North Crater lava flow

On Road Trip 2009, CNET News reporter Daniel Terdiman visited Craters of the Moon National Monument and Preserve near Arco, Idaho.

Formed from thousands of years of activity along the "Great Rift" of the Snake River Plain, lava "welled up," according to a National Park Service brochure, "to produce this vast ocean of rock. The most recent eruption occurred a mere 2,000 years ago, and geologists believe that future events are likely."

This smooth flowing lava is known as pahoehoe.

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A'a lava flow

Thick and viscous lava flow, as seen here at Craters of the Moon, is known as a'a.

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Pahoehoe lava folds

According to the National Park service, pahoehoe, "a relatively smooth lava, takes its name from the Hawaiian word for 'ropy.' Pahoehoe lava flows are highly fluid, flowing easily. As the surface of the flow cools and forms a crust, the hot lava flowing underneath pulls the top layer into ropes or coils. The crust eventually becomes a rigid roof, forming a lava tube."

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Inferno cone

Inferno Cone at Craters of the Moon in Idaho. "Cinder cones form when gas-rich volcanic froth erupts high into the air and then piles into a mound," according to the National Park Service. But those who climb Inferno Cone may find themselves disappointed because they can't find the source of the eruption. "These cinders were actually blown by the wind, and possibly squirted in this direction, from a vent far below."

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Craters of the Moon from Inferno Cone

A look out at Craters of the Moon from the top of Inferno Cone.

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Lichen

While Craters of the Moon is a forbidding landscape, there are many things living there, including several kinds of animals and many different forms of plant life. Among them is lichen, which spreads across the rocky lava in several different colors.

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Wildflowers

Starting in late May, and peaking in mid-June, wildflowers bloom all around Craters of the Moon, including monkeyflowers, bitterroot, paintbrush, syringa and these spread out flowers, dwarf buckwheat. They "grow with such regular spacing that you might think someone planted them," reads a National Park Service brochure. "But the regular spacing occurs because the plants compete for water through their extensive root systems. Many plants here are adapted to resist losing moisture from the heat and wind. Some have small leaves that minimize water loss. Many grow in crevices that give shade and wind protection and collect precious moisture."

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Down into Indian Tunnel

One of the most awe-inspiring features of Craters of the Moon is the series of lava tubes.

"Lava rivers become lava tubes when the exterior of a flow cools, allowing hot, fluid lava to continue to flow beneath the surface," according to the National Park Service. "Within these insulated underground passages the molten lava can continue to flow for many miles, until the source of the lava gets cut off, leaving behind a 'cave.'"

This is the entryway to the Indian Tunnel, one of the lava tubes, and the only large one that doesn't require visitors to bring a flashlight due to total darkness inside.

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Inside Indian Tunnel

A photo from inside Indian Tunnel. The light is coming from holes in the roof where it collapsed over time, as will happen to all lava tubes.

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Inside Indian Tunnel 2

Because there were roof collapses at several places along the lava tube that formed Indian Tunnel, it is possible to enter on one end and come out the other side.

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Floor of Indian Tunnel

The rough, rocky floor of the Indian Tunnel lava tube.

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Spatter cone

This "spatter cone" took shape "when blobs of molten lava were lobbed into the air during the last gasp of an eruption sequence that ended about 2,100 years ago," reads a National Park Service sign at Craters of the Moon.

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Big Crater

Large volcanic eruptions along the Great Rift formed this and other "big craters," as well as the cinder cones at the bottom. "Cinder cones form early in an eruptive sequence when magma is highly charged with gas," reads a National Park Service sign at Craters of the Moon. "The gas produces an explosive eruption that hurls clots of lava hundreds of feet into the air. The airborne clots become cinders which fall back to earth to form cinder cones."

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Big Crater 2

A look down into a second "big crater" at Craters of the Moon in Idaho.

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Young cone

The North Crater at Craters of the Moon. About 2,000 years old, it is one of the youngest cones in the park.

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Crater fragments

As a'a from the North Crater flowed north, it met with pahoehoe flowing east.

"The crater didn't explode," a sign reads. "The wall fragments just fell into the lava, which floated two of them here."

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Air bubbles

Beautiful air bubbles that appear on the outside of a piece of lava rock at Craters of the Moon in Idaho.

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Broken crust

A segment of pahoehoe at Craters of the Moon that has had the top of its surface broken off, revealing a rust color below.

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