Integrated Geomorphological Mapping of Emerged and Submerged Coastal Areas based on the Coupling of Terrestrial and Marine Datasets

A deeper understanding of the processes acting on the coastal areas is crucial for coastal hazard assessment and mapping. To this aim, integrated geomorphological investigations of emerged and submerged areas resulting in geomorphological mapping represent an innovative way to provide the necessary knowledge for preventing hazards and reducing risks. An example is provided from the north-western coast of Malta (central Mediterranean Sea)

Geomorphological analysis of the historic landslide of Sottrù (Badia Valley, Italy) reactivated on December 13, 2012

The historic landslide of Sottrù, located in the Badia Valley (Autonomous Province of Bolzano), was reactivated on 13 December 2012 after a long period of dormancy. According to historic documents, the previous activation dates back to June 1821. At that time, the slope was mobilised after a period of persistent rain and snow melt causing the damming of the Gadera stream. After snowmelting, in June 1827 the natural dam collapsed flooding meadows and villages down valley. In December 2012, the landslide was partly reactivated, showing the first slow movements on the 13th and more rapid displacements on the 14th. A detailed geomorphological survey of the landslide was carried out during summer 2014. A surficial highly permeable level (in-situ or reworked till) has been found laying on top of a thick sequence of clays, shales and marls, both over the landslide body and the surrounding areas. From the landslide scar uphill, the hydrographic pattern is extremely irregular, made of discontinuous drainage lines indicative of higher infiltration rate than superficial run off. The comparison between the current morphology and the pre-2012 one has not evidenced any movement within the historic source area, while relevant displacements occurred at two lateral zones whose dynamics caused the partial collapse of the central part of the landslide, originating a second, lower crown. Since the previous activation (1821), the landslide has been dormant for quite a long period, i.e. 191 years, and its last activation occurred during a season where landslides are usually not frequent. Temperature and precipitation time series, recorded at the nearby meteorological station of La Villa, have been analysed for the last 27 years. It has been found out that November 2014 had many rainy days, three of which with precipitation amounts ranging from 30 to 50 mm. The rainiest day (November 29) was suddenly followed by a dramatic drop below 0°C of maximum and minimum air temperatures, lasting until the 13th of December i.e., the landslide activation day. This probably caused the freezing of the soil which at that time was snow free and completely saturated. Moreover, it is possible that the 13-day period below 0°C enabled also the freezing of a spring located in the lower part of the slope nearby the village of Sottrù thus blocking groundwater drainage, leading to the onset of a confined-aquifer condition and, ultimately, to the rapid increase of pore water pressure inside the clay-rich landslide material. This hypothesis has been made also in consideration of similar events occurred in the Dolomites (e.g., in Zoldo Valley in 1991). However, in order to confirm this hypothesis, geophysical and geotechnical analysis would be needed

Validation of landslide hazard assessment by means of GPS monitoring technique ? a case study in the Dolomites (Eastern Alps, Italy)

International audienceIn the last years a research project aimed at the assessment of the landslide hazard and susceptibility in the high Cordevole river basin (Eastern Dolomites, Italy) have been carried out. The hazard map was made adopting the Swiss Confederation semi-deterministic approach that takes into account parameters such as velocity, geometry and frequency of landslides. Usually these parameters are collected by means of geological and morphological surveys, historical archive researches, aerophotogrammetric analysis etc. In this framework however the dynamics of an instable slope can be difficult to determine. This work aims at illustrating some progress in landslide hazard assessment using a modified version of the Swiss Confederation semi-deterministic approach in which the values of some parameters have been refined in order to accomplish more reliable results in hazard assessment. A validation of the accuracy of these new values, using GPS and inclinometric measurements, has been carried out on a test site located inside the high Cordevole river basin

Some cases of deep-seated gravitational deformations in the area of Cortina d'Ampezzo (Dolomites). Implications in environmental risk assessment

The Authors, after having analyzed the main geomorphological and structural fractures characterizing dee-seated gravitational deformations and presented some terminological problems, describe four cases of deep-seated gravitational deformations in the area of Cortina d'Ampezzo (Dolomites). Moreover the relationships between these phenomena, which often deem to favour the development of "collateral" slope movements and landscape aspects, like Cortina d'Ampezzo, are examined

Backward automatic calibration for three-dimensional landslide models

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Landslide susceptibility analysis exploiting Persistent Scatterers data in the northern coast of Malta

During the last decade a pressing need for more adequate tools to manage the considerable increasing number of hydrogeological emergencies arose among land planning and civil protection authorities. As a consequence, both development and testing of different qualitative and quantitative methods for landslide displacements detection become fundamental in order to provide the best analysis performance in terms of cost-benefit and scientific reliability. Lately quantitative methods to measure deformations of unstable slopes had great advances. In this context, remotely sensed radar techniques, such as PSI (Persistent Scatterers Interferometry), can assist traditional landslide investigations in assessing ground and infrastructure deformations caused by large landslides. The main purpose of this study is exploiting the results of PSI analysis conducted over the Island of Malta to train a Bayesan model for evaluating active landslide susceptibility. This approach has been applied in the NW coast of Malta, where outstanding coastal landslides, such as rock spreads and block slides, have been recognized and mapped. The outcomes of the statistical analysis have been validated through specific field check and GNSS measurements. The results show that the developed susceptibility model predicts an acceptable percentage of landslides and can be considered reliable even if in areas without PSI data

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

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 lowcost tools for landslide susceptibility assessment