Portal:Oregon/Selected article/22

The 1980 eruption of Mount St. Helens was the most significant volcanic eruption to occur in the lower 48 states of the United States in recorded history. The eruption was preceded by a two-month long series of earthquakes and steam venting episodes that created a huge bulge and a fracture system on Mount St. Helens' north slope. An earthquake on May 18, 1980 caused the entire weakened north face to slide away, suddenly exposing the partly molten, gas and steam-rich rock in the volcano to lower pressure. The rock responded by exploding into a super-heated mix of pulverized lava and older rock that sped toward Spirit Lake so fast that it quickly passed the avalanching north face. By the time the ash settled and the lahars stopped advancing, 57 people were dead, many thousands of animals were killed, hundreds of square miles were reduced to a wasteland, and over a billion U.S. dollars in damage was done. Additionally, large mud flows created by the blast flowed into area rivers and made their way to the Columbia River. This resulted in 13-foot (4 m) river depths on the Columbia, and temporarily closed the busy channel to ocean-going freighters, costing Portland an estimated five million US dollars. Portland mayor Connie McCready eventually threatened local businesses with fines if they failed to remove the ash that had accumulated from three blasts from their parking lots.