OJS377 Racano et al.pdf Available online http://amq.aiqua.it ISSN (print): 2279-7327, ISSN (online): 2279-7335 Alpine and Mediterranean Quaternary, 35 (1), 2022, 31-45 1. INTRODUCTION The integration of History and Earth Sciences can lead to the production of datasets useful for understand- ing the impacts of past geological processes on human communities. The collection of historical information has always been of great importance for reconstructing cli- matic, environmental and landscape changes, and par- ticularly to determine the evolution of flood and landslide risks (Guzzetti et al., 2005; 2012). Four basic pieces of information were identified by van Westen et al. (2006) to support landslide risk assessment and management: (1) landslide inventories, (2) information on the environ- ment surrounding the landslides, (3) information on the landslide triggers and (4) information on the elements at risk (in the past or in the present). The integration of several methods is necessary to produce reliable infor- mation that can be combined with geotechnical quantita- tive data in view of modelling (e.g. remote sensing and photogrammetry, Soeters & van Westen, 1996; geomor- phological field investigations, Brunsden, 1985) and public reporting/interviews and archival research for historical contribution (Tropeano & Turconi, 2004; Salva- ti et al., 2009). In general, landslide occurrence is controlled by several predisposing factors (e.g. topography, geology and human activities, Arca et al., 2018) and trigger pro- cesses (e.g. rainfall, glacial melting, stream and coastal erosion, earthquakes and volcanic eruptions, Lichkov, 1938; Crandell et al., 1984; Keefer, 1984; Mathewson et al., 1990; McInnes, 1996; Suarez, 1996). Moreover, several researchers have argued that urbanization im- pacts landslide risk by influencing the severity and fre- quency of landslides, as well as the extent and value of building exposure and the degree of vulnerability to damage (Smyth & Royle, 2000; Douglass et al., 2005; Fedeski & Gwilliam, 2007; Mandasari et al., 2016; Zope et al., 2016). If the fragility of a territory depends on the https://doi.org/10.26382/AMQ.2022.02 A PECULIAR HISTORY OF DESTRUCTION IN THE OLD VILLAGE OF CASTEL FRENTANO, CENTRAL ITALY, FROM RECONSTRUCTION OF LANDSLIDE EFFECTS FOLLOWED BY EARTHQUAKE DAMAGE IN 1881. Simone Racano1, Sara Amoroso2-3, Matteo Del Nobile4, Fabrizio Galadini3 1 Universität Potsdam, Institute für Geowissenschaften, Potsdam, Germany. 2 Department of Engineering and Geology, University of Chieti-Pescara, Pescara, Italy. 3 Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy. 4 Writer and journalist, Castel Frentano, Italy. Corresponding author: Simone Racano < racano@uni-potsdam.de > ABSTRACT: Anthropogenic modifications of the landscape (e.g. urbanization, deforestation and agricultural activities) act as geo- morphic processes, producing fast changes and instabilities, which often lead to landslides along hillslopes and floodings in low- lands. Anthropogenic modifications have increased with the progress of civilization; therefore, coupling historical information and geomorphological data can provide key information to determine the anthropogenic impacts on landscape evolution. The case of Castel Frentano, a village in the Abruzzo Region (Central Italy), has been analysed to shed light on the causes of its destruction in 1881: during the summer of that year, the village was heavily damaged by a peculiar succession of paroxysmal events, i.e. a mas- sive landslide followed by a strong earthquake. This earthquake induced additional damages to the buildings, due to seismic shak- ing and slide reactivation. This study involved geomorphological and geological surveys, which were aimed at mapping and defin- ing the main presently active geomorphic processes in the area of interest; moreover, we researched 19th-century historical docu- ments to reconstruct the genesis and evolution of the events that led to landsliding in 1881. Although the study area has always been prone to instability phenomena (due to its local geological and geomorphological characteristics), our results revealed that sliding was most likely triggered by human activities that had strongly modified the hillslope. Historical sources revealed a general hillslope instability that progressively evolved in the 1881 landslide because of deforestation. That deforestation had been carried out for agricultural exploitation on a previously stable territory. In this view, the case of Castel Frentano exemplifies the relationship between human activities, landscape modifications and their consequences in Italy in terms of risks to both natural and anthropo- genic environments. This is particularly important to assess at present: in a historical period characterized by economic growth, strong demographic expansion and the consequent fast colonization of natural spaces. Keywords: historical geology, human impact, natural hazards, urban changes, landscape response. 32 Racano S. et al. interrelation of natural and anthropogenic factors, then historical knowledge about landscape changes caused by human action and land use is necessary to complete- ly understand the predisposing factors (Dapples et al., 2002; Glade, 2003; Alcántara-Ayala et al., 2006; Beguería, 2006; Gariano et al., 2018). The Castel Frentano landslide (CFL) represents a case study in Central Italy (Fig. 1). In this study, it was investigated through a combination of geological and historical approaches to clarify the evolution of natural processes and their impacts on surrounding buildings. During the summer of 1881, Castel Frentano, a typical Italian hillside village of medieval origin, suffered the effects of a massive landslide that occurred on its east- ern hillslope. This event was followed a few weeks later by a 5.4-magnitude earthquake that struck the central Periadriatic sector, as reported in Nature Notes (1881): “On Thursday (September 10th) last, at noon, further shocks of earthquake alarmed the inhabitants of Orsogna, Lanciano, and Castel Frentano, where a land- slip did serious damage” (Nature Notes, 1881). Differently from many other landslide cases in Italy, which were triggered by earthquakes (e.g. Agnesi et al., 1983; Chiodo et al., 1999), the CFL occurred before a seismic event and was sufficient to cause significant building collapses and damages. The successive earth- quake induced further significant damages and the reac- tivation of the slide about 40 days after its first trigger. This peculiar combination of slope sliding and seismic shaking determined a “continuous” building damage through a period of several months. Although the CFL has been already studied from a geotechnical point of view (Mancini et al., 2001), the genesis and evolution of the event, as well as the pre- disposing factors and triggers, are still not clear. Through this study, we investigated the factors that con- ditioned the CFL in 1881: we combined geological, geo- morphological and topographic information about the eastern hillslope of Castel Frentano with historical infor- mation (not limited to the events of that year, but ex- tending to preceding times). After defining the geological framework and describing the 1881 earthquake event, Fig. 1 - Location of Castel Frentano (yellow) and extent of the geological map of the area shown in Fig. 2 (red). 33 Damages caused in Castel Frentano in 1881 by a landslide and an earthquake. Fig. 2 - (a) Synthetic geological map of the central Abruzzo Periadriatic area; (b) sketch of Castel Frentano’s geology (modified from Raca- no et al., 2020). we discuss the available geomorphological and histori- cal data to provide a realistic interpretation of the land- slide origin. 2. GEOLOGICAL, GEOMORPHOLOGICAL AND SEIS- MOLOGICAL FRAMEWORK OF THE CASTEL FREN- TANO AREA The hill of Castel Frentano is located on Plio- Pleistocene marine to coastal units characteristic of the entire Periadriatic sector (Fig. 2a,b). The relief, whose altitude gradually decreases from the Maiella piedmont to the Adriatic coast, was produced by a regional uplift during the Quaternary (Centamore & Nisio, 2003; Cen- tamore & Rossi, 2009; Racano et al., 2020). The main lithology outcropping in the area consists of bluish clays, sometimes interbedded with silty-sandy layers, that gradually upward to yellow silty-sandy levels and finally to sands interbedded with conglomerates, which mark the end of marine sedimentation (Bigi et al., 1997; Cen- tamore & Nisio, 2003; Racano et al., 2020). The hill is bounded by steep slopes, which have been formed by the linear incisions of creeks draining the area. The main stream channel is the Feltrino Creek (Fig. 2b), which drains the eastern slope of the hill. One of the main geomorphological consequences of the recent geological evolution of the area is its predisposition to large landslides. Due to the recent uplift and the weak- ness of superficial lithologies, the drainage system has produced narrow and steep valleys carved into a highly erodible substratum. These are evident landslide predis- posing conditions that can explain the recent/present landscape evolution (Centamore et al., 1996). The AVI (Italian Vulnerable Areas for landslides and floods, developed by the National Research Council of Italy) and PAI (Hydrogeological Plan, provided by the Abruzzo Region) catalogues list rotational landslides, earth flows and “rill erosion” phenomena on clays (which produce badlands just below the urban centre). In terms of hazard, the Castel Frentano area is classified as a P3 zone (i.e. a high hazard zone: affected by active or sea- sonally reactivated instability phenomena). The most important gravitational movement (i.e. a rotational landslide) has been detected along the east- ern slope of Castel Frentano’s hill (Mancini et al., 2001). The main activation of this landslide occurred on the 31st of July, 1881, generating the collapse of the village’s eastern sector. On the 10th of September, 1881, the landslide was reactivated by an earthquake (Savarese et al., 2011) (Fig. 3a,b). Foreshocks of this seismic event, which preceded the main landslide motion, are not reported in seismic catalogues (e.g. Rovida et al., 2022) and historical sources (Savarese et al., 2011), nor mentioned in the literature published after the occur- 34 Racano S. et al. Fig. 3 - (a) Structural map of buried structures (from Racano et al., 2020) and historic seismicity between 1800-2000 (from Rovida et al., 2022): MT (Maiella Thrust); CBT (Casoli-Bomba Thrust); ACT (Abruzzo Citeriore Thrust); CST1-2 (Coastal Thrusts 1-2); PeL (Pescara Line); AnL (Alento Line); FrL (Foro Line); MrL (Moro Line); FeL (Feltrino Line); AvL (Aventino Line); SgL (Sangro Line); (b) damage distri- bution of the 1881 Orsogna earthquake (from Locati et al., 2022). impact on the landscape (i.e. portion of involved hillslope, temporal evolution of the phenomenon), the extent of damage caused to the village (i.e. involved buildings) and any indication related to the possible trig- gers of the CFL (i.e. geological active processes, cli- mate, seismicity and anthropogenic changes of the land- scape). Most of the data were derived from the Historical Archive of the Castel Frentano Municipality. Many docu- ments produced by the City Council in the 19th century were found to contain suitable information; in particular, the documents archived in folder B9, file F168 (1861- 1881) and folder B10, file F169 (1881-1926) focus on land use activities on the eastern slope of Castel Fren- tano’s hill and on the evolution of the landslide. These bibliographic data were integrated with documents from the Italian State Archives (State Archive of Chieti, Chieti- Section Lanciano, Pescara, L’Aquila-Section Sulmona and the Diocesan Archive of Lanciano), which consisted mostly of telegrams, newspaper reports and climatic reports. The information gathered from the archive re- search was combined with that from published studies on climate and meteorological trends (Giraudi, 1990; Maugeri et al., 2004) and from the local literature (mainly books on Castel Frentano’s history; Del Nobile, 2011; Scioli, 1981, 1998). 4. RESULTS 4.1. Geomorphological features of Castel Frentano’s hill The Plio-Pleistocene deposits representing the substratum of Castel Frentano’s hill are sub-horizontal or gently dip eastwards from the ridge towards the valley bottom. The village is located at the top of the hill: it seats on a narrow plateau composed of consolidated sands and conglomerates, which represent the stiffer lithology of the study area and have a maximum thick- ness of about 20 m (Fig. 4a). An 8-10-m-thick layer of fine sands and silts marks the downward transition to the blue clays of the Mutignano Formation, which perva- sively outcrop in the study area. The hillslopes were and are still exploited by perva- sive agricultural activities, which have led to the devel- opment of soil from the thick silty colluvium covering the bedrock. These colluvial deposits have derived from extensive weathering processes and gravitational defor- mations that have affected all the slopes. Evidence of slow earthflow movements in the absence of large par- oxysmal events was detected along the SW flank of the hill; however, landslides are widespread on the eastern flank. Similarly to the earthflows of the western flank, the landslides on the eastern flank mainly involve the collu- vium cover. This has led to the generation of terraces and sub-circular scarps typically associated with rota- tional landslides. Moreover, the presence of water springs characterized by ephemeral flows, mostly locat- ed in correspondence of the landslide terraces (where the slide planes intersect the surface), indicates a shal- low water circulation influenced by seasonal rainfall vari- ations. The erosional processes are highlighted by linear and V-shaped incisions triggered by run-off and mainly related to the Feltrino Creek catchment, which deeply rence of the paroxysmal events (Niccoli, 1882). Although the occurrence of foreshocks cannot be completely ex- cluded, it is at least highly improbable, since potential precursors are typically reported in the literature and reports coeval to strong historical earthquakes. The seismic event that occurred in 1881 was re- ported to have a 5.4-magnitude (Fig. 3a,b) (CPTI15 catalogue; Rovida et al., 2022) and was attributed to the activation of a blind reverse fault related to the Abruzzo Citeriore thrust system (De Nardis et al., 2011), which represents the external and younger expression of the Central Apennines. The epicentre of that seismic event was located at about 5 km NNW from the study area (Fig. 3a). The mainshock was responsible for moderate damages to Castel Frentano (Mercalli-Cancani-Sieberg Intensity, MCS = 7-8) and nearby villages (Poggiofiorito, MCS = 8; Guardiagrele and Orsogna, MCS = 7-8; Lanci- ano, MCS = 7) according to the DBMI15 macroseismic database (Locati et al., 2022) (Fig. 3b). The earthquake- induced damages added to those caused by the July and September landslide movements. Therefore, the estimation of the effects strictly induced by seismic shaking is very difficult and affected by uncertainties: the present topography and urban setting of the eastern hillslope of Castel Frentano are the overall product of an earthquake and of one main landslide event that oc- curred in 1881. Traces of slope instability related to continuous superficial slow movements (creep) and earth flows have been detected along the western flank of the hill. These events have also affected the urban centre (Buccolini et al., 2000), although they have not evolved in paroxysmal events comparable to the 1881 landslide. 3. MATERIALS AND METHODS This study integrates pieces of information collect- ed through field geological and geomorphological sur- veys with the results of bibliographic and archive re- search on historical sources. The aim was to reconstruct the genesis and sequence of events related to the 1881 CFL. The collected field investigations allowed the pro- duction of a map depicting the landslide area (on the eastern slope of the Castel Frentano hill), in order to highlight the main geomorphic processes acting on it and the lithologies involved. This map was used as a base to define the geometries of the landslide scarp and body, as well as the lithologies involved in the move- ment and the main geomorphic processes that might have triggered it. The field data were digitised in a GIS environment using the open-source software QGIS (https://www.qgis.org). The base map was developed from the regional cartography of the Abruzzo Region at scale 1:5000 (in ESRI shapefile format) and the Digital Elevation Model (in TIFF format) of the region with a resolution of 10 m/px. The GIS data are freely available on http://geoportale.regione.abruzzo.it/Cartanet. Several archives were consulted to determine the sequence of events related to the landslide that oc- curred in 1881. In particular, we searched for descrip- tions of the landslide (i.e. geometry and extension, mag- nitude of the phenomenon and involved lithologies), its 35 Damages caused in Castel Frentano in 1881 by a landslide and an earthquake. 36 Racano S. et al. Fig. 4 - (a) Geological and geomorphological map of Castel Frentano; (b) slope map of Castel Frentano’s hill; (c) topographic and slope profiles. and linearly cuts the eastern hillslope. Despite the differences in slope-movement between the western and eastern flanks of Castel Frentano’s hill, the slope values of the two flanks are not significantly different (Fig. 4b,c). The most significant feature in this regard is a prom- inent scarp located at the southeastern edge of the vil- lage (Fig. 4b), which corre- sponds to the area with the highest slope values in the topographic profile (Fig. 4c) and is located at the north- eastern top of the hill. In top view, the scarp has a sub- circular shape, typical of rota- tional landslides. Moreover, it represents the boundary be- tween the bedrock units of the hilly top and the slope deposits (Fig. 6a,b). The maximum thickness of the landslide de- posits, based on our field ob- servations, and the numerical analysis of Mancini et al. (2001) should be approximately 15 m. A large landslide terrace was detected just below the scarp. Altogether, the above features represent morphologi- cal evidence of the large gravi- tational movements that oc- curred in 1881. 4.2. Description and chronol- ogy of the CFL event Two main landslide epi- sodes occurred in 1881, strongly modifying the eastern hillslope of Castel Frentano and causing heavy damages to the old village (Fig. 5a). As already mentioned, the main event occurred on the 31st of July, 1881; then, on the 10th of September, 1881, an earth- quake reactivated the landslide (Savarese et al., 2011). Historical information helped reconstructing the evo- lution of the gravitational pro- cesses and the chronology of events that occurred be- fore the main landslide event. This event was first de- scribed by Enrico Niccoli (Niccoli, 1882), an engineer who was delegated by the Italian Royal Geological Committee to compile a report on it. Therein, infor- mation on the CFL is presented critically and methodi- cally. “During the afternoon of the 31st of July a wide- spread groundfall began to occur on the eastern hillslope and slide northeastwards, towards the bottom of the Feltrino Creek. The movement continued until night, leading to a very large landslide, which was about 1-km long and 500-m wide. The displaced mass is esti- mated to be about 9 million m3 […]. The ground surface 37 Damages caused in Castel Frentano in 1881 by a landslide and an earthquake. Fig. 5 - (a) GoogleEarthTM view of the Castel Frentano landslide (CFL); (b) historical photograph of the landslide taken in 1881 (from the Historical Archive of the Castel Frentano Municipality); (c) the CFL today. The green arrow indicates the Santo Stefano Protomartire Church. The dashed blue line in (c) indicates the portion of the Feltrino Creek below the hillslopes. 38 Racano S. et al. collapsed at about 30 m close to the village, while it swelled in the lower part of the valley; the landslide […], due to the presence of widespread and deep transverse cracks, was similar in shape to a glacier or even to a lava flow […].” (translated from Niccoli, 1882). This morphological description of the event reflects the characteristics of a rotational landslide, which are confirmed by a photo shot after the event and by the present-day morphology of the hillslope (Fig. 5b,c). Nic- coli (1882) also compiled a geological description of the hill and drew a scheme of the landslide section, which is similar to that obtained based on our geomorphological map: the landslide cuts and exposes the bedrock at the hilltop (Fig. 6a,b). Niccoli (1882) reported that the hill was composed of “Tertiary-Pliocene units” with sub- horizontal strata, mainly composed of grey-yellow marly clays, often interbedded with sands. The sands locally showed a “marly-calcareous” cement, but were general- ly consolidated “and formed an 8-m thick bank at the top of the hill, in correspondence of the urban centre of Cas- tel Frentano”. A detailed description of the catastrophic events can be found in the historical documents of Castel Fren- tano’s City Council. One of them, produced on the 9th of September, 1881 (i.e. the day preceding the earth- quake), reports some instability phenomena that had Fig. 6 - (a) Landslide profile by Niccoli (1882) and section of Fig. 6b; (b) landslide profile interpreted from the geological-geomorphological map (Fig. 4a). already affected the village before the main event of the 31st of July, 1881: “[…] last June, major clues of instabil- ity (depressions in the Orientale Street and in its proxim- ity, and cracks in the surrounding fields) alerted us and we asked for assistance to an engineer.” [translated from City Council historical documents, folder B9, file F168, 1861-1881]. A document produced on the 5th of August, 1881 (City Council historical document, folder B9, file F168, 1861-1881) declares instead that 469 citizens suffered the consequences of the landslide damages (including the complete destruction of their houses), which mainly affected residential buildings (Fig. 7). After the main event, no further significant landslide movements were recorded until the earthquake of the 10th of September, 1881. In his report, Niccoli (1882) wrote: “[…] The move- ments did not stop after the first one, because the earth- quake induced the falling of other slices of soil and con- tinued to damage the area […]”. (translated from Niccoli, 1882). Several damages affected the portion of village closest to the landslide scarp after the earthquake event, as reported by Bucci (1990) in his Memoriae (provided by the personal communication of Ferrante and Paione families). He stated that, after the earth- quake, the pre-existing landslide damaged the most picturesque part of the village, but there were no casual- ties. Other documents found in the Italian State Archive of Chieti - Section Lanciano and in that of Pescara, as well as information collected from newspapers found at the Chieti Library, reveal that also buildings far from the landslide suffered damages induced by the earthquake: “Numerous houses that were not in the landslide area were strongly damaged and a lot of people were injured, although there were no victims” (telegram to the Prefect of Chieti, available in the State Archive of Chieti-section Lanciano, Sottoprefettura, folder 20, file 115, 9th of Octo- ber, 1881); “In Castel Frentano, a lot of houses outside of the landslide zone were damaged […]” (La Gazzetti- na di Chieti, 15th of October, 1881). 4.3. Landslide genesis Although massive slope movements are usually related to rainfalls and/or earthquakes, there is no evi- dence that such triggering phenomena can be attributed to the 1881 landslide. The first evidence of instability was observed in June, while the collapse of the hillslope and of the eastern part of Castel Frentano occurred at the end of July. No detailed climatic records were found for the period of interest (even after consulting the AVI catalogue); moreover, no strong rainfalls, nor unusually wet summers or wet preceding months are mentioned in the available historical documents for 1881 and previous years. This absence of information is of great signifi- cance. In fact, the landslide events that occurred in 1881 had a large resonance, as highlighted by the nu- merous “media reports” of that time and descriptions of the event that have supported hypotheses on its origin (see next paragraphs of this section). Overall, the lack of reference in all documents to anomalously frequent and abundant summer rainfalls (which would have pro- vided an easy explanation for the catastrophe) suggests that the slide processes were likely not triggered by ex- cessive rainfall. Apart from extreme events, the available data (Fig. 8) were searched for irregular trends in the cumulative rainfalls related to specific climatic periods. For the in- vestigated area (the territory of Lanciano) two climatic series can be discussed: they refer to the periods 1834- 1843 and 1886-1902, and include the number of rainy days per month. The number of rainy days per year ranged approximately between 60-100. Figure 8 shows a plot based on data collected between 1834-1842: the average number of rainy days per year varied generally between 95-100; however, a low number of rainy days (only 62) was registered in 1843. No data are available for the period 1842-1885. Between 1886-1895, the aver- age number of rainy days per year was about 70; then, between 1895-1902, this value increased to 95-100. Daily rainfall data were also obtained for the period 1886 -1902: the cumulative number of rainy days during the summer (i.e. the season during which the CFL occurred) of those years was plotted (Fig. 8). The resulting dia- gram shows a regular contribution of summer months to the total yearly rainy days. Additional data from the Fu- cino Basin (Giraudi, 1990), an intermontane depression in the Abruzzo Apennines (about 70 km west of Castel Frentano), indicate a decrease in rainfall between 1855- 1862, when slope instability significantly increased in the area (see next paragraphs of this section). Notably, the average annual rainfall in Central Italy was quite regular between 1850-1905 (Maugeri et al., 2004). Overall, no climate anomalies causing periods of heavy rain can be inferred for the Abruzzo Region and Central Italy in gen- eral during the decades of interest. Some historical doc- uments indicate that the source of instability might have been of completely different nature. Niccoli (1882) wrote: “[…] concerning the description of the phenomenon, […] it was mainly due to the nature of the terrain that consti- tutes the hillslope, which led to a slow but continuous slope movement […]” (translated from Niccoli, 1882). In summary, this author related the origin of the landslide to the characteristics of the soil and shallow subsoil. He also provided some critical details about land use while inferring the causes of the landslide: “[…] before 1815, the collapsed hillslope was covered by trees. Later, however, the expansion of agricultural ac- tivities here and elsewhere encouraged ploughing […] and, soon, [it triggered] some ground movements, most- ly on the higher portion of the hillslope. Nevertheless, the ploughing continued, and increasingly larger and numerous movements occurred from 1831 onwards, causing the fall of several houses. Deforestation oc- curred mostly after 1860 and the landslide area contin- ued to increase […] until, in June 1881, the maximum level of hazard was reached […]” (translated from Nicco- li, 1882). The first reference to a landslide along the eastern hillslope of Castel Frentano has been found in a City Council document dated 1861. This document highlight- ed the evacuation of the population from Contrada Ripitelli (Fig. 7a), which was on the eastern slope of Castel Frentano’s hill before being destroyed by the landslide in 1881 (City Council documents, folder B9, file F168, 1861-1881, 17th of February, 1861). After 1861, 39 Damages caused in Castel Frentano in 1881 by a landslide and an earthquake. 40 Racano S. et al. Fig. 7 - (a) Planimetry of the centre of Castel Frentano, possible location of Contrada Ripitelli and comparison between the (b) present-day and (c) pre-landslide urban fabrics; (d), (e), (f) historical photos, in which the numbers indicate the damaged buildings (as reported in the map (c)). the area of slope instability on the eastern flank of the relief was known as “the landslide”. These conditions led to the destruction of about 100 buildings by 1868. In the documents of the City Council, building crumbling and collapse were attributed to the erosional action of the Feltrino Creek, flowing along the lower portion of the hill. This process “sank and destroyed many valuable houses located in the village” (City Council documents, folder B9, file F168, 1861-1881, 8th of November, 1868). These notes report also the erosional activity of the Feltrino Creek at the base of the hillslope as an addi- tional factor contributing to the evolution of the landslide. Regarding the phenomenon of water seepage in the subsoil, a document of the City Council mentions undetailed problems in the drinking water supply to the village. Drinkable water was lacking, creating inconven- iences to the population. This issue was linked to a mal- functioning of the shallow aqueduct, which would have been penetrated by roots and filled with waste. Appar- ently, water was spilling from the aqueduct and, hence, could not reach the buildings in the village (City Council documents, folder B9, file F168, 1861-1881, 5th of Au- gust, 1863). No further information is available about this issue and we could not find any map of the aque- duct, nor any reference to its position. The potential role of water seepage and land use activities in the activa- tion of the landslide are discussed in Section 5. 5. DISCUSSION Overall, the available information shows that the CFL was a peculiar event: no major natural triggering factors can be invoked for the widespread slope mass movement that struck Castel Frentano. In Italy, cata- strophic landslides are usually associated to heavy rain- falls, as in the case of Valtellina in 1987 (Alexander, 1988) and Sarno in 1998 (Cascini et al., 2011), or to seismic crises, as in the case of Irpinia in 1980 (Del Gaudio & Wasowski, 2004) and Molise in 2002 (which triggered the Salcito landslide; Bozzano et al., 2008). Rainfalls and climatic conditions are generally con- sidered potential triggers of landslide events; however, no evidence of a significant role of these factors in the evolution of the CFL raised from the available infor- mation. The period in which the catastrophe occurred was not anomalous in terms of rainfall amount, and local historical sources do not mention the occurrence of heavy rainfalls before the slope collapse. Mancini et al. (2001) investigated the response of Periadriatic hillslopes to seismic loads, concluding that significant slope movements would tend to involve mainly colluvial deposits saturated by a water table (situated at least 4 m above the colluvium/clays contact surface). However, these authors erroneously considered the CFL to have been seismically induced: the available historical docu- ments have revealed instead that, on the 10th of Sep- tember, 1881, the earthquake led simply to the reactiva- tion of an already displaced mass. Regarding the seis- micity characterizing the period of interest, the shock that occurred on the 14th of August, 1871 (i.e. the only earthquake reported in the catalogue preceding the par- oxysmal gravitational event; Fig. 3a) should not be con- sidered as a potential cause of the landslide. In fact, (1) it occurred ten years after the beginning of slope insta- bility and ten years before the main landslide event; (2) shaking was insignificant, due to the low magnitude of the seismic event (moment magnitude = 3.8; Rovida et al., 2022) and as testified by the lack of associated dam- age in the territory struck by the shock: the effects in the zone of Castel Frentano were well below the damage threshold (the MCS intensity was 4 in the nearby town of Lanciano; Locati et al., 2022). Beyond these considerations, it is well known that changes in land use practices, whether conditioned by natural events or human choices, can influence local and regional slope stability (Sidle et al., 1985; Wasowski, 1998; Glade, 2003; Sidle & Ochiai, 2006; Wasowski et al., 2010). An illuminating case of a land- slide outside of Italy that did not depend on climatic fac- tors is that of the Thompson River Valley (British Colum- bia, US). There, large instability phenomena occurred atop or within silt-clay units, triggered by the irrigation of benchlands above the river (Clague & Evans, 2003). The CFL case has some points in common with that of 41 Damages caused in Castel Frentano in 1881 by a landslide and an earthquake. Fig. 8 - Rainy days per year between 1834-1901 (from “Annali Civili del Regno di Napoli”, State Archive of Chieti-Lanciano) and rainfall rates in Central Italy (Maugeri et al., 2004) and in the Fucino area (Giraudi, 1990). the Thompson River Valley. Our data revealed that the geological characteristics (i.e. the occurrence of clays, sands and colluvium) of Castel Frentano’s hill and the geomorphological processes (i.e. the narrow incisions created by stream channels) affecting it predispose the area to landslide phenomena. The available information also suggests that Niccoli (1882) was probably right in invoking anthropogenic activity as one of the key factors that triggered the catastrophic event. Indeed, the grow- ing need for agricultural fields in Italy is known to have caused massive deforestations in all parts of the Italian Peninsula from the second half of the 18th century (Vecchio, 1974). This has resulted in a widespread growth of slope instability phenomena (Bevilacqua, 1996). Historical sources have revealed that movements along the eastern Castel Frentano hillslopes started to occur with the initiation of deforestation along the slope, which was linked to the expansion of agricultural activi- ties. Deforestation, combined with the agricultural usage of the hillslope, the geology of the area and the erosion activity of the Feltrino Creek, should have led to a pro- gressive loss of hillslope stability, ultimately inducing landsliding. Additional aspects that may have led to landsliding include water leaking from the aqueduct (described by the City Council in 1863). In fact, although the location of the aqueduct could not be reconstructed and no clear evidence was collected on the role of water seepage in the landslide paroxysmal evolution, a potential contribu- tion of this phenomenon cannot be excluded. In any case, water leaking would have had a secondary role compared to the intensive agricultural land exploitation that was affecting the area around 1881. Overall, the analysed historical documents allowed to reconstruct a sequence of landslides that, after 1860 (i.e. when the deforestation process was completed), started to slowly move towards the hilltop. This move- ment would have produced the first important damage to buildings in Castel Frentano in 1868, and would have led to the complete destruction of part of the village in 1881. Nowadays, the eastern slope of Castel Frentano’s hill has still a poor tree coverage and is exploited for agricultural activities (Fig. 5a,c); moreover, it is still af- fected by landsliding (as revealed by our geomorpholog- ical survey). Although landsliding presently occurs on the eastern hillslope, it is predominantly of the rotational type and is much smaller in size compared to the parox- ysmal event that took place in 1881. In fact, present landslides predominantly affect the colluvium and CFL accumulation, and none of them have been capable of cutting and exposing the bedrock on the eastern or western slopes of the hill. Castel Frentano’s case is not the only one in the Abruzzo Region in which landslides have had a proba- ble anthropogenic origin. According to historical reports, the instability of Gessopalena’s hill (about 17 km SW of Castel Frentano; Fig. 1) can be also attributed to the combined action of deforestation and water seepage (Galadini, 2016). In this case, however, the geological setting is completely different: the old village of Ges- sopalena (now abandoned) was settled on a small gyp- sum relief, while the adjacent valleys are characterized by highly erodible clays. Notably, 19th century docu- ments (Galadini, 2016) report that: (1) numerous wells in the houses of Gessopalena were leaking water into the gaps of the subsoil and (2) the underlying valleys were experiencing continuous deforestation. These factors would have triggered the collapse of gypseous boulders from Gessopalena’s hill and mass flows in the underly- ing clayey valleys (i.e. gravitational phenomena different from those of Castel Frentano). The resulting instability became a threat for the old village of Gessopalena dur- ing the 19th century, although interventions were carried out to limit the damages: hydraulic works were done to optimize the water regime and valleys previously denud- ed were reforested (Galadini, 2016). 6. CONCLUSIONS The CFL is an example of a natural catastrophe mainly driven by human activity that caused the loss of cultural heritage. Although Castel Frentano’s hill was already predisposed to slope mass movements due to its geological and geomorphological conditions (i.e. weak lithologies and stream linear incisions), deforesta- tion activities and the consequent agricultural use of the eastern hillslope (possibly combined with water seepage from the aqueduct) may have been the primary causes of the CFL genesis. The collected documents suggest that landslide movement may have begun in the lower part of the hillslope following deforestation and may have been driven by the incision activity of the Feltrino Creek. Then, the landslide may have progressively mi- grated upwards along the landslide scarp until the par- oxysmal event that involved the village on the 31st of July, 1881, leading to the collapse of historical buildings. Based on coeval documents and information on rainfall events, the following hypotheses can be considered remote: (1) the main landslide event may have been preceded by a period of heavy atmospheric precipita- tions and (2) a period of anomalous climate may have occurred during the decades of landslide trigger and evolution. Despite the large volume of documents men- tioning the main landslide event and evaluating its origin, none of them mentions the occurrence of exceptional rainfalls during or before 1881, although this would have represented the simplest explanation. This suggests that climatic factors and weather conditions likely did not play a major role in triggering the main landslide event. In addition, historical evidence of the paroxysmal landslide evolution preceding the 1881 earthquake and the ab- sence of any reference in historical documentation to seismic events in the area of Castel Frentano shortly before the main landslide event indicate that earth- quakes unlikely caused it. Rather, a 5.4-magnitude seis- mic event, which occurred about 40 days after the main landslide event, should have worsened the already criti- cal situation of Castel Frentano. Historical sources clear- ly described the reactivation of the landslide after this earthquake. In conclusion, the CFL case exemplifies what the Italian landscape has experienced since the second half of the 18th century: an increase of landslide occurrence following the expansion of agricultural land exploitation. 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