Volcano

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

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

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

Earth at an early stage of its development had many active volcanoes which constantly erupted for millions of years, resulting in the formation of the planet's granite crust. This was observed by the Fourth Doctor, who found the process marvelous, and Sarah Jane Smith, who found it horrible. (AUDIO: Exploration Earth)

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

On 24 August 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, destroying the Pyroviles and opening a rift in time for a second. The event was also a fixed point in time and could not be changed. (TV: The Fires of Pompeii)

In the 9th century, a Haemovore working with the Twelfth Doctor detonated a volcano on an island in the North Atlantic to destroy the Flood on Earth and avert Fenric's plot to replace the Haemovores with the Flood. (COMIC: The Wolves of Winter)

The Year Without a Summer in 1816 was blamed on volcanic ash, however, the Thirteenth Doctor pondered whether it was really something else which caused it. (TV: The Haunting of Villa Diodati)

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 2011, Professor Saurian attempted to raise the Earth's temperature by causing all the planet's volcanoes to erupt at once. The plan was stopped by the Eleventh Doctor, who limited the eruptions to the volcano containing Saurian's base. (COMIC: Extinction Event)

In 2018, 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)

An unknown incarnation of the Master ended the Monks' rule of a planet by throwing their "lynchpin", a young girl, into a volcano. As Missy, she later told Bill Potts and the Twelfth Doctor of this when they asked about the Monks due to their rule over Earth. (TV: The Lie of the Land)

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)