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Trachyandesitic magma can produce explosive Plinian eruptions, such as happened at Tambora in 1815. [4] The Eyjafjallajökull 2010 eruption (VEI-4 [5]), which disrupted European and transatlantic air travel from 15-20 April 2010, [6] for some time was dominated by trachyandesite. [7]
Cinder Cone comprises five basaltic andesite and andesite lava flows, and it also has two cinder cone volcanoes, with two scoria cones, the first of which was mostly destroyed by lava flows from its base. [6] Cinder cone volcanoes are typically monogenetic, meaning that they only undergo one eruptive period before ceasing activity forever.
For example, andesitic magmatism is associated with the formation of island arcs at convergent plate boundaries while basaltic magmatism is found at mid-ocean ridges during sea-floor spreading at divergent plate boundaries. On Earth, magma forms by partial melting of silicate rocks either in the mantle, continental or oceanic crust. Evidence ...
Andesite is usually light to dark grey in colour, due to its content of hornblende or pyroxene minerals. [2] but can exhibit a wide range of shading. Darker andesite can be challenging to distinguish from basalt, but a common rule of thumb, used away from the laboratory, is that andesite has a color index less than 35. [9]
Extrusive rock refers to the mode of igneous volcanic rock formation in which hot magma from inside the Earth flows out (extrudes) onto the surface as lava or explodes violently into the atmosphere to fall back as pyroclastics or tuff. [1] In contrast, intrusive rock refers to rocks formed by magma which cools below the surface. [2]
The initial magma was basaltic, though this was replaced several hundred years later by more evolved, basaltic andesite magma. [20] Eruptions at Sand Mountain Field were fed by two or three magma chambers, [21] including a number of mafic magma sources over a brief span of distance and time. [22]
The process powering Plinian eruptions starts in the magma chamber, where dissolved volatile gases are stored in the magma. The gases vesiculate and accumulate as they rise through the magma conduit. These bubbles agglutinate and once they reach a certain size (about 75% of the total volume of the magma conduit) they explode.
A further control on the morphology and characteristics of a deposit is the water to magma ratio. It is considered that the products of phreatomagmatic eruptions are fine grained and poorly sorted where the magma/water ratio is high, but when there is a lower magma/water ratio the deposits may be coarser and better sorted. [4]