On May 18, 1980 Mount St. Helens erupted in Skamania County, Washington. For two months prior to the explosion, a series of earthquakes continually rocked Washington state while St. Helens spewed steam. It was obvious that the volcano was going to erupt, but it was just a question of when. At 8:32 a.m., a magnitude 5.1 earthquake that came from directly beneath the mountain triggered the largest rockslide in history.
Following the landslide, a gas charged, partially molten rock and high pressure blast of steam exploded out of the mountain, following a series of smaller bursts that spewed ash and pumice as lava flowed freely from the mountain. The destruction cost nearly $1.1 billion.