Stefano Cremonini

Ground heating and methane oxidation processes at shallow depth in Terre Calde di Medolla (Italy): Observations and conceptual model

The toponym “Terre Calde di Medolla” (literally, “Warm Earths of Medolla”) refers to a farming area, located near the town of Modena (Emilia-Romagna region, northern Italy), which has always been known by the local population for the relatively high temperatures of the soil. This phenomenon is particularly evident in wintertime when the snow cover over this area rapidly melts. A detailed investigation, carried out after the devastating 2012 Emilia earthquake that affected this area, showed soil temperatures up to 44°C, i.e., 20–25°C above the local background value, together with diffuse soil fluxes of CH4 (0–2432 g × m−2 × d−1) and minor, though significant, CO2 (0–1184 g × m−2 × d−1), especially from subcircular (a few meters in diameter) zones. Ground heating and gas seepage appear spatially correlated, thus suggesting a close relationship between the two phenomena. The anomalous high ground temperature is not associated with an anomalous geothermal gradient or with the uprising of deep-seated hot fluids. According to the lateral and vertical distributions of the temperatures as well as the chemical and isotopic compositions of the soil gases, the most reliable explanation is the exothermic oxidation of diffusely uprising biogenic methane at very shallow levels (<1 m). Such a process occurs in the presence of free oxygen and methanotrophic bacteria and can then explain (i) the observed ground heating up, (ii) the diffuse emission from the soil of CO2 characterized by an extremely negative isotopic (13C/12C) signature, and (iii) the lack of diffuse and low CH4 fluxes. According to these hypotheses, the heating phenomena affecting the shallow groundwater and the ground surface, as described by several witnesses in the area of the May–June 2012 Emilia earthquake, could be related to either a coseismic or postseismic onset of new areas affected by CH4 seepage or an increase in preexisting CH4 fluxes.

Evidence of Possible Enhanced Peat Burning by Deep-Origin Methane in the Po River Delta Plain (Italy)

A burning peat site in the Po Valley (Italy) has been investigated for the first time. Beyond the smoke from the smoldering combustion of peat, there are carbonatic concretions and huge amounts of methane in the soil (>60% by vol.), leading to fluxes to the atmosphere of the order of 102–103 mg m-2 d-1. A wide range of analyses (gas composition, stable isotopes of CH4 and CaCO3, methane radiocarbon) were performed in order to understand whether methane is produced by peat layers or seeps from deeper natural gas reservoirs. The quasi-fossil character of CH4, methane-derived carbonates, methane-stable isotopic compositions related to marine carbonates reduction, the presence of helium, and a fault corresponding to the burning site all converge to indicate that the major part of the methane ascends from deep horizons. Such methane seepage is likely to feed the peat combustion, explaining the observed phenomena and the large outbursts of historical gas-emission events.

Ground heating and methane oxidation processes at shallow depth in Terre Calde di Medolla (Italy): Numerical modeling

The area known as Terre Calde (literally “hot lands”) in the plain of the Po River (Italy) is well known for unusual ground temperatures, and up to now, the cause o/f the heating has not been fully investigated. These higher-than-average temperatures are commonly associated with diffuse methane seepage. A detailed study of shallow stratigraphy, temperature profile, and associated gas concentrations and flow rates recently suggested that the observed anomaly could be related to the exothermic oxidation of biogenic methane, possibly rising from a shallow peat layer. In this work, a porous media flow simulator (Transport of Unsaturated Groundwater and Heat 2) was applied to verify a conceptual model of this phenomenon. The model describes a layered system, with a shallow unsaturated zone, where methane is continuously supplied along the base and heat is generated as a result of its oxidation above the water table. To mimic the oxidation process, heat sources are placed within the layer where oxidation takes place, and the heat generation is computed as a function of methane flux entering the layer. Numerical simulations were carried out imposing different methane flow rates along the base of the model. The simulations also explored the efficiency of methane oxidation, considering different heat generation rates and accounting for seasonal effects. The good match between observed and simulated temperature profiles suggests that the main features of the process are captured by the model and that the conceptual model devised on the base of available data is plausible from a physical point of view.

Analysis of Pre-Geodetic Maps in Search of Construction Steps Details

Cartographic Heritage consists in the whole amount of ancient cartographic documents (not only maps, but also atlas, planispheres, globes, ...) the history has brought us, today perceived as a cultural value to be necessarily preserved due to its historical and geographical content as well as its artistic value. It is a great but often poorly known heritage, because usually ancient cartographic documents are kept in places closed to the public, and only occasionally they are proved valuable outside of specific research activities.

Chapter 3 – Italian Peat and Coal Fires

The natural combustion of solid-fossil fuels in Italy is not currently mitigated or actively monitored because of the scarcity of these resources and their relatively low economic value, especially since the World War II. In recent years, the spontaneous combustion of peat in Italy was recorded. A database of about 1000 potential combustion sites was created for all known Italian mining sites to serve as a precursor for evaluating the potential for coal and peat combustion at these locations, including natural combustion linked to climate change. The database is also useful in that it serves as an inventory of solid-fossil fuels in Italy.