Gilda Currenti

Capturing the fingerprint of Etna volcano activity in gravity and satellite radar data

Long-term and high temporal resolution gravity and deformation data move us toward a better understanding of the behavior of Mt Etna during the June 1995 – December 2011 period in which the volcano exhibited magma charging phases, flank eruptions and summit crater activity. Monthly repeated gravity measurements were coupled with deformation time series using the Differential Synthetic Aperture Radar Interferometry (DInSAR) technique on two sequences of interferograms from ERS/ENVISAT and COSMO-SkyMed satellites. Combining spatiotemporal gravity and DInSAR observations provides the signature of three underlying processes at Etna: (i) magma accumulation in intermediate storage zones, (ii) magmatic intrusions at shallow depth in the South Rift area, and (iii) the seaward sliding of the volcanos eastern flank. Here we demonstrate the strength of the complementary gravity and DInSAR analysis in discerning among different processes and, thus, in detecting deep magma uprising in months to years before the onset of a new Etna eruption.

Soil radon measurements as a potential tracer of tectonic and volcanic activity

In Earth Sciences there is a growing interest in studies concerning soil-radon activity, due to its potential as a tracer of numerous natural phenomena. Our work marks an advance in the comprehension of the interplay between tectonic activity, volcanic eruptions and gas release through faults. Soil-radon measurements, acquired on Mt. Etna volcano in 2009–2011, were analyzed. Our radon probe is sensitive to changes in both volcanic and seismic activity. Radon data were reviewed in light of the meteorological parameters. Soil samples were analyzed to characterize their uranium content. All data have been summarized in a physical model which identifies the radon sources, highlights the mechanism of radon transport and envisages how such a mechanism may change as a consequence of seismicity and volcanic events. In the NE of Etna, radon is released mainly from a depth of <1400 m, with an ascent speed of >50 m/day. Three periods of anomalous gas release were found (February 2010, January and February 2011). The trigger of the first anomaly was tectonic, while the second and third had a volcanic origin. These results mark a significant step towards a better understanding of the endogenous mechanisms that cause changes in soil-radon emission at active volcanoes.

Evidence of a shallow persistent magmatic reservoir from joint inversion of gravity and ground deformation data: The 25–26 October 2013 Etna lava fountaining event

To evaluate the volcanic processes leading to the 25–26 October 2013 lava fountain at Mount Etna, we jointly investigated gravity, GPS, and DInSARmeasurements covering the late-June to early-November time interval. We used finite element modeling to infer a shallow magmatic reservoir which (i) inflated since July 2013, (ii) fed the volcanic activity at the summit craters during 25–26 October, and (iii) deflated due to magma drainage related to this volcanic activity. We suggested that this reservoir belongs to a shallow volume, which is located beneath the summit area and is replenished by magma rising from deep reservoirs and fed the short-term volcanic activity, representing a persistent shallow magmatic plumbing system of Etna. In addition, the model results show that there is a large discrepancy between the erupted and shallow reservoir deflation volumes, which could be reasonably attributable to a highly compressible volatile-rich magma.

Microgravity changes at the Laguna del Maule volcanic field: Magma‐induced stress changes facilitate mass addition

Time-dependent, or 4-D, microgravity changes observed at the Laguna del Maule volcanic field, Chile, since 2013, indicate significant (1.5 × 1011 kg) ongoing mass injection. Mass injection is focused along the Troncoso fault, and subparallel structures beneath the lake at 1.5–2 km depth, and is best modeled by a vertical rectangular prism source. The low-density change (156 to 307 kg/m3) and limited depth extent suggest a mechanism of hydrothermal fluid intrusion into existing voids, or voids created by the substantial uplift, rather than deeper-sourced dike intrusion of rhyolite or basalt magma. Although the gravity changes are broadly spatially coincident with ongoing surface deformation, existing models that explain the deformation are deeper sourced and cannot explain the gravity changes. To account for this discrepancy and the correspondence in time of the deformation and gravity changes, we explore a coupled magmatectonic interaction mechanism that allows for shallow mass addition, facilitated by deeper magma injection. Computing the strain, and mean, normal, and Coulomb stress changes on northeast trending faults, caused by the opening of a sill at 5 km depth, shows an increase in strain and mean and normal stresses along these faults, coincident with the areas of mass addition. Seismic swarms in mid-2012 to the west and southwest of the mass intrusion area may be responsible for dynamically increasing permeability on the Troncoso fault, promoting influx of hydrothermal fluids, which in turn causes larger gravity changes in the 2013 to 2014 interval, compared to the subsequent intervals.

GEOFIM: A WebGIS application for integrated geophysical modeling in active volcanic regions

We present GEOFIM (GEOphysical Forward/Inverse Modeling), a WebGIS application for integrated interpretation of multiparametric geophysical observations. It has been developed to jointly interpret scalar and vector magnetic data, gravity data, as well as geodetic data, from GPS, tiltmeter, strainmeter and InSAR observations, recorded in active volcanic areas. GEOFIM gathers a library of analytical solutions, which provides an estimate of the geophysical signals due to perturbations in the thermal and stress state of the volcano. The integrated geophysical modeling can be performed by a simple trial and errors forward modeling or by an inversion procedure based on NSGA-II algorithm. The software capability was tested on the multiparametric data set recorded during the 2008-2009 Etna flank eruption onset. The results encourage to exploit this approach to develop a near-real-time warning system for a quantitative model-based assessment of geophysical observations in areas where different parameters are routinely monitored.

Learning about Hydrothermal Volcanic Activity by Modeling Induced Geophysical Changes

Motivated by ongoing efforts to understand the nature and the energy potential of geothermal resources, we devise a coupled numerical model (hydrological, thermal, mechanical), which may help in the characterization and monitoring of hydrothermal systems through computational experiments. Hydrothermal areas in volcanic regions arise from a unique combination of geological and hydrological features which regulate the movement of fluids in the vicinity of magmatic sources capable of generating large quantities of steam and hot water. Numerical simulations help in understanding and characterizing rock-fluid interaction processes and the geophysical observations associated with them. Our aim is the quantification of the response of different geophysical observables (i.e. deformation, gravity and magnetic field) to hydrothermal activity on the basis of a sound geological framework (e.g. distribution and pathways of the flows, the presence of fractured zones, caprock). A detailed comprehension and quantification of the evolution and dynamics of the geothermal systems and the definition of their internal state through a geophysical modeling approach are essential to identify the key parameters for which the geothermal system may fulfill the requirements to be exploited as a source of energy. For the sake of illustration only, the numerical computations are focused on a conceptual model of the hydrothermal system of Vulcano Island by simulating a generic 1-year unrest and estimating different geophysical changes. We solved (i) the mass and energy balance equations of flow in porous media for temperature, pressure and density changes, (ii) the elastostatic equation for the deformation field and (iii) the Poisson’s equations for gravity and magnetic potential fields. Under the model assumptions, a generic unrest of 1-year engenders on the ground surface low amplitude changes in the investigated geophysical observables, that are, however, above the accuracies of the modern state-of-the-art instruments. Devising multidisciplinary and easy-to-use computational experiments enable us to learn how the hydrothermal system responds to un unrest and which fingerprints it may leave in the geophysical signals.

Coupled Short- and Medium-Term Geophysical Signals at Etna Volcano: Using Deformation and Strain to Infer Magmatic Processes From 2009 to 2017

Due to the frequent eruptive activity of Etna volcano, it is of primary importance to interpret the near-real time geophysical data as best as possible in order to understand the unrest vs. eruptive timescales. After the main flank eruption of 2008-2009 and until 2017, Etna volcano was characterized by a lively eruptive activity of different phases. These comprised 44 lava fountain episodes that formed a new crater named New South East Crater (NSEC) during 2011-2013, two sequences of close episodes of lava fountains from the Voragine crater (VOR) on 3-5 December 2015 (4 events) and May 18-21, 2016 (3 events), as well as some periods of summit effusive activity with a more prolonged supply of lava flows during 2014. Several studies have described and modelled single episodes of lava fountains of both the NSEC and VOR. In particular, during lava fountainings the high precision data from borehole strain-meters revealed short-term changes, which allowedinference into the source of decompression at a shallow level (shallow plumbing system) of at ~ sea level for the events of the NSEC and at deeper level (~2-5 km b.s.l.) for those of VOR, respectively. In this study, we also considered the middle-term volcano recharging/discharging periods preceding/accompanying the different eruptive phases during 2009-2017, and through the deformation recorded by the permanent GPS network, we constrained the position of the sources. Together with the modelling deduced from the strain-meter data we produce a more complete representation of the different sources that characterized the different periods both in the middle-term (i.e. the preparatory phases showing inflation and the eruptive phases showing deflation) and in the short-term (i.e. the fast discharge associated with each eruptive event). Our highly resolved modelling explains the pathway of magma from the intermediate-shallow plumbing system to the surface. Our results are consistent with petrological constraints on the spatio-temporal evolution of magma transfer and storage.

A multidisciplinary strategy for in-situ and remote sensing monitoring of areas affected by pressurized fluids: Application to mud volcanoes: A multidisciplinary environmental monitoring strategy

A multidisciplinary strategy integrating a data set obtained using different mthods and techniques, ranging from remote sensing (UAV system, FTIR, thermal imaging) to direct field measurements (soil heat flux, soil CO2 flux, gravimetry and geomagnetism) proved highly capable of modeling regions affected by pressurized fluids circulation and extreme natural environments. As a test site, the Salinelle mud volcanoes area, located close to the city of Paternò (Sicily), was selected. This area is characterized by gas exhalations through water/mud vents. Detailed morpho-structural information, GIS thematic maps and geochemail signature of the released gas were quickly retrieved. This study showed that by integrating and harmonizing many disciplines of geosciences it is possible to get a comprehensive geological model of the studied area. Results, showed the accurate detection of structural setting of such an area and the opportunuty to monitor the spatial/temporal evolution of water/mud vents. The proposed approach allowed to expand the use of each single technique beyond its traditional applications and to make it a potential tool for many fields of geoscience.

A Second Order Finite-Difference Ghost-Cell Method for the Steady-State Solution of Elasticity Problems

This work presents a second order finite-difference ghost cell method for the steady-state solution of elasticity problems. Numerical results are shown for the application of underground volcano activities.

Model-Based Assessment of Geophysical Observations: From Numerical Simulations Towards Volcano Hazard Forecasting

Geodetic, gravity and magnetic field changes, produced by mass and stress redistributions accompanying magma migration and accumulation within the volcano edifice, are numerically computed by an integrated elastic 3-D model based on Finite Element Method (FEM). Firstly, comparisons are made between analytical and numerical solutions to validate the numerical model and to estimate the perturbations caused by medium heterogeneity and topographic features. Successively, the integrated numerical procedure was applied to interpret geophysical observations collected at Etna volcano during unrest periods. The obtained results highlight that heterogeneity and topography engender deviations from analytical results in the geophysical changes and, hence, the disregard of these complexities could lead to an inaccurate estimate of source parameters in inversion procedure. The FEM approach allows for considering a picture of a fully 3D model of Etna volcano, which advance the reliability of model-based assessments of geophysical observations. This approach, based on observable data and complemented by physical modeling techniques, makes the step ahead in the volcano hazard assessment and in the understanding of the underlying physics and poses the basis for future developments of scenario forecasting.