(covers information from several alternate timelines)
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Volcanoes on Penthara IV were activated when subterranean pockets of carbon dioxide were opened by a phaser drill. The volcanoes started to erupt and produced large plumes of volcanic dust threatening to bring another ice age on the planet. (TNG: "A Matter of Time")
In the alternate reality, a supervolcano on Nibiru threatened to destroy all life on the planet, including the indigenous Nibirans. The threat was averted when Spock activated a cold fusion device in the magma chamber, rendering the volcano inert. (Star Trek Into Darkness)