Volcanic Springs

Geysers, Hot Springs,
Mud Pots, and Fumaroles


Solfatara, 2 km (1.2 miles) southeast of Pozzuoli’s town center, is currently the most active volcanic crater on - or better of - the Campi Flegrei. Already well known in the antique, the Romans called it Forum Vulcani, dedicated to Vulcan, the god of fire.

The roughly 750 m (2,460 feet) in diameter wide caldera, encircled by up to 40 m (130 feet) high tuff cone walls, is one of the smaller ones in this area and has been formed around 4000 years ago. A subsequent hydrothermal (steam-driven) eruption of Solfatara may have occurred in the year 1198.

Solfatara entrance at the west side of the crater:

Solfatara entrance

Among its geothermal features there are mainly fumaroles with sulfur deposits around the vent. Furthermore, also mofette (low temperature gas emissions), and a few murky, bubbling hot springs do occur. Fumaroles and springs are to be found not only inside the crater, but also on a small field called Pisciarelli just east of it. In contrast to the Solfatara cone, where thermal activity is dominated by hot vapor up to 160 °C (320 °F), the temperatures at Pisciarelli are varying between 95 and 110 °C (203 - 230 °F) and the influence of liquid water is more prevailing. Therefore, at Pisciarelli also noteworthy geysers may develop for a short period of time. For example, a geyser-type vent opened in November 2010. In January 2013 a newly emerged fumarole turned into a 5 m (16 feet) high spouting geyser due to heavy rainfall. Already earlier, in October 2006, the formation of a boiling pool with 3 m (10 feet) in diameter was detected, another one was originated in March 2009 by a steam explosion. However, this area has been closed to the public since 2010, so all the pictures shown here were taken at Solfatara.

Solfatara, panorama of the caldera (looking southeast towards Mt. Olibano):

Solfatara Panorama

The first conspicuous feature you come across if you enter the caldera from the west is a slightly bubbling muddy pool. It is called La Fangaia (derived from fango, the Italian term for mud) and located almost in center of the crater. Inside the pool steam and gases from diffuse emission processes mix with rainwater and turn the clay into a constantly bubbling slurry, which stays well below boiling temperature.

La Fangaia:

La Fangaia, Solfatara

An exceptionally tragic accident at La Fangaia claimed the lives of three members of a family of four on September 12th, 2017. Newspapers reported that a 11-year-old boy, who visited Solfatara together with his family from Meolo in northern Italy, approached La Fangaia when suddenly a 1.5 m (5 feet) deep sink-hole opened up and swallowed him. It is still unclear, if this happened inside or outside the prohibited, fenced-off area. His 45-year-old father tried to rescue him, but the collapsing rim of the hole pulled him down, too. The same happened to the mother of the boy when she rushed to the crater, and all three became unconscious by hot toxic gases and died eventually. For the shortly afterwards arriving rescue teams remained nothing but the recovery of the dead bodies. The only surviving member of the family was a seven-year-old boy, who stayed off the dangerous zone.

La Fangaia is located at the edge of the most active, southeastern and northeastern area of the crater, where a system of fractures heats the ground and supplies energy for geothermal features. Fumarolic activity is mainly concentrated in its southeastern part, and the most conspicuous fumaroles are called Bocca Grande (Big Mouth) and Bocca Nuova (New Mouth).

The two fumaroles Bocca Grande (in background left) and Bocca Nuova (right):

Solfatara Fumaroles

For Bocca Grande activity can be traced back more than 2000 years into the past. The emitted gases are up to 160 °C (320 °F) hot and rich in sulfur compounds. Beyond the deposition of pure sulfur, chemical reactions and subsequent condensation processes are continuously coating the area around the vent with other very colorful minerals, including the brilliant red to orange realgar (arsenic sulfide, AsS), the cochineal-red cinnabar (mercury sulfide, HgS), and the deep orange-yellow orpiment (arsenic sulfide, As2S3). However, the stunning micro crystals are quite toxic. Bocca Grande at Solfatara is the archetype of all fumaroles, and for this reason fumaroles emitting sulfurous gases and depositing sulfur minerals around their vent are also called solfataras.

Bocca Grande:

Solfatara Bocca Grande

Solfatara, Bocca Grande
In 1984 the bradyseismic crises gave birth to the fumarole Bocca Nuova only 20 m (66 feet) west of Bocca Grande. Except for being smaller, it is similar to Bocca Grande in almost every aspect. Emission temperatures have been quiet constant at 145 °C (293 °F) over the last decades.

Bocca Nuova:

Solfatara Bocca Nuova

Solfatara, Bocca Nuova
Smaller fumaroles are scattered from the southeast to the northeast all along the crater walls. Steam emissions and bright yellow sulfur deposits indicate their positions.

Fumaroles in the southeastern crater wall:

Solfatara Fumaroles in Crater Wall

Fumaroles in the northeastern crater wall:

Solfatara Fumaroles in Crater Wall

Panorama of the northeastern section of Solfatara:

Solfatara Panorama

In front of the northeastern crater wall a "sauna" shows up, built at the end of the 18th century. It is called Stufe (derived from stufa, the Italian term for stove) and was used to inhale the intense sulfurous gases over a few minutes to cure respiratory diseases, skin diseases, and rheumatism.

The Stufe:

Solfatara Stufe

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