Volcanic ash represents a hazard to aviation and a global network of Volcanic Ash Advisory Centres (VAACs) are tasked with providing advice and guidance to the aviation industry on its presence in the atmosphere. Forecasts of the expected location of the ash cloud are generated using atmospheric transport and dispersion models, initialised with a set of Eruption Source Parameters (ESPs) and driven by forecast meteorological data. In the future the VAACs will be required to adopt a Quantitative Volcanic Ash (QVA) approach of issuing probabilistic volcanic ash concentration information to the aviation industry, as such there is a need to develop a framework for producing a probabilistic forecast which incorporates both the uncertainty in forecast meteorology and in the eruption source parameters (ESPs). Variability in the meteorological forecasts is typically expressed as an ensemble of meteorological data, which can be provided to an atmospheric dispersion model to produce an ensemble of simulations in which ESPs are kept constant, and outputs are aggregated to remove the conditioning on the meteorology. Dispersion model forecasts are also sensitive to the ESPs used to initialise the simulations, notably the plume height and the mass eruption rate (MER) of volcanic ash injected into the atmosphere. The latter is difficult to measure in real-time, and for event response it is assumed to scale with the plume height. There remains a high degree of uncertainty in these linked ESPs, which can be modelled via a Bayesian linear modelling approach. We will present a method for incorporating the combined variability of ESPs and meteorological forcing into the ensemble to obtain values of exceedance probabilities for airborne volcanic ash concentrations of interest, using standard statistical techniques and numerical methods, whilst keeping computational and time costs down for efficient evaluation in an emergency. 

How to cite: Williams, S., Beckett, F., Leadbetter, S., Phillips, J., Lee, A., and Woodhouse, M.: Incorporating eruption source parameter and meteorological variability in the generation of probabilistic volcanic ash hazard forecasts, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9948, https://doi.org/10.5194/egusphere-egu24-9948, 2024.

Accurate forecasts are needed to help mitigate the risks of volcanic hazards to society. Current approaches use probabilistic estimates based on sparse data, supplemented with expert judgment, to describe likely future eruption characteristics. These probabilistic eruption characteristics then inform input parameters required by hazard models.

This process requires a lot of simulations with varying input parameters to constrain uncertainty around a future eruption’s hazard characteristics. It is also computationally intensive, and the outputs may quantify, but do not reduce eruption uncertainty. As hazard models become increasingly more complex, so do the number of input parameters that need to be estimated, thus increasing the number of sources of uncertainty. As input parameters used for volcanic hazard models are fundamentally uncertain before (and often also after) an eruption, how do they affect the accuracy and utility of forecasts made using these models?

This research explores the input space of volcanic hazard models to understand the interactions between model complexity and robustness of hazard model forecasts. We use the exemplar of volcanic ash distribution models Tephra2 and Fall3D at Mt. Taranaki, Aotearoa-New Zealand (30-50% chance of eruption in the next 50 years). Sampling strategies for Tephra2 and Fall3D were developed to ensure that the input parameter space was fully covered and represent real-world values – both through independent and dependent sampling of parameters. For example, plume height is dependent on the amount of mass ejected during an eruption. A Global Sensitivity Analysis is presented here to investigate the input parameters that significantly influence model output variance. This exploration is conducted through the statistical assessment of Sobol’ indices and eFAST (extended Fourier Amplitude Sensitivity Tests) to discern the key parameters that contribute to variations in the model’s outputs. The results also shed light on which inputs are vital to robust short-term and real-time hazard forecasting, and ultimately require better understanding/quantification before an event.

How to cite: Scott, E., Whitehead, M., Mead, S., Bebbington, M., and Procter, J.: Global Sensitivity Analysis of tephra models for forecasting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1402, https://doi.org/10.5194/egusphere-egu24-1402, 2024.

Volcanic hazards are dependent on eruption size and explosivity, thus, the forecasts of these is crucial for emergency management decisions. Monitoring a volcano potentially offers valuable insights to assess when, where, and how explosive a future eruption might be. Data are collected from various monitoring equipment, such as seismometers, tiltmeters, and thermometers, that are installed at different locations and distances, from near-vent to satellite. However, establishing direct links between monitoring signals and even eruption onset remains challenging, especially for volcanoes lacking recent eruptions or without monitoring equipment installed prior to eruption. This challenge extends to eruption explosivity, where establishing links becomes even more difficult.

The Global Volcanism Program (GVP) has compiled monitoring data in bulletin reports recorded by observatories and research institutions. These reports start from 1968 and summarise volcanic activity that occurs before, during and after an eruption. Importantly, these reports include descriptions about activity and/or raw data (number of earthquakes, frequencies, plots of the seismic signals or displacements on tiltmeters) from various monitoring equipment, providing a general understanding of precursor activities preceding an eruption. This is potentially key information for forecasting eruption explosivity.

This study aims to establish a quantitative link between monitoring signals and eruption explosivity across multiple volcanoes. Data are compiled from 23 volcanoes worldwide, utilising information from the Global Volcanism Program (GVP) database and local volcano observatory reports where accessible. The different descriptions obtained by each class of monitoring equipment—whether seismic, thermal, deformation, SO2 fluxes, or crater alterations—will be statistically categorized and calibrated into predictor variables to be used in machine learning algorithms. We hope to develop a procedure for estimating the explosivity of the next eruption, as a step towards statistically forecasting future eruption styles.

How to cite: Contla Hernandez, B., Whitehead, M., Bebbington, M., and Rowe, M.: A quantitative analysis of monitoring signals and eruption explosivity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1510, https://doi.org/10.5194/egusphere-egu24-1510, 2024.

Geodetic observations are key for assessing the unrest status of volcanoes worldwide, providing critical information about magmatic systems and the potential for magma migration and eruption. Analysing these signals relies on a robust data-model framework. One such approach is the Ensemble Kalman Filter (EnKF), a data assimilation method that has been adapted for analyses of volcanic deformation. The EnKF sequentially assimilates and inverts geodetic observations, using a series of model states to ‘nudge’ the model parameters with each iteration, reducing the misfit between the model and observation. We construct thermomechanical Finite Element (FE) models of volcanic regions, providing the necessary flexibility to incorporate complex 3D geometries and material heterogeneity. However, these simulations are computationally expensive when incorporated into the EnKF workflow, where an ensemble of >200 model states can take several hours to evaluate. This is particularly problematic for the analysis of observational data with high temporal resolution, such as daily GPS measurements.

Here, we aim to reduce the computational cost of the EnKF-FE workflow by using regression machine learning algorithms (MLAs), focusing on reducing the number of model states that need to be evaluated by the FE models. We start by using the ‘Mogi’ deformation model, a simple analytical expression that calculates the three-component displacement field (Ux, Uy, and Uz) due to a point source. We employ a tuneable nearest-neighbour approach to identify model states that occupy a ‘similar’ parameter space, using MLAs to predict the resultant displacements. The Mogi model has significantly reduced complexity compared to that of a FE model, providing a simple platform to test different machine learning approaches. Preliminary results suggests that the k-Nearest Neighbours and Linear Regression algorithms can significantly improve the computational efficiency of the EnKF-FE workflow, with negligible impact on the inferred best-fit model parameters, when a magmatic system is in a steady-state (i.e., static overpressure). Future modelling efforts will consider FE models with a 3D deformation source within a flat-topped domain, and time-varying overpressure scenarios.

How to cite: Head, M. and Gregg, P. M.: Improving the efficiency of ensemble-based volcano deformation analyses using Machine Learning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8093, https://doi.org/10.5194/egusphere-egu24-8093, 2024.

In extensional and transtensional basins, the dual action of basin-forming tectonism and explosive volcanic activity results in deposition of complex volcano-sedimentary successions. Since both aspects contemporaneously affect sediment-dispersal systems, it is difficult to distinguish one from the other by analyzing volcano-sedimentary successions. To discriminate tectonic influence, basin fills of the Miocene, pull-apart Janggi Basin were investigated. Here, the contemporaneous influence of tectonic subsidence and explosive volcanism formed <966 m thick, conformable volcano-sedimentary successions composed of laterally extensive, pumice-bearing, unwelded pyroclastic deposits and nonmarine sedimentary rocks formed under humid climatic conditions. Based on Laser Ablation – Multiple Collector – Inductively Coupled Plasma Mass Spectrometry zircon U-Pb age data, these successions were deposited from 21.1 ± 0.2 to 20.1 ± 0.1 Ma. After deposition of basinwide, tens of metres thick, and unwelded pyroclastic deposits, the directly overlying facies successions (FS-1 and FS-2) show contrasting depositional features to the classical model of volcaniclastic sedimentation. Facies succession-1 is represented by fluvial conglomerates composed mostly of (sub)rounded pebble and cobble sourced from basement. The supply of basement-derived clasts through fluvial systems resulted from development of physiographic relief during or soon after the eruption by syndepositional tectonic subsidence. Facies succession-2 occurs directly on pyroclastic deposits that cover FS-1 and show coarsening-upward trends, and is composed of basal lacustrine mudstones and overlying resedimented volcaniclastic sandstones showing a progradational geometry, interpreted as a result of progressive filling of the lake by remobilized volcaniclastic sediments. Occurrence of basal lacustrine laminated mudstones indicates that syndepositional creation of the accommodation by tectonic subsidence exceeded forceful input of pyroclastic and remobilized volcaniclastic sediments, resulting in a delayed sedimentary response to explosive volcanic eruptions. This study shows that, despite voluminous production of volcaniclastic sediments, tectonic activity controlled sediment type and stacking patterns. Therefore, these depositional features allow to discriminate tectonic effects from complex volcano-sedimentary successions, enabling to reconstruct basin evolution. 

How to cite: Gihm, Y., Kim, M.-C., and Chae, Y.-U.: Finding tectonic signals from ancient volcano-sedimentary successions: an example from the Miocene Janggi Basin, SE Korean Peninsula, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6834, https://doi.org/10.5194/egusphere-egu24-6834, 2024.

Ocean-rafted pumice is found on modern and paleo-beaches from the North Atlantic to the South Pacific. Correlation of ocean-rafting events to their volcanic source can help date sedimentary records and landforms, while geochemical fingerprinting of artefacts made from ocean-rafted pumice provides age constraints for pumice-bearing archaeological sites. These pumices also record large explosive eruptions that might not be preserved near the volcano due to extensive erosion or a submarine volcanic source and as such can be used for petrological and geochemical investigations.

This study explores links between spatiotemporal patterns of Holocene pumice deposition along the Norwegian coastline and prehistoric human use of this versatile resource. We first focused on a suite of pumice pieces from archaeological contexts of variable isostatic uplift in Northern Norway with most showing evidence of use as abrasive tools. These samples were geochemically correlated to individual Holocene eruptions or groups of tephras (SILK) from the Katla Volcanic System in Iceland. Our age data revealed that the estimated eruption dates typically predate the contexts by several hundred and up to 2-3,000 years, probably reflecting abundance and availability of certain pumice types at the time.

To investigate how distal resource availability is influenced by geological processes like eruption frequency, ocean-currents, and deposition/preservation we conducted field surveys of two coastal stretches with different climates, geomorphic settings and uplift histories. On Varanger Peninsula in Northern Norway strong Holocene uplift rates and sea-level changes have built a unique record of raised shorelines that provide windows into fossil beach ridges up to the marine limit, covered in little vegetation. We found that pumice was abundant on specific paleo-shorelines and in defined geomorphic settings but absent from older beach ridges. Most samples correlated with the <7 ka Katla record and the distinct mid-Holocene transgression high-stand accumulated the largest variety of pumice types and clast sizes. One sample cluster overlaps with SILK tephra compositions but does not correlate to any known Katla units while a single pumice plots outside the field defined by Katla eruptives, resembling compositions known for Jan Mayen.

In contrast, the Trøndelag and Nordland coast in Southern Norway is heavily vegetated and pumice was only found at isolated sites that displayed the right conditions, important factors being: a) the paleo-setting of the beach (e.g., currents, orientation, morphology) favouring accumulation in the first place, b) rapid uplift and limited erosion enabling preservation of the stranded pumice and c) exposure of pumice-bearing beach ridges (sections cut by rivers/erosion, roads/construction) as subsequent burial by sediment, soil and vegetation further reduces access to previously available pumice resources. This supports our hypothesis of pumice only being readily available for limited periods of time following eruption, rafting and onshore deposition. We will further test this assumption by integrating compositional information of archaeological pumice pieces from a recent archaeological excavation in Lofoten into our data-set.

Overall, our study provides a better understanding of the nature and frequency of Holocene silicic eruptions from Katla while also improving age control for existing relative sea-level curves and archaeological contexts in Norway.

How to cite: Zernack, A., Jørgensen, E. K., Newton, A., and Romundset, A.: Distal records of Katla’s explosive past: Ocean-rafted pumice found in archaeological contexts and raised shorelines in Norway, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7206, https://doi.org/10.5194/egusphere-egu24-7206, 2024.

Depressurisation from edifice collapse events can impact the subvolcanic plumbing system as a propagation wave moves down through the system shifting the fragmentation zone. Understanding how this influences the eruptive behaviour at a volcano is important for understanding changes in hazards following a large edifice collapse event. Mt. Taranaki has experienced at least 16 collapse events within its > 200 kyr history. Two of the largest collapse events the 27.3 ka Ngaere and 24.8 ka Pungarehu debris avalanches occurred in close succession and were encompassed by the Poto and Paetahi tephra formations, made up of 28 subplinian eruptions over ~ 4,000 years. This eruptive period provides a unique opportunity to examine and understand the influence that edifice collapse events have on the subvolcanic plumbing system. Using 3D Micro-Computed Tomography at the Australian Synchrotron bubble textural analysis was undertaken to investigate the changes in pyroclastic textures from large explosive eruptions and how these change following an edifice collapse event. The high-resolution 3D scans indicate that the eruptive products from the Poto and Paetahi Formations are dominated by small bubbles (2.7 x 10^-7 mm³) with high bubble number densities ranging from 2.56 x 10¹⁵ cm^-3 to 1.74 x 10¹⁶ cm^-3. Bubble size distributions for the Poto and Paetahi Formations indicate a range of bubble nucleation and growth processes occurring within the subvolcanic plumbing system below Mt. Taranaki initiating at different depths. Early onset of bubble nucleation and periods of magma stalling are indicated by the presence of large, coalesced bubbles within the eruptive products, while the dominance of smaller bubbles indicates a fast ascent of magma within the system with nucleation occurring higher up in the system. Changes are seen in the textural characteristics of pyroclasts produced following the 27.3 ka 5.85 km³ Ngaere collapse which depressurized the shallow magmatic system and shifted the fragmentation zone. Following the 24.8 ka 7.5 km³ Pungarehu collapse ~2,500 years later the same influence is not seen, due to the cone not having enough time to rebuild between edifice collapse events. The results from this study show that the depressurisation and subsequent propagation wave are dependent on the height above the plumbing system not just the mass removed and therefore two major collapses in close proximity do not show the same systematic impact on the fragmentation zone.

How to cite: Mills, S., Procter, J., Zernack, A., Mead, S., Schipper, I., Stevenson, A., Arhatatari, B., Thompson, D., and Fleming, J.: Using pyroclastic textures as an index for understanding the impact edifice collapse has on the subvolcanic plumbing system. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7230, https://doi.org/10.5194/egusphere-egu24-7230, 2024.

Volcanic communities near long-lived stratovolcanoes are susceptible to the significant threat associated with edifice collapse events which produce volcanic debris avalanches. These events can have runout distances > 100 km and are the largest mass flows on Earth with volumes ranging from 0.1 to 100 km³ which have the potential to bury large sectors of the landscape posing a severe risk to people and infrastructure. However, the emplacement mechanisms of these large destructive phenomena are still poorly understood with the inability to accurately quantify the physical parameters such as frictional regimes, velocity, and temperature which contribute to the extreme runout. The internal structure and minerology of the avalanche deposits hold the key to understanding the transportation mechanisms. During transportation inter-particle collision and shearing occurs reducing grainsize and generating new minerals such as Pseudotachylytes, Frictionites and Silica polymorphs along shear zones between larger clasts and along the base of the flow. Twenty-five volcanic debris avalanches and rock avalanches of varying sizes were sampled from New Zealand and the USA to provide a representative variety of flow types to better understand transportation mechanisms. Using 3D Micro-Computed Tomography at the Australian Synchrotron the internal structure of the avalanche deposits were analysed to identify different minerals and structures present. Analysis of the microstructures of the samples show a variety of different fracture patterns that can be categorized based on the different source lithologies sampled as well as the different rheological emplacement conditions from the collapse and flow.  Features seen at the micro-scale mimic larger centimeter to meter scale features traditionally observed in the flow.  Investigating the formation of new minerals along collision and shear zones can provide insights on the physical constraints of the flow e.g., velocity and temperature. Data from this study will provide quantitative input parameters forming the foundation for developing a model for transportation and emplacement of long-runout volcanic debris avalanches. Data from these models can be used to assess the volcanic debris avalanche hazards from volcanoes globally, better informing risk assessments.

How to cite: Procter, J., Mills, S., Zernack, A., Mead, S., Stevenson, A., and Arhatari, B.: Characterising transport and emplacement mechanisms of volcanic debris avalanches through 3D Micro Tomography. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7208, https://doi.org/10.5194/egusphere-egu24-7208, 2024.

Volcaniclastic debris flows are highly concentrated flows of rock debris, mud and water in which the sediment is of volcanic origin. These phenomena can be syneruptive, posteruptive, or unrelated to an eruption. To be generated, the coexistence of steep slopes, unconsolidated sediments and an adequate amount of water is necessary.

The aim of this project is to investigate the role of water circulation in the initiation processes of debris flows to enhance our ability to anticipate potential new debris flows in the Campanian Volcanism area, focusing on the Sarno area. Sarno is a small municipality located in the Vesuvius Volcanism area (western side of the Campanian Apennines) that is sadly infamous for the major debris flow events that, on the 6th of May 1998, destroyed the town and killed around 150 people.

The study area exhibits a convergence of geomorphological and lithostratigraphic settings that contribute to enhancing its exposure to hazards: i) the presence of a calcareous bedrock with very steep slopes (30-45°) mantled by ii) an alternation of colluvium and pyroclastic deposits, and iii) natural scarps and man-made cuts that further worsen the stability conditions.

This research employs a multimethodological approach including i) geotechnical and rheological analyses of the sediments; ii) X-ray Diffraction for the mineralogical characterisation, particularly of the clay fraction; iii) large-scale experiments to investigate the role of water circulation in the sediments during simulated rainfall in the triggering of volcaniclastic debris flows; iv) in situ Time-Domain Reflectometry measurements at Pizzo D’Alvano for soil moisture vertical distribution and v) simultaneously acquisition-surveys by using a drone-mounted passive radiometer for spatial soil moisture distribution. Integrating these methods aims to achieve understanding of the water content distribution in the debris flow initiation process that could be potentially used in the rainfall-triggered landslide early-warning systems.

How to cite: Pace, L., Domenico, C., Giovanna, C., Gabriele, C., Fabio, D., and Roberto, S.: The role of hydrological circulation in the initiation process of debris flows in the Campanian volcanic terrain, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16350, https://doi.org/10.5194/egusphere-egu24-16350, 2024.

The two "hottest" areas of Italy from the point of view of forecasting and mitigating volcanic hazard at the moment are the Phlegraean Fields and Vesuvius. At the Phlegraean Fields the bradyseismic crisis continues with noticeable changes in the fumarole regime and bradyseismic movements in the Solfatara area. Depending on the various conceptual models created by the various groups of scientists working in this area, it is possible to foresee different possible future scenarios, also assuming the persistence of magmatic degassing and conductive heat transfer from the magma to the overlying rocks and the absence of external, such as the occurrence of one or more regional earthquakes and the release of fresh magma into the reservoir located 8 km deep.

At Vesuvius, different scenarios are possible for the reactivation of the most famous volcano in the world. The first scenario involves the emplacement, maturation and eruption of magma from a sub-surface magma chamber, following the pattern of the last large explosive eruption which occurred in 1631 with the occurrence of a small-scale Plinian eruption. A disastrous scenario but one that requires fairly long warning times. A further scenario, proposed more recently, involves the ascent of magma along fractures linked to regional tectonic trends and its emplacement through rapidly moving flows with probable opening at the base of the volcanic edifice and much shorter warning times.

How can we manage these different situations in terms of Civil Protection and resilience?

How to cite: Principe, C.: Managing different eruptive scenarios at Phlegraean Fields and Vesuvius, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22302, https://doi.org/10.5194/egusphere-egu24-22302, 2024.

Lahars represent some of the most dangerous phenomena in volcanic areas for their destructive power, causing dramatic changes in the landscape with no premonitory signs and impacting on population and infrastructures. In this regard, the Campanian Plain turns out to be very prone to the development of these phenomena, since the slopes of the Somma-Vesuvius and Campi Flegrei volcanoes, as well as the nearby Apennine reliefs, are mantled by pyroclastic deposits that can be easily remobilized, especially after intense and/or prolonged rainfall. Our recent studies focus on the analysis of the pyroclastic fall and flow deposits, and of the syn- and post-eruptive lahar deposits related to two sub-Plinian eruptions of Vesuvius, 472 CE (Pollena) and 1631. Historical and field data from the existing literature and from hundreds of outcrops were collected and organized into a database. Stratigraphic, sedimentological, and archaeological analyses were carried out, in addition to rock magnetic investigations and impact parameter estimations. The field data analyses show that in both eruptions the dispersal area of the primary pyroclastic deposits is wider than previously known. Such distribution of the deposits directly affects the one of the lahar deposits, even because a significant remobilization took place during and after the studied eruptions, involving the distal phreatomagmatic ash. From these analyses, it was possible to constrain the timing of the deposition, and to estimate the thicknesses, velocities and dynamic pressures (impact parameters) of the lahars. A new shallow layer model based on depth-averaged variables, named IMEX-SfloW2D, was developed for the simulation of lahar dynamics. A thorough sensitivity analysis was carried out to identify the critical processes (erosion and deposition) and parameters (numerical and physical) controlling lahar runout, using both synthetic and real cases topographies. Effects of erosion and deposition were investigated by comparing field data with the output of simulations including vs. excluding these processes. By comparing observed and simulated flow thickness and area covered by the flows, and their evolution over time, it can be shown that the inclusion of erosion and deposition is important to properly simulate the impact parameters of lahars, particularly on uneven terrain. Lastly, a novel workflow for Probabilistic Volcanic Hazard Assessment (PVHA) for lahars was developed and applied to the Vesuvius case study. Such a workflow explores the effect of uncertainty of the flow initial conditions on the impact parameters of lahars on the target area, by sampling coherent sets of values for the input model parameters and running thousand simulations. The simulation outputs were processed to produce hazard curves, hazard maps, and probability maps for the maximum flow thickness, and hazard surface and probability maps for joint thresholds in flow thickness and dynamic pressure. It is believed that the latter hazard products represent a novel product in PVHA for lahars around Vesuvius volcano and can be applied worldwide. The multidisciplinary approach adopted in this work shows how it is crucial to assess the impact of lahars in densely populated areas, even at distances of several to tens of km from active volcanoes like Vesuvius.

How to cite: Di Vito, M., de'Michieli Vitturi, M., Sandri, L., Costa, A., Bisson, M., de Vita, S., Doronzo, D., Gianardi, R., Rosi, M., Rucco, I., Sulpizio, R., Zanchetta, G., and Zanella, E.: Lahars as repeated hazardous phenomenon around Vesuvius volcano (Italy) during and after impacting explosive eruptions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19093, https://doi.org/10.5194/egusphere-egu24-19093, 2024.

Lahars are two-phase gravity flows which behavior strongly depends on the interaction between the solid phase (large clasts) and the liquid phase (interstitial fluid or matrix). In particular, the rheological behavior of the interstitial fluid is the parameter with the greatest influence on the lahar movement, since the interstitial fluid controls the transportion and sedimentation of the solid phase. The characteristics that define the rheological behavior of the interstitial fluid are particle volumetric concentration, size distribution, and sediment composition. Because of these, here we present the rheological characterization of syn-eruptive and post-eruptive lahars occurred at Popocatepetl volcano, Mexico.

The interstitial fluid characterization was carried out by a strain rate dependence test using a rotational viscometer with a coaxial cylinder geometry. We studied volcanic sediments with different densities and compositions (pumice and lava fragments) sampled from syn- and post-eruptive lahar deposits (at room temperature). In addition, we studied the range of the volumetric sediment concentration that defines the flowage based on the geotechnical characteristics of sediments.

The results suggest a Bingham-type behaviour model with yield strength values between 10^-2 and 10⁰ Pa, for shear rate conditions between 50 and 100 s^-1. In addition, an inverse relationship of apparent viscosity throw values between 10^-2 and 10^-1 Pa s at  the same shear rates, suggesting a thinning behaviour. The data suggest exponential relationships between volumetric sediment concentration and yield strength or apparent viscosity. The fitting coefficients describe volcanic sediments, unlike those found in the literature and often used in lahar simulations for hazard modelling, which are derived from the study of soil materials and mine tailings.

The interstitial fluid of syn-eruptive lahars with monolithologic composition (pumice fragments) has yield strength and apparent viscosity values higher than those of syn-eruptive and post-eruptive lahars with heterolithologic composition (pumice and lava fragments). In addition, the dominant clay-sized interstitial fluid has apparent viscosity values between two and three orders of magnitude higher than the dominant silt-sized interstitial fluid.

Finally, the rheological behavior of the studied lahar samples will contribute to solving  the constitutive equations that describe their movement under a viscoelastic flow behavior for the studied shear rates. Furthermore, this information could be implemented in numerical simulations with similar volcanic sediment characteristics and deformation conditions to those studied, with the aim of estimating the inundation area that would be affected by the occurrence of a similar event.

How to cite: Tranquilino, C., Caballero, L., Flores Guzmán, M., Sarocchi, D., and Dioguardi, F.: First approach to the rheological behaviour of syn-eruptive and post-eruptive lahars., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8213, https://doi.org/10.5194/egusphere-egu24-8213, 2024.

Volcanic plumes associated with propagating pyroclastic density currents can rise tens of kilometers into the atmosphere, dispersing fine ash particles over large areas with a potential hazard for aviation safety. Such plumes originate from the buoyancy reversal of the pyroclastic density currents caused by the entrainment and heating of ambient air combined with the sedimentation of coarse particles. Several experimental and numerical studies investigated the formation, dynamics and impacts of these plumes but the mechanisms controlling the mass partitioning between the buoyant rising plume and the dense propagating current have received less attention despite its crucial importance for hazard assessment. Here, we present a new laboratory study aimed at investigating the controls on the mass partitioning during the plume lift-off. The experimental set-up is designed to simulate a gravity current of ethanol and ethylene glycol (EEG) flowing under a sloping roof in a tank of fresh water. The EEG mixture is less dense than fresh water but may become denser when mixed with water allowing us to generate a plume associated with the gravity current. Depending on the source conditions, the turbulent gravity current may either fully lift-off to form a buoyant plume, separate in a dense propagating flow and a buoyant plume, or propagate along the slope with no plume formation. We show that the transition between the three regimes is strongly controlled by the Richardson number defined at the source and by the slope. The results are consistent with the theoretical predictions of a simple 1D model and provide constraints on the mass partitioning during the formation of the plume.

How to cite: Carazzo, G. and Robert, G.: A laboratory study of plumes associated with pyroclastic density currents, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17769, https://doi.org/10.5194/egusphere-egu24-17769, 2024.

During explosive volcanic eruptions involving felsic magmas, angular porous pyroclasts are generated and ejected into the atmosphere. As these pyroclasts are mechanically weak, transport processes after fragmentation can alter their shape. Rotary tumbling experiments have been used to mimic particle-particle interaction during Pyroclastic Density Currents (PDC) or sedimentation and to understand the role of transport mechanisms on fine ash generation and changes in pyroclast morphology. We used clasts generated by Hornby et al. (2020) to statistically quantify the shape evolution of pre- and post-tumbling pyroclasts. Two types of Laacher See pumice were used as starting material. LSB (Laacher See Bims) was industrially processed by ROTEC^® by wet sieving, while ULST (Upper Laacher See Tephra) represents pristine clasts from fall units of the Laacher See eruption. Four sets of tumbling experiments (T1, T2, T3A, T3B) were performed. All lasted in total 120 minutes and ash generation was quantified after 15, 30, 45, 60 and 120th minutes. In T1 experiments, ash generated was added back into the drum after each increment but left out and stored separately in T2 experiments. In T3 steel balls were added to the drum to simulate the impact of lithics on the mechanical response of pumice lapilli. All other boundary conditions of T3A experiments mimic those of T1 while T3B experiments mimic T2. We quantified three values for each set of clasts: 1) amount of ash generated (dry sieving), 2) clast volumes (following Pisello et al., 2023), and 3) clast morphology. For the latter, we used shadowgraphs of 100 clasts per sample set independently, processed the images on Photoshop (clast contours delimitation and binarization) and calculated shape parameters (Convexity, Solidity, Form factor and Axial ratio, see Liu et al., 2015) using ImageJ. As expected, a striking distinction between starting material and tumbled clasts was found. We present data for 1) ash generation efficiency (≤ 53%), 2) clast volume (reduction), and 3) shape parameters (≤ 0.15 increase) to evidence the importance of pyroclast overprinting during transport-related processes. As clasts collected from fall units (see ULST here or Pisello et al., 2023) are angular, particle-particle interaction during gas-pyroclast flow inside conduits is found to have been of minor importance.

How to cite: Figueiredo, C., Esenyel, H. S., Kueppers, U., and Dingwell, D. B.: Shape evolution of pyroclasts in tumbling experiments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22220, https://doi.org/10.5194/egusphere-egu24-22220, 2024.

The aim of the paper is to identify a key to understanding that allows us to overcome the regulatory trilemma that has emerged, seeking to offer a perspective according to which the exceptional event, an expression of the (ineliminable) complexity of reality, is included (in the competent political and institutional fora) in a broader case, encompassing contingencies. And this is not to foresee them, often asking science to do the impossible, nor to block activities considered dangerous through an exaggeration of the principles of prevention and precaution, but simply to allow the legal system to assume a broader vision, inclusive of the unusual case in point, to provide a toolbox of possible reactions to be triggered in the event (even remote) of the occurrence of an exceptional event.

How to cite: Giani, L. N. E. and Casagrande, G.: Trilemma, complexity, administration and exceptional events, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22289, https://doi.org/10.5194/egusphere-egu24-22289, 2024.

Explosive volcanic eruptions, which are characterized by the discharge of ash and gas from the vent into the atmosphere, are an example of a naturally occurring buoyant jet.  These buoyant jets can significantly impact the surrounding environment; for example, the presence of fine ash particles in the atmosphere can damage aircraft engines, potentially leading to engine failure. Therefore, during an explosive eruption, volcanic ash advisory centers (VAACs) consistently monitor the concentration of ash in the atmosphere using numerical models. These numerical models require the definition of a source term (i.e., source mass eruption rate, plume height and total grain size distribution), which is often obtained from simpler one-dimensional models. One-dimensional models derived from well-established theories successfully replicate the dynamics of the initial buoyant jet; however, they assume time-averaged source conditions which are not observed in field-scale vulcanian and strombolian style eruptions. As such, there is a disconnect between these well-established theories assuming time averaged source conditions and reality. This disconnect may introduce uncertainties in ash concentration forecasts, potentially resulting in practical implications such as unnecessary airspace closures or flights operating in hazardous conditions. The present contribution utilizes scaled laboratory experiments to quantify the influence of source variability on the dynamics of buoyant jets and evaluates potential deviations from time-average assumptions.

Scaled laboratory experiments were conducted in an acrylic tank measuring 1200x670x450 mm, filled with water to a depth of 870 mm. A vertical pipe, 18 mm in diameter, was used to release fresh water (density ρ = 1000 kg/m³), which was combined with dye or particles, into saline water (ambient density  = 1000 - 1030 kg/m³). This configuration resulted in the generation of a vertical buoyant jet.  The flow rate was controlled and measured using a valve and ultrasonic flow meter. For the generation of unsteady discharges, a solenoid valve was employed, facilitating pulsed source conditions with discharge intervals ranging between ½ second to 2 seconds. Image analysis techniques, specifically light-induced fluorescence (LIF) and particle image velocimetry (PIV), were employed to measure buoyant jet characteristics, including concentration profiles, velocity fields, and jet geometry. These characteristics were measured under both steady and unsteady source conditions, facilitating a comparative analysis of the changes in behaviour arising from source condition variations.

The experimental results were compared with integral assumptions of one-dimensional models. These findings will be presented, and their significance will be explored within the context of vulcanian and strombolian style eruptions.

How to cite: Hetherington, M., Cuthbertson, A., Dawson, S., and Dioguardi, F.: Understanding the dynamics of unsteady buoyant Jets: an experimental analogue of Vulcanian and Strombolian style eruptions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15962, https://doi.org/10.5194/egusphere-egu24-15962, 2024.

The topic of exceptions to the ordinary rules of public contracts in the management of risks and emergencies resulting from volcanological phenomena allows for numerous considerations on the aspects of public contracts and administrative law. The topic must obviously be analysed through an interdisciplinary approach focusing on the relationship between technology and law. For example, to verify the legitimacy of the application of derogatory regulations, it is necessary to consider the three-phase structure of volcanic risk: risk assessment, hazard assessment and mitigation of the event. The centrality of the technical issues requires, first of all, an examination of the legal profiles: the first aspect concerns the delimitation of both the concept of "paramount urgency" - a prerequisite for derogating from the ordinary rules - and of which events (whether they have already occurred or have not yet occurred) are susceptible to fall within the scope of the provision. In this context, this research focuses on the practices of individual local authorities from which a significant interpretative and methodological distance emerges.

A further profile of interest concerns organisational issues: this work aims to examine the benefits of a centralisation of competences in the hands of the regions, from two points of view. The first concerns the attempt to reduce potential corruption phenomena that could occur in territories where unpredictable maintenance events frequently occur. The second is based on the consideration that leaving the choice to individual local administrations could lead to different assessments of 'extreme urgency' conditions between neighbouring authorities Centralisation would therefore go in the direction of uniformity of decisions.

There are, in conclusion, two other aspects that deserve further study. The first concerns the need for ex-post controls, linked to the centrality of the assessment of the conditions of extreme urgency, which risks being ineffective given the extremely tight timeframe. The second seeks to understand whether the derogation to the procurement regime also drags on the regime of landscape authorisations or environmental impact assessments: if this were not the case, and if therefore ex ante intervention were still necessary, the process of simplifying the activities of economic operators would inevitably be thwarted. In addition to the theoretical reflections carried out on the derogation to the ordinary regime of contracting in cases of volcanic risk, this work will also analyse the so-called Campi Flegrei Decree, which allows recourse to the derogatory techniques mainly for two reasons: to provide for the acquisition of instrumental resources necessary to ensure the effective management of civil protection activities; and to provide for the setting up of temporary areas and services for the reception of the population.

How to cite: Calabrò, M. and di Martino, A.: Exceptions to the ordinary rules for awarding public contracts: the volcanic risk paradigm, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22294, https://doi.org/10.5194/egusphere-egu24-22294, 2024.

The catastrophic events linked to natural phenomena that periodically strike Italy generate an increasingly irremediable rift between the State and the population, which is also tangible in the litigation that has become an increasingly frequent consequence of disasters in recent times. The media clamour that judicial events take on increasingly generates an image of a State that is impeccable in the solidarity phase but remains highly negligent in risk prevention policies. Compared to this vision, the recent commitment of the legislator to prevent the damaging effects of bradyseism in the Phlegraean Fields area goes against the trend.

However, many of the prevention activities identified, which can be implemented thanks to the appropriations provided, risk being compromised on a practical level due to the considerable rate of abuse in the area concerned, which makes the territory more fragile and the population less safe.     

It is strategically necessary to increase the level of public safety in an area that, on this point, presents undeniable criticalities: among the measures that can be implemented, it is desirable, for example, to perform an immediate analysis of the seismic vulnerability of the public and private building stock so as to allow preventive safety measures. In addition, an update of the General Evacuation Plan is needed, which currently, according to studies, would not allow the area, with its very high population density, to be cleared in a few hours.

How to cite: d'Orsogna, M. and Valentini, F.: Environmental surveillance and volcanic risk. Bradyseismic crisis and vulnerability of built-up areas: new intervention strategies on public and private heritage., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22379, https://doi.org/10.5194/egusphere-egu24-22379, 2024.

This paper aims to analyse the use of artificial intelligence tools to implement an active contact tracing system for individuals living in at-risk territories. Thus, not only a 'state of alert' communication system, but a 'contact tracing' system similar to that used in some States during the SARS pandemic COVID-19. From a legal point of view, it is necessary to balance the right to privacy with the right to health/right to life. In this perspective, the necessary prerequisites will be analysed: state regulation, rigorously proportionate and, furthermore, the security of the data. This must be placed on a server that is strictly publicly owned and managed, to prevent tracing being used as a bargaining chip, and ensure that the personal data collected by the platform or application are only those necessary to warn users of the danger and are not used for any other purpose, without prejudice to the possibility of using them in aggregate or in any case anonymous form, for statistical or scientific research purposes only.

How to cite: Fratto Rosi Grippaudo, E. and Rufo, L.: Data privacy in volcanic hazard scenarios, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22382, https://doi.org/10.5194/egusphere-egu24-22382, 2024.