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Our transcription: All volcanoes erupt gas, which contributes to volcanic explosiveness. The most common substances in volcanic gas: water vapor, carbon dioxide, sulfur and nitrogen are also found in the air and in the oceans. Evidence of volcanic gas can even be found locked within hardened lava. This black volcanic rock is basalt. It's the principal type of lava found in shield volcanoes. Like other types of volcanic rock, basalt forms when lava cools and crystallizes following a volcanic eruption. When an eruption occurs, there's a sudden drop in pressure which causes bubbles of gas to spontaneously form in the lava. This same process occurs when we open a bottle of soda. These holes in the basalt were created by gas bubbles that formed in the lava when it erupted.
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