Answers. Best Answer: Volcanoes form when hot material from below rises and leaks into the crust. The hot material, called magma, rising from lower ground, gathers in a reservoir called the magma chamber.Eventually, but not always, the magma erupts onto the surface and forms lava. volcano is formed when plates hit each other. One of the plates goes under the other. This is where the earth heats and melts the rock into magma and gases. This can happen as deep as 100 miles below the earth.