The froth that runs out of a volcano is called lava.

While lava itself is molten rock, the frothy texture is due to dissolved gases that are released as the lava cools and solidifies. This creates bubbles and a foamy appearance, particularly in a type of lava called pahoehoe.

So, although the term "froth" isn't typically used to describe lava, it's a good analogy for its appearance and the process that creates it.