Site Tour: Caves Area

NPS Illustration

The Caves Area

Background Information

If you choose to visit any of the caves, a free cave permit is required for all visitors including school groups. This is to prevent the spread of white-nose syndrome (WNS), a disease that kills bats, into the caves at Craters of the Moon. Any clothing or any other item that has been in any underground space such as another cave or mine cannot be worn into the caves at Craters of the Moon, even if it has been washed or decontaminated.

This must be discussed with your group before the day of the field trip.

Some of the caves may be very icy in the spring. For safety reasons, we advise that students remain in small supervised groups and not be allowed to explore the caves independently. Seasonally, there are two lava tube caves open to the public in the caves area. The largest is Indian Tunnel. Because of the limited time available, and ease of access, we generally recommend school groups visit only Indian Tunnel.

Each member of your group should have a dependable source of light such as a flashlight. Wear study shoes or boots. The caves are undeveloped and some hiking across broken lava is necessary. The ceilings can be low and the footing uneven. Large holes in the 30 foot high ceiling of Indian Tunnel have created natural skylights. For safety reasons, when on the surface, teachers should not allow students to approach the skylights. Never allow any object to be dropped through a skylight, since the trail through Indian Tunnel runs directly under many of them. No running, pushing, or horseplay should be allowed in the caves or caves area. This area has long been a favorite part of the park. The unique features of this area can be enjoyed safely by taking a few precautions. A brochure about the caves is available at the trail head or from the bookstore.

Trail Head

Introduction

As the hot, fluid pahoehoe lava flows across the surface it forms rivers and channels. As the surface of the molten lava comes in contact with the cooler air, the surface of the lava starts to harden and the flow quickly "crusts" over. Hot lava continues to flow beneath the crust. When the eruption ends and the supply of lava stops, the lava drains out from beneath the crust leaving an empty tunnel or tube.

Stop #1

Dewdrop Cave

From here you can see the source of the Blue Dragon Lava Flow that formed the caves area. The Blue Dragon Flow erupted from a fissure at the base of Big Craters and the Spatter Cones. The Blue Dragon Flow is one of the youngest flows in the park.

Lava tubes are like a giant underground plumbing system for an eruption. They move the lava away from the vent and out onto the plain. Later eruptions can also flow into existing lava tubes if they are still open.

Many different events can cause a lava tube to collapse. Lava tubes often collapse during the final stages of an eruption as the lava begins to drain from the tube. If the lava drains from the tube while the roof is still soft and plastic, the roof may simply sink as it loses its support from the lava beneath. Another cause of collapse in lava tubes is the shrinking and cracking that occurs as lava cools. This cooling process can shatter the roof of a tube. Over long periods of time, the forces of erosion can also cause lava tubes to collapse. Water is a major force of erosion. As water seeps into cracks in the winter it repeatedly freezes and thaws. This freezing and thawing gradually widens the cracks. Bit by bit, the cracks grow wider, weakening the ceiling. Even the roots of trees and shrubs have been known to cause lava tubes to collapse. As plants begin growing in the protected cracks and crevices on the surface where soil and water collect, their roots can extend down through the roof of a tube. Each year as the roots grow longer and thicker, they can weaken the roof to the point where it collapses.

Stop #2

Indian Tunnel

Being the largest lava tube in the caves area, Indian Tunnel is over 30 feet high, 50 feet wide, and approximately 800 feet long. Indian Tunnel contains many of the features common to all lava tubes. On the ceiling of the tube you can see lava stalactites formed as the river of lava pulled away from the ceiling, and molten material began to drip from the hot ceiling.

The amount of lava flowing in a tube fluctuates over the course of an eruption. If the activity at the vent increases, the amount of lava flowing into the tube may increase. This rise and fall of lava levels left marks on the walls of Indian Tunnel. If you look closely at the walls, you can see long linear ridges, called tide marks. These ridges show where the flowing river of lava temporarily held at a constant level long enough for deposits of lava to accumulate on the wall. Since geologists cannot easily observe what happens inside a lava tube during an eruption, they can only speculate on how many features are formed. Most agree that during an eruption, lava tubes are often in a constant state of change. They can form only to be destroyed by the formation of new tubes. Tubes can even burst if the eruption pours more lava into the tube than the tube can hold, splitting it down the middle, like a loaf of bread in the oven.

Several forms of life can be found in Indian Tunnel today. In tubes with skylights, sunlight reaches into the cave and allows yellow and green mosses and lichens to grow on the moist, dimly lit walls. Small animals such as squirrels, chipmunks, and packrats make their home in the cave. Cavity nesting birds, such as violet-green swallows, find plenty of nesting cavities in the cracks of the rock that form the rim of the skylights. Great-horned owls may also nest on the numerous ledges found in Indian Tunnel.

End of Indian Tunnel

Summary

Large eruptions that produce massive lava flows also produce lava tubes to move this great volume of lava away from the vent and out onto the plain. Rivers of pahoehoe quickly crust over, insulating the hot fluid lava beneath, which continues to flow. Lava tube caves are left behind as the eruption subsides and the lava drains from beneath the hardening crust. The lava tubes in the caves area were all formed during the same eruption of the Blue Dragon Flow.