Landslides are among the most effective agents in landform evolution, especially in areas affected by active volcano-tectonic processes. In these areas, besides volcanic and associated seismic risks, hillslope instability processes pose an additional risk to the exposed urban settlements, also during non-active volcanic phases. Landslides contribute to the dismantling of volcanic edifices by displacing rock masses that form the volcanic flanks (Siebert and Roverato, 2021; Di Traglia et al., 2020; Williams et al., 2019; Walter et al., 2019; Oehler et al., 2004; Ablay and Hürlimann, 2000), involving in some cases the submarine domain (Dufresne et al., 2021; Coombs et al., 2007; Masson et al., 2006; Watts et al., 2012; Casalbore et al., 2020; Chiocci et al., 2008). Weakly welded pyroclastic deposits covering volcanic or non-volcanic slopes can be also mobilized in response to rainfall or snow and ice melting by means of rapid or extremely rapid debris and hyperconcentrated flows, occurring both simultaneously with volcanic activity (syneruptive lahars) and during pauses or volcano dormancy, i.e., “post-eruptive lahars” (Lavigne and Thouret, 2002; Capra et al., 2004; Pierson et al., 2014; Thouret et al., 2020). In addition, similar instability conditions can affect wildfire-affected hillslopes covered by volcanic soils (Neris et al., 2013; Esposito et al., 2019; Peduto et al., 2022).

In Italy, the densely urbanized area of Campi Flegrei (Fig. 1) corresponds to an active volcanic caldera considered among those with the highest volcanic risk in the world (De Natale et al., 2006). For this reason, scientific research has been mostly focused on volcanic and seismic hazards, making the Campi Flegrei one of the most monitored and analyzed calderas in the world, as well as a reference to enhance the knowledge on mechanisms controlling volcanic unrest (Troise et al., 2019). On the other hand, relatively poor attention has been paid towards exogenous processes such as landslides, floods, and coastal erosion. As a result, the risk posed by landslides in the Campi Flegrei volcanic area is currently underestimated both among the scientific community and the population. Landslides in this area have been reported since the Roman imperial period (Di Martire et al., 2012). Among the most disastrous recent events documented in the literature that deserve to be mentioned are (1) the huge tuff collapse that occurred along Mt. Echia (Naples) in 1868, causing 60 deaths and dozens of injuries (Calcaterra and de Luca Tupputi Schinosa, 2006); (2) flash floods, debris flows, and rock falls that occurred in Casamicciola, Lacco Ameno, and Forio (island of Ischia) on 24 October 1910, causing six fatalities and widespread damage (Santo et al., 2012); (3) the cliff failure that occurred along the Maronti beach in 1978, killing five tourists (Del Prete and Mele, 1999); and (4) a series of flow-like mass movements that in 2006 hit some buildings at the footslope of Monte Vezzi (island of Ischia), where four people died (De Vita et al., 2007; Di Nocera et al., 2007). These and other minor deadly events indicate that landslides pose a serious societal risk in the Campi Flegrei area (Cascini et al., 2008). This risk has also been confirmed by the recent landslides of 26 November 2022 at Casamicciola, on the island of Ischia, where 12 people lost their lives (https://polaris.irpi.cnr.it/event/colate-di-fango-e-detrito-a-casamicciola-terme-isola-di-ischia/, last access: 8 March 2023). Such an event has further highlighted that Ischia can be considered a kind of hotspot for the geo-hydrological risk in the area.

The compilation of an up-to-date and complete landslide database that records location, types, and, where known, the date of occurrence of mass movements is the simplest initial approach to any study of landslide hazard (Carrara et al., 1995; Soeters and van Westen, 1996; Devoli et al., 2007; Guzzetti et al., 2012; Ardizzone et al., 2023). As underlined by Napolitano et al. (2018), information on historical landslides is important to understand the complexities and dynamics of past events, as well as to construct and validate landslide prediction models able to support the designing of appropriate mitigation measures. In the Campi Flegrei area, preliminary landslide inventories have been provided by Beneduce et al. (1988) and Calcaterra et al. (2003b). Dozens of events have also been encompassed in databases and inventories realized at national scale, based on archive research (AVI database; Guzzetti et al., 1994) and aerial photo interpretation at 1:25000 scale (IFFI landslide inventory map; Trigila et al., 2010). With reference to the city of Naples, the landslide activity has been reconstructed by Calcaterra et al. (2002, 2003b, 2007) and Di Martire et al. (2012) by means of archival and bibliographic research, as well as by Miele et al. (2022). Failures and retreat rates affecting the cliffed coastline have been investigated by Matano et al. (2016), Esposito et al. (2017, 2018b, 2020), and by Caputo et al. (2018). Specifically, decadal retreat rates have been quantified on the order of 1.20 m yr-1 (i.e., Torrefumo cliff during 1956–1974) and short-term (annual) retreat rates within 0.01–0.10 m yr-1 on average (i.e., Coroglio cliff during 2013–2015 and Torrefumo cliff during 2013–2016).

With the aim of providing a comprehensive landslide geodatabase of the Campi Flegrei area referring to the 1828–2017 time interval, we have gathered all the landslide-related information made available from several sources, including a series of events collected by means of local press, news websites, and fieldwork. Data have been organized in a GIS environment to guarantee easy access, management, updating, and sharing with different users. All the collected and revised data have been used to develop a series of statistics about the spatial and temporal distribution of the events, failure types, impact, and relationships with the geological and geomorphological properties of the affected hillslopes. The CAmpi Flegrei LAndslide Geodatabase (CAFLAG) here described may be used for future analyses aimed at evaluating the landslide susceptibility, hazard, and risk conditions, as well as to understand the geomorphic evolution of the study area. In addition, the CAFLAG data may be of relevant interest for the international landslide research community to understand landslide dynamics in volcanic settings during dormant phases and to implement specific numerical models aimed at evaluating the landslide susceptibility in similar areas.

The Campi Flegrei (Fig. 1) is an active volcanic area located in southern Italy within the central part of the Campanian Plain, a graben-like structure that resulted from the tectonic displacement of a Mesozoic carbonate basement. The Campi Flegrei corresponds to a quasi-circular depression extending for about 200 km2, a large part of which develops off Pozzuoli Bay (Sacchi et al., 2011, 2020). The insular sector is represented by the islands of Ischia, Procida, and Vivara (Fig. 1).

The most ancient volcanic activity is associated with the volcanism of Ischia, probably starting earlier than 150 ka (Poli et al., 1987; Vezzoli, 1988), whereas the activity of the island of Procida occurred mostly around 70 ka (De Astis et al., 2004). The emplacement of the Mt. Epomeo Green Tuff Formation (about 55 ka; Vezzoli, 1988) formed the backbone of the highest relief in the area (actually 788 m a.s.l. on the island of Ischia). At about 39 ka, the catastrophic eruption of the Campanian Ignimbrite took place, causing the formation of a large caldera (Rosi and Sbrana, 1987; Orsi et al., 1996; Perrotta et al., 2006) that was reshaped by the more recent phreatoplinian eruption of the Neapolitan Yellow Tuff (NYT), dated at 15 ka (Scarpati et al., 1993; Insinga et al., 2004; Deino et al., 2004). The volcanic activity that occurred after the NYT eruption was subdivided into three main epochs (Di Vito et al., 1999), which were interrupted by long periods of quiescence. In these epochs, minor explosive events occurred within the rim of the NYT caldera, creating at least 52 monogenic phreatomagmatic vents, including tuff rings, tuff cones, cinder, and spatter cones (Di Vito et al., 1999; Insinga et al., 2006; Perrotta et al., 2011). The latest eruption, known as the “Monte Nuovo eruption”, occurred in 1538 CE. Currently, the Campi Flegrei is characterized by very high levels of volcanic risk due to many towns lying in a caldera characterized by unrest conditions, as demonstrated by widespread fumaroles, thermal springs, earthquakes, and ongoing ground deformation.

The current geomorphological configuration of the continental and insular sectors of the Campi Flegrei is the result of volcanic and geomorphic processes that occurred in the last 15 kyr, after the NYT eruption. Relics of volcanic edifices partially dismantled by sea erosion and landslides can be found along or near the present coastline and in the submarine part of the NYT caldera (e.g., Sacchi et al., 2009, 2011). Landslides due to earthquakes, rainstorms, marine erosion, or human actions have repeatedly affected the slopes of the inland volcanos, ravines, and streams, as well as the steep scarps of gullies and coastal cliffs through time (Ducci and Napolitano, 1994; Guadagno and Mele, 1995; Mele and Del Prete, 1998; Del Prete and Mele, 1999, 2006; De Vita et al., 2006; Santo et al., 2012; Esposito et al., 2018b, 2020). Besides volcanic morphologies, the geomorphic setting of Campi Flegrei also includes lowlands that are located between volcanic edifices or close to the NYT caldera rims.

The drainage network is mostly arranged in radial patterns typical of volcanic edifices, with isolated short channels along gentle slopes and plains. Vegetation covering the volcanic hillslopes consists mainly of Mediterranean shrubs that alternate with vineyards and cultivated areas and locally with pine woods. In addition to climatic conditions described in the following section, the widespread vegetation is fostered also by fertile soils (andosols) developed from pyroclastic deposits.

Currently, the study area is inhabited by approximately 500 000 people, with an average population density of 3440 people per square kilometer. Besides, it is visited each year by thousands of tourists due to the archeological, cultural, and environmental attractions.

The CAFLAG geodatabase refers to the Campi Flegrei area (Fig. 1), extending about 230 km2 and including the western part of the city of Naples and the islands of Ischia, Procida, and Vivara. An overview of the attributes associated with each cataloged landslide event is shown in Fig. 2. Information related to both landslide (i.e., data source, localization, date of occurrence, type of movement, volume of displaced material, impact on people and properties, predisposing and triggering factors) and the corresponding affected site (i.e., geomorphological and engineering geological properties, landslide susceptibility, and hazard levels) is provided where available.

The CAFLAG geodatabase encompasses 2302 landslides that occurred throughout the continental, coastal, and insular sectors of the Campi Flegrei during the 1828–2017 time span (Fig. 3). The number of landslides characterized by a highly accurate position is 2122 (about 92 % of the total). The number of those with a temporal accuracy ranging from moderate to high is 482, corresponding to about 21 % of the total. Statistics presented in the following sections describe some general features of the collected data which are useful to characterize the landslide phenomena in the area.

The CAmpi Flegrei LAndslide Geodatabase (CAFLAG) is freely available in the 4TU.ResearchData repository at 10.4121/14440757.v2 (Esposito and Matano, 2021).

Historical catalogs represent unique information to inspect the extent, types, pattern, recurrence, and statistics of slope failures in a given territory (Guzzetti et al., 2012). In volcanic landscapes, these catalogs are even more necessary to reach a comprehensive knowledge about the role played by landslides in the geomorphic evolution of these settings and about processes that lead to slope failures and control their spatial variations (Yano et al., 2019). As highlighted by data reported within the CAFLAG geodatabase, weak geotechnical properties of the volcanic lithotypes (Fig. 13) coupled with a rough topography play a relevant role in predisposing volcanic hillslopes to mass-wasting processes. This should be demonstrated also with numerical analyses by exploiting the twofold contributions provided by the CAFLAG geodatabase, consisting of data related to both landslide processes and geo-environmental properties of the affected sites which can be exposed to new instabilities. These two types of information coincide in fact with inputs required by statistically based landslide susceptibility models, namely “dependent” and “explanatory” variables, respectively (Reichenbach et al., 2018). Therefore, data of the CAFLAG geodatabase may be aimed at calibrating or validating statistical models resulting in landslide susceptibility and hazard maps which, in the study area, may complement the official hazard zonation.

The high spatial accuracy of the cataloged records, detailed information on typologies, and morphometric and geotechnical properties of the affected sites thus provide a valuable opportunity to investigate the occurrence of landslides in relation to other geo-environmental predisposing or triggering factors. For instance, analyses described in the previous sections highlight that mass-wasting processes are concentrated along the coastal sector. Collapses of the coastal cliffs can be considered the most important agents leading to cliff retreat in the area, since these are able to remove large volumes of rocks in short times (Esposito et al., 2017, 2018b). The CAFLAG geodatabase could thus be exploited to assess susceptibility of the rocky coastline against marine erosion or risk conditions affecting the widespread anthropic settlements and the people located there.

Statistics show that rocky slopes formed by lithified volcanic rocks, such as tuff or ignimbrite, were mostly affected by rock falls. In the coastal area, this was documented by Ducci and Napolitano (1991), who analyzed the cliff failures along the coastline of the island of Procida, observing that all of the identified collapses were rock falls and topples involving tuffaceous formations. Similar results were achieved by Del Prete and Mele (1999) for the cliffs of the island of Ischia. In the inland areas, however, many landslides affected the walls of old and abandoned quarries or digging fronts (Calcaterra et al., 2007). Discontinuity systems characterizing rock masses play a fundamental role in predisposing rocky slopes to failure processes, as well as in controlling the volume of the mobilized rocks (Matano et al., 2016). In the study area, discontinuities consist of faults, joints, and fractures associated with volcano-tectonic processes (Vitale and Isaia, 2014). Other failure-predisposing factors include geotechnical properties (e.g., low cohesion in Fig. 13) and weathering processes typical of the Flegrean area, such as the zeolitization and argillification of pyroclastic rocks. Water circulation, earthquakes, sea wave action, or anthropic vibrations and excavations can be considered among the main triggering factors. Besides the dominance of landslides involving solid rocks, the shallow sliding of loose pyroclastic deposits (i.e., pumices, scoria, ashes, and lapilli) and soils covering the lithified formations is also frequent. Commonly, these failures start as translational slides and evolve into debris or hyperconcentrated flows within gullies or into debris avalanches along the steep open slopes (Fig. 6) (Calcaterra et al., 2003b). Intense rainfall represents the triggering factor of the initial slide. Elevated slope angles and geotechnical properties of the involved material (Fig. 13) lead to a rapid or very rapid evolution in flow processes, as observed in the recent event of Casamicciola.

Many events affected hillslopes exposed towards the west, north, and south. This may be explained by the frequent impact of these hillslopes with convective cells and low-pressures systems coming from the Tyrrhenian Sea (Saviano et al., 2019). These meteorological structures are able to release high amounts of rainfall causing also flash flood processes (e.g., Esposito et al., 2015, 2018a) and are often associated with strong winds and storm surges damaging coastal infrastructures, as documented in the city of Naples in 2020 (Fortelli et al., 2021).

Another relevant finding of the current analysis is that in the analyzed time period, 53 landslide events caused 127 fatalities with an average rate of 1.2 fatalities per year (Fig. 9). Most of the people died in the city of Naples, hit by rocky blocks detached from steep tuffaceous slopes; others died because of flow-like mass movements, recurring mostly on the island of Ischia (e.g., Santo et al., 2012). The intense urbanization of the area developed after the Second World War determined an increase in fatal landslides (Fig. 9) and risk conditions in a way that, as highlighted also by the F–N curve (Fig. 10), landslides in the area represent a relevant societal risk. Data contained in the CAFLAG geodatabase may be thus exploited for applications aimed at planning countermeasures for the landslide risk reduction.