Why does liquid magma flow upward ?

Answer 1

Well...just to be clear, all magma is liquid. Anyway...it flows upward for a few reasons.
A) Pressure causes it to head toward a place that it can escape (like a volcano or a sea floor spreading ridge). Think of it as a tube of toothpaste...when you squeeze it, it comes out the top, not the side, because it is the most energy efficient way to release the pressure.
B) Dissolved gases make certain portions of the magma less dense, hence they want to rise above the denser surroundings.
C) Temperature gradients cause cooler magma to sink, and hotter magma to rise. Same principle that causes hot air to rise.

Answer 2

Liquid Magma

Answer 3

Magma Flow

Answer 4

Actually, it is not necessarily true.

Magma flows from an area of high pressure to another area of low pressure. Magma acts like liquid, but is not necessarily liquid in state. More of liquid-solid hybrid (it isn't homogenous, you know). Anyway, this is to attain some sort of equilibrium (Sorry, I'm a geologist, not some chemist, heehee!).

In this case, the hot magma (read: high temperature, thus high pressure; think PV=nRT) would flow to an area where it has lower pressure, which is basically any crevice that is directed towards the surface of the Earth. So saying an "upward flow of magma" holds true for cases such as the events occurring in volcanos. These create discordant igneous bodies such as dikes, since rock strata are forced upwards.

Sometimes, magma flows laterally (i.e. inserts within planes of weakness, such as beddings or joints, that is subparallel to the surface of the Earth). In general, these create concordant igneous bodies like sills, since they are injected between subplanar features. In this case, magma flow does not flow upwards, right?

Hope this helps. Thanks for your time.

Answer 5

Because the magma has become very hot. This causes the magma to expand and become less dense (same mass but greater volume). The lower density magma rises above the more dense surrounding material.

Answer 6

Not only does the magma expand with heat but it is full of gases that help to drive it upwards. The same reason a pot of boiling water will boil over after it passes the boiling point.

Answer 7

Heat rises, generally. It actually expands as much as possible. The mass and pressure within the mantle usually means sideways expansion is less common than upward (out away from the core) expansion.

Answer 8

maybe because heat rises