Built for the World's Fair in 1939 and later moved to Griffin Rock, Mount Magma is a life-sized artificial volcano. In order for it to be as realistic as possible, the builders installed a pipe leading into the Earth's core, allowing real lava to flow up, because that couldn't possibly backfire at any point in the future.
Pressure began forcing lava up through the pipe, entering the sewer system and flooding out into the streets of Griffin Rock. When the Rescue Bots and their new human partners discovered that Mount Magma was the source of the lava, they set about trying to relieve the pressure by opening the volcano's cover. After Boulder and Graham Burns located the control switch, Blades and Dani operated it using Blades' winch, but were promptly caught in a cloud of ash. After they set down, and while Heatwave and Kade were dousing the lava with water, Dani spotted that lava was flowing from the other side of the volcano into the island's cave system. She and Blades eventually managed to stop it by dropping the contents of a water tower onto the lava flow.
While on a mission underground, Heatwave and Optimus Prime stumbled on a cavern filled with energon under the volcano. They later ignited the deposit, using the blast wave to carry them up and out of the volcano's crater.