Craters of the Moon National Monument

Craters of the Moon is a vast darkened field created by the flow of basalt lava from a fissure in the earth's crust. A small portion of it, eighty square miles, contains some of its most interesting features and is managed by the National Park Service as a National Monument. Some see the landscape as one of "overwhelming desolation" stretching to the horizon. It is that, especially when observed from an airplane, where it looks like someone splashed a huge bucket of tar on the desert. But a closer inspection shows why Craters of the Moon also is a fascinating museum of volcanic features.

Visitors to the National Monument can drive around a seven-mile loop, stopping to examine the lava field in short self-guided walks. Basalt lava, dark because of its high iron content, came to the surface not with a violent explosion like that of the St. Helen's volcano, but with a calmer extrusion of molasses-like magma through the cracks in the earth.

"Pahoehoe" is a smooth-surfaced ropy pattern created as the surface of the flow cooled while the material beneath kept moving. Some pahoehoe contains titanium oxide, which creates a beautiful iridescent blue sheen called Blue Dragon. Aa (pronounced AH-ah) has a rough surface created as the lava cooled and became viscous, ending up as chunky piles of rock.

Some eruptions at Craters weren't quite so calm. Cinder cones prove it. Lava was blown out of a vent in the form of cinder and ash. The material piled up in cone-shaped hills, their shape influenced by which way the wind was blowing. Some cones in the Monument area are a composite of two or more cones with overlapping craters and flanks.

Sometimes the lava blown from a vent was heavier, hot and plastic. This material formed spatter cones, where the lava welded onto the outer surface of a cone and quickly hardened into rock. Lava "bombs" also flew out of the vents. These clots of lava were first hot and plastic, then cooled as they sailed through the air, taking any number of bizarre shapes before they landed.

Hot lava flowed downhill, covering vegetation and enveloping trees in its path. Geologists determined the date of the last eruption at Craters by taking radiocarbon readings of charcoal they found buried under the lava or in tree molds. The lava also created casts of tree limbs.

After the extrusions of lava, plant seeds brought by birds or the wind managed to find places to take hold. The lava field in the monument supports over 300 plant species, 150 bird species, and 50 kinds of mammals. Water is available in depressions and caves.

The Craters area fascinated Robert Limbert, a naturalist, promoter, outdoor photographer, taxidermist, entertainer, and explorer all rolled into one individual. Around 1918 he explored the lava fields, at times spending more than two weeks at a time hiking over the jagged aa rock. He was more inclined to be impressed by the "museum" details at the place than be moved by its desolation. He thought people should come from far and near to admire this work of nature. Largely due to his promotional efforts, President Calvin Coolidge created the monument in 1924. The proclamation mentioned the "remarkable" cones, craters, rifts, lava flows, caves, natural bridges, and other phenomena. But it also celebrated the "weird and scenic landscape peculiar unto itself."

Source:
David Louter. "Historic Context Statements, Craters of the Moon, 1995." Seattle: National Park Service, 1995.