My Expedition to the Lava River Cave
Volcanoes...one of Earth‘s geological wonders. No one would think there would be a second wonder beyond the volcano itself, but there is. Lava caves can form after a volcano erupts. The amazing and little known Lava River Cave, north of Flagstaff, Arizona, was chosen for my expedition. The Lava River Cave, located 30 minutes north of Flagstaff, is not well known to the public because it is not advertised, maintained, or easy to find. It is also called Government Cave because it was first discovered on government land owned by the National Forest Service.
About 700,000 years ago, the large array of volcanoes (more than 650) nestled in the San Francisco Peaks near Flagstaff were very active. The most recent volcanic eruption occurred about 10,000 years ago, near Sunset Crater, just outside of Flagstaff. The Lava River Cave formed about 675,000 years ago after the Hart Prairie shield volcano erupted, and lava flowed from it and onto the ground all around it. A shield volcano is the landform created when a vent produces successive basaltic lava flows, stacked one on top of another in eruptive order. The lava from the Hart Prairie volcano flowed, and as it flowed, it cooled. The outer shell of a cylinder cooled, forming the walls of the lava tube, but the hot lava inside kept flowing. The lava inside the tube drained and the sides cooled, leaving behind a hollow tube known as the Lava River Cave (Figure 1).
In the fall of 2001, I decided to go spelunking to explore the Lava River Cave for myself. In addition to my field journal, I also took along a few other necessary tools, including five flashlights with extra batteries, one 100-foot tape measure, a jacket, a thermometer, a water bottle, a notebook, two pencils, a camera and film, a folder containing the rules of the Young Naturalist Contest, a Coconino County map and atlas, and my trusty backpack.
My dad and I drove three hours north from my home in Phoenix, to Flagstaff. I had four goals in mind I wanted to accomplish: a) find out how the Lava River Cave was formed and what the future holds for it; b) learn about the cave‘s physical interior from a geological standpoint; c) learn the difference between a lava cave and a water cave; and d) share this information with others.
October 1, 2001; 9 am: The long dirt road drive to the area where the cave is located finally ended. I stepped out of the car and took in the warmth of the sun and the vanilla scent of the tall ponderosa pine trees surrounding me. I gathered my tools and hiked out in search of the cave. Most lava tubes are found by serendipity. The first people to discover the Lava River Cave were lumbermen in 1915. It is believed that railroad workers used the cave as a refrigerator to store perishable food and raw materials.
I was quite surprised when I unexpectedly came upon the huge opening in the ground known as the Lava River Cave (Figure 2). Fallen boulders and rocks surrounded the opening. I measured the opening at roughly 30 feet by 24 feet (Figures 3-5). As I ventured down into the opening, I began to wonder if my tennis shoes were going to cut it walking on the rough terrain (Figures 6-7). The rocks were damp and sharp, making them very slippery. They had a blue tint to them (Figure 8). The cave looked very dark, and as I descended into the opening, the temperature began to drop rapidly (Figure 9). The coldest point in the cave was about 32F at approximately 20 feet into the cave. There was ice in the spring water because it is just cold enough for water to freeze. The warmest point in the cave was at the very back of the cave because it is closest to the surface. As I continued to make my way back into the cave, the fallen rocks underfoot seemed to decrease in number. The rocks had fallen from the ceiling of the tube when the lava cooled and cracked. The rocks seemed as if they could fit into the ceiling spaces like a puzzle (Figure 10).
Once past the cave‘s entrance, and back about 50 yards into the cave, I realized how really dark it was. When I flipped off my flashlight, I was wrapped in pitch-black darkness. Daylight reached into the cave only near the entrance, which could not be seen from this distance. I was glad to have my dad along on my expedition for company!
There are several different types of lava formations in the Lava River Cave: lava ripples, splashdowns, cooling cracks or crevices, and lavasicles. Lava ripples were found toward the back of the cave. These ripples are "frozen" in the lava, and they detail where the lava continued to flow like a river after the outer shell had hardened. Splashdowns appeared on the floor of the cave. These are rocks that appear to be floating in the lava river. Shortly after the walls hardened, some rocks broke away and fell into the still-flowing lava floor, where they eventually cooled and hardened in the floor. Cooling cracks or crevices were found at the edges of the cave, between the walls and the floor. The size of the cracks I observed varied from six inches to two inches wide. The longest crack I found measured over 20 feet long. These cracks and crevices were formed as the lava cooled and cracked. I also found "lavasicles," which are very small, icicle-like formations, on the walls and ceiling of the cave. These were formed when a hot blast of volcanic gas quickly blew through the newly formed tube and re-melted the surface of the walls and ceiling. The re-melted lava dripped and then quickly hardened again, forming the icicle-like lava features (Figure 11). Some lava tubes have a skylight where the ceiling has caved in to form a hole to the sky. I found no skylights in the Lava River Cave.
The farther back I went in the cave, the smoother the ground became. Molten lava solidifies at 2,100F. A hot Flagstaff day in the summer can reach 95F, and this smoother area of the cave is far from the entrance, so it might have taken a long time for the lava to solidify completely. This may have resulted in the smoother cooled surface.
Although the Lava River Cave is considered a dry cave, I found water droplets and water seepage on the interior walls, which made the walls shiny (Figure 12). When I touched the walls, they were cold. My hypothesis is that the water must be seeping through the walls, similar to the water in a well.
One major difference between a lava cave and a limestone or water cave is the way they are formed. A cave made by water is formed over millions of years, while a lava cave forms in a relatively short time. Water caves may have many passages and rooms. Lava caves, however, generally have one channel, because of the way in which the lava flows. In the Lava River Cave, there was one section where the cave actually split, forming two separate passageways that rejoined after a distance of approximately 80 feet. One of the passages was very narrow and the ceiling was only about four feet high (Figure 13). The other channel had a vaulted ceiling. Throughout the cave, the height of the ceiling varied. The highest point was approximately 30 feet high.
By noon, I had explored the whole cave. It is the longest cave in Arizona of its kind, at just over three-quarters of a mile long. That may not seem that long until you spend three hours exploring with a flashlight. There were no signs of any animals living in the cave itself, but squirrels, porcupines, and bats have been sighted near the entrance.
Looking into the future, the Lava River Cave will probably be around for a very long time. The biggest threat to the cave is graffiti, trash, and other damaging actions by inconsiderate humans. According to Forest Service officials, there are probably other lava caves in the area, but they have not yet been discovered. There is one other known lava cave in the area, near Slate Mountain, but the entrance is far from any road, unmarked, and almost impossible to find.Lava River Cave is a unique museum, though not found in a building or organized for tours or guides. It is a hands-on, one-of-a-kind experience. The history of the lava flow is there to see and experience through careful observations.
"Cave." World Book. Encyclopedia. Chicago: World Book Inc., 2000.
Duffield, Wendell A. Volcanoes of Northern Arizona. Grand Canyon, Arizona: Grand Canyon Association, 1997.
"Lava River Cave." Retrieved from the World Wide Web on October 8, 2001: http://whitethorn.house.home.att.net/lavariver.htm
"Lava River Cave: A Natural Museum." Peaks Ranger District, Coconino National Forest, 1998.
Poturalski, Brian. Park ranger. Interview by Amy Whithey. October 1, 2001.
Copyright © 2002 American Museum of Natural History.
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