- VolcanoMammoth Mountain is a lava-dome complex on the SW rim of Long Valley caldera, California. Despite its close geographic relation, it is believed that it has its own magma chamber different from the ones underlying Long Valley caldera and the Inyo craters.
Volcano type lava domes normal or dormant Location United States Summit elevation 3369 m / 11,053 ft Mammoth Mountain volcano eruptions 1260 ± 40 years Typical eruption style effusiveThe last eruption of the lava dome complex itself took place about 57,000 years ago. There are more than 35 vents fed by the same magma chamber, including Red Cones, two basaltic cinder cones SE of Mammoth Mountain and SE of Devils Postpile National Monument. The cones, whose name derives from their colorful upper scoria deposits, were radiocarbon dated at about 8900 years ago.
Phreatic eruptions on the north side of Mammoth Mountain took place about 700 years ago. The recent unrest, including seismicity, gas emission, and tree kill, at the Long Valley caldera is thought to be related to a dike intrusion beneath Mammoth Mountain in 1989.