Magmatic unrest at Long Valley Caldera, California, 1980-1990

On May 25, 1980, the resort town of Mammoth Lakes, California, was shaken by a remarkable 48-hour-long earthquake sequence that included four M=6, two M=5 and 300 M=3 quakes. The nature of the precursory seismicity plus the unusual character of the May 25-27 sequence itself suggested that it was not typical of tectonic earthquakes in the region. Discovery of 25 cm of domical uplift centred on the resurgent dome within Long Valley caldera strongly implied that this activity was accompanied, if not caused, by influex of magma into the Long Valley magma chamber. -Authors