What type of magma do stratovolcanoes have?
The lava flowing from stratovolcanoes typically cools and hardens before spreading far, due to high viscosity. The magma forming this lava is often felsic, having high-to-intermediate levels of silica (as in rhyolite, dacite, or andesite), with lesser amounts of less-viscous mafic magma.
What are stratovolcanoes layers made of?
Key Takeaways: Composite Volcano Composite volcanoes, also called stratovolcanoes, are cone-shaped volcanoes built from many layers of lava, pumice, ash, and tephra. Because they are built of layers of viscous material, rather than fluid lava, composite volcanoes tend to form tall peaks rather than rounded cones.
Are stratovolcanoes felsic or mafic?
Volcano with steep sides, made of a composite of many types of eruption styles, from low viscosity mafic magma, higher viscosity felsic lava, but most commonly, intermediate andesite lava.
Where do stratovolcanoes typically form?
Stratovolcanoes typically form at convergent plate margins, where one plate descends beneath an adjacent plate along a subduction zone.
What type of magma makes a composite volcano?
The composition of magma that erupts at composite volcanoes is usually felsic (rhyolite) or intermediate (andesite). A cross section of a composite volcano reveals alternating layers of rock and ash.
How is viscosity related to a stratovolcano?
These rocks form Stratovolcanoes (also called composite volcanoes), due to the higher amounts of trapped gasses and the higher viscosity.
How does a stratovolcano generate magma?
Like other types of volcanoes, stratovolcanoes form around vents from which molten rock, or magma, reaches the Earth's surface as lava. They're most common along the planet's great subduction zones, where a tectonic plate plunges beneath another, generating the rock melt necessary to produce volcanic activity.
Are stratovolcanoes mafic?
The compositional spectrum of these rock types may vary from basalt to rhyolite in a single volcano; however, the overall average composition of stratovolcanoes is andesitic. Many oceanic stratovolcanoes tend to be more mafic than their continental counterparts.
What are stratovolcanoes formed from?
Stratovolcano. Stratovolcanoes have relatively steep sides and are more cone-shaped than shield volcanoes. They are formed from viscous, sticky lava that does not flow easily. The lava therefore builds up around the vent forming a volcano with steep sides.
How are stratovolcanoes formed?
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.
What makes a stratovolcano a composite one?
Stratovolcanoes, also called composite volcanoes, are typically steep-sided, symmetrical cones built of alternating layers of lava flows, volcanic ash, and other eruptive products (see animation courtesy of Exploring the Environment).
What is basaltic magma?
Basaltic (or mafic) magma predominates in nonexplosive volcanic eruptions. It is a high-temperature magma (1,200 °C (about 2,200 °F)) characterized by flowing lava, and it is made up of about 45–55 percent silica (SiO2) by weight.
What is viscous magma?
Viscosity of Magmas Viscosity is the resistance to flow (opposite of fluidity). Viscosity depends on primarily on the composition of the magma, and temperature. Higher SiO2 (silica) content magmas have higher viscosity than lower SiO2 content magmas (viscosity increases with increasing SiO2 concentration in the magma).
What is the type of lava flow typically associated with stratovolcanoes and commonly forms lava domes?
Strato Volcanoes comprise the largest percentage (~60%) of the Earth's individual volcanoes and most are characterized by eruptions of andesite and dacite – lavas that are cooler and more viscous than basalt.
How stratovolcanoes are formed?
Stratovolcanoes form through explosive eruptions depositing material near a central vent. The most common eruption types at stratovolcanoes are Strombolian, Vulcanian, and Plinian eruptions. Strombolian eruptions are relatively minor eruptions of lava and tephra lasting a short time.
What is rhyolitic magma?
Rhyolitic lavas are viscous and tend to form thick blocky lava flows or steep-sided piles of lava called lava domes. Rhyolite magmas tend to erupt explosively, commonly also producing abundant ash and pumice.
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).
What type of magma is basaltic?
Basaltic lava is another term for mafic lava. Mafic lava is molten rock that is enriched in iron and magnesium and low in silica. When mafic lava cools on the earth's surface, it forms basalt, which is why mafic lava is commonly called 'basaltic lava.
What is felsic magma?
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 are the characteristics of a stratovolcano?
Stratovolcano. Stratovolcanoes have relatively steep sides and are more cone-shaped than shield volcanoes. They are formed from viscous, sticky lava that does not flow easily. The lava therefore builds up around the vent forming a volcano with steep sides.
What kind of magma produces violent eruptions?
Explosive eruptions are favored by high gas content & high viscosity magmas (andesitic to rhyolitic magmas).
What are 3 types of magma?
It also contains small amounts of dissolved gases such as water vapor, carbon dioxide, and sulfur. The high temperatures and pressure under Earth's crust keep magma in its fluid state. There are three basic types of magma: basaltic, andesitic, and rhyolitic, each of which has a different mineral composition.
What is a basaltic magma?
Basaltic magma is formed by the partial melting of mantle rocks. Basaltic lava is high in iron, magnesium, and calcium but low in potassium and sodium. Fluid basalt flows can extend tens of kilometers from an erupting vent. Basaltic lavas are relatively thin and are very fluid when erupted.
Where is andesitic magma found?
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 is a andesitic stratovolcano?
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 volcanoes have rhyolitic 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.
Is a stratovolcano a andesitic?
Stratovolcanoes are composed of volcanic rock types that vary from basalt to rhyolite, but their composition is generally andesite. They may erupt many thousands of times over life spans of millions of years. A typical eruption begins with ash explosions and ends with extrusion of thick, viscous lava flows.