Craters of the Moon: Idaho's Lava Sea, Where Astronauts Trained for the Moon

The landscape spreading out around you on the Snake River Plain is one of the strangest in North America: a vast black sea of hardened lava broken by cinder cones, spatter cones, and hollow lava tubes, all of it frozen in shapes that still look freshly formed. Craters of the Moon National Monument and Preserve covers over one thousand one hundred square miles of this terrain, and the geological story it tells is remarkably recent.

The lava fields here were produced by fissure eruptions along the Great Rift, a fifty-two-mile crack in the Earth's crust that runs across the eastern Snake River Plain. Eruptions began about fifteen thousand years ago and continued in pulses, with the most recent activity occurring roughly two thousand one hundred years before the present. By geological standards, these flows are practically still cooling. There are sixty distinct lava flows and over twenty-five volcanic cones visible in the monument.

The person most responsible for bringing this landscape to public attention was Robert Limbert, an Idaho taxidermist and adventurer who explored the lava fields in the early nineteen twenties. His nineteen twenty-four article in National Geographic described the terrain in vivid detail and persuaded President Calvin Coolidge to establish the national monument that same year, on May second, nineteen twenty-four.

The name Craters of the Moon was not hyperbole. In August nineteen sixty-nine, just weeks after the first moon landing, NASA sent astronauts Alan Shepard, Edgar Mitchell, Eugene Cernan, and Joe Engle to train here under the guidance of pioneering geologist Eugene Shoemaker. The volcanic geology of this plain resembles the lunar surface closely enough that the astronauts spent a full day walking the lava fields, studying the types of rock they would encounter on the Moon and learning to identify geologically significant samples quickly. They were, in effect, doing rehearsals on Earth for the grandest geology field trip in history.

In two thousand two, the monument was expanded and redesignated a national preserve, adding wilderness and BLM lands to bring the total protected area to its current size. The Great Rift is not considered dormant. Scientists believe it will erupt again.