what gases form when a volcano erupts
Volcanic gases are probably the least showy part of a volcanic eruption, but they can be one of an eruption's most deadly effects. Most of the gas released in an eruption is water vapor (H 2 O), and relatively harmless, but volcanoes also produce carbon dioxide (CO 2), sulfur dioxide (SO 2), hydrogen sulfide (H 2 S), fluorine gas (F 2), hydrogen fluoride (HF), and other gases. All of these gases can be hazardous - even deadly - in the right conditions.