Magma, as lava is called when it is still beneath the earth’s surface, is composed of molten rock.
Magma is molten rock that is still underground. Below the earth’s surface temperatures between 700 and 1,300 °C melt rocks. Most of them contain silica, a compound made of silicon and oxygen.
When rocks melt, those that contain less silica produce the most fluid and fastest magma; those containing more silica produce denser magma, which tends to trap gas bubbles that can make an eruption more explosive. In any case, magma is lighter than the surrounding rocks and therefore tends to rise towards the surface and collect in underground chambers.
Syrup. Many volcanoes, or openings in the Earth’s crust, are located right above these magma chambers. When the magma bursts onto the surface it is called lava which, depending on the silica content, can be similar to a syrup or very dense like mud.
