Fumaroles and Solfataras: The Breath of a Volcano
Even when a volcano is not erupting, it breathes. Through openings called fumaroles, it exhales steam and volcanic gases, sometimes in quiet wisps, sometimes in roaring jets. Where these vents are rich in sulphur, they are known as solfataras, ringed with vivid yellow crystals and the sharp smell of sulphur. These features are a sign of the life within a volcano and a vital clue to its state, watched closely by scientists for signs of unrest.
What a fumarole is
A fumarole is an opening in the ground, usually in a volcanic area, through which steam and volcanic gases escape. The gases, including water vapour, carbon dioxide, sulphur dioxide, and others, rise from magma or hot rock below and emerge at the surface. Fumaroles can be found in craters, on the flanks of volcanoes, and in geothermal fields, marking where heat and gas reach the surface.
Solfataras and sulphur
A solfatara is a fumarole that emits sulphur-rich gases, named after the Solfatara crater near Naples in Italy. As the sulphurous gases cool, they deposit vivid yellow crystals of sulphur around the vent, creating striking colours and a strong smell. These sulphur deposits have been mined in some places, and the solfataric landscape is among the most distinctive of volcanic features.
The Solfatara of Pozzuoli
The original Solfatara, near Pozzuoli in the Campi Flegrei volcanic area west of Naples, gave its name to all such features. This shallow crater steams and bubbles with fumaroles and mud pots, releasing sulphurous gases. As part of the restless Campi Flegrei caldera, it is closely monitored, its changing activity a window into one of Europe's most significant volcanic systems.
Colourful chemistry
The chemistry of fumarole gases creates remarkable colours and deposits. Beyond the yellow of sulphur, fumaroles can deposit a range of minerals, and at some volcanoes, such as Kawah Ijen in Indonesia, burning sulphurous gases produce an eerie blue flame visible at night. The vivid, otherworldly colours of fumarolic areas make them among the most visually striking volcanic landscapes.
A sign of the volcano's state
Fumaroles are a vital clue to what is happening inside a volcano. Changes in the temperature, composition, or output of fumarole gases can reveal whether magma is rising and whether the volcano is becoming more restless. Scientists monitor fumaroles closely, as a change in their behaviour can be an early warning of an impending eruption.
Hazards of fumaroles
Although they may seem gentle, fumaroles carry hazards. The gases they release, including carbon dioxide and toxic compounds, can be dangerous, especially in enclosed or low-lying areas where they can accumulate. The ground around fumaroles can also be unstable and scaldingly hot, making caution essential for anyone exploring these features.
Fumaroles and mining
In some places, the sulphur deposited by fumaroles has been mined by hand, as at Kawah Ijen, where workers carry heavy loads of sulphur from the crater in one of the most gruelling and dangerous jobs in the world. This human use of fumarolic deposits is a striking example of the relationship between people and the chemistry of volcanoes.
Explore on the map
From the Solfatara of Pozzuoli to the blue flames of Kawah Ijen, fumaroles and solfataras mark where volcanoes breathe. Explore these volcanic areas on the interactive map — filter by region to see where the steam and gas of the Earth's volcanoes escape to the surface.