The gases escaping from fumaroles can be rich in hydrogen sulfide. When the hot gases come into contact with the atmosphere, they cool and oxidise and can form yellow crystals of pure sulfur around fumarole vents (inset). The extensive sulfur deposits of Whakaari White Island were mined until the 1930s.
Text courtesy of Te Ara and Manatū Taonga Ministry for Culture and Heritage, CC BY-NC 3.0 NZ.
