Mount St. Helens 1980 Eruption

On May 18, 1980, Mount St. Helens erupted. At 8:32 am PDT, a magnitude 5 earthquake occurred inside of the north flank of the volcano, leading to the first of three massive landslides that ‘uncorked’ the pent-up magma.  Nine hours of a continuous large Plinian eruption column followed.  Since the eruption, we have learned that Mount St. Helens has done this sort of thing fairly often; more than 200 discreet ash layers are associated with Mount St. Helens eruptions within the last 10,000 years, several much larger than the May 18 event.