10 - VOLCANISM The process by which magma and gases are...

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VOLCANISM * The process by which magma and gases are transferred from the Earth's interior to near or on the surface. * 2 basic types: extrusive vs intrusive volcanism Extrusive: When magma (lava) flows out onto the Earth’s surface and then cools to form igneous rock ** Volcano : a landform with a vent, or fissure (crack) on the surface, which is the end of a conduit originating from below the crust in the asthenosphere *Often a mountain landform (fissures usually do not form features of high relief or volcanic peaks) *Magma collects in a magma chamber below the volcano before being expelled * crater : the surface depression at the summit of the volcano * a volcano may be categorized as: Active: currently erupting, or has erupted during recorded history Dormant : an active volcano that is in repose but is expected to erupt in the future Extinct : a volcano that is not expected to erupt again * 75% of volcanoes are on the sea floor * Most convergent and divergent plate boundaries have high volcanic activity * Hot spots * Lava : the molten rock issued from a volcano; the term used for magma once it has erupted onto the Earth's surface *May be two types of material mafic or felsic * Mafic or basaltic lava : high in Mg & Fe, < 50% silica thus less viscous which means it flows readily, and thus less gas is trapped within leading to a less explosive eruption. * Felsic : richer in silica thus more viscous meaning it flows slower: it is also more acidic, and more gases are trapped leading to more explosive eruptions. * Pyroclastics or tephra : solidified magma fragments expelled explosively from a volcano, quite common with felsic magma & explosive eruptions
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* bombs (> 1 m), pumice, scoria, cinders (1-2 in), lapilli, ash, & dust (Based on size; bombs largest, dust/ash smallest.) ** 2 Types of Eruptions
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10 - VOLCANISM The process by which magma and gases are...

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