Search

Over the past two decades, significant advances in the geochemical monitoring of volcanoes have shown how crucial the observation of specific geochemical tracers is for understanding and evaluating eruptive processes. Among these, the monitoring of soil CO2 flux is one of the most important and widely employed geochemical parameters used in volcanic monitoring. At Mt. Etna volcano (Italy) long-term soil CO2 time series (2011–2019) are available from a network of 14 monitoring sites located around the volcano. Although variations in the exhalative regime of soil CO2 flux are recognized as possible proxies for potential emergent eruptive activity, little has yet been explored regarding the significance of the spatial variation of soil CO2 over time. In this paper, we look for possible dependence of CO2 flux on the altitude of the monitoring sites, their distances from the main craters, and their azimuthal positions on the volcano flanks. While for the first two elements there seems to be no evidence of dependence, we found evidence of long-term azimuthal variations in the soil CO2 flux that could depend on the structure of the volcano. In particular, the sites in south-eastern flank behave somehow differently from the ones located in other flanks. At yearly time scale, marked variations affect the CO2 flux at various sites. Such variations can be ascribable to volcano dynamics during the observation period characterized by a sequence of effusive and strombolian activities. Variations within a single eruptive episode also emerge investigating the 2018–19 flank eruption with bi-monthly windows.

Remote sensing (RS) of volcanic gases has become a central tool for studying volcanic activity. For instance, ultraviolet (UV) skylight spectroscopy with grating spectrographs (GS) enables SO2 (and, under favourable conditions, BrO) quantification in volcanic plumes from autonomous platforms at safe distances. These measurements can serve volcanic monitoring and they cover all stages of volcanic activity in long measurement time series, which substantially contributes to the refinement of theories on volcanic degassing. Infrared (IR) remote sensing techniques are able to measure further volcanic gases (e.g., HF, HCl, CO2, CO). However, the employed Fourier transform spectrometers (FTSs) are intrinsically intricate and, due to limited resolving power or light throughput, mostly rely on either lamps, direct sun, or hot lava as light source, usually limiting measurements to individual field campaigns. We show that many limitations of grating spectrographs and Fourier transform spectrometer measurements can be overcome by Fabry-Perot interferometer (FPI) based spectrograph implementations. Compared to grating spectrographs and Fourier transform spectrometers, Fabry-Perot interferometer spectrographs reach a 1-3 orders of magnitude higher spectral resolution and superior light throughput with compact and stable set-ups. This leads to 1) enhanced sensitivity and selectivity of the spectral trace gas detection, 2) enables the measurement of so far undetected volcanic plume constituents [e.g., hydroxyl (OH) or sulfanyl (SH)], and 3) extends the range of gases that can be measured continuously using the sky as light source. Here, we present measurements with a shoe-box-size Fabry-Perot interferometer spectrograph (resolving power of ca. 150000), performed in the crater of Nyiragongo volcano. By analysing the light of a ultraviolet light emitting diode that is sent through the hot gas emission of an active lava flow, we reach an OH detection limit of about 20 ppb, which is orders of magnitude lower than the mixing ratios predicted by high-temperature chemical models. Furthermore, we introduce example calculations that demonstrate the feasibility of skylight-based remote sensing of HF and HCl in the short-wave infrared with Fabry-Perot interferometer spectrographs, which opens the path to continuous monitoring and data acquisition during all stages of volcanic activity. This is only one among many further potential applications of remote sensing of volcanic gases with high spectral resolution.

The massive diffusion of social media has produced disintermediation and it has changed the way in which users inform themselves and participate in public debate. On the other hand, users show a tendency to interact with information that adheres to personal choices and previous opinions. This propensity is “exploited” by algorithms that manage and sort communication on social media, increasingly producing a polarized audience. The essay shows the outcomes of these dynamics by focusing on the communications structure related to the pandemic. In this sense, social media constitute a risk because they convey out-of-control access to unreliable information and because they can result in the absence of correct information, if not in a problem for democracy. On the technical level, at least three complex reticular structures are identified that evolve following different directions, emerged from three sequentially monitored lemmas (no-mask, covid-19, greenpass). Further considerations concern the increasingly dense interweaving between online communication and the genesis of protest movements with evanescent, single-issue structures.