Volcano viscosity definition8/28/2023 ![]() ![]() 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. A mudflow containing volcanic material, called a lahar, may also form when the rock of the pyroclastic flow mixes with water to become a quickly moving slurry.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. Floods may also occur when the flow of hot material melts snow and ice, swelling rivers and streams beyond their banks. Pyroclastic flows may result in flooding as streams are blocked or rerouted by the flow. Not only does it destroy living material in its path, it often leaves behind a deep layer of solidified lava and thick ash. Such a flow can transform the landscape drastically in a short period of time. Above this, a thick cloud of ash forms over the fast-moving flow. ![]() Along the ground, lava and pieces of rock flow downhill. ![]() Pyroclastic flows often occur in two parts. Pyroclastic flows can also form when a lava dome or lava flow becomes too steep and collapses. Another cause is when volcanic material expelled during an eruption immediately begins moving down the sides of the volcano. A common cause is when the column of lava, ash, and gases expelled from a volcano during an eruption loses its upward momentum and falls back to the ground. It may move at speeds as high as 200 m/s. A pyroclastic flow is extremely hot, burning anything in its path. It occurs as part of certain volcanic eruptions. A pyroclastic flow is a dense, fast-moving flow of solidified lava pieces, volcanic ash, and hot gases. ![]()
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