2 17 rock changes from solid to liquid form face diagram shows us what pressure and temp causes rock to change from solid to liquid Geotherm shows temp and pressure change in the crust 2 way to produce melt releasing pressure adding water Volcano Terms magma molten or partially molten rock from igneous rock form usually consists of silicate liq uid although carbonate and sulfide melts occur as well lava magma poured onto earths surface viscosity is a measure of resistance of a fluid to deform under shear stress it is commonly per ceived as Thickness or resistance to flow has something to do w mineralogy most minerals and rocks are made out of silicates creates tetrahedral easy to connect in high energy they don t connect easily when energy is lost more bonding occurs types of volcanoes shield volcano composite cone steeper slope often exists along ring of fire mount St Helen eruption takes 1 5 mins to go ten miles 1 3 of mountain lost process earthquakes and puffs of steam indicate magma is rising bulge develops erup tion causes second block to break free exposing more magma and initiating eruption column earthquake shakes mountain dislodging bugle which slides down mountain decreased pressure on magma initiates lateral blast cinder cone steepest slope biggest deepest craters basaltic flow very fluid like and can travel a great distance forming a thin sheet andesitic flow is too vicious to travel far and tends to break up as it flows rhyolitic spire in some cases rhyoltic lava is too vicious to flow at all and rises out of the vent as a columnar plug rhyolitic dome rhyolitic lava is so viscous that it piles u p at a vent as a dome volcanic dome steep sided mound built by magma