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What kind of magmas produce violent volcanic eruptions?
Magmas with high viscosity and gas content tend to produce violent volcanic eruptions. High viscosity magmas are thicker and have more difficulty releasing gas, leading to pressure build-up and explosive eruptions. This often occurs with felsic or rhyolitic magmas.
Why do volcanic eruptions differ?
The main cause of differences in volcanic eruption characteristics is due to the viscosity of the magma. High viscosity magmas are high in sticky silica which traps gas and produces explosive eruptions. Low viscosity magmas are low in silica and produce eruptions with far less energetic characteristics.
What is a magmas viscosity related to?
The silica content. A higher silica content results in a more viscous magma.
Why are granitic magmas thicker than basaltic magmas?
Granitic magmas are thicker than basaltic magmas because they have higher silica content, which increases viscosity. The higher silica content leads to stronger bonding between the silica tetrahedra, making it more difficult for the magma to flow. Basaltic magmas, on the other hand, have lower silica content and are less viscous, allowing them to flow more easily.
How hot does magma have to be to explode?
The explosive potential of magma depends more on viscosity gas content than on temperature. Most magmas are at temperature of at least 700 degrees Celcius. Interestingly, the most explosive magmas are the high-silica magmas, which have lower melting temperatures.
What kind of magmas are generated in places where volcanoes erupt both explosively and nonexplosively?
Volcanoes that erupt both explosively and nonexplosively typically generate magmas with a range of compositions. This can include basaltic magmas for nonexplosive eruptions due to their low viscosity, and intermediate to silicic magmas for explosive eruptions due to their high gas content and higher viscosity. The mixture of magma types leads to varying eruption styles within the same volcanic system.
Why do silica poor magmas produe broad volcanoes with gentle slopes?
Silica-poor magmas, typically basaltic in composition, have lower viscosity compared to silica-rich magmas. This lower viscosity allows them to flow easily and spread over large distances, resulting in the formation of broad, gently sloped volcanoes. The fluid nature of these eruptions generally leads to less explosive activity, contributing to the broad shape of the volcano. Consequently, the accumulation of layers of low-viscosity lava contributes to the characteristic gentle slopes.
What is the relationship between silicon content and the viscosity of magma?
Higher silicon content in magma leads to higher viscosity. This is because silicon tetrahedra form polymerized chains that hinder flow, making the magma more viscous. Lower silica content results in lower viscosity magma.
A magmas viscosity is directly related to its?
A magma's viscosity is directly related to its temperature and silica content. Higher temperatures and lower silica content result in lower viscosity, making the magma more fluid and able to flow more easily.
What is the relationship in the silicon content and the viscosity of magma?
There is an inverse relationship between magma viscosity and silicon content. Lavas erupting from basaltic volcanoes (like Hawaii) have a much lower viscosity and are much hotter than those erupted by volcanoes whose magmas are rich in silicon. There may be up to 8 orders of magnitude viscosity difference between basaltic magmas (SiO2 contents or about 45 %) and rhyolitic magmas (SiO2 > 70 %).
Does less silica equal greater viscosity?
No, generally speaking, more silica leads to greater viscosity in materials such as liquids or glasses. Silica acts as a network former in these materials and helps to increase their structural integrity, resulting in higher viscosity.
What two main factors affect magmas viscosity?
The main factors that affect magma's viscosity are temperature and silica content. Higher temperatures generally result in lower viscosity, as the magma becomes more fluid. Lower silica content also leads to lower viscosity, as silica molecules tend to create more resistance to flow.
