Federico Di Traglia

The ground-based InSAR monitoring system at Stromboli volcano: linking changes in displacement rate and intensity of persistent volcanic activity

Stromboli volcano (Aeolian Archipelago, Southern Italy) experienced an increase in its volcanic activity from late December 2012 to March 2013, when it produced several lava overflows, major Strombolian explosions, crater-wall collapses pyroclastic density currents and intense spatter activity. An analysis of the displacement of the NE portion of the summit crater terrace and the unstable NW flank of the volcano (Sciara del Fuoco depression) has been performed with a ground-based interferometric synthetic aperture radar (GBInSAR) by dividing the monitored part of the volcano into five sectors, three in the summit vents region and two in the Sciara del Fuoco. Changes in the displacement rate were observed in sectors 2 and 3. Field and thermal surveys revealed the presence of an alignment of fumaroles confirming the existence of an area of structural discontinuity between sectors 2 and 3. High displacement rates in sector 2 are interpreted to indicate the increase in the magmastatic pressure within the shallow plumbing systems, related to the rise of the magma level within the conduits, while increased displacement rates in sector 3 are connected to the lateral expansion of the shallow plumbing system. The increases and decreases in the displacement rate registered by the GBInSAR system in the upper part of the volcano have been used as a proxy for changes in the pressure conditions in the shallow plumbing system of Stromboli volcano and hence to forecast the occurrence of phases of higher-intensity volcanic activity.

Guidelines on the use of inverse velocity method as a tool for setting alarm thresholds and forecasting landslides and structure collapses

Predicting the time of failure is a topic of major concern in the field of geological risk management. Several approaches, based on the analysis of displacement monitoring data, have been proposed in recent years to deal with the issue. Among these, the inverse velocity method surely demonstrated its effectiveness in anticipating the time of collapse of rock slopes displaying accelerating trends of deformation rate. However, inferring suitable linear trend lines and deducing reliable failure predictions from inverse velocity plots are processes that may be hampered by the noise present in the measurements; data smoothing is therefore a very important phase of inverse velocity analyses. In this study, different filters are tested on velocity time series from four case studies of geomechanical failure in order to improve, in retrospect, the reliability of failure predictions: Specifically, three major landslides and the collapse of an historical city wall in Italy have been examined. The effects of noise on the interpretation of inverse velocity graphs are also assessed. General guidelines to conveniently perform data smoothing, in relation to the specific characteristics of the acceleration phase, are deduced. Finally, with the aim of improving the practical use of the method and supporting the definition of emergency response plans, some standard procedures to automatically setup failure alarm levels are proposed. The thresholds which separate the alarm levels would be established without needing a long period of neither reference historical data nor calibration on past failure events.

Shifts in the eruptive styles at Stromboli in 2010–2014 revealed by ground-based InSAR data

Ground-Based Interferometric Synthetic Aperture Radar (GBInSAR) is an efficient technique for capturing short, subtle episodes of conduit pressurization in open vent volcanoes like Stromboli (Italy), because it can detect very shallow magma storage, which is difficult to identify using other methods. This technique allows the user to choose the optimal radar location for measuring the most significant deformation signal, provides an exceptional geometrical resolution, and allows for continuous monitoring of the deformation. Here, we present and model ground displacements collected at Stromboli by GBInSAR from January 2010 to August 2014. During this period, the volcano experienced several episodes of intense volcanic activity, culminated in the effusive flank eruption of August 2014. Modelling of the deformation allowed us to estimate a source depth of 482 ± 46 m a.s.l. The cumulative volume change was 4.7 ± 2.6 × 105 m3. The strain energy of the source was evaluated 3–5 times higher than the surface energy needed to open the 6–7 August eruptive fissure. The analysis proposed here can help forecast shifts in the eruptive style and especially the onset of flank eruptions at Stromboli and at similar volcanic systems (e.g. Etna, Piton de La Fournaise, Kilauea).

Probabilistic evaluation of the physical impact of future tephra fallout events for the Island of Vulcano, Italy

A first probabilistic scenario-based hazard assessment for tephra fallout is presented for La Fossa volcano (Vulcano Island, Italy) and subsequently used to assess the impact on the built environment. Eruption scenarios are based upon the stratigraphy produced by the last 1000 years of activity at Vulcano and include long–lasting Vulcanian and sub-Plinian eruptions. A new method is proposed to quantify the evolution through time of the hazard associated with pulsatory Vulcanian eruptions lasting from weeks to years, and the increase in hazard related to typical rainfall events around Sicily is also accounted for. The impact assessment on the roofs is performed by combining a field characterization of the buildings with the composite European vulnerability curves for typical roofing stocks. Results show that a sub-Plinian eruption of VEI 2 is not likely to affect buildings, whereas a sub-Plinian eruption of VEI 3 results in 90 % of the building stock having a ≥12 % probability of collapse. The hazard related to long-lasting Vulcanian eruptions evolves through time, and our analysis shows that the town of Il Piano, located downwind of the preferential wind patterns, is likely to reach critical tephra accumulations for roof collapse 5–9 months after the onset of the eruption. If no cleaning measures are taken, half of the building stock has a probability >20 % of suffering roof collapse.

Updated landslide inventory of the area between the Furiano and Rosmarino creeks (Sicily, Italy)

ABSTRACT A 1:10,000 scale landslide inventory map has been prepared for the area between the Furiano and Rosmarino creeks, in the Nebrodi Mountains (north-eastern Sicily, Italy), a territory highly prone to slope failures, due to the local geological and geomorphological settings and intense rainfall. The landslide inventory database included within the Hydrogeological Setting Plan of the Sicily Region has been used as a starting point for this work. The updated inventory map has been compiled through a combination of conventional approaches (i.e. aerial photo-interpretation and field surveys) and new remote sensing techniques (ground deformation measurements obtained by interferometric analysis of satellite Synthetic Aperture Radar images). The new landslide inventory consists of 566 events, classified according to their typology and state of activity.

Multi-Temporal Evaluation of Landslide-Induced Movements and Damage Assessment in San Fratello (Italy) by Means of C- and X-Band PSI Data

This work provides a valuable multi-temporal and spatial investigation of landslide effects in San Fratello area (Messina province, Sicily Region, Italy), by means of C-/X-band PSI (Persistent Scatterer Interferometry) data, integrated with in-situ field checks and crack pattern survey. In February 2010 a catastrophic landslide caused casualties and large economic damages. Thus, an accurate mapping and monitoring of ground motions and impacts turn out to be significantly effective. PSI ground motion rates were cross-compared with local failures and displacement features of single buildings observed in-situ. Landslide-induced motions were detected at local scale over almost 20 years, with a validation of radar data and manufactures crack patterns, to finally achieve a complete and reliable assessment.

Susceptibility of intrusion-related landslides at volcanic islands: the Stromboli case study

Susceptibility of intrusion-related landslides in an active volcano was evaluated coupling the landslide susceptibility estimation by random forest (RF), and the probabilistic volcanic vent opening distribution, as proxy for magma injection, using the QVAST tool. In order to develop and test the method proposed here, the RF/QVAST approach was adopted for Stromboli volcano (Southern Italy) since it experienced moderate to huge instability events, it is geomorphologically prone to instability events, and it is affected by active intense volcanic activity that can produce slope instability. The main destabilizing factors of the volcanic flanks are the slope, the aspect, the terrain roughness, the land cover and the litho-technical features of the outcropping rocks. Estimation of volcanic susceptibility shows that the areas with high probability of new vent opening are located in the north-western unstable volcano flank (Sciara del Fuoco), in the volcano summit and the north-eastern volcano flank coherent with the possible re-activation of the eruptive fissures related to the regional tectonic setting. The areas with higher probability of intrusion-related landslides are located in the upper part of the Sciara del Fuoco, while the rest of the island show moderate to low probability of intrusion-related landslide occurrence.

TXT-tool 2.039-3.4 Methods to Improve the Reliability of Time of Slope Failure Predictions and to Setup Alarm Levels Based on the Inverse Velocity Method

Estimating the time of slope failure is a topic of great importance in the field of landslide risk mitigation. Within this framework, time of failure forecasting methods based on the inverse velocity, typically intended as the extrapolation of linear trend lines of the inverse of velocity with time, are widely known as tools for early warning of slopes displaying accelerating trends of deformation rate. Although nominally simple, their correct application is actually tricky as many factors can influence displacement data and eventually heavily reduce the accuracy of the predictions. Such disturbing elements can be classified as noise caused by instrumental precision and as noise representing the diverging of a natural behavior with respect to an ideal inverse velocity trend. Hence correctly preparing the dataset is a pivotal and critical task. The present teaching tool describes how to filter displacement data by presenting three different approaches and discussing the results of their application to three large slope failure case histories in Italy, in order to improve, in retrospect, the reliability of the failure-time predictions. Procedures to automatically setup alarm levels of slope failure occurrence are consequently proposed for supporting the definition of landslide emergency response plans.

Reply to discussion on “Guidelines on the use of inverse velocity method as a tool for setting alarm thresholds and forecasting landslides and structure collapses” by F. Bozzano, P. Mazzanti, and S. Moretto

Abstract■■■The paper “Discussion to: Guidelines on the use of inverse velocity method as a tool for setting alarm thresholds and forecasting landslides and structure collapses by T. Carlà, E. Intrieri, F. Di Traglia, T. Nolesini, G. Gigli and N. Casagli” by Bozzano et al. brings forward new considerations on an issue of extreme concern in landslide risk management. To this day, the ability to predict catastrophic landslide failures from slope surface displacements is a problem dictated more by practical constraints rather than by theoretical uncertainties. In this sense, the development of data interpretation practices is crucial. This short reply provides a few further insights with regard to this subject, also in the context of the recently published literature.

Monitoring Eruption-Induced Mass-Wasting at Active Volcanoes: The Stromboli Case

With the aim of understanding the relationship between eruptive activity and slope instability at active volcanoes, in this work displacement data from a permanent-sited, Ground Based Interferometric Synthetic Aperture Radar (GBInSAR) installed at Stromboli (Italy), were compared with the evolution of reflectivity (amplitude) of SAR images collected by means of X-band, space-borne, COSMO-SkyMed satellites (CSK-SAR). The analysis of the dataset (May-December 2014) cover a period characterized by “normal” Strombolian activity, punctuated by episodes of “high-intensity activity”, with the occurrence of overflows from the crater terrace toward the Sciara del Fuoco (SdF), and by the occurrence of the August 7th 2014–November 13th 2014 flank eruption. The integration of GBInSAR displacement data and the analysis of CSK-SAR amplitude images, allowed us to identify the evolution of the slope instability phenomena and geomorphological process affecting the SdF slope. GBInSAR data recorded the inflation of the summit plumbing system two months before the onset of the 2014 flank eruption. Moreover, evidence of mass-wasting recorded by the GBInSAR preceded the fracture opening by ~11 h, the fracture propagation and North East Crater (NEC) collapse by ~15 h, suggesting that 11–15 h before the onset of the effusive eruption, magma was intruding below the NEC area, inducing the slope instability observed on the NEC. SAR images were used with the aim of understanding the relationship between eruptive activity, geomorphologic evolution and slope instability. CKS-SAR data results highlights phases of erosion of the volcanoclastic deposits of the SdF during the “normal” Strombolian activity, whereas in periods characterized by higher-intensity volcanic activity, amplitude images revealed lava flow emplacement, as well as the deposition of dry gravel/debris flows.