What is the relationship between silica content and viscosity

How do viscosity and gas content relate to temperature of the magma? | Socratic

what is the relationship between silica content and viscosity

Horizontal distance between the crests or between the troughs of two . what is the relationship between silica content gas content, temperature and viscosity. A magma's viscosity is largely controlled by its temperature, composition, and gas Chemical bonds are created between negatively charged and positively Magmas that have a high silica content will therefore exhibit greater degrees of. Answer to How does the relationship between silica content of magma and lava viscosity influence the shape of a volcano?.

Magma Viscosity, Gas Content & Milkshakes

This is called dry melting. If water or carbon dioxide are present within or surrounding the mineral, then melting takes place at a single temperature at any given pressure, but first decreases with increasing pressure Since rocks are mixtures of minerals, they behave somewhat differently. Unlike minerals, rocks do not melt at a single temperature, but instead melt over a range of temperatures.

Thus, it is possible to have partial melts, from which the liquid portion might be extracted to form magma. The two general cases are: Melting of dry rocks is similar to melting of dry minerals, melting temperatures increase with increasing pressure, except there is a range of temperature over which there exists a partial melt.

Melting of wet rocks is similar to melting of wet minerals, except there is range of temperature range over which partial melting occurs. Again, the temperature of beginning of melting first decreases with increasing pressure or depth, then at high pressure or depth the melting temperatures again begin to rise. Three ways to Generate Magmas From the above we can conclude that in order to generate a magma in the solid part of the earth either the geothermal gradient must be raised in some way or the melting temperature of the rocks must be lowered in some way.

The geothermal gradient can be raised by upwelling of hot material from below either by uprise solid material decompression melting or by intrusion of magma heat transfer.

Lowering the melting temperature can be achieved by adding water or Carbon Dioxide flux melting. The Mantle is made of garnet peridotite a rock made up of olivine, pyroxene, and garnet -- evidence comes from pieces brought up by erupting volcanoes. In the laboratory we can determine the melting behavior of garnet peridotite. Decompression Melting - Under normal conditions the temperature in the Earth, shown by the geothermal gradient, is lower than the beginning of melting of the mantle.

Thus in order for the mantle to melt there has to be a mechanism to raise the geothermal gradient. Once such mechanism is convection, wherein hot mantle material rises to lower pressure or depth, carrying its heat with it. If the raised geothermal gradient becomes higher than the initial melting temperature at any pressure, then a partial melt will form.

Liquid from this partial melt can be separated from the remaining crystals because, in general, liquids have a lower density than solids. Basaltic magmas appear to originate in this way.

what is the relationship between silica content and viscosity

Upwelling mantle appears to occur beneath oceanic ridges, at hot spots, and beneath continental rift valleys. Thus, generation of magma in these three environments is likely caused by decompression melting. Upon solidification they lose this heat and transfer it to the surrounding crust.

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Repeated intrusions can transfer enough heat to increase the local geothermal gradient and cause melting of the surrounding rock to generate new magmas.

Rhyolitic magma can also be produced by changing the chemical composition of basaltic magma as discussed later. Transfer of heat by this mechanism may be responsible for generating some magmas in continental rift valleys, hot spots, and subduction related environments. Flux Melting - As we saw above, if water or carbon dioxide are added to rock, the melting temperature is lowered.

If the addition of water or carbon dioxide takes place deep in the earth where the temperature is already high, the lowering of melting temperature could cause the rock to partially melt to generate magma.

One place where water could be introduced is at subduction zones. Here, water present in the pore spaces of the subducting sea floor or water present in minerals like hornblende, biotite, or clay minerals would be released by the rising temperature and then move in to the overlying mantle. Introduction of this water in the mantle would then lower the melting temperature of the mantle to generate partial melts, which could then separate from the solid mantle and rise toward the surface.

Chemical Composition of Magmas The chemical composition of magma can vary depending on the rock that initially melts the source rockand process that occur during partial melting and transport. Initial Composition of Magma The initial composition of the magma is dictated by the composition of the source rock and the degree of partial melting.

Melting of crustal sources yields more siliceous magmas. In general more siliceous magmas form by low degrees of partial melting. As the degree of partial melting increases, less siliceous compositions can be generated.

So, melting a mafic source thus yields a felsic or intermediate magma. Melting of ultramafic peridotite source yields a basaltic magma. Magmatic Differentiation But, processes that operate during transportation toward the surface or during storage in the crust can alter the chemical composition of the magma.

These processes are referred to as magmatic differentiation and include assimilation, mixing, and fractional crystallization. Assimilation - As magma passes through cooler rock on its way to the surface it may partially melt the surrounding rock and incorporate this melt into the magma.

what is the relationship between silica content and viscosity

Because small amounts of partial melting result in siliceous liquid compositions, addition of this melt to the magma will make it more siliceous. Mixing - If two magmas with different compositions happen to come in contact with one another, they could mix together.

The mixed magma will have a composition somewhere between that of the original two magma compositions.

what is the relationship between silica content and viscosity

Evidence for mixing is often preserved in the resulting rocks. Crystal Fractionation - When magma solidifies to form a rock it does so over a range of temperature. Each mineral begins to crystallize at a different temperature, and if these minerals are somehow removed from the liquid, the liquid composition will change. Depending on how many minerals are lost in this fashion, a wide range of compositions can be made. The processes is called magmatic differentiation by crystal fractionation.

Crystals can be removed by a variety of processes. If the crystals are more dense than the liquid, they may sink. If they are less dense than the liquid they will float.

what is the relationship between silica content and viscosity

If liquid is squeezed out by pressure, then crystals will be left behind. Removal of crystals can thus change the composition of the liquid portion of the magma. Let me illustrate this using a very simple case. Cold molasses, for example, has a higher viscosity than water because it is less fluid. A magma's viscosity is largely controlled by its temperature, composition, and gas content see downloadable programs at the bottom of this page.

What is the relationship between silica content and viscosity

The effect of temperature on viscosity is intuitive. Like most liquids, the higher the temperature, the more fluid a substance becomes, thus lowering its viscosity. Composition plays an even greater role in determining a magma's viscosity. A magma's resistance to flow is a function of its "internal friction" derived from the generation of chemical bonds within the liquid. Chemical bonds are created between negatively charged and positively charged ions anions and cations, respectively.

Of the ten most abundant elements found in magmas see aboveoxygen is the only anion. Silicon, on the other hand, is the most abundant cation. Thus, the Si-O bond is the single most important factor in determining the degree of a magma's viscosity. These two elements bond together to form "floating radicals" in the magma, while it is still in its liquid state i. These floating radicals contain a small silicon atom surrounded by four larger oxygen atoms SiO4.

This atomic configuration is in the shape of a tetrahedron. The radicals are therefore called silicon-oxygen tetrahedra, as shown here.

What is the relationship between viscosity and silica of magma?

These floating tetrahedra are electrically charged compounds. As such, they they are electrically attracted to other Si-O tetrahedra. The outer oxygen atoms in each tetrahedron can share electrons with the outer oxygen atoms of other tetrahedra. The sharing of electrons in this manner results in the development of covalent bonds between tetrahedra.