Mt St Helens is a major stratovolcano in the Cascades Range, all of which have formed as a result of the ongoing subduction of the Juan de Fuca tectonic plate beneath the western coast of North America. Prior to 1980, Mt St Helens was a classical cone-shaped volcano, and a well-visited site on the tourist trail.
How is Mount St. Helens formed?
Quick Facts. Mount St. Helens is primarily an explosive dacite volcano with a complex magmatic system. The volcano was formed during four eruptive stages beginning about 275,000 years ago and has been the most active volcano in the Cascade Range during the Holocene.
What plates caused Mt St Helens to form?
In Mount St. Helens’ case, an oceanic plate called Juan de Fuca slips under the North American plate, creating the Cascadia subduction zone. A continental arc brews adjacent to the subduction zone, where high pressures and hot temperatures force molten rock to the surface. The result is a chain of volcanoes.
When was the Mount St. Helens formed?
According to the U.S. Geological Survey (USGS), Mount St. Helens began growing before the end of the Ice Age; its oldest ash deposits date to at least 40,000 years ago. Yet the visible portion of the volcano—the cone—is much younger. Geologist believe it formed over the last 2,200 years.
What are 5 interesting facts about Mt St Helens?
Here are five facts about the stratovolcano.
- Before erupting, the volcano was 9,677 feet.
- Over 230 square miles of forest was destroyed in minutes.
- The volcano has had numerous eruptions.
- The blast killed USGS scientist David Johnston.
- Native Americans abandoned hunting grounds at the volcano 3,600 years ago.
What caused Mount St. Helens explosion?
A wave of decreasing pressure down the volcanic conduit to the subsurface magma reservoir, which then began to rise, form bubbles (degas), and erupt explosively, driving a 9-hour long Plinian eruption. Steam-blast eruption from summit crater of Mount St. Helens.
What is Mt St Helens made of?
Mount St. Helens is an example of a composite or stratovolcano. These are explosive volcanoes that are generally steep-sided, symmetrical cones built up by the accumulation of debris from previous eruptions and consist of alternating layers of lava flows, volcanic ash and cinder.
What is under Mt St Helens?
Geoscientists have for the first time revealed the magma plumbing beneath Mount St. Helens, the most active volcano in the Pacific Northwest. The emerging picture includes a giant magma chamber, between 5 and 12 kilometers below the surface, and a second, even larger one, between 12 and 40 kilometers below the surface.
Is Mt St Helens still active?
Mount St. Helens is the most active volcano in the contiguous United States, which makes it a fascinating place to study and learn about.
Why is it called St Helens?
The modern name, Mount St. Helens, was given to the volcanic peak in 1792 by seafarer and explorer Captain George Vancouver of the British Royal Navy. He named it in honor of fellow countryman Alleyne Fitzherbert, who held the title ‘Baron St. Helens’.
How many died Mount St. Helens?
Fifty-seven people
Fifty-seven people were killed when Mount St. Helens erupted on May 18, 1980. It is the deadliest volcanic eruption in U.S. history.
Did Mt St Helens have lava?
Lava flows from Mount St. Helens typically affect areas within 6 mi (10 km) of the vent. However, two basalt flows erupted about 1,700 years ago extended about 10 mi (16 km) from the summit; one of them contains the Ape Cave lava tube.
What famous person died in Mt St Helens?
| Harry R. Truman | |
|---|---|
| Truman near his lodge in 1980, a few months before his death | |
| Born | October 30, 1896 Ivydale, West Virginia, U.S. |
| Died | May 18, 1980 (aged 83) Mount St. Helens, Washington, U.S. |
| Occupation | Bootlegger, prospector, caretaker of the Mount St. Helens Lodge |
What killed the most people in Mt St Helens?
asphyxiation
Fifty-seven people died when Mount St. Helens erupted in Washington on May 18, 1980 at 8:32 a.m. Autopsies showed that most of the people killed in the eruption likely died from asphyxiation after inhaling hot ash, according to the U.S. Geological Survey.
Why is Mt St Helens so unique?
1—During the past 4,000 years, Mount St. Helens has erupted more frequently than any other volcano in the Cascade Range. 2—Most of Mount St. Helens is younger than 3,000 years old (younger than the pyramids of Egypt).
Will Mt St Helens ever erupt again?
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.
What happened to all the ash from Mt St Helens?
Much of the ash went to what is now Chesterley Park, out by North 40th Avenue, where it was piled up, with soccer fields eventually built over the entombed ash.
How tall was Mt St Helens before blowing?
9,677 feet
Height: Summit elevation now approximately 8,300 feet. Original height before eruption, 9,677 feet.
What rock is St Helens made of?
Like most other volcanoes in the Cascade Range, Mount St. Helens is a great cone of rubble consisting of lava rock interlayered with ash, pumice and other deposits. The mountain includes layers of basalt and andesite through which several domes of dacite lava have erupted.
What kind of lava was Mt St Helens?
The basalt magma erupted by Kīlauea contains about 52% silica and about 0.5 % water while the dacite lava erupted by Mount St. Helens in 1980 contained more of both: about 64% silica and about 4% water.
How old is St Helens?
The eruptive history of Mount St. Helens began about 40,000 years ago with dacitic volcanism, which continued intermittently until about 2,500 years ago.