Geography 2152F/G Lecture Notes - Lecture 8: Pyroclastic Rock, Volcanic Crater, Magma Chamber
12 Oct 2016
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Most volcanoes are located near plate boundaries. (cid:1006)/(cid:1007) of all (cid:448)ol(cid:272)a(cid:374)oes a(cid:396)e fou(cid:374)d o(cid:374) the (cid:858) i(cid:374)g of fi(cid:396)e(cid:859) su(cid:396)(cid:396)ou(cid:374)di(cid:374)g the pa(cid:272)ifi(cid:272) o(cid:272)ea(cid:374). Subductions zones and mid ocean ridges allow molten rock to reach the surface. Magma -it is found deep within the crust and upper mantle. Lava -it is found flowing from an erupting volcano. Esse(cid:374)tially, la(cid:448)a is (cid:373)ag(cid:373)a o(cid:374) the ea(cid:396)th(cid:859)s su(cid:396)fa(cid:272)e. The most abundant elements in magma are silicon and oxygen; when combined they are referred to as silica. Volcanic rocks are formed based on the amount of silica present. Basalt, andesite, dacite, rhyolite low silica to high silica (less common rocks) Magma also contains small amounts of gases (water vapour and carbon dioxide). Volcanoes have different shapes based on the chemistry and viscosity of their magma viscosity- resistance to flow. Magma viscosity is determined by silica amount and temperature. Magma with high silica content ( very explosive rupture)
