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Celleno is a small town located about 80 km northwest of Rome and about 15 km north of Viterbo. It is close to Bolsena Lake, to the west, and the Alviano Lake to the east. The urban area has been inhabited since Etruscan times. The historical part of the town, often referred to as the Orsini Castle, was originally built around 1000 on a tufaceous spur at 341 m above sea level. This spur is located between two small rivers (Briglie and Calenne), which over time have eroded very deep gorges such as the "Gorges of Infernaccio".

The geology of the Celleno area is characterised by the outcropping of more than 100 m thick volcanic and volcano-sedimentary deposits belonging to the Vulsini Volcanic complex, which was active between approximately 490 to 127 thousand years ago (Nappi et al., 1995).

The Vulsini Volcanic Complex, which was formed primarily via explosive activity, is the northernmost of the volcanic districts in Lazio Region. The main structural element is the volcano-tectonic caldera of the Bolsena Lake, formed during repeated phases of eruption and subsidence, controlled by regional faults.  In particular, in the Celleno area, a high volume of air-fall deposits and an ignimbrite (Bagnoregio Tuff or Orvieto Ignimbrite) were erupted about 370 thousand years ago and likely triggered the collapse of the Bolsena Caldera (De Rita, 1993). 

Diffuse Pliocene silty sands and marine silts are also widely found, which cover the Pleistocene clay sediments (Mancini et al., 2003-2004). The entire area of the Bolsena volcanic complex, and of the Vulsini Volcanic District in general, is affected by important degassing phenomena that occur on the surface through thermal springs, gaseous manifestations generally rich in CO2 and travertine deposits (Cinti et al., 2011, 2014). Among these, the Poggio degli Ulivi area, located about 5 km south of Celleno, releases about 200 tons of CO2 to the atmosphere every day (Chiodini et al., 1999), while the extensive travertine deposits of the near-by Caves Santo Stefano were formed by CO2-rich fluids ascending along a NW trending normal fault (Cinti et al., 2014).

The local geology is characterized by volcanic deposits emitted by the explosive phases of the Vulsini Volcanic Complex, which overlie Plio-Pleistocene clays and marls and cover the Tiber Valley eastward.  

Celleno has already been the object of extensive soil gas surveys conducted within the research project “Study of the migration and accumulation processes of radon and other endogenous gases from the ground to living and working places and their relationships with the geological characteristics”, a collaboration between the Istituto Nazionale per l'Assicurazione contro gli Infortuni sul Lavoro  (INAIL) and the Institute of Environmental Geology and Geoengineering of the National Research Council of Italy (CNR-IGAG), partner of RESPIRE. The obtained dataset is available only for research purposes after permission from INAIL. The dataset includes soil gas and flux measurements, radionuclide content in the soil from different outcropping geological units, and indoor radon measurements in 20 private homes (to be increased in the RESPIRE project). The maps of 222Rn and CO2 concentrations in soil gas, as well as the map of the Rn geogenic potential of the Celleno territory, are also available.


  • Chiodini et al.,1999. Chem. Geol. 159, 205–222.
  • Cinti et al., 2014 Chem. Geol. 371, 96–114.
  • De Rita 1993. Il vulcanismo. In: Società Geologica Italiana (ed) Guide Geologiche Regionali: Lazio. 50-64
  • Mancini et al., 2003–2004 Geol. Rom. 37, 175–236.
  • Nappi et al.,1995 Boll. Soc. Geol. It. 114, 599–613.