The Solfatara di Pozzuoli is a shallow volcanic crater at Pozzuoli, near Naples, part of the Phlegraean Fields volcanic area. It is a dormant volcano which still emits jets of steam with sulphurous fumes. The name comes from the Latin, Sulpha terra, “land of sulfur”, or “sulfur earth”. It was formed around 4,000 years ago and last erupted in 1198 with what was probably a phreatic eruption – an explosive steam-driven eruption caused when groundwater interacts with magma. The crater floor is a popular tourist attraction, as it has many fumaroles and mud pools. The area is well known for its bradyseism, the gradual uplift (positive bradyseism) or descent (negative bradyseism) of part of the Earth’s surface caused by the filling or emptying of an underground magma chamber and / or hydrothermal activity, particularly in volcanic calderas. It can persist for millennia in between eruptions and each uplift event is normally accompanied by thousands of small to moderate earthquakes. The vapours have been used for medical purposes since Roman times.
The Solfatara crater still smoulders endlessly today. Located a few metres from the sea, an entrance leads down a tree lined path to a mars-like terrain. The rotten egg smell is inescapable and, depending on the direction of the wind, wafts all the way to the city of Naples.
The slopes surrounding the crater puff with sulfur steam. Along one slope, two fumaroles shum their steam at somewhere around 160°C and turn the rocks around it into a copper-gold color. The Italians call these two vents “La Bocca Grande” or “The Big Mouth.” Behind their plume and hiss, a green algae grows that’s considered a biological rarity seen only when high temperatures and high acidity combine together.
In the middle of the crater, the Fangaia or boiling mud lakes sizzle at temperatures between 170-250° C. The mud contains a bevy of gases and minerals that the Romans once harnessed for their hydrothermal spas.
The Romans said that Vulcan, the god of fire, worked here. The crater is also believed to have been the inspiration for Virgil’s description of Hades. Ruins of a Roman bath still exist at the western side of the crater with sulfur wisping out from the bricks.
If visitors stomp on the ground, they’ll hear a hollow sound – evidence that porous caverns exist underneath. Take a stick, dig a small hole into the sand, and put a finger inside to see how hot the earth feels just beneath the surface!
For those with an interest in Science, four reflectors dot the sandy terrain. They work with two satellites of the European Space Agency (ESA) to reflect their signals and map the volcano’s ground deformations.