During the eruption of Augustine VOlcano in Alaska in 2006 a yellow plume was observed within the larger white plume emitted from the summit of the volcano. I was "told" that it probably was from the SO2 and H2S gases reacting to form elemental sulfur. Reference searching brought me to the Claus method of removing H2S from natural gas. First oxiding the H2S in high temp..(the volcano) resulting in native sulfur and then finishing off the process with SO2 yielding more Native sulfur. This Claus method is the current industrial method for S production. Was witnessing the process in nature. Mike