What type of rocks are found at mount st helens?

Answer 1

Mount St. Helens is a composite volcano or a stratovolcano. The layers of a stratovolcano are rhyolite, dacite and andesite. The fact that all three of these rocks are igneous in origin should be on no great surprise; volcanoes are magmas (molten rocks) that are extruded onto the surface of the Earth. Any metamorphism would be contact metamorphism and would be concealed in walls of the magma chamber under the volcano.

Answer 2

Mt St Helens Rock Type

Answer 3

I don't think "volcanic" is an actual type of rock. How 'bout "Igneous"?

Igneous rocks (etymology from latin ignis, fire) are rocks formed by solidification of cooled magma (molten rock), with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. This magma can be derived from partial melts of pre-existing rocks in either the Earth's mantle or crust. Typically, the melting is caused by one or more of the following processes — an increase in temperature, a decrease in pressure, or a change in composition. Over 700 types of igneous rocks have been described, most of them formed beneath the surface of the Earth's crust.

Answer 4

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Mid- to low- silica felsic rock (granitic and viscous). Specifically, dacite rock was formed. But for more information about the (primary) eruption itself... The eruption began during a relatively quite period in which no steam explosions had occurred for four days. On May 18, at 8:32 a.m., a 5.0-M earthquake triggered a very rapid series of events. The entire northern slope above the bulge failed and the north flank of the volcano began to slide downward from almost the exact site of the east-west fracture at the summit. This gigantic landslide released a tremendous mass from above the hydrothermal system that had driven the precursor steam eruptions. The abrupt loss of confining pressure above the heated groundwater caused a massive flashing to steam, which initiated a hydrothermal blast that was directed laterally through the landslide scarp. The lateral hydrothermal blast rapidly overtook the avalanche and devastated a fan-shaped area to the north, which was nearly 30 km wide over a distance of 20 kilometers. Trees were blown down like matchsticks. The debris avalanche partly filled Spirit Lake, raising the lake bed more than 60 m and doubling the size of the shoreline. However, the bulk of the avalanche entered the North Fork of the Toutle River and flowed 23 km westward to fill the valley with a craggy and hummocky deposit. The length of the avalanche makes it one of the world's largest ever recorded. The debris avalanche incorporated a significant amount of water, which resulted in voluminous lahars later in the day. These flowed down the North Fork of the Toutle River across the avalanche deposit, and continued downstream as far as the Cowlitz River. The avalanche and lateral blast unloaded a large volume of material sitting above the shallow magma source beneath the north-flank bulge. Pressure-release caused the magma to de-gas violently, and within a few minutes a Plinian eruption column began to rise from the former summit. In 10 minutes it had risen to a height of 20 km, where it spread into a umbrella region driven by high-level winds to the east-northeast. Significant ashfall deposits were produced as far as the Great Plains and minor ash was found even much farther east. As the Plinian eruption grew, it continued to ream out the volcanic conduit. The combined destructive forces of the avalanche, the lateral blast, and the Plinian eruption, resulted in the development of a huge amphitheater (1.5 x 3 km) along the volcano's northern flank. The Plinian eruption lasted for 9 hours. In addition to airfall, the Plinian phase was associated with numerous pyroclastic flows from column collapse. Most of these were directed toward the north and deposited as pumiceous ignimbrites above the avalanche deposit. Some of these pyroclastic flows extended into Spirit Lake and down the North Fork of the Toutle River. The heat provided by the flows resulted in secondary steam explosions that formed large craters (20m in diameter) with ash columns as high as 2000 m. Smaller magmatic eruptions followed the main Plinian blast on May 25, June 12, July 22, and October 16-18. Each of these subsequent events lasted several hours and produced eruptive columns more than 10 kilometers high. Degassing of the source magma in the underlying magma reservoir resulted in the waning of Plinian-type eruptions. The pastey magma left in the central conduit, and in magma chamber below it, became increasingly less volatile. Shortly after the June 12 eruption, this residual viscous magma began to rise through the vent crater to form a lava dome. The dome was most likely rising into the central conduit even before the June 12 eruption, but was not yet visible. An indication of this is in the nature of the pyroclastic flows associated with the June 12 eruption. Previous flows (on May 18 and May 25) were pumice-rich ignimbrites produced by column collapse. However, the June 12 flows were block-and-ash flows containing abundant non-vesiculated blocks of dense, gray dacite. These pyroclastic-flow types are typically deposited by nuée ardentes, which are generated by dome collapse. The dome that began to form on June 12 was partly destroyed by the July 22 eruption, was rebuilt, and then partly destroyed again during the October 16-18 eruption. Thus, after each eruption viscous magma rose up the conduit to build a new dome and replug the vent. In total there were three domes (the first two largely destroyed by the July 22 and October 16-18 eruptions. The dome generated after the October 16-18 eruptions grew at impressive rates through 1983.

Answer 5

Lindajune is correct but those can be a variety of types, like obsidian, (volcanic glass) and pumice as well as a variety of solidified lavas.

I will also agree with Nash that we are talking mostly about igneous but there are some forms of metamorphic rocks that can be created by volcanic heat and pressure.

"Metamorphic rocks make up a large part of the Earth's crust and are classified by texture and by chemical and mineral assemblage (metamorphic facies). They may be formed simply by being deep beneath the Earth's surface, subjected to high temperatures and the great pressure of the rock layers above. They can be formed by tectonic processes such as continental collisions which cause horizontal pressure, friction and distortion. They are also formed when rock is heated up by the intrusion of hot molten rock called magma from the Earth's interior."

http://en.wikipedia.org/wiki/Metamorphic_rocks

The point is that volcanic rocks are those associated specifically with volcanic activity and not all igneous rocks are, and not all volcanic rocks are igneous though clearly most are.

"Volcanic rocks are named according to both their chemical composition and texture. Basalt is a very common volcanic rock with low silica content. Rhyolite is a volcanic rock with high silica content. Rhyolite has silica content similar to that of granite while basalt is compositionally equal to gabbro. Intermediate volcanic rocks include andesite, dacite, trachyte and latite.

Pyroclastic rocks are the product of explosive volcanism. They are often felsic (high in silica). Pyroclastic rocks are often the result of volcanic debris, such as ash, bombs and tephra, and other volcanic ejecta. Examples of pyroclastic rocks are tuff and ignimbrite.

Shallow intrusions, which possess structure similar to volcanic rather than plutonic rocks are also considered to be volcanic."
http://en.wikipedia.org/wiki/Volcanic_rock

Answer 6

Volcanic - Mt. St. Helens is a volcano.

Answer 7

Volcanic rocks. It's a volcano.

Answer 8

As it's a volcano I'm guessing volcanic.

Answer 9

Fire formed igneous rock.

Answer 10

Big ones.