Explain why thick,sticky magma may cause a volcano to erupt explosively???

Answer 1

By being thick and viscous the magma may trap gases. After trapping the gases, the pressures may build up until the rocks and magma can't hold it any more and it explodes in an eruption.

Answer 2

The magma comes out for the same reason that tooth paste comes out of the tube -pressure. The magma is sticky and viscous compared with water, but is still fluid enough to travel great distances. The violence of an eruption depends upon the amount of gasses within the magma. These hot gasses expand rapidly as pressure is reduced in the tube of the volcano and then violently push the magma , often explosively. Some volcanic flows are not violent and the resulting lava field is somewhat flat. This is classified as a shield volcano. These flows have very little gas.

Answer 3

You should really be doing your own homework research. This magma is associated with gasses that get trapped underneath and within. The gas pressure keeps building until it counteracts the retaining force of the magma and/or the mantle rock overlying the magma "bulge." The earth above actually rises into a dome until it releases explosively.

There are those who say Yosemite is past due for an explosive release.

Answer 4

Temperature, composition, and volatile (gas) content largely determine the viscosity of lava.

Temperature: The hotter the lava, the lower the viscosity (the thinner it is). The cooler the lava, the higher the viscosity (the thicker it is).

Composition: the more felsic the lava (the more silica in the lava), the higher the viscosity because silica forms chains in the cooling lava even before it crystallizes. The shape of the silica chains, often times forming a chain of rings, allows places for volatiles to become trapped. The more mafic the lava (the less silica in it), the lower the viscosity. It turns out that mafic lava is high temperature lava because high temperatures are required to melt mafic minerals in the first place. Felsic lavas are low temperature lavas because lower temperatures are required to keep felsic minerals molten (and if it was hotter it would have incorporated more iron and magnesium in comparison to silica).

Volatile content refers to gases dissolved in the lava, like carbon dioxide in soft drinks. Lavas may contain up to 6% or more of their mass as gases. The two most abundant gases in lava are water vapor and carbon dioxide. There is commonly also nitrogen, sulfur dioxide, and small amounts of chlorine, hydrogen, argon, and a few other gases. When lava approaches the surface, the pressure on it is greatly reduced and the dissolved gases come out of solution; they form bubbles and rise. The escape of gases may produces tremendous force in a volcano, producing explosive eruptions. In general, the more felsic the magma the greater the volatile content. So mafic/basaltic volcanoes are fairly quiescent, intermediate/andesitic volcanic eruptions are moderately explosive, and felsic/rhyolitic volcanoes may be extremely explosive.

So, mafic lavas are hot , low in silica and volatiles, and have relatively low viscosity. They flow easily outward from the vent (where it comes out of the ground), and may travel great distances before completely solidifying.

Felsic lavas are not as hot, high in silica and volatiles, and have a high viscosity. They are thick and gooey and resist flowing. Their high volatile content makes them potentially highly explosive.

Answer 5

Incredibly high pressure. Under geological pressure even normally stable earth can become liquid-like which causes the collapes of some structures. This is called liquifaction. Magma is thick but the pressure is so great that it has to be dissipated some how.

Answer 6

it is pressure built up from the heat that causes the volcano to erupt. Every put mac and cheese or soup in the microwave too long. After a while, the heat sends the liquid shooting up out of it. Now think of it on a massive scale. That is how they erupt.

Answer 7

Gas under pressure gets released and forces the magma up.

Answer 8

if i recall.. it is because the gases can not excape and build up and then explode...