Located in eastern Idaho, the Hell’s Half Acre Lava Field is the easternmost large field associated with the Snake River Plain, which arcs across the center of the state. Geologists think that the abundant lava flows and other volcanic rocks of the Snake River Plain were created when the North American tectonic plate passed southwest over a mantle plume, a fixed “hotspot” in the Earth’s mantle (the layer of Earth below the crust). The hotspot melted the rock of the tectonic plate as the plate passed over it, and magma rose to the surface.
Volcanism attributed to the hotspot began approximately 15 million years ago in the western portion of the Plain, with lava fields becoming younger to the east. With lavas erupted approximately 4,100 years ago, Hell’s Half Acre is one of the youngest lava fields. This pattern—older lavas in the west and younger lavas in the east—reveals the direction the plate was moving. (If the plate had been moving the opposite direction over the hotspot, areas to the east would have encountered it first, and the eastern lavas would have been older.) Today, the center of hotspot volcanism is located in Yellowstone National Park, where it feeds the extensive geyser system.
Portions of the Hell’s Half Acre Lava Field are a National Natural Landmark and Wilderness Study Area. This detailed astronaut photograph illustrates the forbidding landscape of the basaltic lava field. The complex ridge patterns of the black to grey-green flow surfaces include both smooth, ropy Pahoehoe and blocky ’A’a lava. Regions of tan soil surrounded by lava are known as kipukas. These “islands” are windows onto the older underlying soil surface. The kipukas are used for agriculture (both crops and grazing); several green fields are visible to the northwest of Interstate Highway 15 (image right). Light to dark mottling in the kipukas is most likely due to variations in moisture and disturbance by agricultural activities.
Astronaut photograph ISS018-E-5321 was acquired on October 24, 2008, with a Nikon D2Xs digital camera fitted with a 800 mm lens, and is provided by the ISS Crew Earth Observations experiment and the Image Science & Analysis Laboratory, Johnson Space Center. The image was taken by the Expedition 18 crew. The image in this article has been cropped and enhanced to improve contrast. Lens artifacts have been removed. The International Space Station Program supports the laboratory to help astronauts take pictures of Earth that will be of the greatest value to scientists and the public, and to make those images freely available on the Internet. Additional images taken by astronauts and cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of Earth. Caption by William L. Stefanov, NASA-JSC.
The Hell’s Half Acre Lava Field is the youngest and easternmost lava flow associated with the Snake River Plain basalts.