An Introduction to Mount St. Helens
Mount St. Helens is one of the Pacific Northwest's many volcanic peaks. Part of what is known as the Pacific Rim or the Pacific Ring of Fire, Mount St. Helens is famous because of its recent and continuing activity. Mount St. Helens is part of the Cascade Mountain Range in the state of Washington, about midway between Seattle and Portland.
The mountain itself, along with the surrounding blast zone, has been preserved as Mount St. Helens National Volcanic Monument. The landscape within the monument is being allowed to take its own course to recovery, creating a fascinating learning experience for both scientists and the public. Visitors to Mount St. Helens National Volcanic Monument will find several interesting visitor centers and a multitude of amazing views.
Sequence of Events Leading Up to the Eruption
Mount St. Helens erupted at 8:32 a.m. PST on May 18, 1980, reminding Pacific Northwest residents and people around the world of the powerful and uncontrollable forces of nature. Physical effects of the eruption were experienced in dozens of U.S. states, with ash falling as far away as Oklahoma.
Accompanying the volcanic eruption was a 5.1 magnitude earthquake, an avalanche of rocks, mud, and debris covering a 24-square-mile valley, and a plume of ash and pumice.
Two months before the eruption, on March 15, 1980, Mount St. Helens began to experience a period of low-level seismic activity that escalated over the next couple months.
- March 15 to 19, 1980: A number of very small earthquakes are recorded, but are not recognized as immediate precursors to possible volcanic activity.
- March 20, 1980: A magnitude 4.1 earthquake, unlike any that had been previously detected in the area, occurred just northwest of the summit of Mount St. Helens. Seismologists were uncertain as to whether or not these first earthquakes were related to volcanic activity. They decided to deploy additional seismometers in order to better monitor future activity.
- March 27 to April 18, 1980: Earthquakes and steam-driven explosions occur off and on during this period.
- April 29, 1980: State officials asked the governor to close a large area around the volcano. The plan called for a red zone (no public access) and a blue zone (restricted access). Emergency services officials are frustrated because the public appeared to remain unaware of the danger.
- May 7 to 13, 1980: Small explosions of steam and ash are emitted from the volcano. Intermittent earthquakes occur up to a magnitude of 4.9.
- May 17, 1980: Law enforcement officials escorted about 50 carloads of property owners into the red zone to retrieve possessions.
Impact of the 1980 Eruption
The impacts of the 1980 eruption of Mount St. Helens reached far and wide with a loss of life, property, flora, and fauna. Some of the measurable effect included:
- Mount St. Helens was reduced by over 1,300 feet in height
- Volcanic ash fell as far as 930 miles away
- The debris avalanche and mudflows buried the Toutle valley to a depth of almost 165 feet deep
- The eruption lasted for 9 hours
- 57 people lost their lives, or are still considered missing
- 250 square miles of land was damaged
- Estimates are 7,000 big game animals and millions of birds, fish, and small mammals were killed
- Minor eruptions continued into 1986
Recent Mount St. Helens Activity
Just when you start to think Mount St. Helens is settling down, the volcano vents or rumbles. Take a look at a timeline of recent Mount St. Helens' activity.
- 2005 to present: Mount St. Helens continues to experience low rates of seismic activity, low emissions of steam and volcanic gases, minor production of ash, and the growth of a new lava dome inside the crater.
- March 8, 2005: The Mount St. Helens volcano experienced a small explosive event, with the resulting steam-and-ash plume reaching an altitude of approximately 36,000 feet above sea level.
- January 16, 2005: Explosive eruption that scattered ash and rocks as large as 3 feet in the crater and ash eastward onto the volcano's east side.
- October 11, 2004 to present: A new and distinctive lava dome became evident; it continues to grow and change.
- October 5, 2004: The most vigorous steam-and-ash eruption since the start of unrest. It lasted over one hour. The ash rose to about 12,000 feet and drifted north-northeastward. A light ash dusting fell in the towns of Morton, Randle, and Packwood, about 30 miles away. A light dusting affected the east side of Mount Rainier National Park, 70 miles north-northeast.
- October 1, 2004: A small steam eruption with minor ash issued from a vent just south of the 1980-86 lava dome.
- September 23-25, 2004: A swarm of small, shallow earthquakes (smaller than magnitude 1) began on morning of September 23, peaked in midday on September 24, then declined through the afternoon of September 25.
Historical Mount St. Helens Activity
As mountains go, Mount St. Helens is young. The volcano's oldest known deposits erupted about 50,000 to 40,000 years ago, and the cone that partly collapsed in 1980 is only 2,200 years old. Some Indians of the Pacific Northwest variously called Mount St. Helens "Louwala-Clough," or "smoking mountain." The modern name, Mount St. Helens, was given to the volcanic peak in 1792 by Captain George Vancouver of the British Royal Navy, a seafarer and explorer. He named it in honor of a fellow countryman, Alleyne Fitzherbert, who held the title Baron St. Helens and who was at the time the British Ambassador to Spain. Vancouver also named three other volcanic mountains in the Cascades—Baker, Hood, and Rainier—for British naval officers.
Here are the highlights of Mount St. Helens activity over the last 2,000 years:
- Goat Rocks Eruptive Period (approximately 1800 A.D.): This eruptive period lasted for 100 to 150 years. Known events include ash explosions in 1842, which was followed by the extrusion of the Goat Rocks dome. Contemporary accounts indicate activity several times during the 1840s and 1850s but are non-specific and even contradictory. The last significant activity before 1980 was "dense smoke and fire" in 1857, although minor, unconfirmed eruptions were reported in 1898, 1903, and 1921.
- Kalama Eruptive Period (1479 to 1482 A.D.): This eruptive period included two major ejections of ash, as well as lava flows and dome building.
- Sugar Bowl Eruptive Period (approximately 800 A.D.): Mount St. Helens was reshaped by a combination of dome building, a lateral blast, and pyroclastic flows during this period of volcanic activity.
- Castle Creek Eruptive Period (200 B.C. to 300 A.D.): Major activity during this era included ejections of ash, pyroclastic flows, and lava flows.