They’re both molten rock, so what is the difference between lava and magma? It all comes down to location.
As you probably know, the interior of the Earth is very hot. We stand on the cool crust, but as you travel down through the crust and into the mantle, it gets hotter and hotter. Although the Earth’s mantle is solid, it can have pockets of molten rock trapped between the mantle and the crust. This liquid rock is less dense than the surrounding mantle, and so it makes its way up through the Earth’s crust through cracks and weaknesses. Eventually it reaches the surface, and erupts from a volcano.
Magma is the molten material beneath the Earth’s crust. It usually collects in a magma chamber beneath a volcano, and can then be injected into cracks in rocks or issue out of volcanoes in eruptions. The temperature of magma ranges between 700 C and 1300 C.
When it reaches the surface and comes out of a volcano, magma becomes lava. There are actually different kinds of lava depending on its thickness or viscosity. The thinnest lava can flow downhill for many kilometers, creating a gentle slope. The thicker lavas will just pile up around the volcanic vent and hardly flow at all. The thickest lava doesn’t even flow. It just plugs up the plumbing of a volcano, and can be the cause of violent explosions.
So the different between magma and lava is location. Magma is deep underground, in chambers beneath volcanoes, and lava is the stuff that comes out of volcanoes.
We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.