How Volcanoes Work

 Image Described in Caption
 Fumarole -- The yellow color around this fumarole comes from sulfur crystals derived from the cooling of sulfur vapor escaping from the fumarole opening. Sulfaterra (yellow ground) is the name given to these sulfur accumulations. The fumarole is located on the Kilauea volcano, Hawaii. Courtesy of R.L. Christiansen, USGS.