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.
Cinder Cones and Spatter Cones
Cinder cone
Spatter cone
Cinder Cones When volcanic eruptions of fairly moderate strength throw cinders into the air, cinder cones may be built up. These cone-shaped hills are usually truncated, looking as though their tops were sliced off. Usually, a bowl- or funnel-shaped crater will form inside the cone. Cinders, which cooled rapidly while falling through the air, are highly porous with gas vesicles, like bubbles. Cinder cones hundreds of feet high may be built in a few days. Big Cinder Butte is a cinder cone. At 700 feet high it is the tallest cone in the park. The shape develops because the largest fragments, and in fact most of the fragments, fall closest to the vent. The angle of slope is usually about 30 degrees. Some cinder cones, such as North Crater, the Watchman, and Sheep Trail Butte, were built by more than one eruptive episode. Younger lava was added to them as a vent was rejuvenated. If strong winds prevailed during a cinder cone’s formation, the cone may be elongated—in the direction the wind was blowing—rather than circular. Grassy, Paisley, Sunset, and Inferno Cones are elongated to the east because the dominant winds in this area come from the west. The northernmost section of the Great Rift contains the most cinder cones for three reasons: 1. There were more eruptions at that end of the rift. 2. The lavas erupted there were thicker, resulting in more explosive eruptions. (They are more viscous because they contain more silica.) 3. Large amounts of groundwater may have been present at the northern boundary of the lavas and when it came in contact with magma it generated huge amounts of steam. All of these conditions lead to more extensive and more explosive eruptions that tend to create cinder cones rather than lava flows.
Spatter Cones When most of its gas content has dissipated, lava becomes less frothy and more tacky. Then it is tossed out of the vent as globs or clots of lava paste called spatter. The clots partially weld together to build up spatter cones. Spatter cones are typically much smaller than cinder cones, but they may have steeper sides. The Spatter Cones area of the park (Stop 5 on the [map of the Loop Drive]) contains one of the most perfect spatter-cone chains in the world. These cones are all less than 50 feet high and less than 100 feet in diameter.
Lichens often pioneer new life on Earth. Two plants in one, lichens are composed of an alga and a fungus growing together to their mutual benefit, usually on rock. Hardy and slow-growing, lichens help break down rock to soil-building mineral matter.
Eventually their vegetable matter decays, helping to form the first soils that other plants can then use. Tough in the extreme, some lichens can be heated to high temperatures and still be capable of resuming normal growth when returned to viable conditions.
Life Adapts to a Volcanic Landscape
Two thousand years after volcanic eruptions subsided, plants and animals still struggle to gain toeholds on this unforgiving lava field. Much of the world’s vegetation could not survive here at all. Environmental stresses created by scant soil and minimal moisture are compounded by highly porous cinders that are incapable of holding water near the ground surface where plants and other organisms can make ready use of it. Scarce at best—total average precipitation is between 15 to 20 inches per year—rainwater and snowmelt quickly slip down out of reach of the plants growing on cinder cones. Summer’s hot, dry winds rob moisture from all living things exposed to them. Whisking across leaves and needles the winds carry away moisture precious to plant tissues. On the side of a cinder cone, summer day temperatures at ground level can be more than 150°F.
The secret to survival here is adaptation. Most life forms cope by strategies of either resisting or evading the extremes of this semi-arid climate. To resist being robbed of moisture by winds and heat, a plant may feature very small leaves that minimize moisture loss. To evade heat, wind, and aridity, another plant may grow inside a crevice that provides life-giving shade and collects precious moisture and soil particles. Another plant may spend about 95 percent of the year dormant. It may rush through the germination, sprouting, leafing out, blooming, and fruiting stages and return to the dormancy of its seed stage in just two weeks. The dwarf buckwheat has adapted to life on porous cinders by evolving a root system that may spread out for up to 3 feet to support its aboveground part, which is a mere 4 inches high. This buckwheat only looks like a dwarf because you can not see its roots.
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