Geologic History Summary for Mount St. Helens Active
Mount St. Helens, located in Washington State, is the most active volcano in the Cascade Range, and it is the most likely of the contiguous U.S. volcanoes to erupt in the future.
The volcano is almost 53 km (33 mi) due west of Mount Adams and approximately 80 km (50 mi) northeast of the Vancouver, Washington—Portland, Oregon metropolitan area. Volcanism occurs at Mount St. Helens and other volcanoes in the Cascades arc due to subduction of the Juan de Fuca plate off the western coast of North America.
Over its rich and complex 275,000-year history, Mount St. Helens has produced both violent explosive eruptions of volcanic tephra and relatively quiet outpourings of lava. In the beginning stages of eruptive activity, the volcano mostly consisted of a cluster of domes that was surrounded by an apron of tephra and debris fans of fragmented volcanic rocks.
It was only during the past few thousand years that the volcano grew to its pre-1980 elevation of 2,950 m (9,677 ft), making it the, then, fifth highest peak in Washington. Starting about 3,000 years ago, substantial amounts of basalt and andesite began to erupt as lavaflows between phases of dacite eruptive activity. These lava flows buried large parts of a central cluster of dacite domes and flanking fans, which started the cone building in earnest.
Based upon detailed chemical analysis of the eruptive products from each stage of Mount St. Helens volcanism, scientists deduce that the volcano's magmatic system has evolved from relatively simple to more complex as the volcano matured. The evidence indicates that interaction between more silicic (dacite) magma batches with more mafic (basalt to andesite) magma increased from the earliest to most recent stages of Mount St. Helens volcanism.
Eruption History of Mount St. Helens through start of Holocene
Holocene Activity Prior to May 18, 1980 Eruption
1980 Cataclysmic Eruption
Explosions and Dome Growth
2004-2008 Renewed Volcanic Activity
Glaciation at Mount St. Helens
Future Eruptions at Mount St. Helens
Lakes and Drainages Around Mount St. Helens
Early-Settlement Documentation of Mount St. Helens
The 2004-2008 Eruption of Mount St. Helens and "What ifs"
- Overview
Mount St. Helens, located in Washington State, is the most active volcano in the Cascade Range, and it is the most likely of the contiguous U.S. volcanoes to erupt in the future.
Sources/Usage: Public Domain. View Media DetailsDigital Elevation Map of Mount St. Helens with annotation of pre-1980 topography and deposits from 1980 - 2008.
Location of magma formation, accumulation, and storage beneath Mount St. Helens (locations are inferred from scientific data). The volcano is almost 53 km (33 mi) due west of Mount Adams and approximately 80 km (50 mi) northeast of the Vancouver, Washington—Portland, Oregon metropolitan area. Volcanism occurs at Mount St. Helens and other volcanoes in the Cascades arc due to subduction of the Juan de Fuca plate off the western coast of North America.
Over its rich and complex 275,000-year history, Mount St. Helens has produced both violent explosive eruptions of volcanic tephra and relatively quiet outpourings of lava. In the beginning stages of eruptive activity, the volcano mostly consisted of a cluster of domes that was surrounded by an apron of tephra and debris fans of fragmented volcanic rocks.
It was only during the past few thousand years that the volcano grew to its pre-1980 elevation of 2,950 m (9,677 ft), making it the, then, fifth highest peak in Washington. Starting about 3,000 years ago, substantial amounts of basalt and andesite began to erupt as lavaflows between phases of dacite eruptive activity. These lava flows buried large parts of a central cluster of dacite domes and flanking fans, which started the cone building in earnest.
Based upon detailed chemical analysis of the eruptive products from each stage of Mount St. Helens volcanism, scientists deduce that the volcano's magmatic system has evolved from relatively simple to more complex as the volcano matured. The evidence indicates that interaction between more silicic (dacite) magma batches with more mafic (basalt to andesite) magma increased from the earliest to most recent stages of Mount St. Helens volcanism.
- Science
Eruption History of Mount St. Helens through start of Holocene
Volcanologists have recognized and named four stages of volcanic activity—Ape Canyon, Cougar, Swift Creek, and Spirit Lake—separated by dormant intervals.Holocene Activity Prior to May 18, 1980 Eruption
Summary of Holocene activity prior to the May 18, 1980 eruption.1980 Cataclysmic Eruption
Magma began intruding into the Mount St. Helens edifice in the late winter and early spring of 1980. By May 18, the cryptodome (bulge) on the north flank had likely reached the point of instability, and was creeping more rapidly toward failure.Explosions and Dome Growth
Explosions and Dome Growth, 1980-1986 and 1989-1991.2004-2008 Renewed Volcanic Activity
The sudden reawakening of Mount St. Helens in late September 2004 was surprising because the preceding four years had seen the fewest earthquakes since the 1980-86 eruption ended.Glaciation at Mount St. Helens
Extensive glaciers covered Mount St. Helens and the surrounding vicinity during major Ice Ages of the past few hundred thousand years. Much of the geologic record of these events is sparse and incomplete, having been removed by erosion or buried by volcanic deposits.Future Eruptions at Mount St. Helens
We know that Mount St. Helens is the volcano in the Cascades most likely to erupt again in our lifetimes. It is likely that the types, frequencies, and magnitudes of past activity will be repeated in the future. However, neither a large debris avalanche nor a major lateral blast like those of May 18, 1980 is likely now that a deep crater has formed.Lakes and Drainages Around Mount St. Helens
Streams that head on the volcano enter three main river systems -- the Toutle River on the north and northwest, the Kalama River on the west, and the Lewis River on the south and east. Lahars can form on any of these.Early-Settlement Documentation of Mount St. Helens
The first documented observation of Mount St. Helens by Europeans was by George Vancouver on May 19, 1792, as he was charting the inlets of Puget Sound at Point Lawton, near present-day Seattle. Vancouver did not name the mountain until October 20, 1792, when it came into view as his ship passed the mouth of the Columbia River.The 2004-2008 Eruption of Mount St. Helens and "What ifs"
Information about the 2004-2008 eruption.