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Volcanism of Long Valley, California: The Bishop Tuff Eruption

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Volcanism of Long Valley, California: The Bishop Tuff Eruption

The west coast of North America has been tectonically and volcanically active for billions of years. The Sierra Nevada Mountains in eastern California were born of volcanoes, and magma has been erupting in the Long Valley to the east of the mountains for over three million years (Bailey, et. al., 1989). However, the climactic eruption of the region occurred relatively recently in the region's geologic history. About 760,000 years ago, a huge explosion of magma warped the Eastern Sierra into the landscape that exists today. The eruption depleted a massive magma chamber below the earth's surface so that the ceiling of the chamber imploded, forming what is now known as the Long Valley caldera. The caldera is at the eastern base of the Sierra Nevada Mountains, about 50 km northwest of the town of Bishop, and 30 km south of Mono Lake (Bailey, 1976).

The ejecta from the eruption moved over land and through the air: the ash that fired out of the volcano was blown as far east as Nebraska in a huge, dark cloud of plinian ash. A nuee ardente billowed over the rim of the volcano and spread lava to the south, east and north, forming a volcanic outcrop now called the Bishop Tuff. Today, an expanding resurgent dome in the center of the depression indicates current magmatic activity beneath the caldera, and earthquake swarms in the last 25 years could also be linked to subsurface magma movement. Clearly, the Long Valley caldera is not dormant, so understanding the eruption that formed the caldera and surrounding features is essential to assessing the region's current and, more importantly, possible future activity.

Volcanic activity existed prior to the Bishop Tuf...

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Sheridan, Michael F. Fuarmolic Mounds and Ridges of the Bishop Tuff, California.Geological Society of America Bulletin. v. 81. March 1970. pg 851-868
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