Ask a scientist: What makes lava?

Lava starts its life as magma, which is formed about 20 miles below the surface of Earth. It’s called lava when it reaches the surface. Sometimes it escapes slowly, such as the active volcano in Hawaii that is slowly and continuously pouring lava into the ocean. Other times, it escapes more violently in a volcanic eruption that spews lava up to 2000 feet above the volcano!

Magma and lava are molten rock — a mixture of melted rocks, solid rocks, and gas. Rocks are already hot deep in the Earth, but temperature is not the only important factor. Rocks that form magma melt in two main ways. First, decompression melting forms some magma. This occurs when rock is pushed towards the surface. It maintains its temperature, but is now in a lower pressure area which allows it to melt. The second way is through flux melting, or the adding of water or carbon dioxide into hot, solid rocks. This lowers the rocks melting temperature and allows it to melt and form magma. This process is like adding salt to icy sidewalks in the winter — the salt lowers the freezing point of water, allowing it to melt even though the temperature didn’t change.

Hot magma rises to the surface and collects in chambers. When enough pressure builds up in these chambers, the magma escapes to the surface through volcanoes as lava.

Fun fact: There are volcanoes underwater that release lava into the oceans and seas!