Site Tour 3
The Caves Area
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 are low and the footing uneven. Large holes in the 30 ft. 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 area. The caves 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.
Stop Number 1
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 Number 2
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
Did You Know?
Vast quantities of water stored by the lava rock aquifer below the Eastern Snake River Plain provides for critical human needs throughout southern Idaho...including those famous potatoes!