Emanuele Intrieri

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.

Spaceborne, UAV and ground-based remote sensing techniques for landslide mapping, monitoring and early warning

BackgroundThe current availability of advanced remote sensing technologies in the field of landslide analysis allows for rapid and easily updatable data acquisitions, improving the traditional capabilities of detection, mapping and monitoring, as well as optimizing fieldwork and investigating hazardous or inaccessible areas, while granting at the same time the safety of the operators. Among Earth Observation (EO) techniques in the last decades optical Very High Resolution (VHR) and Synthetic Aperture Radar (SAR) imagery represent very effective tools for these implementations, since very high spatial resolution can be obtained by means of optical systems, and by the new generations of sensors designed for interferometric applications. Although these spaceborne platforms have revisiting times of few days they still cannot match the spatial detail or time resolution achievable by means of Unmanned Aerial Vehicles (UAV) Digital Photogrammetry (DP), and ground-based devices, such as Ground-Based Interferometric SAR (GB-InSAR), Terrestrial Laser Scanning (TLS) and InfraRed Thermography (IRT), which in the recent years have undergone a significant increase of usage, thanks to their technological development and data quality improvement, fast measurement and processing times, portability and cost-effectiveness. In this paper the potential of the abovementioned techniques and the effectiveness of their synergic use is explored in the field of landslide analysis by analyzing various case studies, characterized by different slope instability processes, spatial scales and risk management phases.ResultsSpaceborne optical Very High Resolution (VHR) and SAR data were applied at a basin scale for analysing shallow rapid-moving and slow-moving landslides in the emergency management and post- disaster phases, demonstrating their effectiveness for post-disaster damage assessment, landslide detection and rapid mapping, the definition of states of activity and updating of landslide inventory maps. The potential of UAV-DP for very high resolution periodical checks of instability phenomena was explored at a slope-scale in a selected test site; two shallow landslides were detected and characterized, in terms of areal extension, volume and temporal evolution. The combined use of GB-InSAR, TLS and IRT ground based methods, was applied for the surveying, monitoring and characterization of rock slides, unstable cliffs and translational slides. These applications were evaluated in the framework of successful rapid risk scenario evaluation, long term monitoring and emergency management activities. All of the results were validated by means of field surveying activities.ConclusionThe attempt of this work is to give a contribution to the current state of the art of advanced spaceborne and ground based techniques applied to landslide studies, with the aim of improving and extending their investigative capacity in the framework of a growing demand for effective Civil Protection procedures in pre- and post-disaster initiatives. Advantages and limitations of the proposed methods, as well as further fields of applications are evaluated for landslide-prone areas.

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.

Combined Finite-Discrete Numerical Modeling of Runout of the Torgiovannetto di Assisi Rockslide in Central Italy

AbstractThe combined finite–discrete-element method (FDEM) is an advanced and relatively new numerical modeling technique that combines the features of the FEM with those of the discrete-element method. It simulates the transition of brittle geomaterials from continua to discontinua through fracture growth, coalescence, and propagation. With FDEM, it is possible to simulate landslides from triggering to runout and carry out landslide scenario analyses, the results of which can be successively adopted for cost-effective early warning systems. The purpose of this paper is to describe the results of the FDEM simulations of the triggering mechanism and the evolution scenarios of the Torgiovannetto di Assisi rockslide (central Italy), a depleted limestone quarry face where a rock wedge with an approximate volume of 182,000 m3 lies in limit equilibrium conditions, posing relevant issues in terms of civil protection. The results obtained demonstrate that the FDEM is able to realistically simulate the different p...

Monitoring crater-wall collapse at active volcanoes: a study of the 12 January 2013 event at Stromboli

Crater-wall collapses are fairly frequent at active volcanoes and they are normally studied through the analysis of their deposits. In this paper, we present an analysis of the 12 January 2013 crater-wall collapse occurring at Stromboli volcano, investigated by means of a monitoring network comprising visible and infrared webcams and a Ground-Based Interferometric Synthetic Aperture Radar. The network revealed the triggering mechanisms of the collapse, which are comparable to the events that heralded the previous effusive eruptions in 1985, 2002, 2007 and 2014. The collapse occurred during a period of inflation of the summit cone and was preceded by increasing explosive activity and the enlargement of the crater. Weakness of the crater wall, increasing magmastatic pressure within the upper conduit induced by ascending magma and mechanical erosion caused by vent opening at the base of the crater wall and by lava fingering, are considered responsible for triggering the collapse on 12 January 2013 at Stromboli. We suggest that the combination of these factors might be a general mechanism to generate crater-wall collapse at active volcanoes.

Event scenario analysis for the design of rockslide countermeasures

The Torgiovannetto quarry (Assisi municipality, central Italy) is an example of a site where the natural equilibrium was altered by human activity, causing current slope instability phenomena which threaten two roadways important for the local transportation. The quarry front, having a height of about 140 m, is affected by a 182,000 m3 rockslide developed in intensely fractured limestone and is too large to be stabilized. In 2003 some tension cracks were detected in the vegetated area above the quarry upper sector. From then on, several monitoring campaigns were carried out by means of different instrumentations (topographic total station, extensometers, inclinometers, ground-based interferometric radar, laser scanner and infrared thermal camera), allowing researchers to accurately define the landslide area and volume. The latter’s major displacements are localized in the eastern sector. The deformational field appears to be related to the seasonal rainfall. The landslide hazard associated with the worst case scenario was evaluated in terms of magnitude, intensity and triggering mechanism. For the definition of the possible runout process the DAN 3D code was employed. The simulation results were used in order to design and construct a retaining embankment. Furthermore, in order to preserve both the safety of the personnel involved in its realization and of the roadways users, an early warning system was implemented. The early warning system is based on daily-averaged displacement velocity thresholds. The alarm level is reached if the prediction based on the methods of Saito (1969) and Fukuzono (1985) forecasts an imminent rupture.

The Calatabiano landslide (southern Italy): preliminary GB-InSAR monitoring data and remote 3D mapping

On 24 October 2015, following a period of heavy rainfall, a landslide occurred in the Calatabiano Municipality (Sicily Island, Southern Italy), causing the rupture of a water pipeline supplying water to the city of Messina. Following this event, approximately 250,000 inhabitants of the city suffered critical water shortages for several days. Consequently, on 6 November 2015, a state of emergency was declared (O.C.D.P. 295/2015) by the National Italian Department of Civil Protection (DPC). During the emergency management phase, a provisional by-pass, consisting of three 350-m long pipes passing through the landslide area, was constructed to restore water to the city. Furthermore, on 11 November 2015, a landslide remote-sensing monitoring system was installed with the following purposes: (i) analyse the landslide geomorphological and kinematic features in order to assess the residual landslide risk and (ii) support the early warning procedures needed to ensure the safety of the personnel involved in the by-pass construction and the landslide stabilization works. The monitoring system was based on the combined use of Ground-Based Interferometric Synthetic Aperture Radar (GB-InSAR) and terrestrial laser scanning (TLS). In this work, the preliminary results of the monitoring activities and a remote 3D map of the landslide area are presented.

Definition of sinkhole triggers and susceptibility based on hydrogeomorphological analyses

Sinkholes represent a geological risk that is often underrated, mainly due to its very localized nature. In fact, sinkholes occur only under particular circumstances and typically affect relatively small areas. Despite these characteristics, the difficulty in forecasting the precise location and timing of their sudden collapse creates serious problems for civil protection authorities and urban planners. In this framework, identifying the mechanism and thus the triggering factor of sinkholes is strategically pivotal in developing management plans. The present paper addresses the sinkhole-prone area of Il Piano (Elba Island, Central Italy). The integration of hydrogeological surveys, coupled with a thorough study of historical maps and aerial photographs, suggests that the main triggering factor in this area may not be related to water pumping from the karst aquifer, as initially hypothesized. Instead, sinkholes appear to be caused by ravelling and erosive processes occurring entirely in the sedimentary cover when heavy rainfall induces water overpressure within the superficial aquifer.

Remote Sensing Techniques in Landslide Mapping and Monitoring, Keynote Lecture

Open image in new window The current availability of highly developed remote sensing technologies in the field of landslide detection, mapping and monitoring allows for rapid and easily updatable data acquisitions, improving the traditional investigation capabilities, even in hazardous or inaccessible areas, while granting at the same time the safety of the operators during the fieldwork. In this work various application of remote sensing techniques for landslide detection, mapping and early warning, from spaceborne to ground-based platforms are described. Among earth observation (EO) techniques in the last decades optical and radar images are very effective tools for these implementations, since very high spatial resolution can be obtained by means of optical systems (currently in the order of magnitude of tens of centimeters), and by the new generations of synthetic aperture radar (SAR) sensors designed for interferometric applications, with revisiting times of few days. At the same time in the recent years, ground-based remote sensing techniques have undergone a significant increase of usage, thanks to their technological development and quality data improvement, in terms of spatial resolution and accuracy, fast measurement and processing times, portability and cost-effectiveness of the acquiring instruments. In this paper, the potential of space-borne imaging techniques, ground-based remote sensing methods and the effectiveness of their synergic use in the field of landslide analysis is explored by reviewing their state of the art, and by analyzing various case studies, characterized by different slope instability processes, spatial scales and emergency management phases. After assessing the advantages and limitations of the proposed methods, further fields of applications are evaluated.

A New Approach to Assess the Stability of Rock Slopes and Identify Impending Failure Conditions

Open image in new window Anticipating the failure of unstable slopes is a topic of major concern in the field of landslide risk management. Arbitrary displacement or velocity thresholds are typically used to setup alarms representative of different risk levels. This is a difficult process, since experience showed that failure can occur over a wide range of values of these two parameters. Other approaches, such as the well-known inverse velocity method, aim at forecasting the time of failure; however predictions can be characterized by a significant margin of error. It follows that determining when the failure of a slope is impending is still a great issue. It is therefore important to review monitoring data from past case studies and seek for recurrent correlations between specific variables in order to identify common slope behaviors in proximity of the instant of failure. The analysis of a database of rock slope failures at several coal mines is presented. For each event values of cumulative displacement and velocity measured 48 h before failure, 24 h before failure, 3 h before failure and at failure instant were provided. A straightforward correlation was found between the average acceleration during the final 3 h and the average acceleration during the final 24 h before failure, regardless of the order of magnitude of the deformation. Comparable results were obtained considering data relative to 3/48 and 24/48 h before failure. Consequently, impending failure conditions could be determined with suitable notice for future events of slope instability at the studied mine sites based on the relative intensity of the acceleration. Further development of the methodology requires that the presence of similar correlations in other databases of past slope failures is verified. The nature of the correlation may be influenced by factors such as geology, failure mechanism and mechanical properties of the rock mass.