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Fume rises from Pu`u `O`o (left) and drifts down the light trade winds. This wide-angle view, taken from Chain of Craters Road just west of Kealakomo, shows fume as it passes in front of distant clouds 30 minutes before sunrise. The fume, a mixture of sulfur dioxide and other volcanic gases, becomes vog as it chemically reacts with other substances, oxidizes, and develops aerosols.