Alessandro Bonforte

Structural assessment of Mount Etna volcano from Permanent Scatterers analysis

A study of the deformation pattern of Mount Etna volcano based on the results from the Permanent Scatterers (PS) technique is reported. Ground motion data provided by the interferometric synthetic aperture radar (InSAR) PS technique from 1995 to 2000 are compared and validated by GPS data. An analysis of the ascending and descending line of sight (LOS) components of ground velocities has yielded detailed ground deformation maps and cross sections. This analysis allows detection and constraint of discontinuities in the surface velocity field. LOS velocities have then been combined to calculate the vertical and horizontal (E-W) ground velocities. A wide inflation of the edifice has been detected on the western and northern flanks (over an area of about 350 km2). A seaward motion of the eastern and southern flanks has also been measured. PS data allows the geometry and kinematics of the several blocks composing the unstable flanks to be defined even in the highly urbanized areas, and their displacement rates have been measured with millimeter precision. This analysis reveals the extension of some features beyond their field evidences and defines new important features. The results of this work depict a new comprehensive kinematic model of the volcano highlighting the gravitational reorganization of the unbuttressed volcanic pile on its slippery clay basement on the southern flank, but an additional drag force due to a strong subsidence of the continental margin facing the Etna volcano is necessary to explain the PS velocity field observed on the eastern flank.

The initial phases of the 2008–2009 Mount Etna eruption: A multidisciplinary approach for hazard assessment

Accepted for publication in Journal of Geophysical Research. Copyright (2010) American Geophysical Union

Dynamics of Mount Etna before, during, and after the July–August 2001 eruption inferred from GPS and differential synthetic aperture radar interferometry data

We acknowledge the ‘‘Istituto Nazionale di Geofisica e Vulcanologia’’, the Italian ‘‘Dipartimento per la Protezione Civile’’ and the European Community (contract INGV-DPC UR V3_6/36 and VOLUME Project) for their economic contribution to this research. The SAR data are provided by ESA-ESRIN.

Large scale ground deformation of Etna observed by GPS between 1994 and 2001

We have processed thirty Global Positioning System (GPS) campaigns carried out at Etna from 1994 to early 2001 between the last two main flank eruptions of the Mt. Etna (Sicily, Italy). This rest period allowed us to investigate the deep magma plumbing system of the Mt. Etna. The temporal dynamics of twenty-three points observed three times or more were analyzed. All the time series show a first-order linear trend during the five years period. It suggests that the volcano was continuously deformed by the action of a deep source while a discrete activity of the volcano was observed at the summit. We have interpreted the residual deformation field as the result of an major eastward motion of the eastern flank of the volcano.

Calibration of atmospheric effects on SAR interferograms by GPS and local atmosphere models: first results

Abstract A comparison between the zenith path delay (ZPD), obtained from GPS measurements, and the expected delay, derived from models used to compensate tropospheric effects on SAR interferograms, is made. The results of the two methods are comparable, though the available data set is not large enough for a complete statistical validation of the methods. The results of this preliminary study suggest a possible integration of GPS-based ZPD data with cheap and standard meteorological data, since the estimated atmospheric component proved to be similar. Furthermore, the impact on volcanology of the effects measured by GPS, and in particular on the determination of the depth of the volcanic sources, is discussed.

Twelve Years of Ground Deformation Studies on Mt. Etna Volcano Based on Gps Surveys

GPS (Global Positioning System) monitoring has been performed on Etna volcano since 1988, making this volcano one of those with the longest records of GPS data. The first order network, measured at least once every year in accurate static mode, was progressively augmented from 9 benchmarks in 1988 to ∼70 benchmarks. The whole network is subdivided into seven sub-networks that are surveyed in static, quick-static or kinematic mode, according to the accuracy and density needed, with respect to the volcanic activity. This network provides key constraints to locate the deformation sources inside the volcano (reservoirs, dykes, faults) and track their evolution. Etna has proved an optimum testing ground of new surveying approaches in order to optimize geodetic fieldwork. Several methodological developments related to kinematic surveys and to the correction of tropospheric delays were made on Etna. Here, we discuss the overall picture of the entire data set up to 1999. The results show large scale displacements related to the activity of the volcano during the last twelve years. They are used to infer the location of magma reservoirs acting in this period, identifying a pressure zone beneath the western flank at a depth ranging from 2 to 9 km, several shallow intrusion following the regional NNW-SSE trend, and to quantify the eastward movement of the eastern flank of Mt. Etna, modeling two detachment surfaces beneath the eastern and southern flanks. At a local scale (e.g. in the summit areas and across the Pernicana fault), displacements are also identified and discussed.

Very shallow dyke intrusion and potential slope failure imaged by ground deformation: The 28 December 2014 eruption on Mount Etna

On 28 December 2014, eruptive activity resumed at Mount Etna with fire fountain activity feeding two lava flows on the eastern and southwestern upper flanks of the volcano. Unlike all previous summit activity, this eruption produced clear deformation at the summit of the volcano. GPS displacements and Sentinel-1A ascending interferograms were calculated in order to image the ground deformation pattern accompanying the eruption. The displacements observed by GPS depict a local ground deformation pattern, affecting only the upper part of the volcano. Despite snow cover on the summit, differential interferometry synthetic aperture radar (DInSAR) data allowed obtaining more detail on the ground deformation pattern on the upper eastern side of the volcano. Three-dimensional GPS displacements inversion located a very shallow NE-SW intrusion just beneath the New Southeast Crater. However, this model cannot justify all the deformation observed by DInSAR thus revealing a gravitational failure of the lava flow field.

Why Does a Mature Volcano Need New Vents? The Case of the New Southeast Crater at Etna

Mature volcanoes usually erupt from a persistent summit crater. Permanent shifts in vent location are expected to occur after significant structural variations and are seldom documented. Here we provide such an example that recently occurred at Etna. Eruptive activity at Mount Etna during 2007 focused at the Southeast Crater (SEC), the youngest (formed in 1971) and most active of the four summit craters, and consisted of six paroxysmal episodes. The related erupted volumes, determined by field-based measurements and radiant heat flux curves measured by satellite, totalled 8.67 x 106 m3. The first four episodes occurred, between late-March and early-May, from the summit of the SEC and short fissures on its flanks. The last two episodes occurred, in September and November, from a new vent (“pit crater” or “proto-NSEC”) at the SE base of the SEC cone; this marked the definitive demise of the old SEC and the shift to the new vent. The latter, fed by NW-SE striking dikes propagating from the SEC conduit, formed since early 2011 an independent cone (the New Southeast Crater, or “NSEC”) at the base of the SEC. Detailed geodetic reconstruction and structural field observations allow defining the surface deformation pattern of Mount Etna in the last decade. These suggest that the NSEC developed under the NE-SW trending tensile stresses on the volcano summit promoted by accelerated instability of the NE flank of the volcano during inflation periods. The development of the NSEC is not only important from a structural point of view, as its formation may also lead to an increase in volcanic hazard. The case of the NSEC at Etna here reported shows how flank instability may control the distribution and impact of volcanism, including the prolonged shift of the summit vent activity in a mature volcano.

Experimental study of the interplay between magmatic rift intrusion and flank instability with application to the 2001 Mount Etna eruption

Mount Etna volcano is subject to transient magmatic intrusions and flank movement. The east flank of the edifice, in particular, is moving eastward and is dissected by the Timpe Fault System. The relationship of this eastward motion with intrusions and tectonic fault motion, however, remains poorly constrained. Here we explore this relationship by using analogue experiments that are designed to simulate magmatic rift intrusion, flank movement, and fault activity before, during, and after a magmatic intrusion episode. Using particle image velocimetry allows for a precise temporal and spatial analysis of the development and activity of fault systems. The results show that the occurrence of rift intrusion episodes has a direct effect on fault activity. In such a situation, fault activity may occur or may be hindered, depending on the interplay of fault displacement and flank acceleration in response to dike intrusion. Our results demonstrate that a complex interplay may exist between an active tectonic fault system and magmatically induced flank instability. Episodes of magmatic intrusion change the intensity pattern of horizontal flank displacements and may hinder or activate associated faults. We further compare our results with the GPS data of the Mount Etna 2001 eruption and intrusion. We find that syneruptive displacement rates at the Timpe Fault System have differed from the preeruptive or posteruptive periods, which shows a good agreement of both the experimental and the GPS data. Therefore, understanding the flank instability and flank stability at Mount Etna requires consideration of both tectonic and magmatic forcing.

Mt. Etna volcano high-resolution topography: airborne LiDAR modelling validated by GPS data

ABSTRACT High-resolution digital topography is essential for land management and planning in any type of territory as well as the reproduction of the Earth surface in a geocoded digital format that allows several Digital Earth applications. In a volcanic environment, Digital Elevation Models are a valid reference for multi-temporal analyses aimed to observe frequent changes of a volcano edifice and for the relative detailed morphological and structural analyses. For the first time, a DTM (Digital Terrain Model) and a DSM (Digital Surface Model) covering the entire Mt. Etna volcano (Italy) derived from the same airborne Light Detection and Ranging (LiDAR) are here presented. More than 250 million 3D LiDAR points have been processed to distinguish ground elements from natural and anthropic features. The end product is the highly accurate representation of Mt. Etna landscape (DSM) and ground topography (DTM) dated 2005. Both models have a high spatial resolution of 2 m and cover an area of 620 km2. The DTM has been validated by GPS ground control points. The vertical accuracy has been evaluated, resulting in a root-mean-square-error of ± 0.24 m. The DTM is available as electronic supplement and represents a valid support for various scientific studies.