The Burning Bush is a famous icon of the Hebrew god introduced in the Book of Exodus (3:1-21) and located on Mount Sinai. The magical properties of the bush are that it was on fire, but was not consumed by flames.
It's not hard to suppose how this imaginary thing leaped into the imaginations of ancient story tellers. Peasants or local dwellers who had never experienced or had access to stories about lava flows or volcanic explosions, would have a very limited concept of "fire". For example, without knowledge of the concepts of radiation and particle physics, the Sun was thought to be burning wood or charcoal, etc.
So without knowledge of lava or volcanic activity, how would middle-eastern people explain volcanoes that smoked for weeks or months and glowed at night? It would, to them, seem like a mountain-top forest fire, but after a week or a month of smoking and glowing, a forest fire no-longer makes sense, unless, somehow the forest could "burn" without being "consumed".