Mount St. Helens, like the other volcanoes of the Cascades, is composed of andesitic and rhyolitic pyroclastic materials. Some of the pyroclastic material has been remobilized as landslides and lahars.
What type of rock is Mt 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 type of mountain is Mount Saint Helens?
stratovolcano
Mount St. Helens is a stratovolcano, a steep-sided volcano located in the Pacific Northwest region of the United States in the state of Washington.
What type of magma is 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.
Is Mt St Helens mafic?
Systematic variations in the composition of volcanism over the past several thousand years at Mt. St. Helens imply that the magma chamber is zoned, from more felsic at the top to more mafic at the bottom.
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 the composition of Mount St. Helens?
Volcanic ash samples from the May 18, 1980, Mount St. Helens eruption were analyzed for major, minor, and trace composition by a variety of analytical techniques. Results indicate that the basic composition of the ash consists of approximately 65% SiO2, 18% Al2O3, 5% FetO3, 2% MgO, 4% CaO, 4% Na2O, and 0.1% S.
Is Mount St. Helens basaltic?
Mount St. Helens volcano has intermittently produced mainly dacitic products but occasionally erupted a more diverse suite of lavas including basalts and andesites. Petrogenetic relations between these magmas provide insight into the dynamics of the subjacent magma system.
What makes Mt. St. Helens unique?
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.
What is St Helens classed as?
St Helens ( pronunciation (help·info)) is a town in Merseyside, England, with a population of 102,629. It is the administrative centre of the Metropolitan Borough of St Helens, which had a population of 176,843 at the 2001 Census.
What type of magma is associated with the Mount St. Helens eruption in 1980?
dacite magma
By the time of the climactic eruption, dacite magma intruding into the volcano had forced the north flank outward nearly 500 ft (150 m) and heated the volcano’s groundwater system, causing many steam-driven explosions (phreatic eruptions).
What type of volcano is Mt. St. Helens quizlet?
Mount St. Helens is an active stratovolcano located in Skamania County, Washington, in the Pacific Northwest region of the United States.
What type of eruption is Mt Helens?
explosive pyroclastic eruptions
Mt. St. Helens typically generates explosive pyroclastic eruptions, in contrast to many other Cascade volcanoes, such as Mt. Rainier which typically generates relatively non-explosive eruptions of lava.
What volcanoes are mafic?
Mafic lava flows can travel quite far before solidifying completely, and the type of volcano that forms from mafic lava is called a shield volcano (Figure 9.9). Shield volcanoes are very broad at the base and have relatively gentle slopes.
Are volcanoes mafic or felsic?
Explosive Eruptions
They will probably describe great explosions and towering ash clouds. The volcanoes that produce this kind of eruption are powered by felsic magma. Felsic magma forms at lower temperatures and has a different chemical composition than mafic magma (see table above for comparison).
What type of volcano is felsic and mafic?
So mafic/basaltic volcanoes are fairly quiescent, intermediate/andesitic volcanic eruptions are moderately explosive, and felsic/rhyolitic volcanoes may be extremely explosive. So, mafic lavas are hot , low in silica and volatiles, and have relatively low viscosity.
What made Mt St Helens explode?
On the morning of May 18, 1980, after weeks of small tremors, a magnitude 5.1 earthquake shook beneath Mount St. Helens and triggered an enormous eruption.
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.
How was Mt Helens formed?
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.
Does Mount St. Helens have high silica content?
Mount St. Helens has the highest average silica content at 64 percent. For more information about magma, visit the Magma Mash activity and the Internet Resources Page.
Is Mount St. Helens bigger than Yellowstone?
The three caldera-forming eruptions at Yellowstone (2.1 million years ago, 1.3 million years ago, and 640,000 years ago), were respectively about 2,500, 700, and 1,000 times larger than the 1980 eruption of Mt. St. Helens in the state of Washington.