In order to find out when there is a volcanic eruption, you should consider the structure of the Earth.The outer shell of the planet called the lithosphere (from the Greek. "Stone shell").Its thickness on the land up to 80 km, and at the bottom of the ocean - only 20-30 km.This represents about 1% of the radius of the earth's crust.Layer following the crust - mantle.It has two parts - an upper and a lower.The temperature in these beds reaches several thousand degrees.In the center of the Earth - a solid core.

bottom layer of the mantle, located closer to the core, is heated more than the upper.The temperature difference results in that the fibers are mixed: hot material rises up and cold - falls.Simultaneously wit
h this process is the cooling of the surface layers and internal heating.For this reason, the mantle is in constant motion.His consistency it resembles hot tar, because in the center of the planet very high pressure.On the surface, this viscous environment "floats" lithosphere plunged into it its lower part.

Since the stone shell immersed into the mantle, it inadvertently moves along with it.Some of its parts, lithospheric plates can crawl on each other.Stove, which has appeared below, more and more immersed in the mantle and melted at high temperatures.Gradually it becomes a magma (from the Greek. "Test") - a thick mass of molten rock, water vapor and gases.

Through the collision of lithospheric plates are formed magma chambers.They are going to the magma rises to the surface.In outbreaks, it behaves like a test, rises by leaps and bounds: increases in volume, rising from the depths of the earth cracks and fills all space.Where the crust is thinned or has faults, there is a volcanic eruption.

it comes when there was a degassing (gas outlet to the outside) of magma.The focus of the mixture under high pressure, which pushes it out of the bowels as soon as it becomes possible.Climbing up, deprived of gas and magma turns into flowing lava.