Fumaroles: A Sign of Volcanism

Also kKown as Solfataras, these Features let off a lot of Steam

Sep 27, 2007

Often less captivating than erupting geysers and colorful hot springs, fumaroles are fascinating signs of volcanism at work.

Fumarole Basics

Fumaroles may seem boring compared to water-spurting geysers and rainbow colored hot springs but the environmental processes behind them are just as interesting. Fumaroles are the hottest of the three features. Whereas geysers and hot springs contain liquid water, fumaroles do not. Only water vapor is present in fumaroles. The intense heat transforms any groundwater entering a fumarole into steam instantly. All that is released from a fumarole is steam and gases.

Geologic Location of Fumaroles

Fumaroles can occur on the surface of lava flows and thicker pyroclastic flows. The flows require a release of heat to cool off. Small cracks and crevices in the crust also allow steam from deeper within the Earth to escape. Fumaroles can be present singularly or in large fields full of them. Fumaroles are common globally wherever volcanism is occurring. Depending on the heat source, fumaroles can be short or long term feature, ranging anywhere from weeks to many hundreds of years. The hotter the heat source is, whether it be an internal rock mass or a volcanic flow, the longer it will take to cool off, so the longer the fumarole will exist.

Force Relates to Sounds

Fumaroles are not quiet geothermal features. They have been described as hissing, roaring, and even thundering. The sounds are dependent on the force of the steam being released into the atmosphere. Slowly diffusing emissions will have lessened sounds. Forceful, blasting emissions produce greater sounds. Yellowstone Park’s famous Roaring Mountain is covered with fumaroles and gets its name from the sounds coming from the mountainside. If there is enough force, the ground around a fumarole can actually tremble as steam is released.

The Chemistry of a Name

Fumaroles are commonly called by the word solfataras, whose origins relate in Italian and Latin to sulfur. The general public tends to use fumarole interchangeably with solfatara, unrelated to chemistry. Less commonly, the term mofette is used. Technically speaking, solfatara describes a steam vent rich in sulfuric compounds, such as sulfur dioxide or hydrogen sulfide, while moffetes are rich in carbon dioxide.

A few possible chemical reactions around fumaroles are interesting to note. Atmospheric water reacting with sulfur dioxide gas can produce acid rain. Carbon dioxide emissions can be a hazard to human and animal health. Air is lighter than carbon dioxide, so the carbon dioxide may concentrate in areas close to Earth’s surface. Hydrogen sulfide reacts with oxygen from the atmosphere to produce sulfuric acid and later transforms into the native element sulfur, which appears in yellow deposits around fumaroles.