A fumarole is an opening in Earth's crust, often in the neighborhood of volcanoes, which emits steam and gases such as carbon dioxide, sulfur dioxide, hydrochloric acid and hydrogen sulfide. The steam is created when superheated water turns to steam as its pressure drops when it emerges from the ground. Fumaroles may occur along tiny cracks or long fissures and on the surfaces of lava flows and thick deposits of pyroclastic flows. A fumarole field is an area of thermal springs and gas vents where magma or hot igneous rocks at shallow depth release gases or interact with groundwater. Fumaroles could be described as a hot spring that boils off all its water before the water reaches the surface.