The types of gas expelled from a volcanic eruption include water vapor (the most abundant of volcanic gas), carbon dioxide, hydrogen sulfide, hydrogen halides and sulfur dioxide. When volcanoes erupt, they have a negative effect on the atmosphere and planet because all of the gases emitted (except water vapor) are hazardous to people, animals, plants, and property. These gases can add to the Greenhouse Effect by causing an increase in temperature. Some particles such as ash and sulfur dioxide act as an exact opposite by creating a cooling effect, reflecting sunlight away from Earth. There is also evidence that proves these eruptions can affect short-term weather.
