Middletown was an English village.
Lord Urton and his wife lived there in the late 19th century. He owned and operated a tin mine, which by the time of the Eighth Doctor's arrival had been worked out.
Around the same time, a fire elemental emerged from the Earth's crust near the mine. When it decided the time was right to expand its control, it sent a wave of lava to engulf the town, turning it into a wasteland. The Doctor killed the creature by a huge flood released by the destruction of the Middletown dam. (PROSE: The Burning)