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Magmatism is the emplacement of magma within and at the surface of the outer layers of a terrestrial planet, which solidifies as igneous rocks. It does so through magmatic activity or igneous activity, the production, intrusion and extrusion of magma or lava. Volcanism is the surface expression of magmatism.
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]
Magma that cools slowly within a magma chamber usually ends up forming bodies of plutonic rocks such as gabbro, diorite and granite, depending upon the composition of the magma. Alternatively, if the magma is erupted it forms volcanic rocks such as basalt , andesite and rhyolite (the extrusive equivalents of gabbro, diorite and granite ...
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.
When the magma finally reaches the surface as lava and cools, the rock solidifies around the gas bubbles and traps them inside, preserving them as holes filled with gas called vesicles. [ 2 ] A related texture is amygdaloidal in which the volcanic rock, usually basalt or andesite , has cavities, or vesicles, that are filled with secondary ...
These gas bubbles within the magma accumulate and coalesce into large bubbles, called gas slugs. These grow large enough to rise through the lava column. [14] Upon reaching the surface, the difference in air pressure causes the bubble to burst with a loud pop, [13] throwing magma in the air in a way similar to a soap bubble.
Magma exists in three main forms that vary in composition. [3] When magma crystallizes within the crust, it forms an extrusive igneous rock. Dependent on the composition of the magma, it may form either rhyolite, andesite, or basalt. [3] Volatiles, particularly water and carbon dioxide, significantly impact the behavior of each form of magma ...