Understanding how volcanic systems evolve over time is a major challenge due to their complex behaviour and constantly changing conditions. This study explores a novel approach to detecting significant changes in multiparametric signals of volcanic unrest by analysing how different types of data, such as ground deformation, gas emissions, temperature, and earthquakes, interact with each other. Focusing on the Solfatara–Pisciarelli volcano system, which is a more active area in the Campi Flegrei Caldera (Southern Italy), we used two advanced methods to identify critical transitions in the system: one to model the nonlinear relationships between variables, and the other to detect key moments when the system’s behaviour shifts. By including time delays between signals (LAG), we found that our model became much more accurate in identifying these changes. In contrast, models that ignored time lags showed higher uncertainty. The results highlight the importance and effectiveness of using integrated multivariate approaches such as Multivariable Fractional Polynomial Analysis (MFPA) and Global Critical Point Analysis (GCPA) to gain deeper insights into the systemic behaviour of the caldera and its temporal evolution within a complex area like the Campi Flegrei over the selected time period.

PLINIVS-based seismic vulnerability mapping during volcanic unrest in Campi Flegrei: a replicable DRM model

Abstract Deciphering the signal of external processes on active hydrothermal dynamics represents a critical challenge in understanding volcanic unrest. At the Pisciarelli hydrothermal site, located within the densely populated Campi Flegrei caldera (Italy), we investigate the role of meteoric water influx in modulating shallow hydrothermal fluid discharge. Our analysis reveals a persistent seismic tremor generated at shallow depths, whose amplitudes fluctuate noticeably and closely follow rainfall patterns. Hydrothermal activity also emits distinct acoustic signals related to boiling and steam venting. Importantly, we observe an inverse relationship between tremor and acoustic amplitudes: as tremor increases, acoustic emissions decrease. The influx of cold water is also linked to a rise in hydrothermal water level, indicating increased conduit pressure, which is supported by ground tilt data showing conduit inflation. We propose a conceptual model in which pressurization cycles in the shallow hydrothermal system result from the interplay between steam condensation, meteoric water influx, and steam outgassing. These pressurization cycles may promote seismicity, as evidenced by the seasonal patterns observed in earthquake rates. However, these seasonal effects are secondary to the dominant, accelerating multi‐year trend of increasing earthquake rates due to volcanic unrest. Our findings demonstrate that seismo‐acoustic monitoring provides a sensitive tool for detecting transient changes in hydrothermal dynamics, offering valuable insights into the interpretation of volcanic unrest signals. This, in turn, contributes to more refined volcanic hazard assessments. Although developed at Campi Flegrei, this approach holds potential for application to other active hydrothermal systems worldwide.

Abstract The Laguna del Maule volcanic field in Chile has been uplifting at exceptional rates since 2007, offering a unique opportunity to examine the interplay between crustal deformation and magma dynamics. To understand this relationship, we integrate GNSS with local seismic observations from 2013 to 2024 to model the reservoir strain field, relocate earthquakes, and determine focal mechanisms. Our preferred model identifies a shallow spheroidal reservoir at ∼4 km depth that underwent ∼15 MPa of overpressure and a volume change increase of ∼0.23 km 3 . Seismicity clusters align with dilatational strain, and focal mechanisms are dominated by strike‐slip faulting consistent with the regional NE–SW tectonic stress regime. We distinguish two phases of unrest: 2013–2018, when seismicity concentrated in dilatational faults, and 2018–2024, when swarms became more energetic with increased magma flux and strain rates. These results demonstrate how magma input, crustal deformation, and faulting interact during prolonged volcanic unrest.

This work presents the results of an integrated monitoring of soil radon gas and seismic activity at Mt. Etna from August 2023 to May 2025, aimed at enhancing comprehension of magma migration and eruption dynamics. Radon data were collected using a permanent station with an alpha particle probe, aggregated hourly. The INGV-OE network monitored seismic activity at 100 Hz; volcanic tremor was analyzed using Root-Mean-Square (RMS) values from the Serra La Nave station. Earthquakes were located using the Hypoellipse algorithm and a 1D crustal velocity model. A robust correlation was found between radon and RMS anomalies, with the former preceding the latter with increasing probability over time (e.g., 30.1% within 1 day, 46.4% within 3 days). Correlations were also found between radon anomalies and Strombolian activity at the summit craters (e.g., 23.8% within 1 day for the Central Crater), suggesting a potential predictive role for radon. Conversely, correlations with paroxysmal events were weaker in the short term but increased over longer time windows. No clear correlation was found between radon anomalies and seismic strain release, likely due to differing temporal resolutions. These results support the idea that radon plays a role as a short-term precursor in volcanic unrest.

Abstract Magma intrusion often drives uplift of the overburden and free surface. Analytical modeling of such surface uplift at active volcanoes allows us to estimate intrusion geometries and positions, as well as volume and pressure changes; these insights have proven critical to forecasting volcanic unrest and eruptions. However, it is rarely possible to compare geodetic source parameters retrieved from analytical models to known intrusion geometries. Seismic reflection data offer an opportunity to image and quantify ancient, buried intrusion geometries and their overburden deformation (i.e., a forced fold). Here, we use 3D seismic reflection data offshore NW Australia to investigate an Early Cretaceous forced fold developed above a laccolith emplaced at ∼0.6–1 km depth. We remove the effects of post‐emplacement, burial‐related compaction and estimate surface displacement patterns for the forced fold. Analytical modeling of these surface displacements, using both thin plate bending and elastic half‐space solutions, suggest source (intrusion) estimates of position and lateral dimensions are similar to those of the actual laccolith. There are some differences between measurements of the laccolith and modeled source estimates, which we attribute to syn‐intrusion space‐making mechanisms (e.g., compaction). We particularly find penny shaped crack and rectangular dislocation elastic half‐space solutions underestimate source emplacement depth by ∼0.2–0.9 km, probably reflecting a lack of heterogeneity (layering) in our models. Our novel approach highlights seismic reflection data is a powerful tool for understanding and testing how magma emplacement translates into surface deformation at active volcanoes.

Abstract The 2021 eruption of Cumbre Vieja on La Palma, Canary Islands, provided a unique opportunity to investigate the dynamics of magma migration and storage during a large effusive eruption. In this study, we employ repeated seismic tomography to image temporal changes in the subsurface structure beneath La Palma, using body‐wave travel times from local earthquakes recorded before and during the eruption. By carefully selecting paired data sets with identical numbers of events and similar ray path distributions, we minimize biases introduced by variations in seismicity patterns and ensure robust detection of velocity changes. Our results reveal a complex magma plumbing system characterized by a deep magma storage zone below 8 km depth and a shallow, fluid‐saturated region extending to ∼3 km depth. During the eruption, a high Vp/Vs anomaly, interpreted as a magma conduit, formed and ascended through a rigid barrier at 5–8 km depth, facilitating the transport of significant volumes of magma to the surface. The conduit evolved from a diapir‐like structure with a stable head at 6–7 km depth in the early stages of the eruption to an ascending plume reaching 3 km depth in later stages. This study highlights the utility of repeated seismic tomography in unraveling the dynamic processes driving effusive eruptions and provides new insights into the evolution of magma systems during volcanic unrest.

Remote sensing of surface thermal anomalies on the Reykjanes Peninsula, SW-Iceland from 2016 to 2023, preceding and coinciding with recent volcanic unrest

The possibility of forecasting volcanic eruptions remains a major challenge for the volcanological scientific community. To date, various techniques based on volcano-tectonic seismicity, endogenous gas emission and satellite imagery have been widely applied in an effort to understand and anticipate short-term volcanic behaviour leading to eruptions. The rescaled range analysis (R/S) applied to time series of volcano-tectonic earthquakes is a quantitative method for determining the short-term and long-term memory of seismic activity during volcanic unrest. By using the Hurst exponent, it is possible to identify the precise transition from anti-persistence to persistence in volcano-tectonic earthquake time-series (VT) associated with volcanic dike ascent. We calculated the Hurst exponent of volcano-tectonic earthquakes during the 2021 Tajogaite eruption (La Palma, Canary Islands), the temporal evolution of the GEOS diagram and its correlation with the sustained dynamics of the volcanic eruption. Our study suggests that the volcanic unrest system transitions from anti-persistence to persistence approximately two days before the eruption, indicating a non-return point and the imminent onset of the eruption. Furthermore, we identified five magma deep injections during the eruption. The final stage and potential cessation of the eruption can also be inferred from the asymptotic trend of the Hurst exponent.Supplementary InformationThe online version contains supplementary material available at 10.1038/s41598-025-28566-6.

Santorini Island is of volcanic origin and has historically faced repeated volcanic and seismic activity. In early 2025, increased volcanism and intensified earthquake activity, similar to 2011-2012, caused residents’ concern. This study aims to characterize ground deformation on Santorini Island during its volcanic unrest in 2025 using InSAR observations. For this purpose, 74 synthetic aperture radar (SAR) images of Sentinel-1A satellites in descending and ascending orbits were acquired from early January 2024 to late March 2025. Line-Of-Sight (LOS) velocity values of the descending and ascending orbits were decomposed to determine the east-west and vertical displacement velocities. According to the results obtained, uplifts up to +60 mm/year velocity values were detected in the central parts of the island called Caldera, and subsidence up to –30 mm/year velocity values were detected in the outer regions. In addition, eastward horizontal movements reaching velocities of +60 mm/year and westward horizontal movements reaching velocities of –50 mm/year were also detected throughout the island. In the second stage of the study, a total of 4 points were selected on the islands of Thira, Thirasia, Nea Kameni, and Palea Kameni, considering the Kameni and Kolumbo fault zones. For these points on the island of Santorini, the displacements occurring over 15 months were analysed by time series analysis, and the temporal behaviour of the deformation (increasing/decreasing trend) was monitored. The analysed data indicate that the ongoing horizontal and vertical movements on the island could be caused by volcanic rather than seismic effects, which is consistent with previous studies. This situation shows that volcanic risk assessments in the region should be monitored for the upcoming processes.

Abstract Deep long‐period (DLP) earthquakes have been observed at many volcanic settings around the world and linked to the magmatic processes that drive volcanic unrest. At the Lassen Volcanic Center (LVC) of the Cascade arc, limited detection of DLP activity hinders classification of anomalous seismic behavior and its relationship to the LVC magmatic system. This study uses a template matching approach with seismic data from temporary nodal and permanent stations to detect and locate DLP earthquakes near the LVC between 2017 and 2024. Within the DLP catalog of 611 events, a transition occurs from scattered (2017–2020) to oscillatory (2021–2024) occurrence rates. During the oscillatory period, regional earthquakes with large amplitude velocity waveforms observed near the LVC are associated with abrupt changes in DLP occurrence rates. Continued monitoring of DLP activity has the potential to better define the processes that drive volcanic unrest at the LVC in the future.

Temporal evolution of fumarolic gas geochemistry at the Nevados de Chillán Volcanic complex (2013−2023): Signals of volcanic unrest and insights into the hydrothermal system

Abstract Seismicity offers insights into the mechanisms of magma generation, transportation, and the status of volcanic activity. Changbaishan is considered the most dangerous volcano in China. However, there was only one permanent seismic station (CBS) near Changbaishan Tianchi caldera before 2007. The limited number of stations posed a significant challenge in accurately locating earthquakes and herein investigating magma transport. In this study, we developed a Siamese Neural Network (SNN) with ConvMixer network (a hybrid SNN‐ConvMixer) that could regress back‐azimuth differences from continuous single‐station seismic recordings. Trained on paired reference–target events, this architecture mitigates the effect of limited lightweight data set. Comparative tests against conventional methods showed that our approach delivers relatively accurate estimates of back‐azimuth. We then combined its back‐azimuth predictions with traditional travel time grid‐search to infer hypocentral locations at Changbaishan volcano (CBV). Using this method, we successfully located 10,790 local seismic events beneath CBV 2000 and 2007. The spatiotemporal distribution of earthquakes indicates intense seismicity from 2002 to 2003 from deep to shallow depth, consistent with magma upward during the period of volcanic unrest. This deep learning technique demonstrates the potential for seismic analysis on other planets where seismic station networks are sparse.

Monitoring the spatio-temporal evolution of fumarolic activity is key to understanding volcanic unrest at dormant volcanoes. Here, we present the results of periodic gas surveys conducted at La Fossa (Vulcano Island, Italy) between 2021 and 2024, in which a portable Multi-GAS instrument is used to map the spatial variations in gas composition across the fumarolic field. We identify substantial spatio-temporal changes in gas composition. The crater rim fumaroles exhibit the highest CO2, SO2, H2S, H2 concentrations and stable, relatively low CO2/SO2 ratios (around 20–30), all indicative of a larger magmatic contribution. In contrast, the inner crater fumaroles display more variable and generally higher CO2/SO2 ratios, indicating a larger hydrothermal influence. These data, combined with infrared thermal imaging and SO2 flux results, are indicative of a volcanic unrest that, after having reached its climax in late 2021, has gradually vanished since, although not fully returning to pre-unrest conditions

Real-time seismological applications are essential for monitoring active volcanoes, offering valuable tools for the early detection of volcanic unrest and eruption. Very Long Period (VLP) seismicity, commonly observed at open-vent volcanoes with mild and persistent explosive activity, is a key indicator of volcanic activity intensity as changes in the rate of occurrence and VLP event magnitude can be a signal of impending unrest. In this study, we introduce a new method for the automatic and near real-time detection and characterization of VLP seismicity. Our approach was tested on Stromboli Volcano (Italy), where VLP seismic activity has been well-documented for over two decades. The detection algorithm is based on three-component amplitude analysis, derived from waveform polarization and spectral characteristics of continuous seismic records. It extracts key parameters such as detection time, event duration, azimuth, and incidence (polarization) angles. VLP events are distinguished from other signals through a single-station statistical analysis of polarization parameters, providing a reliable near–real-time catalog of VLP detections. Optimal detection thresholds for each station were determined using a machine-learning hyperparameter optimization approach. Here, we focus on the year 2007, which was characterized by highly variable VLP activity, including a major effusive eruption at Stromboli. The algorithm’s performance was validated using an independent, manually inspected dataset from 2007, yielding a false alert rate of 23% and a missed alert rate of 27% for the best-performing station. The results show that the method accurately reproduces the temporal evolution of the different activity phases throughout the year, with clear implications for enhancing and integrating VLP detection into existing volcano monitoring strategies. We applied the method to 16 years of seismic data (2009–2024), successfully reconstructing the temporal evolution of the VLP event rate in close agreement with manual inspections. The automatic detections show a strong correlation with manually derived daily rates, demonstrating that our automatic VLP detection time series reliably captures long-term fluctuations in volcanic activity over the entire period of investigation.Supplementary InformationThe online version contains supplementary material available at 10.1038/s41598-025-25636-7.

Ground Motion Models (GMMs) are empirically-calibrated equations relating ground motion intensity measures to earthquake magnitude, source-to-site distance, geological local site conditions, and possibly other covariates. GMMs are employed for applications such as probabilistic seismic hazard analysis and post-event rapid shaking estimation. Since early 2014, the densely populated Campi Flegrei caldera in Southern Italy has experienced increasing seismicity, concomitant to the volcanic unrest and ground uplift, with over ten thousand recorded events, with duration magnitude larger than − 1.1. In the period between March 2022 and May 2024, seismic activity has intensified, including approximately seventy events with duration magnitudes between 2.5 and 4.4, most of them widely felt, in some cases causing non-negligible seismic structural actions close to the source, and ultimately sparking large public concern. In this study, we calibrated site-specific GMMs for peak ground acceleration, peak ground velocity, and 5% damped spectral pseudo-acceleration for 18 vibration periods $$\:T$$ ranging from $$\:0.02\:s$$ to $$\:5\:s$$ . The dataset includes recordings from the events with duration magnitude greater than or equal to 2.5 over the period 03/22 − 05/24 recorded by more than 50 accelerometric and velocimetric seismic stations at epicentral distances $$\:{R}_{epi\:}<40\:km$$ . Moment magnitude, which is the scale used in the GMMs, was derived for the events from their displacement Fourier amplitude spectrum. The GMMs show larger spectral amplitudes at short periods( $$\:T<0.4\:s$$ ), and faster attenuation with distance ( $$\:{R}_{epi}\ge\:5km)$$ as compared to some existing ground motion models for Italy.

Although not all volcanic unrests lead to eruptions, it is commonly believed that magma rising through the shallow crust drives volcanic awakening. When eruptions do not occur, hydrothermal activity is often claimed to be responsible for inflation and deflation processes. Yet, a causal process explaining long-lasting non-eruptive unrest is still missing. Vulcano, the southernmost island of the Aeolian volcanic archipelago, Italy, entered in unrest in September 2021. The island experienced intense ground deformation, a sustained increase in fumarole temperatures, gas emissions, and shallow seismicity. CO 2 diffuse soil degassing increased at the foothill of La Fossa cone, causing the evacuation of inhabitants. Very Long Period (VLP) seismic events with a daily rate of up to 450 events/day were found in the seismic records for the first time since the deployment of the broadband network in 2005. With the benefit of hindsight, new VLPs were also discovered hidden in the 2018 seismic records. Geodetic data show inflation occurring in 2021, suggesting the pressurization of the shallow portion of the magmatic plumbing system beneath Vulcano. A similar behaviour occurred also in 2018. However, a few aspects of these unrests are not fully compatible with traditional causative models invoking a shallow dike emplacement or with a hydrothermal scenario. In particular, the long-lasting transient character of VLPs during 2021–22 has never been encountered before in hydrothermal-driven unrests. We propose that deep-seated fluid pressure, possibly promoted by a destabilizing event at depth, either of magmatic or tectonic origin, may have driven the unrests and be responsible for a discrete and transient release of lithostatic fluid pressures from the plumbing system. In particular, NE-striking normal faults highlighted by a high-resolution nodal ambient noise tomography seem to play a key role in modulating the transient character of the 2021 unrest. Once released, overpressure fronts travel across a rheologically complex domain causing VLPs. Once entering the hydrothermal system, fluids (e.g. H 2 O and CO 2 dominated mixtures) phase-separate and expand. This pressurizes the shallow plumbing system leading to intense shallow microseismicity. Our model is supported by the long-lasting transient character of the VLP events occurring in swarms and reconciles multiple interdisciplinary observations impacting how we understand the interplay between tectonics, volcanism and natural hazards. • We analyse a multiparametric dataset of Vulcano, Italy, including, seismic, temperature, and geodetic information. • We discover an rest in 2018 that went unnoticed and that was also characterized by VLPs. • We propose a tectono-magmatic model to explain the recent unrests of Vulcano.

The ongoing volcanic unrest at the highly populated Campi Flegrei caldera is accompanied by incremental seismic activity, ground uplift and geochemical anomalies that are raising severe public concern. Here we apply an unsupervised least root square method and a tailored Monte Carlo approach to the 2019-2024 earthquake hypocenter locations and show that since 2023 seismicity has progressively clustered along a preferential N249° ± 4°, 53° ± 1°plane near the center of the caldera, concentrating more than 50% of seismic events and most of the released seismic energy. This clustering is evidence for an internal process that drives the transition from diffuse micro-seismicity to the development of an extensional volcanotectonic fault in its initial stages. The nucleation (or reactivation) of this fault suggests that caldera rocks are experiencing conditions for critical failure and may have overcome elastic deformation resulted, until 2023, in an almost perfect axisymmetric uplift, thus representing an important change for volcanic and related hazards evaluation at Campi Flegrei. Spatial analysis of seismicity within the Campi Flegrei caldera suggests it has become progressively clustered since 2023 around a central plane which is consistent with the development of an extensional volcanotectonic fault

Abstract This study investigates the seasonal dynamics and environmental controls on radon (222Rn) concentrations in Los Verdes Cave, a volcanic lava tube in Lanzarote, Spain. Continuous monitoring of radon levels, together with external and internal climatic parameters (temperature, humidity, atmospheric pressure, wind speed), over an annual cycle, revealed distinct ventilation regimes characterized by pronounced seasonal variability. Radon concentrations exhibited peak values during the summer–autumn period (up to 882 Bq/m³), with minima observed in winter–spring (as low as 17 Bq/m³), indicating thermally driven ventilation inversions. A time-series ARIMA model identified external air temperature as the principal driver, wherein elevated temperatures led to reduced convective exchange and enhanced radon accumulation within the cave. Relative humidity and atmospheric pressure were also significant contributors, with underground air humidity exceeding 70% promoting radon retention. The validated model was used to forecast future radon scenarios under IPCC RCP4.5 and RCP8.5 climate trajectories, forecasting radon concentration increases of 5–60% by the year 2100 as a function of projected surface warming. These projections underscore implications for occupational exposure in confined volcanic environments, contribute to the broader understanding of subterranean greenhouse gas behaviour, and offer analog insights for astrobiological exploration in extraterrestrial lava tubes. The modeling framework enhances the ability to decouple radon variability associated with climatic forcing from geogenic anomalies potentially indicative of volcanic unrest. Overall, this study demonstrates the utility of statistical time-series approaches for forecasting radon behaviour under evolving climatic conditions and highlights the necessity of long-term environmental monitoring in geologically active subsurface ecosystems. Graphical Abstract The graphical abstract aims to highlight the most important aspects of the research presented. The lava tube under study, Cueva de Los Verdes, is located on the island of Lanzarote, one of the Canary Islands (Spain). To the right, the green box shows the annual concentration of 222Rn in Cueva de los Verdes (hourly records and daily mean). The average annual concentration was 169 Bq/m³, with recorded values ranging from a minimum of 17 Bq/m³ to a maximum of 882 Bq/m³. In addition, measurements were obtained for internal temperature and relative humidity (Tint and RH), external temperature (Text), atmospheric pressure, and average wind speed, which allowed the assessment of the environmental parameters influencing 222Rn concentrations in the cave. The grey box presents part of the conceptual model: the winter–spring phase of maximum ventilation, characterized by the lowest 222Rn concentrations. During this phase, a thermal inversion occurs, whereby colder, denser external air displaces the warmer, lighter cave air, enhancing ventilation and promoting air renewal. Understanding the influence of environmental parameters on 222Rn concentrations has enabled the prediction of its behavior and the forecasting of radon levels under climate change scenarios. The yellow box represents the worst-case scenario for 2100, in which 222Rn concentrations could increase by up to 60% compared to current levels.

Abstract The Campi Flegrei caldera, west of Naples, Italy, is currently experiencing volcanic unrest, a process that started 75 years ago. The magmatic origin of past uplift crises has been questioned by studies based on 14C data from marine organisms, suggesting three rapid uplifts; only the last, in the fifteenth century, was followed by the Monte Nuovo eruption (1538 CE). New 14C dating and water composition analyses from the thermal spring in the Roman Macellum of Pozzuoli (Serapeo) show that the two supposed non-eruptive medieval unrest phases are unreliable, because they are based on two-old ages due to absorption of deep 14C-depleted CO2 by marine fauna. The implication of this finding is that the current unrest has a high probability of being linked to the resumption of magma supply to the shallow plumbing system of the caldera, and that this process could result in a renewal of volcanic activity in the area.