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The lava flowing from stratovolcanoes typically cools and solidifies 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. [4]
In engineering, the unit is usually Stoke or centiStoke, with 1 Stoke = 0.0001 m^2/s, and 1 centiStoke = 0.01 Stoke. For liquid, the dynamic viscosity is usually in the range of 0.001 to 1 Pascal-second, or 1 to 1000 centiPoise. The density is usually on the order of 1000 kg/m^3, i.e. that of water.
With such a high silica content, these magmas are extremely viscous, ranging from 10 8 cP (10 5 Pa⋅s) for hot rhyolite magma at 1,200 °C (2,190 °F) to 10 11 cP (10 8 Pa⋅s) for cool rhyolite magma at 800 °C (1,470 °F). [21]
Rhyolite (/ ˈraɪ.əlaɪt / RY-ə-lyte) [1][2][3][4] is the most silica -rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral assemblage is predominantly quartz, sanidine, and plagioclase.
High-temperature magma, most of which is basaltic in composition, behaves in a manner similar to thick oil and, as it cools, treacle. Long, thin basalt flows with pahoehoe surfaces are common. Intermediate composition magma, such as andesite , tends to form cinder cones of intermingled ash , tuff and lava, and may have a viscosity similar to ...
This high viscosity can be obtained in two ways: by high levels of silica in the magma, or by degassing of fluid magma. Since viscous basaltic and andesitic domes weather fast and easily break apart by further input of fluid lava, most of the preserved domes have high silica content and consist of rhyolite or dacite.
Rhyolitic magma is felsic and the most abundant in silica, potassium, and sodium but the lowest in iron, magnesium, and calcium. [1] [3] The silica composition of rhyolitic magma ranges from 65-75 wt.%. [1] It forms in the lowest temperature range, from about 1200 °F to 1470 °F. [1], [3] Rhyolitic magma has the highest viscosity and gas ...
Pinatubo in the Philippines on 15 June 1991, which produced 5 km 3 (1 cu mi) of dacitic magma, a 40 km (25 mi) high eruption column, and released 17 megatons of sulfur dioxide. [ 46 ] Kelud , Indonesia erupted in 2014 and ejected around 120,000,000 to 160,000,000 cubic metres (4.2 × 10 9 to 5.7 × 10 9 cu ft) volcanic ashes which caused ...