Natural gas seepage in Rome

Surface manifestations of petroleum and natural gas (mostly methane) represent a natural geological process, called “seepage”, with a wide range of scientific, social, historical, economic and environmental implications. This process indicates the presence of geological (tectonic) faults, subsurface rocks with pressurized fluids, it is a natural source of greenhouse-gas for the atmosphere, and it may represent hazard for people and buildings. Petroleum and gas seepage also had a peculiar role in ancient cultures, driving mythological legends and religious traditions (Etiope, 2015)

Petroleum and gas seepage has been historically documented in Rome and in the adjacent Tiber delta along the Tyrrhenian coast. Legends and chronicles from the Roman epoch speak of gas and oil manifestations that are often associated with religious practices, pagan altars, and the successive construction of Christian churches (Etiope, 2015). More recent drilling for construction of buildings and infrastructures led to the discovery of gas emanations in several sites in Rome and along the Tiber river valley down to the Tiber Delta around the Fiumicino international airport (Ciotoli et al. 2016).

Of particular interest is the potential existence of gas seepage in the Rome city centre, as it may reveal interesting connections with historical chronicles, such as the petroleum release in Trastevere area (the “fons olei” within the Basilica of Santa Maria in Trastevere) and the origin of the Vesta fire in the Roman Forum.

The presence of hydrocarbons in boreholes, or in the soil along the Tiber valley around Rome, has already been verified by geological studies. The occurrence of natural gas in the deep rocks underlying Rome is therefore very likely. It needs to be confirmed by direct measurements.

In this project, we plan to carry out field surveys to detect gas seepage within selected areas of Rome city. The work will include measurements of methane in the soil, natural springs and, if possible, within subterranean caves, for example Mythraic temples, often associated with water sources and sacred sites. Rome is characterised by a vast network of underground hypogea (e.g., catacombs, tunnels, bunkers, villas, aqueducts and baths). Therefore, gas seepage can be detected on the surface (soil) only in those areas where underground cavities are absent. The deepest caves, where the basement is in direct contact with the geological substratum, may however reveal signals of gas seepage. In addition, gas may accumulate in certain hypogea resulting in degradation of air quality with potential risk for visiting people and workers. Accordingly, field surveys will be conducted on the surface taking into account the distribution of underground cavities and soil-covered zones (parks, gardens). The possibility of performing underground surveys will depend on collaborations with authorized speleologists, special permissions from local authorities and financial support. Methane (and associated gases, such as carbon dioxide) will be detected using portable sensors and selected air samples will be analysed in specialised laboratories for determining the gas origin (isotopic analyses). Gas seepage data will be interpreted taking into account geological maps, with particular reference to the location of faults.

The results can be used to optimize the management and access constraints in certain underground hypogea. The discovery of gas emanations could have relevant impact on the interpretation of some archaeological structures, historic and legendary events of ancient Rome. The knowledge of gas occurrence and migration within the Rome geological basement will have a considerable scientific value.

Coordination: G. Ciotoli (IGAG) and G. Etiope (INGV)

Bibliographic references:

- Ciotoli G., Etiope G., Marra F., Florindo F., Giraudi C., Ruggiero L. (2016). Tiber delta CO₂-CH₄ degassing: a possible hybrid, tectonically active Sediment-Hosted Geothermal System near Rome. J. Geophys. Res. - Solid Earth, 121, 48-69.

- Etiope G. (2015). Natural Gas Seepage. The Earth’s hydrocarbon degassing. Springer, Switzerland, pp. 199