Idaho
On the ground at Craters of the Moon, craters and collapsed lava tubes make for difficult navigating across the lava field.
Long before aerial imagery was possible, thousands of pioneers made their way west on the Oregon Trail. The journey on foot and by ox-drawn cart was arduous, but few sections were more miserable than a stretch through south central Idaho that is now Craters of the Moon National Monument and Preserve. It is one of the largest basalt lava flows in North America, with jagged black basalt covering nearly 1200 square miles of desolate ground. The barren rock supports little plant life and scarce game—a true no-man’s-land.
From the air, Craters of the Moon appears as three black splotches, but the lava field is actually made up of sixty distinct lava flows, between 15,000 and 2100 years old. The more recent volcanic eruptions were likely witnessed by the Shoshone; tribal legends tell of a serpent coiling around a mountain until the black rocks liquefied and the mountain exploded.
More than twenty-four volcanic cones also occupy the landscape, created as lava piled up around a central vent in the planet’s crust. The source of the lava is Idaho’s Great Rift, a crack in the crust that extends fifty-three miles across the Snake River Plain and is thermally connected to the hot spot under Yellowstone National Park in Wyoming. Craters of the Moon is currently dormant, but not extinct. The time between eruptive periods averages 2000 years and some scientists think the area is due for another eruption within the next hundred years.
The extensive lava fields at Craters of the Moon National Monument and Preserve are made up of at least sixty distinct flows that have erupted over the past 15,000 years.
On the ground, the variety of lavas and volcanic features is apparent. Hot, oozing basalt can take many forms as it cools, including block lava, which often forms in large, angular chunks with smooth sides; aa lava, with a jagged texture; and pahoehoe lava, with a smooth or ropey texture—all of which helped form the Hawaiian Islands as well as occurring at Craters of the Moon. Other volcanic features at the Idaho site include vents, fissures, cinder cones, lava bombs, spatter cones, and lava tubes.
Lava tubes form when the top of low-viscosity lava forms a hard exterior crust as it cools, while the interior is still hot and flowing, creating a roof over the active lava stream. After it cools, a long, tube-like cave is left behind. Native Americans may have used those that were accessible for shelter or ceremonies. One such cavern is the Shoshone Ice Cave, near Craters of the Moon and open to the public. This ancient rock tube was created by fiery hot lava but is now cold enough to maintain a thick, skatable sheet of ice on the floor year-round.
Lava tubes such as those at Craters of the Moon develop when the top of low-viscosity flowing lava forms a hard ceiling crust as it cools, while the interior is still hot and moving, creating a roof over the active lava stream. Once the lava cools, a long cave is left behind. Lava tubes can be fifty feet wide and many miles long, and may show at the surface or be completely hidden underground.
It’s easy to spot the splotches of black rocks spread out over the Snake River Plain in the middle of Idaho. A flight to Idaho Falls, Pocatello, or Boise, Idaho, could provide an aerial view.
