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.
What is the composition of Mt. 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 Mt. St. Helens mafic or felsic?
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.
Does Mt. St. Helens have magma?
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.
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 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.
What type of magma erupted from Mt St Helens?
The range of rock types erupted by the volcano changed about 2,500 yr ago, and since then, Mount St. Helens repeatedly has produced lava flows of andesite, and on at least two occasions, basalt.
What type of magma is felsic?
Felsic refers to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium. Felsic magma or lava is higher in viscosity than mafic magma/lava. Felsic rocks are usually light in color and have specific gravities less than 3.
What is felsic and mafic magma?
Mafic magmas are low in silica and contain more dark, magnesium and iron rich mafic minerals, such as olivine and pyroxene. Felsic magmas are higher in silica and contain lighter colored minerals such as quartz and orthoclase feldspar. The higher the amount of silica in the magma, the higher is its viscosity.
What is mafic magma?
Describes magma that contains lower amounts of silica and is generally less viscous and less gas-rich than silicic magma. Tends to erupt effusively, as lava flows. Includes andesites (57-63 percent SiO2), basaltic andesites (53-57 percent SiO2), and basalts (47-53 percent SiO2).
How much magma is released during the eruption of Mt. St. Helens?
Mount St. Helens is located on the state of washington. 3: How much magma is released during the eruption? Over a million tons of magma were released during the eruption.
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.
How viscous is Mt. St. Helens lava?
St. Helens has been studied experimentally and found to have a viscosity that declines from about 1015 at 800°C to 103 poise at 1500°C. Its yield strength declines from about 2 × 106 dynes cm−2 at 800°C to less than the precision of our measurements (104 dynes cm−2) above 1050°C.
Is Mt. St. Helens composite or shield?
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.
Is Mt. St. Helens rhyolitic?
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 igneous rock is at Mt. St. Helens?
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 magma is Vulcanian?
A Vulcanian eruption is a short, violent, relatively small explosion of viscous magma (usually andesite, dacite, or rhyolite). This type of eruption results from the fragmentation and explosion of a plug of lava in a volcanic conduit, or from the rupture of a lava dome (viscous lava that piles up over a vent).
Why is silica rich magma explosive?
Answer and Explanation: Silica-rich magma is highly explosive because the gases within the magma build up within the highly viscous magma and burst when pressure is too great. Viscosity is defined as the stickiness or thickness of a liquid when flowing, and silica can create this stickiness within magma.
Is Mt. St. Helens a lava dome?
A steep lava dome (dark area just left of center) is swelling rapidly inside the crater of Mount St. Helens, next to an older dome that emerged after the volcano erupted in 1980.
What types of magma are erupted from the volcanoes?
There are three basic types of magma: basaltic, andesitic, and rhyolitic, each of which has a different mineral composition.
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.