Geologic Activity

Lava River

Past

Between 15,000 and 2,000 years ago, the Craters of the Moon Lava Field formed during eight major eruptive periods. During this time the Craters of the Moon lava field grew to cover 618 square miles. The Wapi and Kings Bowl lava fields formed contemporaneously about 2,200 years ago.

Present and Future

This region is experiencing basin and range type faulting, which is stretching or pulling apart the crust. The Lost River Range north of the town of Arco provides good evidence that these forces are still active. In 1983 these forces caused a magnitude 6.9 earthquake, during which Mount Borah rose about 1 foot and the Lost River Valley in that vicinity dropped about 8 feet. On the Eastern Snake River Plain, rather than producing mountain ranges, the tensional forces have caused decompression melting, which results in dike emplacement and periodic eruption of molten rock onto the surface. As long as these forces continue to act, more eruptions will eventually occur. The recurrence interval for eruptive activity in the Craters of the Moon Lava Field averages 2,000 years and it has been more than 2,000 years since the last eruption. The constancy of most recent lava output rates suggests that slightly over one cubic mile of lava will be erupted during the next eruption period. In the past, eruptions in the Craters of the Moon Lava Field have generally shifted to the segment of the Great Rift with the longest repose interval. Therefore, the next eruptive period is expected to begin along the central portion of the Great Rift in the Craters of the Moon Lava Field, but may well propagate to the northern part of the monument in the proximity of the loop road. Initial flows, based on past performance, will probably be relatively non-explosive and produce large-volume pahoehoe flows. Eruptions from potential vents on the northern part of the Great Rift may be comparatively explosive and may produce significant amounts of tephra (airfall material ejected from a volcano), destroy cinder cones by both explosion and collapse, and build new ones.

Until the next eruption, ongoing -but subtle- changes continue to affect the geology of Craters of the Moon. These environmental factors include gravity, weather, as well as other natural and human caused effects on this volcanic landscape.

Identifying Human Influences on Geologic Processes (PDF)