GG231 Chapter 5: Volcanoes
Document Summary
Mid ocean ridges, subduction zones where magma reached surface and erupts as lava. 2/3 of all volcanoes on ring of fire. Volcanoes lie above subduction zones bordering pacific ocean, nazca, cocos, philippines, juan de fuca plates. Most magma is from the asthenosphere (where rock is close to its melting temp. : decompression melting. Pressure exerted on hot rock in the asthenosphere is reduced. @ divergent plate boundaries, continental rifts lithosphere is stretched and thinned mantle wells up toward surface where pressure lower causes decompression melting. @ hot spots, plumes of rot rock deep in asthenosphere well up to shallow depths generating magma. Ilicate rocks (cid:373)elt @ (cid:1005)(cid:1006)(cid:1004)(cid:1004) degrees @ earth"s surface. Temp is exceeded within upper 100 km of earth, pressure increases with depth: adding volatiles. Volatiles = chemical compounds in gaseous state @ earths surface (water vapour, co2) Lowers melting temp by breaking chemical bonds within silicate minerals. evaporate easily. (released when oceanic plates are subducted)
