Sulfur dioxide and hydrogen sulfide gases

Sulfur dioxide and hydrogen sulfide gases themselves are not visible, but dramatic plumes are sometimes visible at Kīlauea Volcano's summit (shown here) and Pu‘u ‘Ō‘ō. These plumes are a result of atmospheric conditions rather than increased volcanic activity, and frequently occur when warm volcanic gases condense as they are released into cooler air temperatures of early mornings or evenings.