![]() ![]() These low temperature lava flows have a high viscosity, which clogs the inner workings of volcanoes trapping and compounding gases. Liquids that have a HIGH viscosity flow slowly (ie. Its chemical composition A high volatile content decreases viscosity (like adding water to treacle), and is probably the main factor in enabling some highly viscous (but also volatile-rich) melts to reach the surface at all. Why are some eruptions from volcanoes explosive while Early volcanic activity in the Snake River Plain (up to 17 million years ago) consisted of calamitous rhyolitic eruptions that created enormous calderas up to several 100 miles square. Viscosity of Magmas Thus, basaltic magmas tend to be fairly fluid (low viscosity), but their viscosity is still 10,000 to 100,0000 times more viscous than water. To give you a better idea of different viscosity levels or centipoise (cP) measures, water measures at 0.894 cP, castor oil at 650 cP and ketchup at 50,000 - 100,000 cP. Water, for example, is a low viscosity fluid. Mafic lava leads to weaker volcanic eruptions. In turn, felsic magma is associated with the volatile stratovolcano characterized by Plinian eruptions (mushroom cloud) followed by a deadly pyroclastic flow of hot ash, gas, and lava. Low viscosity refers to substances that are thin, such as water, while high viscosity substances are thick. The high viscosity of the lava also makes felsic volcanoes highly explosive, causing the lava to "clot" the mouth of the volcano. ![]() ![]() Another point to emphasize is that mafic has a lower level of silica (45% to 55%) whereas felsic has a higher level of silica (70% to 85%). In other words, SAE 10W-30 has a base rating of 10 when cold. Cold syrup, on the other hand, has a higher viscosity. If an erupting lava has low viscosity ( like water) and little or no dissolved gases, it simply flows out of the central vent and spreads far and wide over the surface (see low water/low silica figure). ![]()
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