Though its name might suggest something formed by the meandering of an ancient river, the Snake River Plain of southern Idaho had a far more violent birth. Scars from its relatively recent geologic origin are printed on its surface, visible in this summer scene captured by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite on August 29, 2008.
The plain formed as the North American plate drifted southwest over a hot spot in Earth’s crust. Today, the hot spot fuels the hundreds of geysers that give Yellowstone its fame. The thermal bulge pushed the land up, and the difference in elevation is apparent in this image. The Yellowstone Plateau is covered in dark green forest, which only grows at high elevations in this desert region. Lava flows, volcanic buttes, a caldera, and even the course of the Snake River provide evidence for the hot spot’s passage under the Snake River Plain southwest of Yellowstone.
The most obvious sign of the volcanic activity associated with the Yellowstone/Snake River Plain hot spot is the dark lava flows that spill across the plain. The largest of these is the Craters of the Moon, but the Wapi Lava Field to the south and Hells Half Acre in the east also darken the plain. In these regions, lava seeped to the surface through rifts in the Earth’s surface.
Immediately east of Craters of the Moon is the Big Southern Butte. Rising to a height of 2,300 meters (7,550 feet), the butte towers over the relatively flat Snake River Plain. It formed as lava slowly built up around a vent. A circular shadow on the brown plain in this image, Big Southern Butte is one of the largest volcanic domes in the world. It is not the only butte on the Snake River Plain to lay claim to the “largest” title. The twin Menan Buttes are among the world’s largest tuff cones, volcanoes formed when magma erupts through ground water. In this case, the erupting volcano pushed through the Snake River. The lava cooled instantly into tiny glasslike crystals that burst to the surface in a cloud of steam. The Menan Buttes grew as hot ash accumulated around the volcano. The are unique in the United States because they are the only tuff cones formed by a freshwater eruption.
The last volcanic feature that ranks among the world’s largest is the oval-shaped Island Park Caldera. Measuring 18 miles by 23 miles, the caldera may be the largest symmetrical caldera in the world, according to the Digital Atlas of Idaho. The caldera formed when a dome of magma built up and then drained away. The center of the dome collapsed, leaving a caldera. The rim is visible in this image as a distinct ring of green.
The final evidence of the Plain’s geologic past lies in the surrounding landscape. The expanse of land between the Rocky Mountains and the Cascade and Sierra Nevada Mountains is dominated by range after range of mountains separated by dry desert scrub. This basin and range feature is visible on either side of the Snake River Plain. The Plain itself, however, cuts diagonally across the parallel lines of mountains—something a river is unlikely to do. The Plain itself is a depression, sinking under the weight of the volcanic rocks that formed it. Following gravity, the Snake Rivers winds through the center of the plain.
NASA image courtesy the MODIS Rapid Response Team at NASA GSFC. Caption by Holli Riebeek.