Volcano

A volcano is a geological formation on the surface of a planetary body. Molten rock is called magma within a volcano, and lava after it's been expelled.

Background
Volcanoes form in tectonically active areas. Magma movement forces the crust to flex, sometimes producing tremors and earthquakes, and pressure forces magma up through the top of the volcano. Two eruption stages are called Vesuvian and sub-Plinean. A stratovolcano is one type of volcano. 

Lava from erupting volcanoes can form islands in oceans. Over a span of eons, the lava breaks down into highly nutrient soil. 

Free hydrogen can be extracted from volcanic gases. 

Volcanoes can reach great heights in lower gravity environments. Mazama Mons on the moon Skaftar was 6,000 meters tall and 20 km across at the bottom. 

History
10,000 years ago, Mount Seleya on erupted, expelling with such strength that debris crated nearby moons. 

1400 years ago, according to Klingon legend, Kahless the Unforgettable made the first bat'leth out of a lock of his own hair on the slopes of Kri'stak volcano on Qo'noS. 

In 2259 in an alternate reality, Spock planted a cold fusion device within an active volcano on Nibiru to save the lives of indigenous villagers. 

In 2266, James T. Kirk commented that the scream made by Jobo, a Rykunian octopus, would freeze a volcano on the planet Mercury. 

In 2267, a lava river from an erupting volcano dragged along the Galileo shuttlecraft. 

In 2267, volcanoes formed during an attempt to force the planet Rimillia to rotate, breaking the tidal-lock to its star. 

In 2269, during a Vedala mission to retrieve and return the "Soul of the Skorr” on an unidentified planet, Kirk and his expedition were threatened by an erupting volcano. They hastily repaired their Vedala cart to outrun the lava flow..

In 2274, the Totality tapped the geothermal energies of an active volcano on a planet near Zaran II. 

In 2275 during a layover, Spock studied volcanoes for a day near Reykjavik, Iceland. 

In 2293, during his retirement, Kirk rafted on flows of lava from the Valtarik volcano. 

As of 2369, the most recent eruption of Mount Vesuvius lasted nine hours. 

Lifeforms
In 2267, a non-humanoid Tactisian lifeform lived within an active volcano on the asteroid Tactis II. A video camera robot was sent to probe the dangerous interior. 

In 2273, a colony of sentient crystalline lifeforms was discovered within Rakatan Mons on Skaftar. They were made of coagulated silicates and communicated by producing vibrations in magma. 

Volcanoes

 * Firefalls of Gal'Gathong, Karethvek (Romulus) • Graveyard of Lost Ships (Sanctuary) • Krakatoa (Earth) • Kri'stak volcano (Kra'ta plains, Qo'noS) • Mandara (Tohvun III) • Mazama Mons (Skaftar) • Mount Seleya • Mount Vesuvius (Pompeii, Earth) • Olympus Mons (Mars) • Proutu (Tkon) • Rakatan Mons (Skaftar) • Shiluzeya (Shilu island, Akkalla) • Valtarik volcano • Near Vulcan's Forge

Planets and moons with volcanoes

 * Akkalla • Aluwna • Ahmista • Belle Terre • Betazed • Ceti Alpha V • Devron II • Drenar IV • Dyson homeworld • Earth • Elysium • Etolos • Farius Prime • Helva • Heronius • Koorn • Lorca • Mars • Myrmidon • Nibiru • Ocampa V • Okeanos • Ostratus • Phaedra • Qo'noS • Rator II • Rimilia • Rithra • Romulus • Remus • Sanctuary • Selva • Sigma 1212 • Skaftar • Tactis II • Tezwa • Tkon • T'Khut • Tohvun III • Tycho IV • Vanìmel •