Fumarole on Kīlauea Volcano, Hawaiʻi

Fumarole on Kīlauea Volcano, Hawaiʻi. Elemental sulfur vapor escaping from the fumarole has cooled to form yellow-colored crystals around its margins. Credit: Robert L. Christiansen.

http://volcanoes.usgs.gov/vsc/glossary/fumarole.html