![]() ![]() The viscosity of obsidian must be lower than rhyolite so it can flow difference in eruption temperature is the greatest control over this difference. Initially the magma erupts at a temperature around 900 degrees C however this first eruption is rich in volatiles producing pumice, so this stage still has a greater viscosity than obsidian. When it comes down to it the temperature ot the obsidian magma is the may property controling the viscosity over any of the other properties. The low amount of water in comparison with rhyolite pumice indicates that the flow of obsidian must take place at the end stage of the explosive eruption phase of rhyolite magma (Bakken Barbara., 1977) end stage indicating after the vent of the volcano has released a large amount of gas through the explosive eruption stage. The average water content of obsidian is (0.3 wt %) where as crystalline rhyolite is <2.0 wt % water (Bakken Barbara., 1977). For these explosive types of eruptions not occur in the emplacement of obsidian the volatile content for the obsidian must be low. Volatiles within highly viscous magmas can produce eruptive events due to the inability for the volatiles to escape easily so as they rupture, burst, they release an enormous amount of pressure producing an eruption such as the Mount. This difference is due to the difference in composition, specifically volatile, gas, content. Obsidian occurs as a flow, not as an explosive eruption in contrast to a vesiculated rhoylite pumice or dacite. The gas content of obsidian is very low so for this to occur the gas has to be released in some way before the eruption of the obsidian. The formation of obsidian could also be the melt, liquid remaining from a magma after crystallization, of a rhyolite magma that has been erupted before any crystals can form as stated earlier. For this process to occur during a lava flow the lava is caught just below crystallization temperature, thus forming a glass due to the inability to form a crystalline solid. Therefore leaving a magma that is unable to crystallize will form (glass) obsidian. Viscosity is a measure on the ability of substance to flow, high viscosity means poor ability to flow and low viscosity means good ability to flow, an example of magma with a low viscosity is basalt and magma with high viscosity is rhyolite.įor obsidian to form, magma is trapped below the eutectic, point of crystallization, by loss of heat. This makes silicic magmas more dangerous: As more gas builds up in the magma, it becomes more explosive, like adding more and more carbonation to a soda.Volcanic glasses such as obsidian form when some physical property of lava restricts ion mobility preventing an ordered crystalline pattern to develop, and for obsidian it is the viscosity that has the greatest control on the ordered crystalline pattern, the measure of viscosity is dependent on the temperature, crystal content and chemical composition. Since silicic magmas are colder and goopier than mafic magmas, dissolved gases have a harder time venting out of them. Why do so many people live near active volcanoes? Rhyolite, an especially silica-rich type of lava, hits temperatures between only 1,200 degrees to 1,500 degrees Fahrenheit. These magmas are more than 63 percent silica, which makes them more viscous: At their runniest, silicic magmas flow about as well as lard or caulk-which is to say not well at all. Silicic magmas, on the other hand, tend to form when the lighter continental crust melts. ![]() What are the biggest dangers from Hawaii's erupting Kilauea volcano? They're also the hottest variety of magma, reaching temperatures between 1,800 degrees to 2,200 degrees Fahrenheit. ![]() As far as molten rocks go, mafic magmas are fairly runny, with viscosities ranging from molasses to peanut butter. They contain between 47 to 63 percent silica, the mineral that makes up glass and quartz. ![]() Mafic magmas like those in Hawaii tend to form when the heavier crust that forms the ocean floor melts. Hawaii’s Kilauea volcano erupted on May 3, 2018, and the lava continues to flow. ![]()
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