>While it may vary by volcano, the most abundant gas released during volcanic activity on average is water vapor. This is followed closely by carbon dioxide and sulfur oxide.
Other gases such as hydrogen chloride, carbon monoxide, helium, hydrogen fluoride and hydrogen chloride are also released during volcanic activity. The amount of gases released depends on the size of the volcano and the strength of the eruption.
Many of these gases are harmful to people, animals and the landscape. Hydrogen fluoride is the most harmful, followed by sulfur oxide. Most also contribute to air pollution, which results in a weakening of the Earth's ozone layer.