A fumarole is an opening in the Earth’s crust, often near volcanoes, that emits steam and gases such as carbon dioxide, sulfur dioxide, and hydrogen sulfide. Fumaroles are significant in volcanology for studying the degassing processes of magma, the chemical composition of volcanic gases, and the potential hazards associated with volcanic activity.
Reference: Symonds, R. B., Rose, W. I., Bluth, G. J. S., & Gerlach, T. M. (1994). Volcanic-Gas Studies: Methods, Results, and Applications. In: Carroll, M. R., & Holloway, J. R. (Eds.), Volatiles in Magmas. Reviews in Mineralogy.