows cover an area of more than 100 square miles. Hidden beneath are miles of lava tubes, but collapsed roof sections called skylights provide entry to only a small part of the system. Only time, with the collapse of more roofs, will reveal the total extent of the system.
Icicles (ice stalactites)
Lava stalactites
Stalactites Dripped from hot ceilings, lava forms stalactites that hang from above. Mineral deposits Sulfate compounds formed on many lava tube ceilings from volcanic gases or by evaporation of matter leached from rocks above. Ice In spring, ice stalactites form on cave ceilings and walls. Ice stalagmites form on the cave floor. Summer heat destroys these features. Wildlife Lava tube beetles, bushy-tailed woodrats (packrats), and bats live in some dark caves. Violet-green swallows, great horned owls, and ravens may use wall cracks and shelves of well-lit caves for nesting sites.