QUESTION 1 In part, the viscosity of magma is dependent on the amount of sika te

Question

QUESTION 1 In part, the viscosity of magma is dependent on the amount of sika tetrahedrons in the me why does a high amount of slica ncrease the myna's from being pushed together and flow O The silica let ahed ons are much larger than the other ions found ite magma melt O A melt rich in silica electrically and These largo iors i pede te ement of hemd mechanically exclude other lons. These excluded ions (notatly iron and calckm) collect along the siders of megea's passageway and constrict the magma's flow QUESTION 2 What influence does the temperature of a melt have on its viscosity? O Temperature has no affect on the viscosity 0 The viscosity goes up as the temperature goes up O The viscosity goes down as the temerature increases QUESTION 3

Explanation / Answer

Question 1:

Magmas are fluids but they possess structure in the form of silicon-oxygen building blocks, that are linked together to form tetrahedra. Magmas that are rich in silicon form many linked tetrahedra that result in the polymerization of the liquids. The bonds that form between shared oxygen atoms are strong, thus giving the liquid strength and high viscosity.

A high silica concentration causes an increase of viscosity due to the polymerization of silicon-oxygen bonds. Silicon has a 4+ valence, meaning it has 4 electrically positive bonds repelling each other; that’s why they orient themselves in space at the maximum available distance: along the 4 vertices of a tetrahedron. Each vertex bonds one of the 2 negative valences of an oxygen atom (SiO44

The answer is “Because all of the silica tetrahedrons have the same charge, they mutually repel eath other. With high number of silica tetrahedrons, the repulsive forces prevent the melt from being pushed together and flow”

Question 2

The temperature dependence of liquid viscosity is the phenomenon by which liquid viscosity tends to decrease (or, alternatively, its fluidity tends to increase) as its temperature increases. This can be observed, for example, by watching how cooking oil appears to move more fluidly upon a frying pan after being heated by a stove.

The answer is “The viscosity goes down as the temperature increases”

Question 3

The abundance of gases varies considerably from volcano to volcano. Water vapor is consistently the most common volcanic gas, normally comprising more than 60% of total emissions. Carbon dioxide typically accounts for 10 to 40% of emissions.

Hence the answer is “Water (stream)”

Question 4

First, it is important to realize that gases can be both dissolved in a magma chamber at depth and can be emitted from volcanoes at the surface. It is dissolved gases that cause volcanoes to erupt and it is gases emitted at the surface that can cause hazards and changes in climate.

The amount of dissolved gas in the magma provides the driving force for explosive eruptions. The viscosity of the magma, however, is also an important factor in determining whether an eruption will be explosive or non-explosive. Low viscosity magma, like basalt, will allow the escaping gases to migrate rapidly through the magma and escape to the surface. However, if the magma is viscous, like rhyolite, its high polymerization will impede the upward mobility of the gas bubbles. As gas continues to exsolve from the viscous melt, the bubbles will be prevented from rapid escape, thus increasing the overall pressure on the magma column until the gas ejects explosively from the volcano. As a general rule, therefore, non-explosive eruptions are typical of basaltic-to-andesitic magmas which have low viscosities and low gas contents, whereas explosive eruptions are typical of andesitic-to-rhyolitic magmas which have high viscosities and high gas contents.

The answer would be “The higher the percentage of volatiles, the more explosive the eruption is likely to be”

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