On May 18, 1980, at 8:32 a.m., Mount St. Helens in Skamania County, Washington experienced a catastrophic explosive eruption which had a volcanic explosivity index of 5. It was the first to occur in the contiguous United States since the much smaller 1915 eruption of Lassen Peak in California.[2] The main eruption was preceded by a series of volcanic explosions, pyroclastic flows, and phreatic blasts beginning in March 1980. It has often been considered the most disastrous volcanic event in U.S. history.