Ciro Del Negro

Forecasting lava flow hazards during the 2006 Etna eruption: Using the MAGFLOW cellular automata model

The MAGFLOW cellular automata (CA) model was able to fairly accurately reproduce the time of the lava flow advance during the 2006 Etna eruption, leading to very plausible flow predictions. MAGFLOW is intended for use in emergency response situations during an eruption to quickly forecast the lava flow path over some time interval from the immediate future to a long-time forecast. Major discrepancies between the observed and simulated paths occurred in the early phase of the 2006 eruption due to an underestimation of the initial flow rate, and at the time of the overlapping with the 2004-2005 lava flow. Very good representations of the areas likely to be inundated by lava flows were obtained when we adopt a time-varying effusion rate and include the 2004-2005 lava flow field in the Digital Elevation Model (DEM) of topography.

Lava flow hazards at Mount Etna: constraints imposed by eruptive history and numerical simulations

Improving lava flow hazard assessment is one of the most important and challenging fields of volcanology, and has an immediate and practical impact on society. Here, we present a methodology for the quantitative assessment of lava flow hazards based on a combination of field data, numerical simulations and probability analyses. With the extensive data available on historic eruptions of Mt. Etna, going back over 2000 years, it has been possible to construct two hazard maps, one for flank and the other for summit eruptions, allowing a quantitative analysis of the most likely future courses of lava flows. The effective use of hazard maps of Etna may help in minimizing the damage from volcanic eruptions through correct land use in densely urbanized area with a population of almost one million people. Although this study was conducted on Mt. Etna, the approach used is designed to be applicable to other volcanic areas.

Advances in Multi-GPU Smoothed Particle Hydrodynamics Simulations

We present a multi-GPU version of GPUSPH, a CUDA implementation of fluid-dynamics models based on the smoothed particle hydrodynamics (SPH) numerical method. The SPH is a well-known Lagrangian model for the simulation of free-surface fluid flows; it exposes a high degree of parallelism and has already been successfully ported to GPU. We extend the GPU-based simulator to run simulations on multiple GPUs simultaneously, to obtain a gain in speed and overcome the memory limitations of using a single device. The computational domain is spatially split with minimal overlapping and shared volume slices are updated at every iteration of the simulation. Data transfers are asynchronous with computations, thus completely covering the overhead introduced by slice exchange. A simple yet effective load balancing policy preserves the performance in case of unbalanced simulations due to asymmetric fluid topologies. The obtained speedup factor (up to 4.5x for 6 GPUs) closely follows the expected one (5x for 6 GPUs) and it is possible to run simulations with a higher number of particles than would fit on a single device. We use the Karp-Flatt metric to formally estimate the overall efficiency of the parallelization.

Ground and marine magnetic surveys of the lower eastern flank of Etna volcano (Italy)

Abstract In 1996 and 1997, two high-resolution magnetic surveys, one on land and the other at sea, were carried out on the lower eastern flank of Mount Etna. The magnetic surveys, covering an area of about 400 km2, aimed to elucidate the relationships between the main tectonic and morphologic features of this flank of Mount Etna. Major features include widespread NNW- and NNE-trending active faults and the Valle del Bove, a depression considered to be the source area of the Chiancone deposit, the largest Etnean volcaniclastic sequence. Magnetic surveys show anomalies that roughly follow the trend of active main structures. Although few magnetization measurements are available for the most representative outcrops of the lower eastern side of Mount Etna, interpretation of the anomalies defines the underground geometry of the Chiancone deposit and its relationship with volcano stratigraphic units and the underlying sedimentary rocks. In particular, a volume of about 14 km3 was ascribed to the Chiancone deposit. Such a large amount of material was likely produced by a catastrophic event, and deposited at different periods at the exit of the Valle del Bove in an area produced by the interaction, on a regional scale, of the main tectonic structures affecting this flank of the volcano.

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.

A texton-based cloud detection algorithm for MSG-SEVIRI multispectral images

A new statistical texton-based method for cloud detection through satellite image analysis is presented. The ultimate goal is to improve the performance of remote sensing techniques used to support the observations of active volcanic processes. The proposed method is a supervised classifier that exploits radiance spatial correlation in satellite images using a statistical descriptor of texture called texton. Cloudy and clear-sky models are determined using cluster analysis over the image features. The pixels to be classified are compared with the estimated models and assigned to the closest model. The cloud detection algorithm has been tested on a data set of MSG-SEVIRI images acquired during 2008 (about 35,000 images) of the Sicily area. Results show that the texton-based approach is robust in terms of percentage of correctly classified pixels, reaching more than 85% of success in both daytime and nighttime images.

MAGFLOW: a physics-based model for the dynamics of lava-flow emplacement

Abstract The MAGFLOW model for lava-flow simulations is based on the cellular automaton (CA) approach, and uses a physical model for the thermal and rheological evolution of the flowing lava. We discuss the potential of MAGFLOW to improve our understanding of the dynamics of lava-flow emplacement and our ability to assess lava-flow hazards. Sensitivity analysis of the input parameters controlling the evolution function of the automaton demonstrates that water content and solidus temperatures are the parameters to which MAGFLOW is most sensitive. Additional tests also indicate that temporal changes in effusion rate strongly influence the accuracy of the predictive modelling of lava-flow paths. The parallel implementation of MAGFLOW on graphic processing units (GPUs) can achieve speed-ups of two orders of magnitude relative to the corresponding serial implementation, providing a lava-flow simulation spanning several days of eruption in just a few minutes. We describe and demonstrate the operation of MAGFLOW using two case studies from Mt Etna: one is a reconstruction of the detailed chronology of the lava-flow emplacement during the 2006 flank eruption; and the other is the production of the lava-flow hazard map of the persistent eruptive activity at the summit craters.

Lava flow hazard modeling during the 2014–2015 Fogo eruption, Cape Verde

Acknowledgments Thanks are due to European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) for SEVIRI data (www.eumetsat.int) and to National Aeronautics and Space Administration (NASA) for MODIS data (modis.gsfc.nasa.gov). Landsat 8 OLI and Eo-1 ALI images are courtesy of the U.S. Geological Survey (earthexplorer. usgs.gov). We are grateful to the Copernicus emergency management service (emergency.copernicus.eu/ mapping/list-of-components/EMSR111) for mapping the actual lava flow field by Cosmo-SkyMed and Pleiades images. We thank the Cartografica de Canarias, S.A. (www.grafcan.es) for making the Digital Elevation Model of Fogo Island available. HOTSAT and MAGFLOW were developed in the frame of the TecnoLab, the Laboratory for the Technological Advance in Volcano Geophysics, organized by INGV-CT and UNICT (Italy).

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.

Magnetic Field Monitoring at Mt. Etna During the Last 20 Years

Over the past few decades we have been intensively monitoring the magnetic field on Mt. Etna. The largest anomaly, about 10 nT, was observed in the geomagnetic time series recorded in 1981 and associated with the March 17-23 eruption. It was interpreted as the joint effect of piezomagnetism and thermal demagnetization engendered by an intrusive dike. A convincing case of thermomagnetic effects was observed during the 1989 fissure eruption, when repeated measurements at intervals of 3 months for two years revealed the slow buildup of a 130 nT anomaly. The anomaly vanished laterally within 0.2 km from the surface expression of the fissure system. The nature and structure of the anomaly is consistent with the location and time of cooling of a shallow dike. Between September and December 1995 geomagnetic changes, greater than 8 nT, associated with the renewal of the NE craters activity were detected. The center of the magnetic anomaly source, which was thought to be the region heated by high-temperature fluids and gases originating from fresh magma, was estimated, by the spatial distribution of the variation rate, to be at a depth of 500 m near the 1991-93 eruptive vents. Finally, significant changes, ranging from 2 to 7 nT, in the local magnetic field closely related to the main phases of the 2001 eruption were observed. Piezomagnetic models were used to calculate the expected geomagnetic changes for each volcanic process. Model parameters were based on estimated fault geometry using seismic and ground deformation data from each event.