火山气体是指高温高压下地球内部岩石熔融而形成的岩浆中的挥发性成分。火山气体在火山喷发和喷发前后大量产生。随火山活动的强弱，火山气体的温度有高有低。高于当地水的沸点时，气体中的水蒸汽含量最多，低于当地水的沸点时气体中以二氧化碳为主。火山气体中还有一部分是固体矿物的蒸气，它们到达地面后常在喷口附近凝结，形成硫黄、砂等矿物。
洞穴的形成需要火山气体和热量的稳定释放，海拔高到足以防止每年的大量降雪在夏季融化。
The cave-making recipe calls for a steady emission of volcanic gas and heat, a heavy annual snowfall at an elevation high enough to keep it from melting during the summer.
火山气体与岩浆加热地下水，使之变成一种高温的酸性水，将演岩石溶解为泥浆。
Volcanic gases and magma heat the groundwater, turning it in a hot acid that dissolves rock into a slurry of mud and clay.
在此之前，古生物学家普遍认为这一恢复过程需要上千万年——考虑到“大消亡”的程度，或者由于这些火山气体导致对地球环境的毒化程度。
Until now, palaeontologists have thought the recovery took tens of millions of years—a reflection either of the profundity of the Great Dying or of the toxic desert planet that the eruptions created.
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