The picture below is a fossilized fish that was preserved by volcanoes. There are five gases that are produced by volcanic activity. All of these gases are harmful except for water vapor. These five gases are water vapor, carbon dioxide, sulfur dioxide, fluorine, and chlorine. Carbon dioxide is one of the main causes of the Greenhouse effect, but there are not significant amounts for the carbon dioxide emitted from volcanic eruptions to contribute to the Greenhouse effect.
Sulfur dioxide can have a short-term effect on the weather.
This aerosol blocks the sun and causes cooler temperatures globally. The sulfur dioxide eventually depletes, but is replenished by each eruption rich in sulfur dioxide. Fluorine can be a deadly to animals after an eruption. The fluorine is poisonous to animals that eat the fluorine-coated grass and plants. Chlorine is emitted as hydrochloric acid into the atmosphere.