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 Supervolcanoes Activity Report
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Details of Supervolcano
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| VEI Index: |
7 |
| Name: |
Long Valley Caldera |
| Volcano ID: |
120314-A |
| Country: |
USA |
| Location: |
State of California |
| Diameter: |
600 km³ |
| Last Eruption: |
~760,000 years ago |
Long Valley Caldera is a depression in eastern California that is adjacent to Mammoth Mountain. The valley is one of the largest calderas on earth, measuring about 20 miles (32 km) long (east-west) and 11 miles (18 km) wide (north-south). The elevation of the floor of the caldera is 6,500 feet (2,000 m) in the east and 8,500 feet (2,600 m) in the west. The elevation of the caldera walls reach 9,800-11,500 feet (3,000-3,500 m) except in the east where the wall rises only 500 feet (150 m) to an elevation of 7,550 feet (2,300 m). Long Valley was formed 760,000 years ago when a huge volcanic eruption released very hot ash that later cooled to form the Bishop tuff that is common to the area. The eruption was so colossal that the magma chamber under the now destroyed volcano was significantly emptied to the point of collapse. The collapse itself caused an even larger secondary eruption of pyroclastic ash that burned and buried thousands of square miles. Ash from this eruption blanketed much of the western part of what is now the United States. Geologists call topographic depressions formed in this manner calderas.
Subsequent eruptions from the Long Valley magma chamber were confined within the caldera with extrusions of relatively hot (crystal-free) rhyolite 700,000 to 600,000 years ago as the caldera floor was upwarped to form the resurgent dome followed by extrusions of cooler, crystal-rich moat rhyolite at 200,000-year intervals (500,000, 300,000, and 100,000 years ago) in clockwise succession around the resurgent dome. At its height 600,000 years ago, an Owens River-fed 300 foot (91 m) deep lake filled the caldera and rose to an elevation of 7,800 feet (2,400 m) above sea level. The lake was drained sometime in the last 100,000 years after it overtopped the southern rim of the caldera, eroded the sill and created the Owens River Gorge. A dam in the gorge has partially restored part of that lake which is now known as Lake Crowley. Since the great eruption many hot springs developed in the area and the resurgent dome has uplifted. During the last ice age, glaciers filled the canyons leading to Long Valley, but the valley floor was clear of ice. Excellent examples of terminal moraines can be seen at Long Valley: these moraines are the debris left from glacial sculpting. Laurel Creek, Convict Creek, and McGee Creek all have prominent moraines.
In May of 1980, a strong earthquake swarm that included four Richter magnitude 6 earthquakes struck the southern margin of Long Valley Caldera associated with a 10 inch (25-cm), dome-shaped uplift of the caldera floor. These events marked the onset of the latest period of caldera unrest that continues to this day. This ongoing unrest includes recurring earthquake swarms and continued dome-shaped uplift of the central section of the caldera (the resurgent dome) accompanied by changes in thermal springs and gas emissions.[1] After the quake another road was created as an escape route. Its name at first was proposed as the "Mammoth Escape Route" but was changed to the Mammoth Scenic Loop after Mammoth area businesses and land owners complained. In 1982, the United States Geological Survey under the Volcano Hazards Program began an intensive effort to monitor and study geologic unrest in Long Valley Caldera. The goal of this effort is to provide residents and civil authorities in the area reliable information on the nature of the potential hazards posed by this unrest and timely warning of an impending volcanic eruption, should it develop.[1] Most, perhaps all, volcanic eruptions are preceded and accompanied by geophysical and geochemical changes in the volcanic system. Common precursory indicators of volcanic activity include increased seismicity, ground deformation, and variations in the nature and rate of gas emissions. |
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Map of Supervolcano
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Latest seismic activity
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| Date |
Time |
Magnitude |
Depth |
| 2013-06-18 | 00:01:46 | 2.4 | 7.90 Km |
| 2013-06-18 | 00:00:59 | 1.9 | 8.00 Km |
| 2013-06-18 | 00:09:26 | 2.1 | 8.30 Km |
| 2013-06-18 | 00:06:56 | 1.5 | 8.40 Km |
| 2013-06-18 | 00:10:33 | 2.5 | 7.90 Km |
| 2013-06-18 | 00:21:25 | 1.5 | 7.80 Km |
| 2013-06-18 | 00:23:00 | 1.3 | 7.30 Km |
| 2013-06-18 | 00:27:17 | 2.3 | 8.00 Km |
| 2013-06-18 | 00:41:33 | 1.4 | 8.10 Km |
| 2013-06-18 | 00:43:37 | 1.1 | 6.60 Km |
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