![]() There are many sorts of explosive eruptions, varying significantly in size, shape and duration. Typically, this eruption column is composed of hot gas, ash and pyroclastic rocks - volcanic material in solid form. If there is a good deal of pressure, however, a volcano will begin its eruption with an explosive launch of material into the air. While these effusive lava flows can reap considerable damage on wildlife and manmade structures, they are not particularly dangerous to people because they move so slowly - you have plenty of time to get out of the way. If the viscosity and the gas pressure are low enough, lava will flow slowly onto the earth's surface when the volcano erupts, with minimal explosion. Most eruptions occur in several stages, with varying degrees of destructiveness. Volcanic eruptions don't often fall into easy categories, however. Gas content varies depending on what sort of material melted to form the magma.Īs a general rule, the most explosive eruptions come from magmas that have high gas levels and high viscosity, while the most subdued eruptions come from magmas with low gas levels and low viscosity. Generally, viscosity is determined by the proportion of silicon in the magma, because of the metal's reaction to oxygen, an element found in most magmas. Both factors are determined by the composition of the magma. Of course, this is balanced with gas content - if the magma contains more gas bubbles, it will erupt more violently, and if it contains less gas, it will erupt more calmly. If the magma has a lower viscosity, the gas bubbles will be able to escape from the magma more easily, so the lava won't erupt as violently.Īn effusive lava flow from Pu`u `O`o Cone on Kilauea Volcano in Hawaii. If the magma has a high viscosity, meaning it resists flow very well, the gas bubbles will have a hard time escaping from the magma, and so will push more material up, causing a bigger eruption. Viscosity is just the ability to resist flow - essentially, it is the opposite of fluidity. The nature of this eruption depends mainly on the gas content and the viscosity of the magma material. As the bubbles escape, they push the magma out, causing a spewing eruption. If you shake the bottle up first, the bubbles are all mixed up in the soda so they push a lot of the soda out with them. When you decompress the soda (by opening the bottle), the tiny gas bubbles push out and escape. This is the same thing that happens when you open a bottle of soda, particularly after shaking it up. In either case, what you get is magma filled with tiny gas bubbles, which have a much lower density than the surrounding magma, and so push out to escape. The vapor pressure increases because the magma cools, initiating a crystallization process that enriches the gas content of the magma.The confining pressure decreases, due to decompression from the magma rising from a higher pressure point to a lower pressure point.Volcanoes with steep slopes tend to form from very viscous magma, while flatter volcanoes form from magma that flows easily. The viscosity (thickness) of the magma that erupts from a volcano affects the shape of the volcano. Both the temperature and mineral content of magma affect how easily it flows. ![]() It occurs in the temperature range of about 650oC to 800oC (1202oF to 1472oF). Rhyolitic magma is high in potassium and sodium but low in iron, magnesium, and calcium. Andesitic magma has moderate amounts of these minerals, with a temperature range from about 800oC to 1000oC (1472oF to 1832oF). It is proposed to ex- amine the latter of these problems. It ranges in temperature from about 1000oC to 1200oC (1832oF to 2192oF). DISCUSSION ON THE VISCOSITY OF LAVA channel as means of estimating the vis- cosity of the lava. Basaltic magma is high in iron, magnesium, and calcium but low in potassium and sodium. All types of magma have a significant percentage of silicon dioxide. There are three basic types of magma: basaltic, andesitic, and rhyolitic, each of which has a different mineral composition. Lava is erupted during either nonexplosive activity or explosive lava fountains. The high temperatures and pressure under Earth’s crust keep magma in its fluid state. Lava flows are streams of molten rock that pour or ooze from an erupting vent. It also contains small amounts of dissolved gases such as water vapor, carbon dioxide, and sulfur. ![]() ![]() Like solid rock, magma is a mixture of minerals. When magma flows or erupts onto Earth’s surface, it is called lava. This magma can push through holes or cracks in the crust, causing a volcanic eruption. Much of the planet’s mantle consists of magma. Earth has a layered structure that consists of the inner core, outer core, mantle, and crust. Magma is extremely hot liquid and semi-liquid rock located under Earth’s surface. ![]()
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