Hi All. 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 most intense of these swarms began in May 1980 and included four strong magnitude 6 shocks, three of which struck on the same day. Dr. Bruce Julian later identified these four quakes as non-double-couple quakes although not everyone is in agreement with this. 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 unrest—a 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.
An interesting episode of seismic activity in the Long Valley region followed the 28 June 1992 Landers earthquake (M 7.4) in southern California, 400 km south of Long Valley Caldera. Local increases in seismicity triggered by the Landers earthquake were also recognized in the Geysers geothermal area and in Yellowstone National Park, over 1,200 km from the epicenter. A series of 60 long-period earthquakes began beneath the SW flank of Mammoth Mountain during a mid-1989 earthquake swarm, and continued through 1993. These events lacked significant energy at frequencies above 5 Hz, distinguishing them from the much more common volcano-tectonic earthquakes. What this indicates is that the quakes were caused by the movement of magma.
The one thing that has to be kept in mind is that everytime the magma moves towards the surface it removes a little bit of the wall that supports the dome. When it reaches a point that the dome is to large to be supported by the surrounding walls it will collapse into the magma beneath it. Its sort of like a large sink hole.
As of right now the hottest area, or spot is under Mammoth Mountain. This also the area of the tree kill.
One other tid bit of information. As of the report given Sunday afternoon 17 Dec. 2000 at the AGU, the resugent dome is desending although the amount was not given. This may be nothing more then a cycle its going through, or it could be the beginning of the collapse. Take Care…Don in creepy town.