Location:
East California, USA With an area of 16 x 32 km, the Long Valley Caldera was formed around 760,000 years ago by the last super eruption of the volcano. The latest eruptions that happened in the caldera were 50,000 years ago. Though those were not of the same proportion of the one that made the caldera itself. The large eruption produced 600 km3 of material. About half the material was ejected as Pyroclastic flow. The rest was blown about 40 km into the atmosphere, where the wind distributed it as far away as Kansas and Nebraska.
The caldera is extinct though the area is still thermally active, with hot springs and fumeroles dotted around. Seismic mapping shows that the magma underground is mostly crystallized not molten anymore. The thermal energy has been utilized to make electricity for the surrounding area. A geothermal system inside the caldera fuels the Casa Diablo power-plant. This power-plant produces enough electricity to power 40,000 homes.
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Long Valley Caldera has experienced periods of unrest over the last few decades (earthquakes, ground uplift and volcanic gas emissions). The floor of the caldera is about 6,500 ft in the East and 8,500 ft in the west. The range of mountains surrounding the caldera are even higher, ranging from 9,800 - 11,500 ft. The eruption that caused this massive caldera was comparable to that of eruptions produced by Yellowstone supervolcano. Shortly after the eruption a resurgent dome was formed in the center of the caldera. More domes formed in a series of smaller eruptions between 110,000 and 50,000 years ago, building a volcano that is now 11,059 ft in elevation. Because Long Valley has only ever experienced one super-eruption it is safe to predict that another one is unlikely to be coming soon, if at all.
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