Ash cloud
An ash cloud was a toxic cloud produced by an erupting volcano, during the time in which it expelled volcanic gases. (; ; ; ) 

On the planet Nibiru in the alternate reality of 2259, a volcano threatened to destroy the entire world as well as the pre-warp civilization inhabiting it – the Nibirans. Captain  decided to neutralize the volcanic threat by having Commander , along with Lieutenants  and , place a cold fusion device inside the volatile volcano's chamber and thereby save the planet. To achieve this plan and not violate the Prime Directive, Spock, Sulu, and Uhura's shuttlecraft was concealed within the volcano's ash cloud. The ash cloud was eventually dissipated with the cold fusion device Spock, after much trouble, successfully  detonated. ()

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Meteorology
Geology