A Chronological Catalogue of Sinkholes in Italy: the First Step Toward a Real Evaluation of the Sinkhole Hazard
Total Page:16
File Type:pdf, Size:1020Kb
A CHRONOLOGICAL CATALOGUE OF SINKHOLES IN ITALY: THE FIRST STEP TOWARD A REAL EVALUATION OF THE SINKHOLE HAZARD Mario Parise, Carmela Vennari CNR-IRPI, Via Amendola 122-I, 70126, Bari, Italy, [email protected] Abstract of attention by scientists, practitioners and authorities on Among the many different types of geological hazards this subtle hazard. affecting the Italian territory, sinkholes have often been underestimated (if not neglected entirely), and only in Introduction some sectors of the country have they been effectively Italy is affected by a high number of geological hazards considered in hazard and risk analysis. Nevertheless, that cause severe losses every year and are at the origin sinkholes affect large parts of Italy, covering the whole of many casualties, thus producing a very high toll to territory with a variety of typologies, and exhibit both the society. Earthquakes, volcanic eruptions, slope natural and anthropogenic origin. The latter clearly movements, and floods are probably the most well- originate from the long history of Italy, with the known and studied hazards in the country (Guzzetti et complex historical vicissitudes that have characterized al., 1994; Boschi et al., 2000; Gasperini & Valensise, this territory, during which different types of artificial 2000). To these, further phenomena, at least in part cavities have been realized underground for different caused by man, have to be added: for instance, wildfires, purposes in different epochs. Over time, many of these with the consequent effects on loss of vegetational cover cavities have been abandoned, and the consequent loss and soil erosion. of memory resulted in their inclusion in newly developed parts of towns, thus creating a serious risk to the built-up Within such a framework, sinkholes have often been environment above. under estimated if not entirely neglected, and only in some sectors of Italy have they been effectively considered in Starting from these considerations, an archival research hazard and risk analysis. Nevertheless, sinkholes affect was started to collect information about the occurrence large parts of the country, covering the whole territory of sinkholes in Italy, with particular attention to their with a variety of typologies, and showing both natural precise site and date of occurrence, in order to make an and anthropogenic origin. The latter clearly derives from effort in assessing, respectively, the susceptibility and the long history of Italy, with the complex historical the hazard related to the particular phenomenon under vicissitudes that have characterized this territory, during study. As concerns date of occurrence, the accuracy of which different types of artificial cavities have been the information is provided (depending upon the amount realized underground for different purposes in different of available data), with the highest quality when hour, epochs (Parise, 2012). Over time, many of these cavities day, month and year of occurrence are indicated, and a have been abandoned, and the loss of memory about such decrease in quality when one or more of these data are features resulted in their inclusion in newly developed lacking. In order to be included in the database, at least parts of towns, thus creating a serious risk to the built-up some kind of temporal reference (even if general) of the environment above (Pepe et al., this volume). sinkhole has to be known. When unstable underground caves are located below The present article illustrates the first results of this study, buildings or infrastructures, their collapse may result describing the catalogue obtained so far which consists in significant economic losses. Further, the rapid of more than 650 sinkhole events for which at least some evolution of the failure processes (in particular during information about temporal occurrence of the event the catastrophic phase of rupture, and the resulting have been found. The data, even though not definitive, sudden collapse) can also represent in some cases a risk represent a good starting point for analysis of the sinkhole to human life. In this regard, the high rate of evolution hazard at a national scale, aimed at increasing the level is related to either the propagation of fractures through 13TH SINKHOLE CONFERENCE NCKRI SYMPOSIUM 2 383 the intact rock surrounding the caves (Kowalski, In the case of natural sinkholes, the related surface effects 1991; Liu et al., 2000) or the slip movement of rock may go unnoticed, especially when they occur in rural portions along pre-existing discontinuities, both areas; further, land owners often prefer not to spread the of these being generally controlled by progressive news, in order to avoid loss of value of the land. failure conditions, that sometimes induce catastrophic collapse (Diederichs and Kaiser, 1999a, b; Lanaro, In Italy, some databases about sinkholes are already 2000; Starzec and Tsang, 2002; Pine et al., 2006; available. The most significant are managed by ISPRA Parise, 2008; Parise and Lollino, 2011). and by University of Rome Tre. These databases, however, do not focus in particular neither on time Several aspects make sinkholes differ from other types of of occurrence of the sinkholes, nor in the distinction hazards, such as landslides and flooding: first, a sinkhole between the natural or anthropogenic origin. They are is a phenomenon which at the surface appears as punctual not specifically addressed to assessment of the sinkhole (site-located), and that is found at a very specific site, hazard, but rather to indicate the areas of the territory generally of limited dimensions. This, however, does not where sinkholes do occur (at the national or regional mean that the affected area is limited to that point, since scale). In several cases they also include unverified underground the caves responsible for the event may information, or a number of cases related to leakage from also show a wide extension. Consequently, sinkholes water pipelines, which may bring to wrong or incorrect are rarely taken into account in the analysis of hazard conclusions. and risk assessment, even though they may represent the main geological hazard in specific settings. To fully evaluate the hazard related to natural danger, the return time of the phenomena needs to be estimated. With respect to natural sinkholes, these typically are Lacking such information, there is no possibility to found in areas with soluble rocks affected by karst effectively determine the hazard, and the research has processes, or alluvial sediments in peculiar geological generally to stop at the stage of susceptibility assessment situations. Thus, the zonation of the sinkhole-prone areas (Varnes, 1984). Thus, availability of documentation may be done for natural sinkholes based solely upon about past events is crucial. geology as a first approximation. Unfortunately, very often the record of what occurred The situation is quite different for anthropogenic even in the recent past is difficult to be found. Further, sinkholes, because the distribution of artificial cavities when some documentation is available, most of the depends upon many other factors, such as historical, information show low reliability, and are based on cultural, and social issues. In this regard, it is important memories, or are not supported by real documents. This to highlight that we excluded from the catalogue all those represents a very important drawback that often has to be events of anthropogenic origin which were reported as faced in the search for historical information on different due to water leakage from pipelines, with the consequent types of hazards (see, for instance, Calcaterra & Parise, erosion in the subsoil, without any evidence of an 2001; Glade et al., 2001; Calcaterra et al., 2003). underground man-made cave. Thus, in our catalogue anthropogenic sinkhole means a sinkhole caused by Actually, it would be useful to better understand the the presence of a cavity created by man underground, conditions that are likely to cause sinkhole formation regardless of the cavity typology. (Benson at el., 2003). One of the purposes of this research is to evaluate the timing of sinkholes in Italy, In general, there is more detailed information about also to provide clues for assessing the specific settings anthropogenic sinkholes than for those of natural origin. (climatologic, meteorologic, seismic, etc.) under which This because the first category generally affects built-up they formed. areas, and causes direct damage and negative effects to society (blockage of roads and communication routes, There is a great variety of sinkhole types in Italy disrupting lifelines, etc.). At least some of these effects (Buchignani et al., 2008; Nisio, 2008; Del Prete et al., are generally reported, which helps in defining the time 2010; Margiotta et al., 2012), with events triggered by and site of occurrence of the phenomenon. very different factors, including rainfall, seismic shocks 384 NCKRI SYMPOSIUM 2 13TH SINKHOLE CONFERENCE and human actions. In fact, even though most of the The catalogue structure cases seem to occur in response to meteoric events, Based upon the considerations presented in the previous and the deriving runoff and groundwater circulation, section, the catalogue on Italian sinkholes (Figure 2) has reactivation of sinkholes may be a consequence of been structured giving a crucial role to the information on earthquakes too, as recently experienced at the Sinizzo time of occurrence of the sinkhole, and,