The Nature of a Volcanic Eruption
...g volcanoes. Next is the eruption itself. The type of eruption that occurs, either violent or quiet, depends on the viscosity of the magma. Viscosity is the measure of a substance’s resistance to flow. The viscosity of a magma is determined by three primary factors: the magma’s composition, temperature, and the amount of dissolved gases it contains. The composition of the magma is mainly dependent upon the amount of silica it contains. The more silica a magma contains the more viscous it will be, meaning it will move slower. When a magma becomes thicker, due to an excess of silica, gases cannot escape. This will result in a more violent eruption caused by a buildup of intense heat and pressure. The magma’s temperature has an effect that is easily seen. An example is the heating of syrup. As the syrup gets warmer it becomes less viscous. The same effect is shown in magma. Therefore, if a magma is hotter there will be a quieter eruption. The amount of dissolved gases in a magma is the most prominent factor in the eruption of a volcano. The more dissolved gases contained in the magma, the greater the chance of a violent eruption. Finally, there are three types of flow after an eruption: gas flow, lava flow, and pyroclastic flow. Gas flow is generally the first stage of an eruption. “All magmas contain dissolved gases that are released both during and between eruptive episodes (USGS 1).” As previously stated if there is an excess of dissolved gases within a magma the more violent the eruption will be. The most common gases emitted from an eruption are steam, carbon dioxide, nitrogen, chlorine, hydrogen, and argon. Lava flow is generally the second stage to the eruption. The ‘aa’ lava flow is a slow moving lava flow with a broken surface containing an excess of silica content, and ‘pahoehoe’ lava flow is a rapid moving flow with a smooth surface. The pyroclastic flow is usually the last and most violent stage of a volcanic eruption. This flow consists of pulverized rock and magma produced...