As you probably all know, the Long Valley Caldera is one of Earth’s largest calderas and sits adjacent to Mammoth Mountain in eastern California.
The 3,000 feet (910 meters) deep caldera was created by a gigantic eruption 760,000 years ago.
The super-eruption formed the Bishop tuff common to the area, emptied the magma chamber, blanketed much of the western part of the United States and released pyroclastic flows that burned and buried thousands of square miles. A real disaster!
According to latest measurements, the 20 miles (32 km) long, 11 miles (18 km) wide caldera has a vast reservoir of semi-molten magma measuring a staggering 240 cubic miles… Can you imagine that?
And the scientific paper concluded: “the mid-crustal reservoir is still melt-rich. We estimate the reservoir currently contains enough melt to support another super eruption comparable in size to the caldera-forming eruption at 767 ka.”
Is magma filling the Long Valley Caldera?
Moreover, recent relative gravity scientific study conducted in Long Valley (California) in 1982 and 1998 reveals a decrease in gravity of as much as −107 ± 6 microgals (1 microgal = 10−8meters per square second) centered on the uplifting resurgent dome.
Assuming a point source of intrusion, the density of the intruding material is 2.7 × 103 to 4.1 × 103 kilograms per cubic meter.
The gravity results require intrusion of silicate magma and exclude in situ thermal expansion or pressurization of the hydrothermal system as the cause of uplift and seismicity.
So yes, magma is filling up the supervolcano.
Is the Long Valley Caldera about to blow?
The southern margin of the Long Valley Caldera was hit by a strong swarm including four M6.0 earthquakes in May 1980.
The seismic series was accompanied by a 10-inch (250 mm) dome-shaped uplift of the caldera floor.
The resulting ongoing unrest includes recurring earthquake swarms and continued dome-shaped uplift of the central section of the caldera accompanied by changes in thermal springs and gas emissions.
According to geologists, a major eruption of Long Valley Caldera in the next 100 years is extremely unlikely – and more probable in several thousand years.
What are indicators for volcanic activity?
Common precursory indicators of volcanic activity include increased seismicity, ground deformation, and variations in the nature and rate of gas emissions.
Although a major eruption in the next 100 years is extremely unlikely at the Long Valley Caldera in California, its present quantity of magma would release 140 cubic miles of material into the atmosphere. And it is continuously filling up! To put this into persperctive, the 1980 Mount St. Helens eruption resulted in the release of 0.29 cubic miles. Are you ready?
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