CRATERS of the MOON National Monument & Preserve

A GUIDE TO THE CAVES TRAIL

The caves area contains many stark contrasts: searing heat on the black surface versus the cool of the cave interiors, roaring afternoon wind versus the dampened stillness below ground, brilliant light and expansive views versus the enclosed darkness of the lava tubes. The drama of these contradictions draws people into this strange world.

THE BLUE DRAGON FLOW

About 2,100 years ago, sheets of red-hot lava ran down slope from a fissure where the Spatter Cones now stand. In some places the lava flowed in channels. The surface of these channels hardened, forming tubes which transported enormous quantities of molten rock.

The volume of lava was so great that it burst through the tube roofs and collected in ponds. The ponds developed a solid crust as they cooled. When the eruption finally waned, the lava in the ponds drained back into the tubes. With nothing to support them, the pond crusts collapsed, forming a series of bowl-shaped depressions, such as Big Sink.

From the lava ponds, the flow advanced to the northeast. Lava tubes more than 30 feet high formed in the thicker sections, while many smaller tubes branched off to distribute lava to an ever-widening flow front. Eventually the flow covered an area of 100 square miles. In places the lava is an iridescent blue, the result of titanium magnetite crystals suspended in the glassy rock surface. An early explorer thought the lava resembled a scaly blue reptile, and named this the "Blue Dragon Flow."

Most of the lava tubes in the caves area formed during the eruption of the Blue Dragon Flow. This network of passageways distributed the lava up to 18 miles from its source.

TUBE FORMATION

The formation of tubes is a complex process dependent on eruption rate, topography, and the chemical and physical properties of the lava. Often, rather than flowing as a broad sheet, lava becomes restricted in channels. Lava channels usually form in the fastest moving part of a flow, along older lava channels, tubes, stream beds, or other depressions.

Once a channel stabilizes, a roof can form in a variety of ways. Congealing lava can fuse to the channel sides and accumulate until it bridges the channel. This crust thickens through overflows onto its surface and accretion of cooled lava on its underside. Or surface crusts may form on the lava, tear loose, and drift along until they reach a constriction, fuse and bridge over the channel. In turbulent lava flows, splashing and overflow along the channel form levees which may arch over the channel and join.

LAVA TUBE FEATURES

CURBS Ridges on the walls mark places where the receding lava temporarily held at a constant level. Lava deposits built up on the walls like a bathtub ring.	LAVA STALACTITES Unlike other stalactites, these are not a product of dripping water. Receding lava leaves molten rock on the ceiling, heat within the tube may cause the ceiling to remelt, or lava may be splashed. The molten rock drips and hardens, forming small stalactites.
MINERAL DEPOSITS There are mineral deposits, primarily sulfate compounds, on the ceilings of many lava tubes. Geologists are not in agreement about the source of these minerals. They may have been deposited by either volcanic gases, percolating surface water, or a combination of these two processes.	ICE & WATER As snow melts in spring, runoff seeps through the porous cave roofs. At night, the temperature drops and dripping water freezes into ice stalactites and stalagmites. In most caves, the summer heat destroys these formations, but in a few, ice remains all year.
PLANTS Enough sunlight enters some lava tubes through ceiling collapses for lichens, mosses, and algae to grow on the cave walls. In older caves, soil builds up on the floor beneath openings and other plants may grow.	WILDLIFE Due to the lack of water, food, and light in most caves, animal life is scarce. However, there are some creatures which take advantage of the shelter the caves provide. While it is unusual to see bats in the caves along this trail, you may see other winged creatures. Violet-green swallows, mountain bluebirds, great-horned owls, and rock doves all nest on the rocky ledges around cave entrances. Bushytail woodrats also build their nests in lava tubes. Squirrels, chipmunks, foxes, snakes, mourning doves, and various other creatures occasionally enter the caves.

DESTINY OF CAVES

Regardless of how it forms, the roof of a lava tube shrinks as it cools, causing numerous cracks that weaken the roof and will eventually cause it to collapse. A roof which collapses while still hot and plastic sags, creating a bowl-like depression. A roof that has hardened completely fractures into a pile of broken rubble. If a tube roof survives the cooling process, it can be stable and stand for thousands of years. The main agent causing collapse today is frost wedging or ice forming in cracks.

HELP TO PRESERVE THE CAVES

Lava flows are very fragile, please stay on established trails. Do not leave any trash in the caves. A trash can is located in the parking area for your convenience. Remember that all cave features are fragile and irreplaceable. Do not remove any rocks or other objects from the caves area.

SAFETY - BE PREPARED!

These caves are undeveloped and contain many hazards. There is no artificial lighting, nor are there paved trails. The floors are uneven and possibly icy; ceilings may be low with sharp stalactites.

1. Take at least one dependable source of light. Only Dewdrop Cave and parts of Indian Tunnel may be visited without a flashlight.
2. Sturdy shoes and long pants are recommended. Move slowly and watch for obstacles.
3. During the off-season do not enter the caved alone. Help can be a long time in coming.

© 2003 Craters of the Moon Natural History Association, Inc.
© 1994 Cave Maps by Scott & April Earl of the Idaho Cave Survey
© 1994 Illustrations by Priscilla Marden
Lava Tube Diagram by Business Design Center - Boise, Idaho.