Craters of the Moon National Monument—a little bit of Hawai’i in Idaho
If you ignore the arid climate and sagebrush vegetation in the Snake River Plain of Idaho, and just look at the landscape of lava, you can imagine yourself on the Big Island of Hawai’i. This photograph shows basalt-type lava in pahoe’oe and a’a flows, with cinder cones in the background. The area is still considered to be volcanically active, with the basalt flows at the surface ranging in age from 15,000 to 2,000 years. Although the youngest flows are 2,000 years old, they appear younger because of the arid climate. Flows this old in Hawai’i would have long ago turned into soil and would be hosting a luxuriant vegetative cover (especially on the rainy Hilo side of Hawai’i).
Like Hawai’i, these volcanoes are the result of a hot spot located deep beneath Earth’s surface that is causing rock to melt and rise to erupt above ground. Movement of a plate over the hot spot results in a chain of volcanoes—in Hawai’i, the above-surface chain on the Pacific Plate extends from Kauai (about 5 million years old) to the Big Island (currently active). Unlike Hawai’i, the hot spot that has created Craters of the Moon is beneath continental crust rather than oceanic crust. As the North American plate has moved southwest over this hot spot, the chain of volcanoes has extended from SE Oregon (about 16 million years old) to Yellowstone (currently active; the most recent eruption was 600,000 years ago). The hot spot was located beneath the Snake River Plain, where Craters of the Moon is located, about 10 million years ago.
When the hot spot first begins breaking through continental crust, it produces silica-rich magmas that erupt explosively and are very dangerous. This is because the magma picks up more silica-rich materials as it travels through the continental crust. Yellowstone is called a “super volcano” because of its propensity to produce huge eruptions—estimated at about 2,000 times the amount of material that was erupted at Mt St Helens in 1980! This explosive type of volcano erupted here about 10 million years ago, but it has now been buried by lavas of the relatively silica-poor type of lava (basalt) that creates less explosive volcanoes. It appears that the conduit for the magma has now been cleared of continental material and is coming directly from greater depths. The quantity of lava is augmented by rifting of the continental crust, as the extensional province of the Basin and Range (think Nevada) has extended northward.
Other features in Craters of the Moon that resemble features found in Hawai’i are lava tubes and tree molds. In the photo below, a tree fell as a result of the hot flow and left an impression in the lava.
In June, the wildflowers were blooming—they created a beautiful carpet on the pumice plains.
While a geology student at San Francisco State University, John Niles mapped volcanic features in the National Monument as a Geocorps summer intern. It was exciting to see his map for sale in the visitors center. Although many others contributed to the work, his contribution was deemed largest—he is listed as first author. The different colors outline cones and flows of different ages and compositions.
The monument has enough interesting features to fully occupy visitors for a day or two. It is possible to camp within the monument; for other types of lodging, it is necessary to drive to a nearby town. The nearest is Arco, a small town with its small piece of fame. Adjacent areas of open space were used for bomb testing by the federal government, and the Idaho National Laboratory is still operating between Arco and Pocatello, but it now focuses on “changing the world’s energy future”.