Volcano

You may be looking for the episode of The Daleks' Master Plan.

Flames bursts from a volcano on Sarn. (TV: Planet of Fire)

A volcano was an opening in a planet's surface, usually mountainous, which allowed hot lava, ash and gases to escape from below the surface. The word was coined by Pompeiian Lobus Caecilius on witnessing Vesuvius' eruption in 79. He believed that the "great god Vulcan must [have been] so enraged" and described the eruption as "so volcanic" and that it was "like some sort of volcano". (TV: The Fires of Pompeii)

Volcanoes on Earth

The First Doctor, John and Gillian once visited a South Seas island and witnessed a volcanic eruption. (COMIC: Guests of King Neptune)

In 79, the Roman city of Pompeii was destroyed in the eruption of the volcano Vesuvius. (AUDIO: The Fires of Vulcan, TV: The Fires of Pompeii) The eruption was set off by the Tenth Doctor and his companion Donna Noble and it destroyed the Pyroviles and opened a rift in time for a second. The event was also a fixed point in time and couldn't be changed. (TV: The Fires of Pompeii)

In 1883, the Doctor witnessed the eruption of the volcano Krakatoa. (TV: Inferno, Rose) The explosion released at least one captive Xylok to the surface. (TV: The Lost Boy)

In 1984, the Dominator Haag set up base in an Icelandic volcano and attempted to acquire Earth's core for his fleet, causing an increase in volcanic activity. UNIT soldiers investigated and turning his equipment against him, creating an explosion which destroyed the aliens and causing the volcano to erupt. (COMIC: The Fires Down Below)

In the 21st century, Salamander triggered volcanic eruptions in Hungary as part of his plan to take control of Earth. (TV: The Enemy of the World)

In 2167, the Daleks' attempt to mine Earth's core resulted in a volcanic eruption in Bedfordshire. (TV: The Dalek Invasion of Earth)

Volcanoes on other worlds

On Dulkis, the Dominators' attempt to turn the planet into starship fuel resulted in a volcanic eruption that threatened the Second Doctor's TARDIS. (TV: The Dominators)

A massive volcano on Mars created the Olympus Mons crater. (PROSE: Transit)

On Skaro, the invading Monstrons made their base inside an extinct volcano. A Dalek sacrificed its life to set off a volcanic eruption that destroyed the Monstrons. (COMIC: The Menace of the Monstrons)

On one planet, a volcano served as the Extortioner's secret base. (COMIC: The Extortioner)

On Spiridon, the city that the Daleks used as a base was cooled by molten ice from the ice volcanoes. (TV: Planet of the Daleks)

Planets with high levels of volcanic activity included Gehenna (PROSE: Mean Streets), Krop Tor, (TV: The Impossible Planet / The Satan Pit) Sarn (TV: Planet of Fire) and Tigus. (TV: The Daleks' Master Plan)

Hallucination of a volcano

Clara Oswald, after entering a dream like state with a mood patch, believed that she visited a volcano to destroy the TARDIS keys in lava to blackmail the Twelfth Doctor into saving Danny Pink's life. (TV: Dark Water)