Flowing lava shapes unearthly land

November 21, 2006 

The sun peeks through a skylight of Indian Tunnel on an overcast November afternoon at Craters of the Moon National Monument and Preserve. Indian Tunnel is a lava tube that formed when the exterior of a lava flow cooled and the molten interior continued to flow, similar to a river when it begins to freeze. Skylights form in a lava tube when weather or a passing animal breaks through a thin layer of the tube. This skylight is roughly 25 feet in diameter.

KERRY MALONEY — Idaho Statesman

Two thousand years ago, lava flowed out of a huge rip in the Earth and over part of the Snake River Plain in eastern Idaho with such power that it floated a warehouse-sized chunk of volcanic rock for two miles.

The three-story “warehouse block” is just one of the surprises at Craters of the Moon National Monument and Preserve, a land that is testament to the volcanic activity that shaped the landscape near Arco through more than 60 lava flows beginning some 15,000 years ago.

It’s a landscape so unearthly that scientists create terms like spindle bomb, lava tubes and spatter cones to describe the bizarre legacy of the molten lava. It’s a place where the Earth burped and spat, building up cinder cones hundreds of feet high. It’s a land that looks almost lifeless, but far beneath the surface may hide more molten rock that could burst forth once again.

The lava spawned a history as unique as the landscape. An American Indian legend tells of a serpent, angered by lightning, that turned the rock into liquid. Historians say pioneers who crossed Craters’ northern tip in the mid-1800s branded the land “black vomit.”

“It really is a wonderland,” says Terry Maley, a retired Department of Interior geologist who lives in Boise. In many parts of the nation, Maley says, visitors would have to drive 50 miles or more to see all the kinds of volcanic formations they can see in a 7-mile loop through Craters of the Moon.

The volcanic activity that formed Craters of the Moon has a modern-day cousin — the eruptions in Hawaii, says Ted Stout, Crater’s chief of interpretation: “The same processes are occurring in real time in Hawaii that occurred here 2,000 years ago.”

The Great Rift

Craters wouldn’t exist if not for the Great Rift, a 52-mile-long tear in the Earth’s crust that gave molten rock a path to the Earth’s surface from as deep as 25 miles. During eight eruption periods roughly 2,000 years apart, super-heated rock poured out of the cracks and through vents, spreading lava up to a mile thick across hundreds of thousands of acres.

From the air, Craters of the Moon looks as if someone had smeared pitch over the land. Grass and trees find little soil or water in the harsh terrain of the black lava.

On the ground, Craters is a blend of eerie landscapes.

In summer, much of the ground at Craters of the Moon is blackish with lava. A fresh autumn snow turns the landscape white, but does little to change the oddness: The rolling lava and volcanic cones still signal the senses that this isn’t Earth as usual.

Acres of once-chunky molten rock are stopped in mid-flow, as if a choppy river were suddenly frozen. The sharp rocks could rip apart a pair of boots or cow’s hooves. In the 19th century, American Indians escaped cavalry by fleeing into the treacherous terrain at Craters, Stout says. Yet a few steps away is a more gentle kind of cooled lava. It’s smooth, looking like stretched taffy or braided hair.

Along the Great Rift, occasional spatter cones — mini volcanoes — straddle the crack where lava once flowed. It is there you can walk into a crater and see and feel a volcano from the inside out.

Young in geologic time

Craters’ story begins with the Great Rift.

As sections of the Earth were pulled apart, they created a crack that plunges up to 700 hundred feet below the surface in some places.

Wes Collins, Butte County’s 41-year-old sheriff, has backpacked the length of the rift. His office in Arco is not far from Craters and the rift. He has rappelled into crevices and caves in the rift, searching for snow to melt into drinking water to supply his walk across the arid landscape.

He hasn’t descended more than about 40 feet into the rift. “I would run into an ice block and couldn’t do any more,” he says.

The Great Rift produced a vast inventory of volcanic formations, Maley says. Many formations are young by geologic time — just 2,000 years old — and hardly weathered or worn.

Craters’ cinder cones were formed as debris tossed out of a vent along the rift loosely compacted into some 25 mounds as tall as 700 feet.

Some bits of volcanic matter were barely the size of a fingernail. Others are as big as cars, Stout says.

Lava hurled into the air occasionally — called “bombs” — took on odd shapes. Lava stretched into elongated shapes is called a ribbon bomb. Lava that looks like cotton candy spun onto a stick is called a spindle bomb. Blobs of lava shot into the air that smushed on landing earned the name cow pie bombs.

Not all the lava shot skyward. Huge amounts flowed across land.

Maley explains: As the molten rock on top cooled, the hotter lava kept moving forward. The shells left behind — called lava tubes — can be hundreds of feet long and 30 feet high. Descend into one of those caves, and you can see where the lava slowly drained, leaving marks on the tube wall akin to rings around an empty bathtub.

Lava tube ceilings often are fragile. In 800-foot-long Indian Tunnel, parts of the roof have caved in. The breaches let in sunlight that spills on mounds of fallen stone below, as if through a craggy skylight.

In other parts of the ceiling, bits of once-melted rock look as if they will drip on your forehead. They were created when lava inside the tube remelted parts of the hardening ceiling.

‘Nature bats last’

Lava last flowed across Craters 2,100 years ago. American Indians, whose presence dates back about 12,000 years, may have seen the eruptions.

A Shoshone-Bannock story talks of “a giant serpent who was angered by lightning,” Stout says. The story goes on to describe the rock turning into a fluid and “flowing as the great serpent came out of the ground.” Stout thinks the story may be describing the last lava flow across the eastern portion of the Snake River Plain.

On a recent fall day, Craters was quiet. The tourists were gone. Little wind moved across the open spaces.

But that silence may be temporary. Scientists think molten rock remains beneath the Great Rift. Eruptions at Craters have come about every 2,000 years.

“We’re overdue,” Maley says.

The thought fascinates Stout, who also is a geologist: “I would love to be here.” But, he adds, “Mother Nature bats last, and she decides when she wants to go again.”

Contact Bill Roberts at 377-6408 or broberts@idahostatesman.com

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