Page 78 - Geothermal Energy Renewable Energy and The Environment

62 Geothermal Energy: Renewable Energy and the Environment

system that began erupting over 3.5 million years ago along a north–south trend on the eastern edge
of the Sierra Nevada Mountain Range.
For more than 2.5 million years, the volcanic system poured out various lavas and other volcanic
rocks, while magmas accumulated at depth. At 760,000 years ago, a catastrophic eruption occurred
that spewed more than 600 cubic kilometers of rock into the atmosphere, spreading ash and other
volcanic debris as far east as Kansas and Nebraska and as far west as the Pacific Ocean. The erup-
tion partially emptied the magma chamber, causing a collapse of the overlying volcanic complex.
This collapse process resulted in the formation of the Long Valley Caldera, a 17 km by 32 km
depression that is elongate east-west (Figure 4.10). During the eruption a large volume of the ejected

119 00' 118 45'

395

Glass
mountain
Inyo volcanic
37 45'
Owens
Resurgent dome River topographic boundary
Long valley caldera
Chain
West moat Medial graben East moat Hot creek

LVEW
Casa diablo
203
Mammoth Chance
Lakes meadow
Mammoth Mammoth Creek
37 37'30'' mountain South moat
Crowley
lake
Owens River
S I E R R A
N E V A D A
395
Hilton creek fault
0 5 10 Kilometers

Western

Study U.S.A.
San C A L I F O R N I A area
Francisco

Los
Angeles

FIGUre 4.10 Location map and topography of the Long Valley caldera. (From Farrar, C. D., Sorey, M. L.,
Roeloffs, E., Galloway, D. L., Howle, J. F., and Jacobson. R., Journal of Volcanology and Geothermal Research,
127:305–28, 2003.)