4.3.2. Roccamontepiano Landslide

The case study area is located next to the northeastern front of the Maiella Massif. It is characterized by the presence of a pseudo-rectangular-shaped travertine plateau (Montepiano) which dominates both topographically and morphologically the landscape of the area. Montepiano is a flat tabular relief 610–650 m.a.s.l. high, with a maximum length of about 2.3 km (along NW–SE direction). It generally dips gently north-east with an average gradient of about 5%, and it is bounded by vertical cliffs and scarps up to 30 m high [82,83]. Furthermore, the landform is cut by a series of small SW–NE-oriented fluvial incisions that raise the relief values along the slopes.

From a lithological standpoint, the area is characterized by an approximately 40 m thick travertine layer that overlies arenaceous-pelitic and pelitic-arenaceous deposits, with thin conglomerate layers in between, pertaining to the *Mutignano Formation* [78]; also, these bedrock layers are gently dipping towards the NE. Physical–mechanical parameters show a significant variability in terms of rock resistance and behavior according to lithological nature (travertine layer and arenaceouspelitic lithotypes) and subsequent loosening and weathering phenomena [84]. Quaternary continental deposits include eluvial–colluvial deposits mainly observed along the southwestern flank of the plateau. The landslide phenomenon covers a wide area (~4 km2) with high slope gradients (seldom less than 30%) and high variability in width and thickness due to repeated historical landslide events (Figure 8a). The maximum width of more than 2 km can be found downstream of the Ripa Rossa, whilst the maximum thickness of more than 20 m is located immediately above Roccamontepiano village. From historical sources, the first landslide events that occurred in the area took place on 24 June 1765, causing severe damage to the village and 2000 casualties [82,85].

**Figure 8.** Roccamontepiano landslide: (**a**) multitemporal geomorphological map (derived from unpublished data and modified and updated from [82,83]); (**b**) geomorphological cross-section.

Therefore, the relief is almost surrounded by wide complex landslide bodies and related scarp, which characterize most of the area south of Roccamontepiano village. Other historical movements occurred in the second half of the 1950s, reactivating pre-existing ones and causing extensive damage to the village of Roccamontepiano but this time without the report of victims [86]. Evidence of this second historical event is represented by wide counterslopes located at ~500 m.a.s.l. Actually, the landslide body is formed by a thick heap (up to 17 m) of travertine blocks and fragments with secondarily reworked sandstone-conglomerate deposits, active especially in the northeastern and northern part of the Montepiano plateau (Figure 9a). The overall mechanism could be referred to a complex landslide system, including lateral spreading with rockfalls, rotational, and translational movements.

**Figure 9.** Photo documentation of geomorphological features of Roccamontepiano landslide. (**a**) Panoramic view of the landslide area. Red lines show the planimetric development of main landslide scarps, red circles show travertinous blocks in the landslide body; (**b**) detail of NE–SW trending traction fractures (red lines) in the travertine cliff scarp near Ripa Rossa.

The geomorphological cross-section (Figure 8b) shows how the landslides are strictly connected with the structural framework of the study area; the mechanism implies the involvement of the plastic clays that underlie the travertines in the mass movement.

The presence of a thick layer of massive rocks over plastic lithologies leads to tension stresses along the edge of the travertine layer and the progressive opening of preexisting fractures. The travertine layer exhibits NW–SE and NE–SW trending fracture systems, probably caused by tectonic activity (Figure 9b). Fracture of tectonic genesis up to 10 m wide and in different stages of evolution are sub-parallel to the plate edge and the major fracture systems all along the cliff scarps. When these fractures reach the clays, large blocks of travertine are isolated over the plastic materials, and lateral spreading accelerates, defining sliding surfaces; the movement evolves as a complex landslide.

#### 4.3.3. Montebello sul Sangro Landslide

The case study area is located in the transition zone between the central Apennines chain front and the piedmont area on the left side of the middle Sangro River valley. It is on a narrow-faulted anticline ridge, more than 900 m.a.s.l. high, trending N–S. The landscape outlines a strongly asymmetric calcareous hogback ridge, with a gentler eastern slope and a steeper western one, resulting from the erosion of the anticline flank; northwards the ridge is deeply incised and separated by a second hogback ridge on which the Pennadomo village is located.

From a lithological standpoint, bedrock lithology is made of rocks pertaining to allochthonous pelagic deposits. Clayey deposits with embedded terrigenous siliciclastic deposits (*Argille varicolori formation*) outcrops in the western side of the ridge; alternating calcareous-marly and calcirudite rocks (*Tufillo formation*) represent the backbone of the ridge; pelitic-arenaceous deposits (*Flysch of Agnone formation*) mostly outcrop in the eastern side of the ridge [39,87]. Physical–mechanical properties of chaotic marly–clayey deposits reflect the grea<sup>t</sup> amount of lithological variability within them, and consequently the rock behavior is not constant. Moreover, detailed analysis showed that outer area of the scree slope deposits appears plasticized, and the most superficial zones are at yield in tension [87]. Quaternary continental deposits include eluvial–colluvial and scree deposits mainly observed along fluvial incisions and slopes.

The landslide phenomenon covers an area of ~1.1 km2, and it is affected by strong variations in the state of activity. Large landslides (mostly dormant and/or abandoned) and small landslides (generally more recent and active) constitute the wide and complex landslide system. Historical documents and chronicles show multiple activations of the main event, involving the western side of the Montebello hogback and spreading out on the eastern side (Figure 10a). These worrying geomorphological dynamics are testified by the involvement of the Montebello village. The first evolution of events occurred in the second half of 1800 (1864, 1891, and 1899); after that, the new village of Montebello sul Sangro was reconstructed in a more western site [86–88]. It was characterized by a complex dynamic including earth flows, complex landslides, rotational and translational landslides, and localized rockfalls. Another significant landslide event occurred in 1971 [89], and it was mainly characterized by earth flows due to the activation of several small mass movements composing the large one. Nowadays, a principal earth flow is present, and the activity of this movement is demonstrated by a range of surface expressions such as irregular mounds, landslip troughs, and several tension fractures that opened both longitudinally and transversely to the main landslide. The main landslide is characterized by a mass that flows down along a narrow channel and then spreads out in a wide accumulation lobe, with depressions and undulations. Thrust features in the accumulation area point out at least three overlapped flows, suggesting an intermittent movement (Figure 11). Moreover, the geomorphological complexity of the area is evidenced by the presence of several families of rotational and translational landslides, complex landslides, and rockfalls, present especially along the steep western side of the hogback.

The geomorphological cross-section (Figure 10b) shows that the landslide movements are strictly controlled by the geological and morphostructural setting of the carbonate hogback (east overturned faulted anticline trending from N–S to NNW–SSE) and chaotic clay rocks; the main earth flow is influenced by the progressive involvement of the clay units in the landslide movement, and the rockfalls in the upper part of the ridge are linked to fractures and jointing in the calcareous strata. The scarp area involves the steep western calcareous slope of the ridge down to the gentle lower slope on clay units; the regressive enlargement of the landslide scarp, close to the Montebello village, involves the western side of the calcareous ridge, with systems of tension fractures and reverse slope areas, affecting the Montebello village (Figure 11b).

**Figure 10.** Montebello sul Sangro landslide: (**a**) multitemporal geomorphological map (derived from unpublished data and modified and updated from [87]); (**b**) geomorphological cross-section.

**Figure 11.** Photo documentation of geomorphological features of Montebello del Sangro landslide. (**a**) Panoramic view of the main earthflow; (**b**) detail of allochthonous pelagic deposits involved in the landslide phenomenon, with regressive enlargement of the landslide scarp near the Montebello sul Sangro village.
