Here on the surface of the Earth, the ground is relatively cool. But as you descend into the Earth, things get hotter and hotter, eventually reaching hundreds or even thousands of degrees C. The hot temperatures inside the Earth’s mantle can melt rock; this is magma.
Magma collects in large pools underneath the surface of the Earth in vast magma chambers. Because it’s lighter than the surrounding rock, it makes its way upwards through weaknesses in the Earth’s crust until it reaches the surface. When the magma reaches the surface, it can extrude as lava, or even erupt violently throwing up ash and even rocks.
The temperature of magma can range between 700 and 1300 degrees Celsius depending on the chemical composition of the rocks. You might be surprised to know that the interior of the Earth is a solid, not liquid. The magma only forms in regions where the temperatures are high and the pressures are low; typically within a few kilometers of the surface of the Earth.
The melted magma comes from rocks under huge temperatures and pressures. Most rocks are a collection of different minerals, which can have different melting points. When one part of the rock starts to melt, the rest remains solid. This causes the melted material to squeeze out in small globules. These globules collect together to fill up the magma chamber underneath a volcano.
All igneous rock found on the Earth was originally formed as magma.
We have written many articles about the Earth for Universe Today. Here’s an article about the difference between magma and lava.
We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.