Interactive comment on “ Multidisciplinary Approach to Rainfall-Triggered Rockfalls : the Case Study of the Disaster of the Ancient Hydrothermal Sclafani Spa ( Madonie Mts . , Northern-Central Sicily , Italy ) in 1851

our opinion, your attempt has failed. Indeed, your comments lack an objective assessment of the fundamental role that historical datasets (documentary data, ancient maps, ancient engravings, etc.) play in the study of past landslide events. Your comments oversimplify and underestimate our archival contribution, reducing it to a mere “summary of the historical documents that describe the event". Our meticulous archival research work, with three documentary appendices (see Supplementary Information) including plenty of selected historical data, most of which unpublished (e.g. those from manuscript sources), was intended to offer a comprehensive analysis of historical sources in support of our assumptions and not just a list of collected data.

Rockfalls may be regarded as relatively "minor" landslides, since they are confined to the removal and fast downslope movement of distinct fragments (of different size) of fresh rock, usually detached from a steep rock wall 35 or cliff (Carson and Kirkby, 1972;Selby, 1982).
The types of rock movements may be: toppling, falling, bouncing, rolling and sliding, accompanied by the Nat. Hazards Earth Syst. Sci. Discuss., doi:10.5194/nhess-2016-397, 2017 Manuscript under review for journal Nat.Hazards Earth Syst.Sci.Published: 4 January 2017 c Author(s) 2017.CC-BY 3.0 License.monthly rainfall of September 1850 (138.57mm) was the peak value of the month, in the period from 1827 to 1866, recorded by the non-official INP station (Tacchini, 1868).The 1850-51 winter, snowy and rainy, was followed by scarce rainfall in spring.This fact had phenological effects: insufficient wheat and olives production and extraordinary blooming of fruit-trees (e. g. apricot trees) and a species of Poaceae (Ampelodesmos mauritanicum), a typical example of Mediterranean bunchgrass used for making strings and ropes, followed by limited production of 110 foliage.In the summer, the anomalous proliferation of harmful Coleoptera destroyed many vineyards (Minà Palumbo, 1854).

Topographic, Geological and Tectonic Setting
Sclafani Bagni is a picturesque town of medieval age, just as its castle rising at the top of its slope (813 m a.s.l.); it is 115 located in central-northern Sicily (Madonie Mts.), about 80 km from Palermo.
In the past, its three hot sulfur springs, lying at the foot of Mt.Sclafani and used for thermal balneology, were among the most famous in Sicily (Vinaj andPinali, 1916-1923).
The history of the thermal baths of Sclafani is divided in three phases.An original heterogeneous group of buildings was used for bathing and lodging (the so-called "thermal bath houses").Some nearby houses were used for additional 120 lodging (the so-called "Giambelluca's houses", see Cacciatore, 1828;Cappa, 1847).In the years 1846-50, the first thermal establishment (the so-called "ancient Sclafani spa"), with two-floors and 113 beds (Cappa, 1847), was built on the orders of the Hispanic nobleman Giuseppe Àlvarez de Toledo, Duke of Ferrandina, Count of Sclafani, which included the original "thermal bath houses", was destroyed by the catastrophic rockfall of 1851 (see Di Marzo, 1859).
After the disaster, the same Count of Sclafani, commissioned the construction (1856-57) of a new one-floor thermal 125 establishment (the so-called "Masseria Bagni" i.e. "thermal bath farm"), in a site near the previous one, at an elevation of about 402 m a.s.l.The new thermal establishment, a unique example in the Madonie region, featuring a new aqueduct and about 200 beds (Marieni, 1870) and covering an area of 1960 m 2 , was totally abandoned after 1985.
The Madonie are the tallest mountains (1,979 m a.s.l. at Pizzo Carbonara) of the Sicilian northern chain.These reliefs, 130 a segment of the Sicilian Maghrebid chain, consist of stacked tectonic units, which originate from the deformation of distinct ancient paleogeographic domains, emplaced in Neogene times.The homonymous regional natural park was established (1989) in the Madonie Mts., given their high environmental value.The study area covers 82,7 km 2 and has an average altitude of 600 m a.s.l. and a maximum altitude of 1,794 m a.s.l. at Monte dei Cervi.
The Imerese units derive from the deformation of a carbonate and carbonate-siliciclastic deep-sea succession (basinslope, from the upper Triassic to the Oligocene, thickness 1,200-1,400 m, e. g.Basilone and Lo Cicero, 2009).
The structural edifice is unconformably overlain by a syntectonic wedge-top basin, filled with terrigenous, evaporitic and clastic-carbonate rocks (of Serravallian-Pliocene age).The most recent deposits include a local debris cover, colluvia and landslide deposits (Holocene).155 During the Miocene and Pleistocene interval, two main tectonic events took place (Catalano et al., 2000): I) a first thrust system (currently SW-dipping), consisting in a quasi-horizontal, NE-SW-trending maximum compression (shallow-seated structures, middle Miocene); II) a more recent strike-slip and/or transpressional fault system, consisting in an N-S-trending maximum compression (deep-seated structures, after the beginning of the Tortonian).
The data about the tectonic architecture at the deep subsurface of the study area and nearby areas were obtained by 160 interpreting the northern portion of the SI.RI.PRO ("SIsmica a RIflessione PROfonda", deep seismic reflection) borehole-calibrated seismic profile (Accaino et al., 2011;Catalano et al., 2013).
The upper portion of the SI.RI.PRO (Fig. 4) exhibits a stack of N-dipping, imbricated thrust sheets, affecting the thin basinal successions of Meso-Cenozoic age (Imerese unit, Numidian flysch and Sicilidi); the latter were emplaced during compressional event I.The Imerese thrust sheets appear to have been cut by deep-seated high-angle faults 165 (generated at a deeper structural level) and then folded and lifted, giving rise to N-dipping features (i.e.backthrusts).
During the Pleistocene, NW-SE-and NE-SW-trending normal faults, correlated with an extensional tectonic event of a high angle, involved the study area.Finally, the occurrence of N-S-and E-W-oriented transtensional faults is consistent with a quasi-vertical maximum compression.
In the study area, N-S high-angle (about 70°) faults show an approximate rake of 60°.Kinematic indicators suggest a 170 dextral transtensional movement.
The geomorphological setting of the study area shows two different landscapes, each with well-defined landforms, depending on outcropping lithotypes and dominant morphogenetic processes: i) carbonate and carbonate-siliciclastic, 175 with more or less steep slopes and numerous karst and morphoselection features; (ii) clayey-marly with uneven and gently inclined slopes (<20°), usually affected by shallow gravitational movements (landslides).Alternating lithotypes with different erodibility and tectonic features justify the development of structural morphologies (cuestas, hogbacks and flatirons).Locally, NE-trending scarps display deep-seated gravitational deformations.N-S-and NE-SW-trending faults/fault lines, whose height was increased by selective erosion, dominate the landscape.On the ridge 180 of the mountain (Cervi-Rocca di Sciara-Sclafani Anticlinorium, hereinafter CRSSA), the terrigenous covers (Numidian flysch) have been gradually dismantled since the salinity crisis of the Messinian, exposing calcareousdolomitic and/or calcareous-siliciclastic levels to a different extent.The Plio-Quaternary uplift enhanced this process (Contino et al., 2015).
Mt. Sclafani is a morphostructural high of the large CRSSA, markedly dissected by the recent faults with the highest angle.This typical isolated relief with a pyramidal shape and a triangular base is bordered on its E and W sides by an N-S-trending normal fault/fault line scarp.Its NW slope is bounded by a fault line scarp that was interpreted in 190 different ways (see discussion).Mt.Sclafani consists of three S-dipping slopes, separated by less steep slopes.Owing to selective erosion, this morphology corresponds to carbonate and siliciclastic levels, respectively.These levels give rise to fall-prone hard-on-soft landforms (see Fig. 3): -Lower Cliff: about 230-10m high, calcareous-dolomitic (Scillato and Fanusi fms.); it shows selective erosion steps, with small caves and protruding ledges and is locally shaped by arcuate rockfall niches; 195 -Lower Talus Slope: roughly 240-40m high, siliceous and subordinately calcareous-marly (radiolarian member, Crisanti fm.), with morphoselection ledges; -Middle Cliff: approximately 30-20m high, calcareous (Ellipsactinia breccias member, Crisanti fm.) and crowned by the ruins of the medieval castle; its steep undercut cliffs are rockfall-prone; this is the source area of the 1851 event (height approximately 730-750m a.s.l.); 200 -Middle Talus Slope: marly-calcareous (marly-spiculitic member, Crisanti fm.); -Upper Cliff: calcareous (Rudistid breccias member, Crisanti fm.); also these steep undercut scarps are rockfallprone; -Upper Talus Slope: calcareous-marly (Caltavuturo fm.) and terrigenous (Numidian flysch).Mts. have a cold climate in winter (December to February) and relatively mild summers.Average yearly temperature is roughly 14°C, whereas average yearly precipitation is about 800 mm.Precipitation is unevenly distributed over the different seasons.85% of yearly precipitation is concentrated in September and April, whereas in summer (June-210 August) precipitation drops to less than 4% (Drago, 2002).
A relative peak occurs in September or October.On the highest reliefs (more than 1,000m a.s.l.), the yearly temperature excursion is equal to 10°C, while it decreases to 5-6° C in coastal areas.
The northern Imera river valley is open on its northern side, on the windward side of the northern Sicilian ridge; therefore, it is strongly exposed to the influence of the sea.220 The monthly value of real evapotranspiration (ETR) was estimated with Thornthwaite's formula at 300 mm, based on the soil water balance for a field capacity of 20mm.Average surface discharge values (Ds) account for 24% of yearly precipitation (P) (see Drago, 2002) The main aquifers of the Madonie Mts. are hosted in the calcareous-dolomitic (Scillato and Fanusi fms.) and calcareous (Crisanti fm.) rocks of the Imerese succession.The hydrostratigraphy of the Imerese succession, its 225 structural geometries (ramps, faults and discontinuities) and karst landforms (of short length) govern groundwater flow.

Documentary Evidence
Written archives offer a large spectrum and an adequate resolution of evidence on past weather extremes and related natural disasters.Documentary evidence consists of different types of data: references; central and local public 235 authorities reports and acts, engineers and experts synchronous relationships; ancient (Salemi, 1833;Massa, 1846-50) and recent series of maps , including satellite ones; synchronous engravings and drawings.
The documentary datasets are structured as follows: the selected evidences previous to the disaster of the ancient hydrothermal Sclafani spa in 1851 (4 original documentary sources are found in Supplementary Information, Table S1) and relatively to the disaster (22 original documentary sources are found in Supplementary Information, Table  S3).
A significant legacy of documentary data, related to Sclafani event, was collected in the pandects of Bourbon The collected historical documentary data have been submitted to an essential critical analysis (homogenisation, cross-checking, validation and interpretation).

Results and Discussion 250
Geological and geomorphological mapping, field surveys and a critical analysis of documentary data have considerably improved the understanding of the rockfall event in the study area.Unfortunately, no detailed eyewitness reports of the event are available.
In the Madonie Mts., very active infiltration processes, as well as weather and erosion agents, are significantly altering the bedrock, especially along structural discontinuities.The spacing between discontinuities has led to the 255 development of unstable rock masses -which are prone to falling, especially during maximum intensity and/or duration of precipitation and under moisture-saturated freeze-thaw conditions -and to the formation of alluvial fans and talus deposits downslope (e. g.Scheidegger, 1975;Gardner, 1983;Whalley, 1984).
Given its geological, geomorphological and structural features, the calcareous-dolomitic and carbonate-siliciclastic relief of Mt.Sclafani is extremely prone to rockfalls.260 Regional tectonics plays a key role.In previous studies, the NW slope of Mt.Sclafani was interpreted as a tectonic line (Sclafani Fault, SF) with extensional kinematics (Agnesi et al., 2004;Catalano et al., b;Gugliotta and Gasparo Morticelli, 2012), or as an indefinite fault/fault line scarp (Di Maggio et al., 1999).By contrast, in the study reported in this paper, the NW slope of Mt.Sclafani was interpreted as a transpressional fault line, juxtaposing lithotypes with different resistance to exogenous processes.The topographic expression of this transpressional line (Transpressional 265 Sclafani Fault, hereinafter TSF), locally associated with normal faults, is marked by an abrupt scarp.This scarp, of arcuate shape and variable height, was shaped by the progressive collapse/retreat of the wall and by the incision of small fluviokarst canyons.
Therefore, in this study (see structural sketch map in Fig, 2), the TSF was interpreted as the SW prolongation of the TCF.In agreement with these data, the SI.RI.PRO crustal seismic profile displays the buried Imerese tectonic high Nat.Hazards Earth Syst.Sci.Discuss., doi:10.5194/nhess-2016-397,2017 Manuscript under review for journal Nat.Hazards Earth Syst.Sci.Published: 4 January 2017 c Author(s) 2017.CC-BY 3.0 License.
uplift was ascribed to the Pliocene-lower Pleistocene (Catalano et al., 2013).The general uplift of this sector of the Madonie Mts. has accelerated the effects of exogenous processes and, consequently, gravitational movements.
In Mt.Sclafani, carbonate rock masses are segmented by discontinuity planes, intersected by a number of major vertical joints, which may increase the likelihood of future disasters.
Unfortunately, no published data are available about the level of fracturing of the bedrock and/or joints in the slopes 280 of the study area, which are extremely steep and locally inaccessible or accessible only with mountaineering techniques.Discontinuities in the carbonate rock have been altered by protracted exposure to rainwater.At the surface, the carbonate rock, divided into blocks, has given rise to ruiniform reliefs and trapezoidal spires.
During intense rainstorms (likely to induce water saturation and increase water pressure from precipitation-induced seepage), surface waters erode the weathered interspace materials.285 Rockfalls associated with diffuse erosion and detrital slips occur along the edge of the carbonate layers that lie at the bottom and top of the site.These phenomena cause the toppling and rolling of carbonate blocks and rockfalls, especially as a result of intense rainstorms and under moisture-saturated freeze-thaw conditions.The same mechanism has been observed to be at work throughout the area.
A detailed analysis of documentary evidence (including historical maps) made it possible to identify the exact 290 position of the ancient Sclafani spa, which collapsed owing to and was buried by the 1851 rockfall.
In the 18 th and early 19 th centuries, the "thermal bath houses" were located at an elevation of about 430 m a.s.l., on a flat land (Mongitore 1743), near a small NW-SE-oriented valley, at the foot of the NW slope of Mt.Sclafani (Cacciatore, 1828).Before the event, the hydrothermal waters gushed out from the talus deposits at a distance of 30 m from the foot of a steep rock slope.An underground aqueduct conveyed water from the hot springs to the "thermal 295 bath houses" (Cacciatore, 1828).The first improvements of the Sclafani baths date from between the end of the 18 th century and the beginnings of the 19 th century (1792-99;1825-27, see Campisi, 2015)).
The ancient maps of the land-surveyors, Gaetano Salemi (1833) and Giuseppe Massa (1846-50), respectively, show the "thermal bath houses" and the "ancient Sclafani spa".The map of Salemi (Fig. 6), despite his naiveness, clearly shows the prominent spur at the base (Lower Cliff) of Mt.Sclafani, the position of the "thermal bath houses" and 300 Giambelluca's houses, the thermal pond ("Gorga") and the four water mills.The map of Massa (Fig. 7), clearly shows the location of the "ancient Sclafani spa" at the foot of the slope of Mt.Sclafani and the mule track connecting the small town with the thermal establishment.
The site of the ancient spa at the footslope of Mt.Sclafani is clearly visible in the pioneering geological and hydrogeological sketch (based on Bourbon maps) drawn by Felice Giordano (Fig, 8), a mining engineer who worked 305 in Sicily in 1860 (Daubrée, 1887).Furthermore, the 1847 very detailed engraving (Cappa, 1847), portraying the "ancient Sclafani spa" prior to the disaster, shows a site with a gentle topographic slope; this is due, in part, to the expansion work carried out at the time at the foot of the slope (Fig. 9).Owing to an obvious misprint, Di Marzo (1859) reported this disaster on 19 March 1851 and this erroneous date was submissively repeated by many subsequent researchers.
In the synchronous documentary sources the landslide of Sclafani was called "scoscendimento".Stoppani (1866) defined it as a "landslide of formidable proportions", with catastrophic effects.In the Italian geological literature, the 325 term "crollo di roccia" (rock fall) can be found only in the 19 th century (see Almagià, 1910), but Gortani (1948) still uses "scoscendimento" or "rovina" (collapse).
The disaster involved the catastrophic falling of carbonate rocks from the crest of the middle cliff (Ellipsactinia breccias), crowned by the ruins of a medieval castle.The detached rocks slid along the slope, removing undisturbed rock from ledges or talus areas.The debris from the rockfall continued their movement along the lower slope, hitting 330 the edge of the lower cliff.The material, coming down along transport channels, fell downslope and reached the spa that consequently collapsed.The large building of the ancient spa, the access road, the nearby Giambelluca's houses, the banks of the thermal pond, the water mills and a segment of a mule track were completely destroyed and/or buried under rock fragments.Conversely, the hot springs were unaffected, keeping the same chemical property and the same discharge (Di Marzo, 1859).Fortunately, the disaster did not cause injuries or deaths because the thermal bathing 335 season would start on the following 20 April (Vinaj andPinali, 1916-1923).According to Jervis (1868), the event was particularly disastrous owing to the unfavourable choice of the site of the ancient thermal spa.The zone of accumulation of displaced material had an estimated area of 63,403 m 2 .
The catastrophic event was preceded by some premonitory signs around one year before.A resolution by the municipal council (so-called "decurionato") of Sclafani, adopted on 1 April 1850 (Anonymous, 1849-60) documents 340 that a landslide had damaged the mule track connecting the small town with the thermal establishment.After the Nat.Hazards Earth Syst.Sci. Discuss., doi:10.5194/nhess-2016-397, 2017 Manuscript under review for journal Nat.Hazards Earth Syst.Sci.Published: 4 January 2017 c Author(s) 2017.CC-BY 3.0 License.
disaster, the source area continued to show signs of instability.The above-mentioned mule track was again damaged in January 1854 (based on the records, a detached rock blocked the passage).
In the 20 th century, no rockfalls occurred during the serious weather event of 21-25 February 1931, but its effects may have been mitigated by the removal of part of the rocks (near the source area of the 1851 event) during the 345 construction of the road of access to the built-up centre, opened in 1930 (Termotto, 2009).The severe weather events that occurred on 21 January 1981, 10-12 January 1987, 23-24 November 1991and 13-14 November 1996 are likely to have reactivated landslides in Mt.Sclafani.During the 1990s, to mitigate the effects of these events, the site was provided with a rockshed, as well as with nets and anchoring systems.Recently, eight active rockfall areas (one in the source area of the 1851 event) have been inventoried at Sclafani (Regione Siciliana, 2004).350

Conclusions
Detailed field geological and geomorphological surveys in the study area highlighted multiple slope instabilities, especially at shallow depth, such as the emblematic rockfall of 1851.
This study represents the starting point for a future Sicilian rockfall inventory database, a precious tool to shed more 355 light onto these catastrophic events.The dynamics of the catastrophic rockfall involving the ancient Sclafani spa was reconstructed by conducting a multidisciplinary study.The study combined thorough geological and geomorphological studies with the interpretation of aerial and satellite photos and was integrated with the analysis of ancient and modern maps and a critical assessment of historical records.
The relevance of historical data in assessing the rockfall disaster was demonstrated by the investigation conducted as 360 part of this case study.Detailed documentary data are crucial to identifying the mechanisms triggering rockfalls, quantifying the susceptibility of the various slopes to rockfalls and developing magnitude-frequency relationships (Porter and Orombelli, 1980;Wieczorek and Jäger, 1996).Often, documentary data are the only evidence of the socio-economic impacts of major disasters, such as rainstorms, severe floods and landslides, in periods preceding the deployment of instrumental monitoring networks (beginning in 1921 in Sicily).365 The comparison of ancient and modern maps made it possible to determine the exact position of the ancient Sclafani spa, of paramount importance to carefully reconstruct the rockfall of 13 March 1851.The collected data are beginning to provide a first picture of this catastrophic event.
The main causes of the rockfall disaster may be attributed to a number of intrinsic and extrinsic factors: geological, structural, geomorphological and, in particular, meteorological (extreme precipitation event).Unfortunately, the time, 370 place and frequency of occurrence of rockfall disasters, as well as their scale, are unpredictable (Zellmer, 1987).The Sclafani rockfall of 1851 was an exceptional event that can hardly be framed in statistical terms.
In the 1986-2015 period, global warming induced by climate change expressed itself in different ways, including an increase of extreme precipitation and of catastrophic geomorphological processes (Katz and Brown, 1992;Rosenzweig et al., 2007;Sillmann and Roeckner, 2008).The higher frequency and intensity of rainfall activated Nat. Hazards Earth Syst. Sci. Discuss., doi:10.5194/nhess-2016-397, 2017 Manuscript under review for journal Nat.Hazards Earth Syst.Sci.Published: 4 January 2017 c Author(s) 2017.CC-BY 3.0 License.landslides and/or debris flows (Evans and Clague, 1994;Keefer et al., 1987).High-impact events are expected to be more frequent and intense in the future, as a consequence of continuing global warming (Krautblatter and Moser, 2006;Field et al., 2012).Therefore, given the intensification of extreme weather events, the risk of recurrence of a catastrophic event, like the one of the ancient Sclafani spa, is always impending.
Future investigations based on direct and/or indirect methods (structural and geomechanical reconnaissance, seismic 380 and/or microseismic monitoring, surveys via digital high-resolution photos, terrestrial and/or aerial laser scanning) may yield relatively new data to improve the assessment of rockfall susceptibility and adequately plan and manage disaster prevention and mitigation actions in the Mt.Sclafani area (especially to the safeguard the site of the thermal springs, which are particularly vulnerable).Unquestionably, a detailed study of past events is the starting point of any conceptual plan to mitigate rockfalls, as well as to design and develop systems for rock slope stabilisation.Finally, we 385 hope that a future archaeological survey and excavation in the site of the ancient Sclafani spa can discover the remains of the collapsed establishment.
Nat. Hazards Earth Syst.Sci.Discuss., doi:10.5194/nhess-2016-397,2017   Manuscript under review for journal Nat.Hazards Earth Syst.Sci.Published: 4 January 2017 c Author(s) 2017.CC-BY 3.0 License.The rockfalls of the 1851, transformed entirely the landscape of the northern footslope of Mt.Sclafani (Fig.10), and the position of the hydrothermal springs.Today, the site displays two mounds of rocky material 310 (doloarenites/dolorudites, Ellipsactinia breccias, radiolarites, calcilutites), longitudinally sorted, with large rocks and masses (the largest ones are approximately equidimensional, 4 m in size), at the foot of the Lower Cliff and a marked vegetational difference on the rockfall debris as against the surrounding areas.The morphological change took place on 13 March 1851 after the maximum intensity of rainfall, when the landslide ravaged the "ancient Sclafani hydrothermal spa".This event is very consistent with the data recorded by the two rain gauge stations of the city of 315 Palermo (OAP and INP), indicating a rainfall peak on the same day.The pandects of the Bourbon administrative office (Intendenza) of Palermo (Anonymous, 1847-59), documented that the extraordinary torrential rains (the peak) battered the western Madonie on the night of 13 March 1851 streams swelled, provoking damages to structures (e.g. the aqueduct of Caltavuturo).Because of the landslides, the water spring called "Xhanimirici" (location unknown) disappeared and the inhabitants of Sclafani remained without 320 drinking water (Anonymous, 1849-60).

Figure 03 -
Figure 03 -Schematic N-S geological and geomorphological profile at the Mt.Sclafani.Details and explanation in the text, location of section in Fig. 5.Note the sequences of caprocks and soft rocks enhanced by selective weathering and erosion.585

Figure 10 -
Figure 10 -The present landscape surrounding the site of ancient Sclafani spa.The arrow indicates the location of 615 the new thermal new one-floor thermal establishment (1856-57, the so-called "Masseria Bagni" i.e. "thermal bath farm").The star indicates the today's location of Sclafani's thermal springs.