A volcano is an opening in the Earth's crust where magma  from the mantle reaches the surface, sometimes in a slow, dribbling fashion, called an effusive eruption, and sometimes in a violent event called an explosive volcanic eruption. Volcanoes usually occur in divergent boundaries between tectonic plates, places where the crust is weak and magma can rise to the surface due to the immense pressure of the mantle below. When magma from beneath a volcano reaches the surface, it is called lava

What looks like fire when a volcano erupts is really molten rock and ash

 deep inside, the earth is formed of molten rock, which is called magma. In most places the earth’s crust is so thick the magma cannot escape. But in others it escapes in the form of volcanoes. Magma, gas and water collect in a reservoir and, when the pressure becomes too great, force their way out onto the surface, where the magma, now called lava, becomes solid.

To the Parent

Magma, molten rock in the earth’s mantle, is formed at extreme depths within the earth and is forced upwards by high temperatures and pressure. It forms reservoirs a few kilometers below the surface and is forced out through fissures in the earth’s crust in periodic eruptions. When magma erupts it is known to us as lava.