What causes andesitic volcanoes

Granitic, or rhyolitic, magmas and andesitic magmas are generated at convergent plate boundaries where the oceanic lithosphere (the outer layer of Earth composed of the crust and upper mantle) is subducted so that its edge is positioned below the edge of the continental plate or another oceanic plate.

What volcano has andesitic magma?

Shield volcanoes are formed by basaltic magma, typically above a mantle plume, whereas the stratovolcanoes (sometimes referred to as composite volcanoes) are formed by andesitic/rhyolitic magma.

Why are andesitic volcanoes explosive?

Lavas and pyroclastics are usually andesitic to rhyolitic in composition. Due to the higher viscosity of magmas erupted from these volcanoes, they are usually more explosive than shield volcanoes.

What are rhyolitic volcanoes?

Rhyolite caldera complexes are the most explosive of Earth’s volcanoes but often don’t even look like volcanoes. They are usually so explosive when they erupt that they end up collapsing in on themselves rather than building any tall structure (George Walker has termed such structures “inverse volcanoes”).

Why is andesitic lava viscous?

Andesitic lava is an example of a high viscosity lava whereas balastic lava has a low viscosity, so is more runny. High silica content in the andesitic lava contributes to causing this high viscosity and low silica content in the basaltic lava means it is of a lower viscosity.

What is the difference between basaltic lava and andesitic?

Basaltic magma is high in iron, magnesium, and calcium but low in potassium and sodium. It ranges in temperature from about 1000oC to 1200oC (1832oF to 2192oF). Andesitic magma has moderate amounts of these minerals, with a temperature range from about 800oC to 1000oC (1472oF to 1832oF).

Which of the following is an example of andesitic rock?

Andesites occur mainly as surface deposits and, to a lesser extent, as dikes and small plugs. Many of the deposits are not normal lava flows but rather flow breccias, mudflows, tuffs, and other fragmental rocks; the peperino near Rome and the trass of the Eifel district in Germany are examples.

Is andesitic magma viscous?

Alternating andesitic lava flows and layers of explosively ejected pyroclastics. Magma is intermediate, making the lava viscous and difficult to erupt. Explosive eruptions due to buildup of gases.

How do andesitic magmas form?

Andesitic magma is formed through wet partial melting of the mantle. The mantle under the ocean has contact with water. … Basaltic magma with a high water content is the result. If this type of basaltic magma melts with continental crust that has a high density of dioxide silicon, andesitic magma will form.

How viscous is andesitic lava?

Andesitic magmas, in particular, have a wide range of magma viscosities, from 102 to 107 Pa s, which is due to a wide range in phenocryst contents from 0 (phenocryst‐free andesitic melt) to ∼50 vol % (50 vol % rhyolitic melt + 50 vol % phenocrysts). Focusing on andesitic‐to‐rhyolitic magmas, the r changes to −0.1.

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What is the difference between basaltic andesitic and rhyolitic magma?

BASALTIC magmas have a LOW SILICA content (45-55%) and referred to as MAFIC in composition. RHYOLITIC magma contains more than 65% SILICA and is referred to as FELSIC. ANDESITIC magma is INTERMEDIATE in composition (55-65% SILICA).

What is the viscosity of andesitic?

Summary TableMagma TypeAndesiticSolidified RockAndesiteChemical Composition55-65 SiO2 %, intermediate in Fe, Mg, Ca, Na, KTemperature800 – 1000 oCViscosityIntermediate

Which type of volcano is the most explosive?

Stratovolcanoes are considered the most violent. Mount St. Helens, in Washington state, is a stratovolcano that erupted on May 18, 1980.

How far does andesitic lava flow?

Andesitic lava flows at a rate of a few kilometers per hour, whereas basaltic lava can flow up to 10 km/h. Because of their viscosity, andesitic lavas “rarely extend beyound 8 km from their vents”.

What type of igneous rock is andesite?

Andesite is a fine-grained, extrusive igneous or volcanic rock. It is dark grey and made up of equal amounts of light and dark minerals, although the crystals are too small to be seen without a magnifier. Occasionally andesite may contain some larger crystals.

Is andesitic lava thick or thin?

ANDESITIC LAVA These viscous lavas have relatively high aspect ratios (thickness/area), generally > 1/100, and some are thick enough to form as lava domes. Andesite commonly erupts from stratovolcanoes, where they form small-volume flows that typically advance only short distances down the flanks of a volcano.

What does lahar mean?

Definition: A lahar is a hot or cold mixture of water and rock fragments that flow quickly down the slopes of a volcano. … Lahars can be extremely destructive and are more deadly than lava flows.

What is the importance of magmatism?

Magmatism plays a key role in mountain formation, as new ascending magmas produce additional mass and volume to the Earth’s surface and subsurface. Magmas form by partial melting of silicate rocks either in Earth’s mantle, the continental or the oceanic crust.

What are the characteristics of andesitic rocks?

Andesite is a dark, fine-grained, brown or greyish intermediate volcanic rock which is a commonly found in lava. The mineral composition of andesite includes biotite, pyroxene, or amphibole.

Is andesite volcanic or plutonic?

Andesite (/ˈændəzaɪt/) is an extrusive volcanic rock of intermediate composition. In a general sense, it is the intermediate type between basalt and rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predominantly of sodium-rich plagioclase plus pyroxene or hornblende.

Is andesite a Hypocrystalline?

Vitro-porphyry Andesite Structure: hypocrystalline, porphyry-vitreous Texture: unoriented (massive), compact.

What is basaltic andesitic and rhyolitic?

Magma is characterized by high temperatures and the ability to flow. … High temperature and low SiO2 content result in fluid magma (basaltic). Lower temperature and high SiO2 contents result in viscous magma (andesitic and rhyolitic magma).

What is basaltic volcano?

Basalt is a hard, black volcanic rock with less than about 52 weight percent silica (SiO2). Because of basalt’s low silica content, it has a low viscosity (resistance to flow). Therefore, basaltic lava can flow quickly and easily move >20 km from a vent. … Basalt is erupted at temperatures between 1100 to 1250 ° C.

What is the magma composition of a composite volcano?

Composite volcano magma is felsic, which means it contains silicate-rich minerals rhyolite, andesite, and dacite. Low-viscosity lava from a shield volcano, such as might be found in Hawaii, flows from fissures and spreads.

Does caldera erupt?

A caldera-causing eruption is the most devastating type of volcanic eruption. It permanently alters the environment of the surrounding area. A caldera is not the same thing as a crater. Craters are formed by the outward explosion of rocks and other materials from a volcano.

Which type of igneous magma is most rich in SiO2?

Compositions of Some Magmas (wt% of oxides)oxideSilicic magmasMafic magmasNa2O3.513.92K2O5.136.53H2O0.470.63

What causes lava to erupt as Pyroclasts?

Pyroclastic flows form in various ways. A common cause is when the column of lava, ash, and gases expelled from a volcano during an eruption loses its upward momentum and falls back to the ground. … Pyroclastic flows can also form when a lava dome or lava flow becomes too steep and collapses.

Where are andesitic rocks found?

Andesite is a rock typically found in volcanoes above convergent plate boundaries between continental and oceanic plates.

What is the difference between basaltic volcanoes and rhyolitic volcanoes?

Basaltic magma has a low viscosity whereas rhyolitic magma has a high viscosity. Volcano – a hill or mountain formed by the extrusion of lava or ejection of rock fragments from a vent. … The eruption from a shield volcano is relatively nonviolent because the lavas are fairly fluid (less viscous).

How do you tell basalt from andesite and rhyolite?

1. Basalt is an extrusive mafic volcanic rock. …
2. Andesite is an extrusive volcanic rock with a composition that is intermediate between basalt and rhyolite. …
3. Rhyolite is an extrusive felsic (silicic) volcanic rock.

Which magma type flows the fastest?

PAHOEHOE – has a shiny, smooth, glassy surface. It tends to be more fluid (lower viscosity), hence flows more quickly and produces thinner flows (typically 1-3 m).