what likely causes magma to rise?

Answer 1

Hot things (such as magma compared to solid {cooler} rock) rise because they are less dense. When magma is surrounded by solid rock which is cooler it rises because it is less dense than the surrounding material - the same reason why gasses (the atmosphere) rise above the crust of the earth. Gravity pulls more at the more dense materials (solid rock, metals, etc) so they sink compared to the less dense materials (gasses, magma, water, etc).

Basically it has to do with the number of molecules in a given space. As materials cool the molecules that make them up move less and so there are more molecules per cubic meter -- which means they weigh more per cubic meter and will feel the effect of gravity more than the same material which is at a higher temperature (but has less molecules per cubic meter).

Water is the exception to this rule because of the hexagonal shape of ice crystals which captures pockets of air and makes solid H20 less dense than liquid water.

Answer 2

magmas erupt in areas above subduction zones. This suggests a relationship between the production of andesitic magma and subduction. An earlier theory suggested the wet partial melting of subducted oceanic lithosphere, but newer theories suggest that it is wet partial melting of mantle. Since the oceanic lithosphere is in contact with ocean water there should be much water in the pore spaces of upper oceanic crustal rocks as well as water contained within clay minerals that have settled to the sea floor. When this material is subducted, it begins to heat up and water is driven off. If the water enters the overlying asthenospheric mantle, it will lower its melting temperatures and thus melting will occur.



Volcanic Eruptions

In general, magmas that are generated deep within the Earth begin to rise because they are less dense than the surrounding solid rocks.

As they rise they may encounter a depth or pressure where the dissolved gas no longer can be held in solution in the magma, and the gas begins to form a separate phase (i.e. it makes bubbles just like in a bottle of carbonated beverage when the pressure is reduced).

When a gas bubble forms, it will also continue to grow in size as pressure is reduced and more of the gas comes out of solution. In other words, the gas bubbles begin to expand.

If the liquid part of the magma has a low viscosity, then the gas can expand relatively easily. When the magma reaches the Earth's surface, the gas bubble will simply burst, the gas will easily expand to atmospheric pressure, and a non-explosive eruption will occur, usually as a lava flow (Lava is the name we give to a magma when it on the surface of the Earth).

If the liquid part of the magma has a high viscosity, then the gas will not be able to expand very easily, and thus, pressure will build up inside of the gas bubble(s). When this magma reaches the surface, the gas bubbles will have a high pressure inside, which will cause them to burst explosively on reaching atmospheric pressure. This will cause an explosive volcanic eruption

Answer 3

Areas of high temperature always rise. Hot air rises, hot water rises, and since magma is hot it too rises.

Answer 4

Density differences. Magma rises because it is less dense than the country rock. This is because it is a liquid, and because it is hotter. Being a liquid means that it is less dense than a solid. Being hotter means that it is less dense than cooler solids around it.

Answer 5

its the pressure because magma contains very high temperature and under the earth is very hot it pushes the magma....... remember that hot air rises.......