andesite.
The range of rock types erupted by the volcano changed about 2,500 yr ago, and since then, Mount St. Helens repeatedly has produced Mount St. Helens of andesite, and on at least two occasions, basalt.
What type of lava 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.
Does Mt. St. Helens have high viscosity lava?
In contrast to shield volcanoes, there are stratovolcanoes, like Mt. St. Helens. These volcanoes produce sticky, higher viscosity magma (andesite and rhyolite) that does not travel very far.
Does Mt Saint 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 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 is viscous lava?
An eruption of highly viscous (very sticky) magma tends to produce steep-sided volcanoes with slopes that are about 30–35°. That’s because the viscous volcanic material doesn’t flow that far from where it is erupted, so it builds up in layers forming a cone-shaped volcano known as a stratovolcano.
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 type of lava has high viscosity?
Rhyolitic magmas
Rhyolitic magmas tend to have even higher viscosity, ranging between 1 million and 100 million times more viscous than water.
What is thick lava called?
If the lava is very hot and has a low viscosity (runny with a low gas and silica content) the lava flow is called Pahoehoe. If, on the other hand, the lava has a high viscosity (thick and pasty with a high gas and silica content) it is called Aa.
What type of lava is very viscous?
rhyolite
Felsic lava
They include rhyolite and dacite lavas. With such a high silica content, these lavas are extremely viscous, ranging from 108 cP (105 Pa⋅s) for hot rhyolite lava at 1,200 °C (2,190 °F) to 1011 cP (108 Pa⋅s) for cool rhyolite lava at 800 °C (1,470 °F).
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.
Will St Helens 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.
Is St Helens in the Ring of Fire?
Mount St. Helens sits on the plate boundary between Juan de Fuca and the North American plates (map above). The boundary is part of the so- called ‘Ring of Fire’ – the string of volcanoes that congregate around the margin of the Pacific Ocean.
What type of volcano is Mt St Helens and what typical eruption style occur?
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.
Is Mt St Helens felsic or 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.
How is magma formed at Mt St Helens?
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.
What happens if you touch lava?
Lava won’t kill you if it briefly touches you. You would get a nasty burn, but unless you fell in and couldn’t get out, you wouldn’t die. With prolonged contact, the amount of lava “coverage” and the length of time it was in contact with your skin would be important factors in how severe your injuries would be!
Is lava a fire or earth?
Both fire and eruptions were viewed as mysterious natural sources of heat that must somehow be related. But we have made progress in understanding nature. We now know that lava (and its underground equivalent, magma) is formed, not by burning anything, but by slow heating under great pressure within the earth.
What are the 3 types of lava flow?
The 3 types of lava flow are Pahoehoe, A’a, and Blocky lava flow. All of these lava flows are found on the ground. Pahoehoe has a smooth and glassy surface, A’a has a rough surface, while blocky lava flow has a block-like surface.
What volcano has basaltic lava?
Most lava flows, including the ones from Kīlauea and Mauna Loa volcanoes in Hawai’i Volcanoes National Park, have basaltic compositions.
What volcano has basaltic magma?
Shield Volcanoes
Shield volcanoes are the largest volcanoes on Earth that actually look like volcanoes (i.e. not counting flood basalt flows). The Hawaiian shield volcanoes are the most famous examples. Shield volcanoes are almost exclusively basalt, a type of lava that is very fluid when erupted.