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Functional interaction between landslides: the Gorga landslide system (Cilento geopark, southern Italy)
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Integration of object-oriented modelling and geomorphometric methodologies for the analysis of landslide systems
Full text linkThe main objective of my PhD research is to develop an object-oriented, hierarchical and multi-scale geomorphological approach to studying “landslide systems” meaning sets of landslides of different type evolving on the long-term with mutual interaction (sensu Guida et al. 1988, 1995; Coico et al. 2013; Valiante et al. 2016). The proposed approaches aim: 1) to improve the existing or new inventories, defining an object capable of storing both spatial and temporal relations between landslides in a single dataset, avoiding physical data fragmentation and logic inconsistency; 2) to build a robust conceptual model for the practical management of complex arrangements of landslides and their evolution.
This work also aims to contribute to the overall theme of landslide hazard assessment and mitigation, focusing on those cases where complex spatio-temporal arrangements of landslides interacts with engineering structures or infrastructures, for better understanding and quantify the interactions at various spatio-temporal scales between engineering works and natural processes.
The research has been conducted following three main strategies: 1) a “Top-Down approach” based on morphometric analyses on Digital Elevation Models (DEMs) to find whether a portion of landscape shows a set of “topographic signatures” ascribable to landslide systems; 2) a “Bottom-Up approach” based on the reconstruction of the landslide system through field activities starting from any of the landslides composing the system itself; 3) comparison of the above strategies using a training-target approach on selected case studies significant for different Italian landscapes.
The “Top-Down” approach is based on the application of morphometric techniques using Digital Elevation Models, such as Topographic Position Index (TPI) (Weiss 2001; Paron and Vargas 2007; De Reu et al. 2013), useful for the semi-quantitative delineation of main landforms, and Slope – Area Plots (Montgomery and Foufoula-Georgiou 1993; Booth et al. 2013; Tseng et al. 2015), exploited for the estimation of the erosional processes type acting on the slopes, and extended also to gravity-driven processes. Basically, the graphical plot of the topographic steepness as function of the drainage area can be subdivided in four main plot regions or curve segments, each one representing a dominant geomorphic process: I) hillslopes; II) hillslope-to-valley transition; III) debris flow dominated channels or landslides driven channels; IV) alluvial channels.
The “Bottom-Up” approach follows the GmIS_UniSA method proposed in Dramis et al. 2011. In the first steps data collected from field activities were stored referring to a symbol-based representation (SGN 1994; APAT 2007; ISPRA 2018) similarly to what has been done by many authors (Gustavsson et al. 2006; Devoto et al. 2012; Miccadei et al. 2012; Del Monte et al. 2016 among the others), in the next steps the original data is extended from the symbol-based to a full-coverage representation. The latter is then reclassified using the proposed object-oriented data model.
Such object-oriented data model is based on the assumption that any entity can be represented by exactly one object regardless of its complexity or inner structure (Egenhofer and Frank 1992). Complexity is then handled through the classification process: a real-world feature and its behaviour is described and encapsulated in a class definition, then any operation of simplification or generalization can be performed defining a set of sub-classes and super-classes. Any feature described by a class definition is an object (an instance of that specific class); simplifying, a class is the description of a feature and its behaviour while an object is the feature itself (Atkinson et al. 1990; Chaudhri 1993; Kösters et al. 1997).
The described classification process results in a set of classes linked by parent-child relationship (generalized and specialized classes) and sibling relations (classes sharing a common super-class) in a hierarchical structure. Hierarchies are usually exploited to model, and therefore better handling complexity of natural systems; in this perspective a hierarchy is defined as a multi-level or layered system where each level can be decomposed in a number of interrelated subsystems until a non-decomposable elementary subsystem is defined (Simon 1962; Odum and Barrett 2005; Wu 2013). Depending on the objectives of a particular study or analysis, the hierarchical level closer to the study object is called focal level or level 0 which sets the starting point for decompositions (levels -x) or generalizations (levels +x) (Wu 1999).
Applying the previous concepts, the basic landslide inventory is built by means of usual techniques, such as field survey, remote sensing, desk studies, etc., then an object-oriented hierarchical model is applied resulting in a hierarchical classification of landslides. The focal level is set at the input inventory containing individual landslides as one object differentiated by type of movement. The proposed model assumes that a “functional interaction” (i.e. dynamic interaction) exists if the condition of spatial and temporal overlap between landslides is verified. This assumption can be evaluated through the integration of two topological models. The Dimensional Extended nine-Intersection Model (DE-9IM) (Egenhofer and Herring 1990a, b; Egenhofer and Franzosa 1991; Clementini et al. 1994) and the Region Connection Calculus (RCC8) (Randell et al. 1992; Cohn et al. 1997). Starting from the focal level, 2 levels of generalization are defined based on the topological relation between landslides: i) if two or more landslides of the same type have a 2-dimensional relation between their interior portion, they can be simplified in a landslide complex object having the same type of movement as the input features; ii) if two or more landslide complexes have a 2-dimensional relation between their interior portion or with the interior of another landslide which is not part of the input complex, they can be simplified in a landslide system object. A level of decomposition has been also implemented describing landslide components.
Once derived a landslide system, it is useful to define its Reference Hillslope, meaning the minimal portion of territory in which it is likely to evolve. To address this task Surface Networks can be a valid technique in order to objectively define the minimal portion of the topographic surface in which a gravitational process can develop and evolve. The extraction of Surface Networks from DEMs (Pfaltz 1976; Wolf 1991; Schneider 2003; Rana 2004) is based on the detection of the characteristic features of a surface called critical elements, such as critical points (local minima, local maxima and local saddles) and critical lines (ridgelines, connecting peak and passes, and courselines, connecting pits and saddles). This data structure has been exploited to decrease complexity of topography representing just its “mathematical skeleton” (Guilbert et al. 2016).
In order to test these methodologies, three italian case studies have been selected choosing sites with different geological settings and thus landsliding style. The choice of the study areas has been made also picking landslide recently reactivated with a great impact on anthropic activities. The selected case studies are:
• Corniolo - Poggio Baldi (FC) along the Bidente River valley;
• Roscigno (SA) on the south-western slopes of Mt. Pruno;
• North-eastern slope of the Rocca di Sciara relief in the valley of the Northern Imera river, close to Scillato village (PA).
The Corniolo – Poggio Baldi case study has been selected for the last reactivation of the Poggio Baldi landslide in March 2010. The movement developed as a rock-wedge slide evolving in a flow-like movement that produced the damming of the Bidente river and the formation of the Corniolo Lake, which is partially still present today. The main geological settings of the area are made of a sandstone-marly flysch with a dip-slope attitude.
The case of Roscigno refers the history of the abandoned “Old Roscigno” rural village. This ghost town has been transferred from about sixty years due to landsliding activity and is nowadays part of the Cilento UNESCO - Global Geopark. The village was built on the south-western slope of Mt. Pruno, mainly composed of terrigenous deposits such as calcarenitic-marly flysch, tectonically overlapping a clayey-marly flysch. The main movement affecting the slope is a deep-seated rock slope deformation, on top of which several shallow landslides developed, such as rotational slides and mud flows.
The Rocca di Sciara case study has been chosen for the last reactivation of the lower portion of the slope in April 2015. The event caused severe damages to the road network, also involving the Palermo – Catania highway leading to the failure of the Imera viaduct. The geological settings of the slope are made of a dip-slope bedding heterogenous sequence of limestone megabreccias and thick-bedded calcarenites, thin-bedded or laminated calcilutites and clayey flysch.
During these three years of research, several survey activities have been performed in order to reconstruct the geological and geomorphological setting of the case studies. All these activities were supported by the object-oriented perspective defined before, allowing objects definition and description directly on the field.
Both the “Top-Down” and the “Bottom-Up” strategies have been applied to the case studies. As for the first strategy, the contributing area reclassification shows mainly the hypothetical landslide-related channel as linear features, while the TPI reclassification highlights concave morphologies that can be related to landslides components, such as detachment areas, trenches, counterslopes, and so on. Both these methods can be useful techniques to assess potential landslides affected areas for a better planning of further activities such as field surveys, which are the starting point of the second strategy. Following the data collection, by direct surveys, desk studies or remote sensing, all the information has been rearranged within the object-oriented logic perspective; then, the hierarchical model allows to derive higher rank units, such as landslide complexes and landslide systems. Based on these derived objects, through the integration of Surface Networks it is possible to define the so-called “Reference Hillslope” for each landscape object.
Every landslide is characterized not only by its attributes but also by it spatial and temporal relations with the other movements. Coupling this object-oriented hierarchical approach with a temporal characterization of landslide features in the form of “events”, semantically defined, it is possible to build an object-oriented and event-based database capable of storing both spatial and temporal relations between landslides.
The Top-Down approach showed some limitation in the recognition of deep-seated movements, while the Bottom-Up approach allowed the automatic reconstruction of the landslide hierarchies starting from the landslide inventory. A landslide system built with an accurate spatio-temporal inventorying of landslides can be a tool for the fast retrieval of useful information such as “how many events affected a slope and how they developed, their magnitude and frequency and how they interacted”. All these data regarding the past and present activity of a slope are the assumption for understanding its most likely evolution, thus, to contribute to the formulation of reactivation scenarios. Moreover, the definition of the “reference hillslope” allow to objectively define the area/volume to be investigated starting from a reference object – a landslide, a landslide complex or a landslide system - , both for the planning of remediation and monitoring activities and as a starting point to search whether a landslide interacts with other geomorphic processes or anthropogenic activities
The Sant'Andrea-Molinello landslide system (Mt. Pruno, Roscigno, Italy)
No full textThis paper illustrates the landslide processes that affect the
southern hillslope of Mt. Pruno in the Sant’Andrea-Molinello area
close to Roscigno village (Cilento, Vallo di Diano and Alburni
Geopark, Campania region, Italy). The area involved by the slope
instability is about 0,7-1 km2 extended and it includes the provincial
road no. 342 between the Roscigno and Corleto Monforte villages and
other rural roads and farms. The landslide occurred and evolved
during the first week of December 2010, as a consequence of the
intense rainfalls fallen during the previous month. A detailed field
survey highlighted that the 2010 event was only a partial reactivation
of a larger landslide system with a very complex structure and longterm
evolution.
Peculiar geological and hydrogeological conditions control the
general instability. The structural setting of the slope is made by the
tectonic overlapping of two different structurally complex formations:
the Torrente Trenico Marls and Calcarenites Fm. (B1/B2 class),
constituting the local upper aquifer, over the Argille Varicolori
Superiori Fm. (B2/B3 class), sheared marly clays, as basal aquitard.
The primary gravitational event, classified as multiple rock block
slide, was probably induced by rapid, local relief creation during the
Late Pleistocene, following the downstream Sammaro River’s gorge
incision. During Holocene and historical times, secondary landslide
phenomena, triggered by an increased water pressure within perched
layers, affected and progressively disarticulated the primary one by
rock slide complexes evolving in complex earth slide-flows.
Based on the above geomorphological model and original
geotechnical data, stability analyses were carried out in the northern
portion of the landslide area. The safety factors, evaluated under
different recharge conditions and the sensitivity analysis to pore water
pressure confirm the hypothesis of rainfall-induced, partial
reactivation with an about 50-years return time
Object-Oriented Mapping as a Tool for the Assessment of Landslide Hazard in Higly Urbanized Areas
No full textThe assessment and mitigation of landslide risk affecting hillslopes in highly urbanized and infrastructured environments are often problematic due to the inadequacy of the traditional approach based on landslide inventories and the absence of a shared language between the different scientific-technical operators (geologists, engineers, architects, environmentalists, economists, jurists) and recurrent understanding problems with policymakers, stakeholders, and property owners. Therefore, innovative technologies and working procedures are required to address these problems. In this context, the European INSPIRE Directive and the Italian national Catalog of Territorial Data with the related Geo-Topographic DB provide positive responses in terms of data standardization and transdisciplinary interoperability. On the other hand, the application of the object- oriented geomorphological mapping of landslides and, even more, the recently proposed Landslide Object-Oriented Model (LOOM) make it possible to develop a more thorough approach to assess the spatial and temporal relationships between landslides and affected slopes. Following the above perspective, the InterUniversity Research Center for Prevision and Prevention of Great Risks (C.U.G.RI.) produced the LOOM-based “eventory” of landslides over a sector of the Tyrrhenian coastal belt, northwest of Salerno city, in the framework of a multi-disciplinary investigation project launched by the Campania Regional Administration to assess the landslide risk. The quantitative assessment of the geomorphological expert-judgment procedures has been carried out exploiting morphometric indexes: the Topographic Position Index (TPI) for automatic slope features recognition, and the Slope-Area plots for surficial process domains. Furthermore, the application of the INSPIRE, and related Italian National Geo- Topographic DB standards allowed transdisciplinary interaction between scientists, technicians, and managers. Such proposal can support the risk management procedure, adding in the Value Judgement and Risk Tolerance Criteria simplicity and effective interoperability in trans-disciplinary frameworks
Geomorphological map of Mt. Pruno southern slope, Roscigno, Cilento, Vallo di Diano and Alburni Geopark
No full textThis work refers the application of the method proposed by Dramis et al. (2011) to the gravitational phenomena
mapping that affect the southern slope of Mount Pruno, the highest peak of the Roscigno municipality (Cilento, Vallo di
Diano and Alburni Geopark) as operative contribution to the geomorphological mapping applied to landslide risk
management end their mitigation on hilly area on structurally complex terrains.
The Mount Pruno area is located in the upper section of the Calore Salernitano river basin; this area is characterized
by the outcropping of terrigenous formations defined “Internal Units” (Cammarosano et al, 2004) which promote the
establishment of a complex deepening hydrographic network from at least Early Pleistocene (De Riso & Santo, 1997).
This peculiar geomorphological setting favours big landslides processes on the slopes with intermittent and long-term
evolution.
This representation can be considered a hierarchical and a multiscale mapping: once a focal level (scale) it’s been
established, it’s possible to move to a larger or a smaller scale by polygon decomposing or generalizing operations; in
this nested sequence each hierarchy level summarize the effects of the lower levels (Dramis et al, 2011)
A spatiotemporal object-oriented data model for landslides (LOOM)
No full textLOOM (landslide object-oriented model) is here presented as a data structure for landslide inventories based on the object-oriented paradigm. It aims at the effective storage, in a single dataset, of the complex spatial and temporal relations between landslides recorded and mapped in an area and at their manipulation. Spatial relations are handled through a hierarchical classification based on topological rules and two levels of aggregation are defined: (i) landslide complexes, grouping spatially connected landslides of the same type, and (ii) landslide systems, merging landslides of any type sharing a spatial connection. For the aggregation procedure, a minimal functional interaction between landslide objects has been defined as a spatial overlap between objects. Temporal characterization of landslides is achieved by assigning to each object an exact date or a time range for its occurrence, integrating both the time frame and the event-based approaches. The sum of spatial integrity and temporal characterization ensures the storage of vertical relations between landslides, so that the superimposition of events can be easily retrieved querying the temporal dataset. The here proposed methodology for landslides inventorying has been tested on selected case studies in the Cilento UNESCO Global Geopark (Italy). We demonstrate that the proposed LOOM model avoids data fragmentation or redundancy and topological inconsistency between the digital data and the real-world features. This application revealed to be powerful for the reconstruction of the gravity-induced deformation history of hillslopes, thus for the prediction of their evolution
Landslide and settlements interaction: the case of Mt. Pruno (Cilento Geopark, Italy)
No full textThis work is focused on the gravity-driven instability that affect the Mt. Pruno relief and its impact on successive human settlements through historical time. The southern slope of Mt. Pruno nowadays hosts the Roscigno village but has also hosted two main settlements in the past: an Enotrian village (VI-III century B.C.) on the flat-top and the “Old Roscigno” rural village (XVI-XX century) on the southern slope, to the west of the present village.
The relief is mainly composed of deformed terrigenous successions composed by varicoloured shales, mudstones and marly-clayey thin layered sequences passing upward to lithic sandstones affected by complex stratigraphic and tectonic contacts. This geological setting favoured the development of heterogeneous and complex successions of mass movements along the slopes.
In this study, two main landslide systems are described. The first developed along the south-western slope of the relief and it is composed of a complex, spatio-temporal superimposition of heterogenous gravitational events, such as initial, large and deep-seated rock slope deformations, whose rock mass was affected by multiple and successive rotational slides, finally evolving in flowslides and earth flows. These movements caused the abandonment of the so called “Old Roscigno” village during the second half of the XX century and probably they could be one of the causes that induced the decline of the summit early Enotrian settlement during the III century B.C. The second landslide system developed on the southern hillslope and is mainly composed of rotational slides and flowslides, resulting from historical successive evolutionary cycles of dormant and reactivation phases. The last reactivation of a portion of the system dates back to December 2010. It was triggered by prolonged and heavy rainfalls, inducing: i) the collapse of the main provincial road that connect the “New Roscigno” village to its neighbours; ii) the strong damages of many rural buildings; and iii) the destruction of the typical terraced cultivations. Historical chronicles, multi-temporal analysis of remote sensing data and original, hierarchical and multiscale geomorphological surveys and mapping, allowed us to model the space-time topological relation of the two landslide systems and to perform different predictive evolutionary scenarios useful for the knowledge-based assessment and monitoring of the hydro-geological risk. In this perspective, the case study of Mt. Pruno can be considered as an emblematic example of how academic and administrative subjects can effectively face the recurrent landslide phenomena, avoiding further settlements deallocations. This was possible by managing the “Monte Pruno and Old Roscigno World Heritage Sites” both as the prototypal “moving geosites” and “open museum” of the rural tradition and as part of contemporary cultural cohabitation between rapid evolving landscape and human land occupation and uses
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