We propose a MATLAB toolbox for the computation of the strain rate field from the coordinate time series of some continuous GNSS stations. It consists of several functions, also compatible with GNU Octave, implementing the following steps: (i) time series download from a data repository (e.g., the Nevada Geodetic Laboratory database); (ii) calculation of velocities of the selected stations by means of the Maximum Likelihood Estimation (MLE) method implemented in the external package Hector, including modeling of offsets, outliers, noise and periodic components; (iii) (optional) filtering of Common Mode Errors; (iv) calculation of the strain rate field with the modified least squares method, in which a scale factor can be introduced to define the locality of the deformation analysis and, besides uncertainty estimation, a geometric evaluation of the significance of the results is provided; (v) visualization of the results for immediate use and easy interpretation for scientific purposes. The toolbox is divided into two components: the first one, named StaVel, performs the steps (i)-(iii) and the second component, GridStrain, performs the steps (iv) and (v). The potential of the toolbox is demonstrated on a real dataset. Time series from several continuous GNSS stations in South-Eastern Sicily (Southern Italy) are processed by means of StaVel and GridStrain in order to provide the strain rate field.

Previous experiments highlighted the possible existence of a relation between repeatability of point clouds obtained from Structure-from-Motion photogrammetry (SfM), represented by the standard deviation (𝜎), and the nominal ground sampling distance (GSD). In particular, the empirical relation 3𝜎 ∼ 2.5 GSD was found. For this reason, in-situ tests aimed at studying this relation were carried out. Data from seven surveys carried out in 2018-2022 time span allowed the comparison between 20 pairs of almost contemporary point clouds, generated by means of relative bundle adjustment (BA) without ground control points (GCPs) and then relatively scaled and aligned. In this way, the relation 3𝜎 = aGSD was found, where a = 2.5 ± 0.4. This result also suggested the use of the reverse procedure, where the scale factor (SF) is estimated from the standard deviation of non-metric point clouds, 𝜎nmu, by using the relation SFa = aGSD/3𝜎nmu. Additional checks proved that SFa differs from SF by 3%. This error is not acceptable error for length, area or volume measurements, but the estimated SFa is more than adequate for a fast, rough registration of photogrammetric models aimed at searching patterns or precursors of incipient phenomena in impervious/inaccessible areas or in emergency conditions.

Hule and Río Cuarto are maar lakes located 11 and 18 km N of Poás volcano along a 27 km long fracture zone, in the Central Volcanic Range of Costa Rica. Both lakes are characterized by a stable thermic and chemical stratification and recently they were affected by fish killing events likely related to the uprising of deep anoxic waters to the surface caused by rollover phenomena. The vertical profiles of temperature, pH, redox potential, chemical and isotopic compositions of water and dissolved gases, as well as prokaryotic diversity estimated by DNA fingerprinting and massive 16S rRNA pyrosequencing along the water column of the two lakes, have highlighted that different bio-geochemical processes occur in these meromictic lakes. Although the two lakes host different bacterial and archaeal phylogenetic groups, water and gas chemistry in both lakes is controlled by the same prokaryotic functions, especially regarding the CO2-CH4 cycle. Addition of hydrothermal CO2 through the bottom of the lakes plays a fundamental priming role in developing a stable water stratification and fuelling anoxic bacterial and archaeal populations. Methanogens and methane oxidizers as well as autotrophic and heterotrophic aerobic bacteria responsible of organic carbon recycling resulted to be stratified with depth and strictly related to the chemical-physical conditions and availability of free oxygen, affecting both the CO2 and CH4 chemical concentrations and their isotopic compositions along the water column. Hule and Río Cuarto lakes were demonstrated to contain a CO2 (CH4, N2)-rich gas reservoir mainly controlled by the interactions occurring between geosphere and biosphere. Thus, we introduced the term of bio-activity volcanic lakes to distinguish these lakes, which have analogues worldwide (e.g. Kivu: D.R.C.-Rwanda; Albano, Monticchio and Averno: Italy; Pavin: France) from volcanic lakes only characterized by geogenic CO2 reservoir such as Nyos and Monoun (Cameroon).

La fotogrammetria Structure-from-Motion (SfM) si basa su algoritmi che permettono, in modo automatico e rapido, di individuare una quantità elevata di punti omologhi tra le immagini acquisite durante il rilievo. L’individuazione di tali punti consente di realizzare l’allineamento delle immagini e quindi la calibrazione esterna ed interna delle fotocamere. L’efficienza di tali algoritmi e la quantità, qualità e distribuzione spaziale dei punti omologhi sono il fulcro della procedura di restituzione fotogrammetrica. In alcuni casi, per una combinazione tra strategia di acquisizione, tipo di fotocamera e software utilizzato, potrebbero verificarsi delle anomalie che danno luogo a distorsioni delle nuvole di punti finali. Il lavoro presenta i rilievi SfM realizzati nell’ambito di un progetto per lo studio delle deformazioni dovute al fenomeno della liquefazione mediante il confronto di modelli multi-temporali; si tratta dell’unico caso da noi osservato in anni di esperienza di rilievo SfM in cui sono presenti effetti sistematici che hanno reso problematico l’uso diretto delle nuvole di punti ottenute utilizzando Photoscan. Si mostrano i tentativi per ridurre tali effetti sia mediante un sotto-campionamento delle immagini, al fine di equilibrare la distribuzione dei punti omologhi, sia inibendo l’aggiustamento dei parametri interni, fino ad ottenere risultati utilizzabili, seppur non completamente liberi da sistematismi. Nella valutazione dei problemi è stato utilizzato un rilievo di riferimento realizzato mediante Terrestrial Laser Scanning (TLS). Infine tutti i dati sono stati rielaborati con un software migliorato, Metashape, ottenendo risultati non affetti da sistematismi, il che indica che le procedure per l’individuazione dei punti omologhi sono state migliorate. Poiché Photoscan (nelle versioni ancora utilizzate dalla 1.2 alla 1.7) è un prodotto molto diffuso, si ritiene che questa esperienza possa essere utile a quanti sono coinvolti in attività di monitoraggio e studio delle deformazioni superficiali.

With this study a nine-year hiatus (May 2010-April 2019) in the quantification of the CO2 content of Lago Albano by our working group has been resolved through the acquisition and analysis from two new field campaigns. Based on a CO2 budget analysis the dynamics of CO2 degassing throughout the past thirty years (1989-2019) is detailed and quantified. The decreasing CO2 content (expressed as dissolved inorganic carbon, DIC) in the lake, since the co-seismic CO2 input during the 1989-1990 seismic swarm beneath Colli Albani volcano, was accelerated at lake bottom layers (-140 m to bottom, near -160 m) in the 4-5 years after the swarm, continued afterwards at lower depths (-125 to -95 m), and seems to have reached steady-state conditions during recent years. The peculiar lake basin morphology has control on the degassing dynamics. The low chemical gradients detected during the April 2019 survey have induced near-zero degassing conditions, and arguably stopped the gas-self lifting process: Lago Albano might not become CO2-free in the future. This finding has implications for gas hazard when the next seismic swarm will hit the area. The updated degassing model also takes into account the lake level drop, and hence the volume decrease of Lago Albano, caused by excessive well pumping for anthropic purposes. This volume decrease appears to have a destabilizing effect on the degassing dynamics, which renders Lago Albano’s gas release less predictable in the future. Enhanced gas surveys (high-frequency and fine-scale spatial measurements) are needed to shed light on how Lago Albano degasses in this quiescent stage during the Anthropocene. A submersible infra-red detector to directly measure in-lake dissolved CO2 concentrations, applied satisfactorily during this study, is an adapted instrument to do so.

Here we present digitization and analysis of the thermal springs of the world dataset compiled by Gerald Ashley Waring in 1965 into a collection of analog maps. We obtain the geographic coordinates of ~6,000 geothermal spring areas, including complementary data (e.g., temperature, total dissolved solids, flow rate), making them available in electronic format. Using temperature and flow rate, we derive the heat discharged from 1483 thermal spring areas (between ~10−5 and ~103 MW, with a median value of ~0.5 MW and ~8300 MW in total). We integrate this data set with other global data sets to study the relationship between thermalism and endogenous and exogenous factors with a supervised machine learning algorithm. This analysis confirms a dominant role of the terrestrial heat flow, topography, volcanism and extensional tectonics. This data set offers new insights and will boost future studies in geothermal energy exploration.

Limnic eruptions represent a natural hazard in meromictic lakes hosted in volcanoes releasing CO2-rich magmatic gases. Biogeochemical processes also contribute to dissolved gas reservoirs since they can produce significant amounts of gases, such as CH4 and N2. Dissolved gases may have a strong influence of the density gradient and the total dissolved gas pressure along the vertical profile of a volcanic lake. An external triggering event, possibly related to uncommon weather conditions, volcanic-seismic activity, or landslides, or spontaneous formation of gas bubbles related to the progressive attainment of saturation conditions at depth, may cause a lake rollover and the consequent release of dissolved gases. This phenomenon may have dramatic consequences due to i) the release of a toxic CO2-rich cloud able to flow long distances before being diluted in air, or ii) the contamination of the shallow water layer with poisonous deep waters. The experience carried out over the past twelve years at Lake Nyos, where a pumping system discharges CO2- rich deep water to the surface, has shown that controlled degassing of deep water layers is the best solution to mitigate such a hazard. However, the application of this type of intervention in other lakes must be carefully evaluated, since it may cause severe contamination of shallow lake water or create dangerous density instabilities. Monitoring of physical and chemical parameters controlling lake stability and the evolution in time of dissolved gas reservoirs can provide essential information for evaluating the risk associated with possible rollover phenomena. Conceptual models for the description of limnological, biogeochemical and volcanic processes regulating water lake stability have been constructed by interpreting compositional data of lake water and dissolved gas compositions obtained by applying different sampling and analytical techniques. This study provides a critical overview of the existing methodological approaches and discusses how future investigations of Nyos-type lakes, aimed at mitigating the hazard for limnic eruptions, can benefit from i) the development of new technical and theoretical approaches aimed to constrain the physical-chemical mechanisms controlling this natural phenomenon, and ii) information from different scientific disciplines, such as microbiology, fluid dynamics and sedimentology.

Natural reservoirs that release CH4 can substantially increase atmospheric greenhouse gas levels, posing environmental and safety risks. Degassing phenomena in the Emilia-Romagna region (Italy) have been documented across a variety of fluids and reservoir types, with a focus on their origin and evolution. This study combines ground measurements and satellite data analysis to explore the relationships between CH4 seepage, thermal anomalies, and vegetation stress at the Santa Maria Nuova (SMN) site in southern Po Valley. The explosion of a CH4-saturated water well in July 2021 prompted a two-year investigation in the adjacent cultivated field (1.5 ha), revealing significant spatial and temporal variations in diffuse CH4 fluxes (ranging from 0 to 917 g m− 2 d− 1) and corresponding CO2 fluxes (1.9–466 g m− 2 d− 1). Soil temperature measurements and thermal imaging identified localised ground heating, attributed to methanotrophic exothermic oxidation of CH4 to CO2. These hotspots correspond to areas of visibly stressed vegetation, marked by reduced vitality and barren areas. Satellite-derived Ratio Vegetation Index (RVI) data confirmed persistent vegetation stress over the anomaly site from 2017 to 2024. Geochemical analysis of soil gases indicated a primarily biogenic origin of CH4, supported by isotopic signatures (δ13C–CH4 values <− 60 ‰ V-PDB) and the presence of shallow Pleistocene carbonate deposits beneath the site, which can generate CH4 seepage. These findings demonstrate the utility of integrating ground-based and remote sensing techniques for monitoring CH4 seepage and its environmental impacts.