1800s: Mount St. Helens erupts explosively in 1800; intermittently from 1831 to 1857; then enters a 123-year quiet phase.
March 1980: Magnitude 4.1 earthquake signals reawakening. Eruption of ash and steam March 27, opening a 250-foot crater.
May 1980: Swelling on the north face creates an ominous bulge. Hundreds of earthquakes shake the mountain.
8:32 a.m. May 18, 1980: St. Helens' eruption, with its lateral blast, debris avalanche, mudflows and floods, claims 57 lives and obliterates virtually everything within an eight-mile radius. An ash column rises 15 miles and travels east at 60 mph, circling the globe in two weeks.
June-October 1980: Continuing eruptions destroy a lava dome inside the crater. A new dome forms.
September 1980: Weyerhaeuser Co. begins salvaging some of the 62,000 acres of timber and young plantations damaged by the blast.
Aug. 27, 1982: President Reagan signs a bill establishing the 110,000-acre Mount St. Helens National Volcanic Monument.
1987: Volcano summit reopened to recreational climbing.
1987: U.S. Army Corps of Engineers builds a dam to hold back sediment carried downstream by the North Fork of the Toutle.
1994: The reconstructed 52-mile-long Spirit Lake Memorial Highway opens to traffic, connecting Castle Rock to stunning viewpoints in the blast zone.
1997: The U.S. Forest Service opens the Johnston Ridge Observatory five miles from the crater.
Sept. 23, 2004: The mountain stirs with a flurry of earthquakes.
Oct. 2, 2004: Sustained tremors inside the mountain indicate movement of magma. The Forest Service evacuates visitors from Johnston Ridge Observatory.
Oct. 11, 2004: Lava emerges on the crater surface for the first time in 18 years.
Nov. 5, 2004: New dome reaches 26 million cubic yards.
Jan. 16, 2005: A 17-minute explosive eruption destroys instruments inside the crater.
March 8, 2005: The mountain sends ash and steam to an altitude of 36,000 feet, wowing spectators just before sunset.'
Early 2008: Dome-building slows to a halt and seismic activity drops.
July 13, 2008: Scientists declare that the 2004-2008 eruption has ended after building a new, 125-million-cubic-yard lava dome.