Cavers’ lights illuminate narrow ledges they must traverse where a section of floor has collapsed in a southern Idaho lava tube.
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I'm standing under a warm, late-summer sun in the southern Idaho desert near Shoshone, gazing at a typical southern Idaho scene. Around me is a sea of sagebrush. On the horizon to the north is a row of buff-colored hills topped by dark lava buttes.
A few yards in front of me, supposedly, is a cave. In fact, according to the five members of a local caving group who are accompanying me, it's the second-longest lava tube in the United States outside Hawaii. But all I see is a pile of basalt.
We walk toward the rocks and one of the cavers kneels down, slithers forward and disappears. I crawl in too, and watch the guy ahead of me unlock a stout, steel-rail gate installed by the U.S. Bureau of Land Management. We creep through the tiny opening, then continue crawling for another 15 yards or so until the cave becomes high enough to stand in. I probe ahead with my headlamp and see that it expands into a tube about 30 feet tall and at least as wide. The cave's year-round temperature in the 50s makes me glad I've worn a jacket.
Our trip was organized by Chris Anderson, vice chairman of the Silver Sage Grotto, a caving group in Twin Falls affiliated with the National Speleological Society.
"Caving is one of the few activities I know of where you can become completely and utterly isolated from any signs of civilization," Anderson says as we peer into the darkness. "I like the sense of being in a wild place instantly."
He informs me that the cave extends on three levels for a total of two and a half miles. It's the longest of the approximately 300 lava tubes so far discovered along the Snake River Plain.
Almost all caves are formed either by water percolating through limestone or by flowing lava. The northwestern United States is one of the few places in the world where there are lava caves.
According to Shawn Willsey, assistant professor of geology at the College of Southern Idaho, most of the lava rock underlying the area south of the Wood River Valley is about a million years old, but more recent flows have formed much younger rock on the surface. The most recent is in Craters of the Moon National Monument, where molten lava oozed out of the ground only about 2,000 years ago.
Across southern Idaho, lava has poured from fissures in low, "shield" volcanoes, flowing in river-like channels. As air cooled the tops of the moving lava, crusts formed on the surface while the lava beneath continued to flow. After the lava drained out, hollow tubes remained.
Most lava tubes meander horizontally just below the surface and don't have big drops in them like some limestone caves do. However, collapsed floors can create voids.
"There are places here where you'll need to watch your footing," Anderson says as we begin our exploration of the cave, "where if you slip, there's some air below you."
The cave looks like a big train tunnel with a jumble of rocks on its floor. Anderson admits that Idaho's lava tubes can't compete with limestone caves for spectacular formations. There aren't any stalactites or stalagmites. However, he says, there are more subtle attractions that keep cavers spending one weekend after another underground. Two gray-haired members of our group, Marc and Randy James, are brothers in their mid 50s who have been exploring southern Idaho caves since their parents took them to Craters of the Moon when they were boys. By now, they say, they've been in at least a hundred caves.
Anderson, a tall 44-year-old with a ponytail, is coordinator of the astronomical observatory at the Herrett Center for Arts and Science at the College of Southern Idaho. He brings his scientific curiosity to his spelunking, and he and the James brothers are clearly cave geeks. They love to argue conflicting theories about how the tubes were formed. They point out horizontal lines on the walls that are scour marks from flowing lava. They show us places where the walls have peeled off in several-inch-thick layers as they were reheated by subsequent flows, then became frozen in place as they cooled. Hundreds of nipple-shaped formations where lava has dripped from the ceiling indicate that the same re-heating and cooling process happened there. Those are the closest thing the cave has to stalactites.
Pretty soon, the going gets rougher. We come to spots where the floor has collapsed and where we have to carefully traverse narrow ledges, looking down about 10 feet to the level below us. At some points, it's easier to climb down and crawl under. We're all wearing helmets, kneepads and leather gloves. As we crawl over the sharp basalt and I bang my head on a low ceiling, I'm glad I'm wearing all three items.
Sulfur and iron deposits have left tracings of yellow and dark red around the mosaic of basalt chunks that make up the ceiling. Then we see an interesting-looking orange blotch. Unfortunately, it's not a natural formation—it's spray paint. The cavers tell me that most of the caves in southern Idaho have been vandalized. The BLM has erected gates on 11 caves, partly to keep people out in the winter when bats are hibernating and partly to reduce damage year-round. Anyone who wants to visit those needs to go with an experienced caver and get a key from the BLM office in Shoshone.
Lava caves are particularly vulnerable to damage since they're not being constantly re-formed, as are limestone caves. Once they're damaged, they're damaged forever. For that reason, most cavers are tight-lipped about the locations of the caves they've visited.
"We'd rather be known as elitist snobs than endanger our caves by giving too much information out," Anderson says.
As we get a mile or so into the cave, we start searching the floor for gypsum crystals, formed temporarily when percolating water carries calcium and sulfur into the cave through cracks in the ceiling. However, water flow is greatest in the spring. Now, in late summer, white gypsum lies like talcum powder several inches thick on the floor, but the crystals seem to have dried up and disappeared. Then the cavers' practiced eyes spot some of the delicate, clear, inch-long filaments growing out of the powder. When we turn our lights off, they continue to glow pale green for a few seconds in the darkness.
As we move through the cave, several bats flutter around us. Of the 14 species of bats that live in Idaho, two species—Townsend's big-eared bats and Western small-footed myotis—live here. The bats seem to be intentionally sticking with us.
"They're mapping the cave with their sonar to figure out what these new obstructions are that keep moving around," Anderson tells us. "It's always good to see bats because it's a sign of a healthy ecosystem."
It didn't always appear so healthy. Before the gate was installed across the cave's entrance in 1998, the bat population had declined precipitously. People had been entering the cave during the winter, sapping the bats' energy at a time when the insects they eat are not available.
"They're down to a heartbeat and a breath per minute so they can make it through up to seven months of hibernation," said Justin Barrett, non-game biologist with the Idaho Department of Fish and Game.
In addition, some people had been involved in a warped pastime known locally as "bat bopping"—clubbing hibernating bats to death with baseball bats. The population decline was not only a shame from a biodiversity standpoint, but had practical consequences for humans. The bats are voracious eaters of insects that damage crops and forests.
"They eat substantial numbers of mosquitoes every night, in the thousands for an individual bat," Barrett said.
According to BLM Shoshone District biologist Gary Wright, between 20 and 360 bats hibernate every winter in each of about 20 caves on the district. However, he said, not enough data has been collected to enable biologists to determine whether installation of the gates has begun to restore their populations.
Six bats stay with us all the way to the end of the cave. At least it's almost the end; from here, the ceiling slopes gradually downward and we'd have to start crawling. We call it close enough and head back.
As we approach the light, we see rats' middens, and someone says to watch out for rattlesnakes.
Other than a few species of small invertebrates, no other animal besides bats lives in these caves. However, an animal occasionally wanders in and gets lost in the dark. The cavers tell me that in another cave they found a grizzly bear skull later dated at 8,000 years old.
"One cave has a natural animal trap," Anderson says. "There's a 15-foot drop near the entrance. An animal walking in there in the dark would just fall in. Who knows how may thousands of bones are in there under the soil?"
According to biologist Wright, southern Idaho caves have divulged the remnants of numerous ice-age mammals, including musk ox, camels and a giant bison with a horn span of six feet. He said ice-age-era vegetation—in the form of ferns and moss—still lives in one cave that has an opening in its ceiling that allows sunlight to reach the cave floor.
"It's a remnant of the cool, boreal forests from the Pleistocene," he said. "The area was much cooler, much wetter. This little community has maintained a micro environment to support what would have been common at the time."
Wright said some of the caves also contain evidence of human habitation, in the form of stone scrapers, projectile points and pieces of baskets. Traces of several-thousand-year-old, frozen bison and pronghorn blood indicate that Native Americans used the ice-covered floors of some caves as freezers to store meat.
It's the hope of making such discoveries that keep these cave geeks exploring.
"There's the lure of the possibility of seeing something no one's laid eyes on before," Anderson says. "It's taken jamming myself into some tight, nasty hole, but I think I can say I've been, very rarely, down a passage that no human being had ever seen."
Information on nearby, non-gated lava caves and maps to locate 10 of them can be obtained from the BLM office at 400 W. F St. in Shoshone, (208) 732-7200. To enter any of the locked caves with Silver Sage Grotto trips, contact Chris Anderson at (208) 732-6666. For information on scheduled explorations, visit the Silver Sage Grotto's Web site at www.caves.org/grotto/ssg.
