Alessandro Pasuto

Landslide monitoring by using ground-based SAR interferometry: an example of application to the Tessina landslide in Italy

Abstract An innovative technique, based on radar interferometry and implemented using ground-based instrumentation, has been applied for monitoring the Tessina landslide (Italy, Belluno). The technique has allowed us to derive multitemporal surface deformation maps of the entire depletion zone of the landslide with a high spatial resolution and accuracy. The portable device used in this application is known as Linear SAR (LISA), and it is able to provide measurements at 17 GHz with a synthetic aperture of up to 2.8 m. The results have been validated by comparing the recorded pixel displacements with independent measurements carried out by a motorized theodolite and Electronic Distance Meter (EDM) on two benchmarks.

A critical review of landslide monitoring experiences

Over the past few years, the monitoring of natural phenomena has acquired great importance for the scientific community. It aims to understand the mechanisms of disruptive processes, define adequate prevention measures for the mitigation of their effects and reduce the loss of human lives and assets. In order to detect the stability conditions of slopes belonging to different geological and environmental contexts, geotechnical investigations have been carried out since 1982. The various types of landslides to be investigated, and the diverse socio-economic contexts involved, have shown the need for constant surveillance, using the most up-to-date technology available. For this purpose, automatic recording systems connected to different sensors have been installed, (and also serve civil defence purposes). During this research activity, several problems arose, and several solutions had to be found. In this paper, some of the main problems concerning the installation and management of monitoring equipment used for the study of three landslides will be discussed.

Monitoring landslides from optical remotely sensed imagery: the case history of Tessina landslide, Italy

Collecting information on landslide occurrence and activity over wide areas is a crucial task for landslide hazard assessment. Field techniques, despite being very precise, are usually not sufficient to achieve this goal, since they mostly provide pointbased measurements. Mainly because of its synoptic view and its capability for repetitive observations, optical (visible-infrared) remotely sensed imagery acquired at different dates and at high spatial resolution can be considered as an effective complementary tool for field techniques to derive such information. An image-processing method to map and monitor landslide activity using multitemporal optical imagery is proposed. The method entails automatic change detection of suitably pre-processed (geometrically registered and radiometrically normalised) sequential images, followed by thresholding into landslide-related change pixels. Subsequent filtering based on the degree of rectangularity of regions can also be considered to eliminate pixel clusters corresponding to man-made land use changes. The application of this method is illustrated in the complex Tessina landslide in the Eastern Italian Alps. It has focused on discriminating the effects of a major reactivation that occurred in 1992, hence inferring the dynamics of the landslide at that time. Although the method has been devised for optical remote sensing imagery in general, in the absence of high-resolution satellite imagery covering that period, digital images derived by scanning existing aerial photograph diapositives at 1-m pixel size have been used. The method is able to classify image pixels according to landslide activity conditions. D 2003 Elsevier Science B.V. All rights reserved.

A visco-plastic model for slope analysis applied to a mudslide in Cortina d'Ampezzo, Italy

Abstract This paper describes a visco-plastic model which, using recorded groundwater levels, is capable of simulating the velocity trend in landslides. It also deals with the phenomenon of shear strength regain that occurs in montmorillonitic clays constituting slopes during periods when landslides are stationary. The model has been validated with long-term observations of a clay slope affected by a mudslide.

A multidisciplinary approach for rock spreading and block sliding investigation in the north-western coast of Malta

Landslides are widespread along the north-western coast of the Island of Malta and are strictly linked to the structural setting. Exemplary cases of rock spreading and block sliding phenomena characterise this stretch of coast. They are favoured by the overposition of two different geological units widely outcropping there, the Blue Clay Formation and the Upper Coralline Limestone Formation. The latter forms a wide plateau, bordered by vertical cliffs. At the foot of the cliffs, clayey terrains crop out and develop gentle slopes covered by large blocks detached and moved by rock spreading and block sliding phenomena. These mass movements are favoured by the fragile behaviour of limestones, which cap clays, otherwise characterised by visco-plastic properties. In order to investigate the kinematics and the evolution of these types of coastal landslides, a multidisciplinary and multitechnical approach was applied on a study site, named Il-Prajjet, which provides a spectacular case of rock spreading evolving into block sliding. This paper illustrates the results achieved by means of different engineering geological and geophysical techniques allied with traditional detailed geomorphological survey and mapping. In particular, the surface displacements of the landslides were determined using long-term GPS observations, acquired approximately every 6 months, over a 4.5-year period. A network of GPS benchmarks were distributed on the edge of a limestone plateau affected by rock spreading and on a series of displaced blocks making up a large block slide, finally enabling the definition of the state of activity and the rates of movement to be performed. In addition, the results deriving from two continuous fissurimeters more recently installed at the edge of two persistent joints over the block sliding area are outlined, with reference to the correlation between variations of crack apertures and precipitation input. In order to identify main structural discontinuities and to reconstruct variability of underground surface contact between clays and overlying limestones, Resistivity Tomography profiles and GPR investigations were carried out. Finally, the results obtained by combining the outputs of geophysical surveys and different field monitoring activities can be considered a first step on which numerical models can be developed and validated, in order to assess landslide hazard and risk of this stretch of Maltese coastline.

A combined hillslope hydrology/stability model for low-gradient clay slopes in the Italian Dolomites

Abstract The temporal trend of displacement of a landslide on a low-gradient clay slope in the Italian Dolomites as a function of precipitation was simulated with a combined hydrological-slope stability model based on groundwater and surficial displacement observations. Piezometric records and lithological profiles from boreholes suggest the occurrence of preferential groundwater flow through a very permeable top layer of about 1 m thickness, which overlies a less permeable, compact clay layer penetrated by dead-end cracks. To simulate groundwater levels in this system, a linear reservoir model with two outlets was applied, where the upper outlet drains the permeable top layer, and the lower outlet drains the dead-end cracks in the clay layer. The reservoir was assigned a bottom boundary level varying in time. This was done to represent an inferred yearly fluctuation of a matric groundwater level due to regional flow, which controls the thickness of the unsaturated part of the clay layer absorbing water from the cracks. Groundwater output from the model was used in a visco-plastic stability model to simulate the velocity of landslide movement, taking into account a phenomenon of strength regain that occurs in the clays along the slip surfaces. Calibration and validation on 3 years of groundwater and displacement data showed that both models yield good results. Thus, good estimates of cumulative landslide displacement were obtained as a function of precipitation. The general concepts underlying the models offer possibilities for regionalization because from a geological point of view, this landslide is typical of many others in the Dolomites.

Geomorphological map of the NW Coast of the Island of Malta (Mediterranean Sea)

This paper presents the results of geomorphological investigations carried along the north-western coast of the Island of Malta. Field surveys, accompanied by aerial photo-interpretation, have led to the production of a geomorphological map at 1:7500 scale which outlines the main processes and related landforms. The latter are the result of the complex interplay of structural, gravitational, coastal and karst processes. Particular attention was devoted to the recognition, identification and mapping of landslides which affect large coastal sectors of the study area, locally giving rise to hazardous conditions.

Major risk from rapid, large-volume landslides in Europe (EU Project RUNOUT)

Abstract Project RUNOUT has investigated methods for reducing the risk from large-volume landslides in Europe, especially those involving rapid rates of emplacement. Using field data from five test sites (Bad Goisern and Kofels in Austria, Tessina and Vajont in Italy, and the Barranco de Tirajana in Gran Canaria, Spain), the studies have developed (1) techniques for applying geomorphological investigations and optical remote sensing to map landslides and their evolution; (2) analytical, numerical, and cellular automata models for the emplacement of sturzstroms and debris flows; (3) a brittle-failure model for forecasting catastrophic slope failure; (4) new strategies for integrating large-area Global Positioning System (GPS) arrays with local geodetic monitoring networks; (5) methods for raising public awareness of landslide hazards; and (6) Geographic Information System (GIS)-based databases for the test areas. The results highlight the importance of multidisciplinary studies of landslide hazards, combining subjects as diverse as geology and geomorphology, remote sensing, geodesy, fluid dynamics, and social profiling. They have also identified key goals for an improved understanding of the physical processes that govern landslide collapse and runout, as well as for designing strategies for raising public awareness of landslide hazards and for implementing appropriate land management policies for reducing landslide risk.

A web-based platform for automatic and continuous landslide monitoring: The Rotolon (Eastern Italian Alps) case study

In the Small Dolomites group (Eastern Italian Alps), the Rotolon catchment is affected by a landslide that historically threatened the nearby village of Recoaro Terme. After the last re-activation on November 2010, the need to deploy devices to monitor deformations on the unstable slope became of paramount importance. This paper deals with the methodology, the techniques and the integrated services adopted for the design and the realization of a web-based platform for automatic and continuous monitoring of the Rotolon landslide. The choice of a web environment simplifies data collection, while a remote control permits technical maintenance and calibration on instruments and sensors in the field. Data management is straightforward on a single server, with the dataset being continuously updated. There is a user-friendly web interface which allows a practical up-to-date solution for decision-makers. This web-based monitoring platform represents the first step in the implementation of a complete early warning system. We design a multi-source and web-based platform for automatic and continuous monitoring.A user-friendly web interface allows a practical up-to-date solution for decision-makers.A better knowledge of the processes improves the quality of research.The framework is open and supported for custom requests.

Landslide susceptibility modeling assisted by Persistent Scatterers Interferometry (PSI): an example from the northwestern coast of Malta

Abstract Persistent Scatterers Interferometry (PSI) techniques are widely employed in geosciences to detect and monitor landslides with high accuracy over large areas, but they also suffer from physical and technological constraints that restrict their field of application. These limitations prevent us from collecting information from several critical areas within the investigated region. In this paper, we present a novel approach that exploits the results of PSI analysis for the implementation of a statistical model for landslide susceptibility. The attempt is to identify active mass movements by means of PSI and to avoid, as input data, time-/cost-consuming and seldom updated landslide inventories. The study has been performed along the northwestern coast of Malta (central Mediterranean Sea), where the peculiar geological and geomorphological settings favor the occurrence of a series of extensive slow-moving landslides. Most of these consist in rock spreads, evolving into block slides, with large limestone blocks characterized by scarce vegetation and proper inclination, which represent suitable natural radar reflectors for applying PSI. Based on geomorphometric analyses and geomorphological investigations, a series of landslide predisposing factors were selected and a susceptibility map created. The result was validated by means of cross-validation technique, field surveys and global navigation satellite system in situ monitoring activities. The final outcome shows a good reliability and could represent an adequate response to the increasing demand for effective and low-cost tools for landslide susceptibility assessment.