A series of earthquakes inside Long Valley Caldera , coincidentally starting two weeks after the May 1980 eruption of Mount St. Helens in Washington , alerted geologists to the possibility of renewed volcanic activity in the region . Four magnitude 6 earthquakes struck the southern margin of Long Valley Caldera in an area that was close to the Mono – Inyo fissure system . The caldera floor had also uplifted by in five years . Upward movement of magma under the caldera was thought to be the cause of the earthquakes and uplift
1980 eruption of Mount St. Helens
1980 eruption of Mount St. Helens
Mono–Inyo Craters