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1、Chapter$:Magma门cy=2小庆沥-gIntroduction:喜Earth?sInternal-ThermalEngine。MagmaismoltenrockbeneathEarth?ssurface.。Becauseliquidmagmaislessdensethansurroundingsolidrock,andobyviouslymoremohbife,magIna,0nceformed,risestowardtheSUrfaee.。MagmathatreachesthesurfacedoessobyeruptingthroughventsWecallvolcanoes。薯V
2、olcan0es丁hetermvolcarzocomesfromthenameoftheRomangodoffire,Vulcan.。万herearedifferenttypesofvolcanoes.Eruptionvaryfromgentleflows(HawaiiandTeeland)t0catastrophicexplosions(MountSt.Helens,Mt.Pinatubo,SoufriereHills).Themajorityoferuptionnevermakethenewsbecausetheyoccurbeneaththeocean,unobserved.薯Magma
3、。Magmahasawiderangeofcompositions,butsilica(SiO2)alwaysdominatesthemix.。Magmahashightemperatures.。Magmaisfluid一ithastheabilitytoflow.。Mostmagmaactuallyisamixtureofliquid(oftenreferredtoasmelt)andsolidmineralgrains.薯CompositionofMagmasandLavas。Thecompositionofmagmasandlavasiscontrolledbythemostabunda
4、ntelementsintheEarth一Si,AbFe,Ca,Mg,Na,K,H,and0.。Threedistinettypesofmagmaaremorecotniontail0tieis:。Basaltic,containingabout50percentSiO2,“Andesitic,about60percentSiO2,。Rhyolitic,about70percentSiO2.AndesiticRhyoitic园司A20。医司Moo+Cao医咏Feo+Fes03区司Nazo+ko0匿命AlothersolicomponentsThethreemainMagmas薯Basaltic
5、MagmasBasalticmagmasareeruptedbyapproximately80percentofvolcanoesworldwide(theseafloorworldwideismostlyDasait).,MagmafromHawaiianvolcanoessuchasKilaueaandMaunaLoaisbasaltic.TheentireislandofIcelandisbasaltic.暑AndesiticandRhyoliticMagmas。Andesiticmagmasareabout10percentofthetotalmagma.。MagmafromMountSt.HelensinWashingtonStateanQdKrakatauinIndonesiaisusuallyandesitic.。Rhyoliticzsagimasareabout10percentofthetotalmagma.。MagmaseruptedfromvoleanoesthatonceWereactiveatYellowstoneParkaremostlyrhyolitic.“医p一仁林.士PastfloWinglava:Joga菊cositybasalticlava,Havaiiin1983nP友
