Mofetta refers to a vent or opening in the crust of a celestial body such as the Earth through which gases escape, or to the gases that escape from such an opening. It is associated with or is a form of volcanic discharge, so these openings thus often happen along fault lines between tectonic plates. Associated with ancient religion, these structures are interesting to scientists because they provide a chemical snapshot of geographical processes, represent weak points in the crust that might also generate problems such as volcanic eruptions and earthquakes, and occasionally are able to provide medicinal advantages.
In ancient times, a mofetta commonly held spiritual connections. An Italian term, mofetta comes from the Latin mephitis, associated with Mephitis or Mefitis, a goddess of the pre-Roman Samnites. Mefitis was so named in part because the gases released from the Earth tended to be so foul-smelling — mefitis means "skunk." People believed that this goddess had the power to protect humans and other creatures from the gases, so her worship was more common where volcanic activity was present.
The association with Mephitis, along with the appearance and smell of fumes rising from the mofetta, led to the adoption of another term to describe the structure or gases: fumarole, from the Latin "fumus." Over time, fumarole became the more popular term. Mofetta thus is a more archaic label, although it still is in use.
The gases and structure of these structures vary widely. Commonly, they include carbon dioxide gas. Sulfur dioxide, hydrochloric acid and hydrogen sulfide are other examples of gases. Steam and water vapor may occur as well.
Geologists and vulcanologists have a great interest in the makeup and structure of a mofetta. The gases of a mofetta are the result of specific chemical processes, for example, so they provide clues about what is happening below the Earth's crust. They can show where particular elements and compounds are more plentiful to provide a sort of geographical map of the Earth's composition or processes.
In some cases, depending on exactly what gases are released from a mofetta, people might use it as a medicinal treatment. The best example is a carbon dioxide dry bath, which professionals and spa workers have recommended for problems such as rheumatism and poor circulation. When mofettas are used for medicinal purposes, patients must adhere to safety regulations. Many spas have recreated the effects of a natural mofetta artificially to make the benefits available to those who are not near such a vent.