JC, we were discussing Western US volcanoes, and large scale permanent future evacuations. What you had to say about the Mammoth area is intriguing.
Living With a Restless Caldera - Long Valley, California
Scientists have monitored geologic unrest in the Long Valley, California, area since 1980. In that year, following a swarm of strong earthquakes, they discovered that the central part of the Long Valley Caldera had begun actively rising. Unrest in the area persists today. The U.S. Geological Survey (USGS) continues to provide the public and civil authorities with current information on the volcano hazards at Long Valley and is prepared to give timely warnings of any impending eruption.
In the 1850's, gold fever brought the first waves of European settlers through the Long Valley area of eastern California. Today, thousands of visitors are attracted to the area year round by the spectacular mountain scenery of the eastern Sierra Nevada. This landscape has been sculpted over the past 4 million years by glaciers, earthquakes, and volcanic eruptions.
Long Valley Caldera in eastern California Long Valley Caldera in eastern California (here viewed from its southwest rim toward its northeast rim on the horizon 18 miles away) was formed about 760,000 years ago in a violent volcanic eruption that blew out 150 cubic miles of magma (molten rock) from beneath the Earth's surface. U.S. Geological Survey scientists are tracking continuing dome-like swelling centered in the low forested hills in the middle of the caldera. This swelling affects more than 100 square miles and is caused by magma rising beneath the Earth's surface. (USGS photo by Roy Bailey)
About 760,000 years ago a cataclysmic volcanic eruption in the area blew out 150 cubic miles of magma (molten rock) from a depth of about 4 miles beneath the EarthÕs surface. Rapidly moving flows of glowing hot ash (pyroclastic flows) covered much of east-central California, and airborne ash fell as far east as Nebraska. The EarthÕs surface sank more than 1 mile into the space once occupied by the erupted magma, forming a large volcanic depression that geologists call a caldera.
map of the Long Valley Caldera showing distribution of volcanic rocks
aerial view of Long Valley Caldera, eastern California
Much of the Long Valley area of eastern California is covered by rocks formed during volcanic eruptions in the past 2 million years. A cataclysmic eruption 760,000 years ago formed Long Valley Caldera and ejected flows of hot glowing ash(pyroclastic flows), which cooled to form the Bishop Tuff. Wind-blown ash from that ancient eruptionówhich was more than 2,000 times larger than the 1980 eruption of Mt. St. Helens, Washington, that killed 57 people and caused several billion dollars in damage&emdash;covered much of the Western United States. The photo shows a volcanic cone (Panum Dome) formed by eruptions about 600 years ago at the north end of the Mono Craters. The most recent volcanic eruptions in the area occurred in Mono Lake sometime between the mid-1700's and mid-1800's.
Today, Long Valley occupies the eastern half of this 10-mile-wide, 20-mile-long caldera. Magma still underlies the caldera and heats underground water. The heated water feeds local hot springs and natural steam vents and drives three geothermal power plants, producing a combined 40 megawatts of electricity.
The Long Valley Caldera is only one part of a large volcanic system in eastern California that also includes the Mono-Inyo Craters volcanic chain. This chain extends from Mammoth Mountain at the southwest rim of the caldera northward 25 miles to Mono Lake. Eruptions along this chain began 400,000 years ago, and Mammoth Mountain itself was formed by a series of eruptions ending 50,000 years ago. The volcanic system is still active. Scientists have determined that eruptions occurred in both the Inyo Craters and Mono Craters parts of the volcanic chain as recently as 600 years ago and that small eruptions occurred in Mono Lake sometime between the mid-1700's and mid-1800's.
Although no volcanic eruptions are known to have occurred in eastern California since those in Mono Lake, earthquakes occur frequently. These earthquakes are caused by movement along faults and by the pressure of magma rising beneath the Earth's surface, two closely related geologic processes. In 1872, the magnitude 7.6 Owens Valley earthquake was felt throughout most of California, and a number of moderate (magnitude 5 to 6) earthquakes have shaken the Long Valley area during this century.
A period of ongoing geologic unrest in the Long Valley area began in 1978, when a magnitude 5.4 earthquake struck 6 miles southeast of the caldera. This temblor ended two decades of low quake activity in eastern California. The area has since experienced numerous swarms of earthquakes, especially in the southern part of the caldera and the adjacent Sierra Nevada.
Map of seismicity and uplift in Long Valley Caldera Earthquake activity in the Long Valley area of eastern California increased greatly after 1978. This volcanically active area is located along the major faults (black lines) that form the eastern edge of the Sierra Nevada. The quake activity is caused by two closely related geologic processesómovement along faults and the pressure of magma (molten rock) rising beneath the Earth's surface. Following four strong magnitude 6 shocks in May 1980, the U.S. Geological Survey (USGS) detected dome-like swelling in the middle of Long Valley Caldera (inset graph). In response to these signs of renewed volcanic unrest, USGS scientists intensified their monitoring of the Long Valley area.
The most intense of these swarms began in May 1980 and included four strong magnitude 6 shocks, three of which struck on the same day. Immediately following these shocks, scientists from the U.S. Geological Survey (USGS) began a reexamination of the Long Valley area and detected other evidence of unrestóa dome-like uplift in the caldera. Their measurements showed that the center of the caldera had risen almost a foot since the summer of 1979, after decades of stability. This continuing swelling, which by early 2000 totaled nearly 2.5 feet and affects more than 100 square miles, is caused by new magma rising beneath the caldera.
In response to this escalating geologic unrest, the USGS intensified its monitoring program in the Long Valley Caldera and Mono-Inyo Craters volcanic system. An expanded network of seismometers installed in 1982 closely monitors earthquake activity in the area, and other instruments track the continuing swelling in the caldera. Data from these instruments help scientists to assess the volcano hazards in the Long Valley area and to recognize the early signs of possible eruptions. In cooperation with the California Office of Emergency Services and civil authorities in eastern California, the USGS has established procedures to promptly alert the public to a possible eruption.
Today there is a warning for aircraft over an eruption in the Aleutian Islands.
(CNN)A volcanic eruption Sunday prompted the temporary raising of the highest aviation alert, the Alaska Volcano Observatory (AVO) said Sunday.
The event, which took place on Alaska's Bogoslof Island, part of the Aleutian island chain, caused the issuance of a code "red" aviation alert, which was subsequently downgraded to "orange."
The cloud from the eruption reached at least 35,000 ft., and possibly as high as 45,000 ft., the Observatory said.
"We actually went to color code red this afternoon because of numerous lightning detections and increased seismic signals," Jeffrey Freymueller of the Geophysical Institute at the University of Alaska, Fairbanks tells CNN.