Recent history of Mount St. Helens in southwestern Washington, as provided by Mount St. Helens National Volcano Monument and the U.S. Geological Survey:

1979 - The mountain is a recreational haven. Half a million people a year visit the Spirit Lake area below the cone-shaped, 9,677-foot summit.

March 1980 - The volcano begins to show signs of unrest. Earthquakes and steam eruptions continue for several weeks.

8:32 a.m., May 18, 1980 - A 5.1-magnitude earthquake about a mile below the summit triggers a massive eruption and landslide, flattening 230 square miles of forest northwest of the summit and killing 57 people. A plume of ash extends 15 miles into the sky and coats towns 250 miles away.

Summer 1980-October 1986 - Repeated minor eruptions build a 925-foot-tall dome of hardened lava inside the crater left by the eruption.

1982 - Congress and President Reagan create the 110,000-acre Mount St. Helens National Volcanic Monument for research, recreation and education. Inside the monument, the environment is left to respond naturally to the disturbance.

1990-present - Steady progression in the variety and number of plants and animals returning to the blast zone.

1998 - First major seismic activity since 1986, with earthquakes located as deep as 6 miles forcing magma to within about a mile of the dome, scientists believe.

2001 - Another flurry of small earthquakes, but once again, no magma surfaces.

Sept. 23, 2004 - The first of thousands of tiny, shallow earthquakes are recorded at St. Helens.

Sept. 26 - The U.S. Geological Survey declares a notice of volcanic unrest, closing the crater and upper flanks of the volcano to hikers and climbers.

Sept. 29 - Earthquakes increase to about four per minute, ranging in magnitude from 2.0-2.8. The USGS raises its warning system to the third of four levels and warns that a blast could send rocks and ash three miles from the summit.

Oct. 1 - Mountain briefly belches a plume of smoke and ash. Quakes subside, but resume a short time later. Four more steam and ash explosions occur through Oct. 5.

Oct. 5 - Ashfall from explosion affects populated areas. A light dusting of ash extended north-northeast as far as 60 miles to the northeast part of Mount Rainier National Park.

Oct. 11 - Molten rock reaches the surface, marking a new period of dome-building that had stopped in 1986.

Jan. 16 - An explosion destroyed a camera and some measuring equipment that had been placed in the crater two days earlier. The blast was on a similar scale to explosive events in early October.

March 8 - An explosion shot gritty volcanic ash to about 36,000 feet.

May 6 - Johnston Ridge Observatory, five miles from the mountain, reopened. It had been closed since Oct. 2.

May 18 - 25th anniversary of 1980 eruption.

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Sources: U.S. Geological Survey,

U.S. Forest Service