ERSC 1F90 Lecture Notes - Lecture 8: Continental Crust, Mantle Plume, Geophysics
Volcano: a mound of igneous material that is extruded to the earth"s surface from a vent that"s connected to a magma chamber via a feeder conduit. They"re classified according to their form: the form of volcano depends on the type of material making it up. The nature of the extruded material (and the volcano) depends on the properties of the magma. Magma: molten rock within the earth: called lava above the surface, composition of magma determines the type of rock that forms when cooling and its behaviour during an eruption. Main controls on behaviour: chemical composition (silica dioxide content sio2 content controls viscosity, gas content (water vapour and co2) Viscosity: how easily a fluid flows (water has low viscosity, molasses has a higher viscosity) Viscosity controls the amount of gas that gets trapped in the magma. The greater viscosity the more gas in the magma. Three types of magma: basaltic magma, andesitic magma, rhyolitic magma.