Pages

Landslides have been known in the municipality of Agnone since at least the beginning of the twentieth century. The oldest report describing an instability event refers to a phenomenon that occurred in March 1905 in the San Nicola Valley due to the combination of a period of intense rainfall combined with snow-melting. This event damaged the bridge that carried the main access road to the historical center of Agnone. The municipality of Agnone has been successively affected by several small and large landslide events. Archival and bibliographical landslide research, reported in the nationwide AVI Project, revealed more than 60 landslides that occurred in the municipality of Agnone and the surrounding territory. After an intense rainfall event that affected southern Italy between the 23rd and the 27th of January 2003, with more than 200 mm of rain falling over 72h, an important remobilization involved a large area of the historically dormant Agnone landslide due to an unusual increase in pore pressure. The event caused deformations over the whole basin and forcing the local authorities to adopt restrictive measures for 13 edifices occupied by 17 families located within and nearby the landslide. Furthermore, two country roads adjacent to the landslide remained closed due to the substantial damage caused by the reactivation. The mass movement subsequently reactivated in 2004, 2005 and between 2006 and 2007, induced the local administration to allocate resources for some urgent interventions to intercept superficial waters and drain a pond formed in the upper portion of the affected area, in addition to geomorphological reshaping work. Inclinometer and GPS stations were installed and the landslide was monitored by PS data. Sources: Del Soldato, M., Riquelme, A., Bianchini, S., Tomàs, R., Di Martire, D., De Vita, P., Moretti S. & Calcaterra, D. (2018). Multisource data integration to investigate one century of evolution for the Agnone landslide (Molise, southern Italy). Landslides, 1-16. Del Soldato, M., Di Martire, D., Bianchini, S., Tomás, R., De Vita, P., Ramondini, M., Casagli N. & Calcaterra, D. (2018). Assessment of landslide-induced damage to structures: the Agnone landslide case study (southern Italy). Bulletin of Engineering Geology and the Environment, 1-22.

According to informal interviews to local people, the first movement of Randazzo Landslide (RL) occurred between August and September 1995, after an anomalous rainy month. It consisted in a series of slight rotational motions, which gave rise to a counter slope sector in the middle of the slope, where a new spring fed a small pond. After the following winter, on March 20th 1996, a further movement affected the slope at 900 m of elevation a.s.l. in the form of a rotational sliding (RLa). This movement represents the beginning of an unrelenting landslide, which soon involved the higher portions of the slope in the proximity of SS116. In a few days, the road itself was dislocated downslope by the landslide, while another independent slope movement was triggered south-west of the first landslide (RLb). On March 26th 1996, RLa showed the features of an earth flow, dark in color and visibly saturated with water, which was sliding towards the downstream Alcantara river. On the other hand, the retrogressive evolution of RLb had completely disrupted the roadway and the landslide body kept moving downslope, with an estimated speed of about 0.3–0.4 m/h. In the morning of March 28th 1996, RLa reached the Alcantara river, which was completely dammed within the next 5 days, when the RLa toe reached the volcanic rock scarp located on the opposite side of the valley. This event gave rise to the formation of a landslide lake, whose level quickly grew until a maximum height of 17.5 m, with a held volume of water of about 350,000 m3. The neighboring portions of the slope were affected by deformations and were soon incorporated by the RLa body. The dam was removed some months later to reduce the risk of flood at the downstream villages (Pappalardo et al., 2018- DOI 10.1007/s10346-018-1026-9)

Maierato is located in Vibo Valentia’s territory, few kilometers from the Mar Tirreno in central Calabria. The Maierato’s town rises on a slope without particularly accentuated inclinations, but it is deeply disturbed by an enormous and ancient gravitational deformation (Guerricchio et Al., 2010). Moreover, the territory is characterized by ancient and “Great Lands”, these probably born as a result of marine regressions during glacial periods. In addition, the predisposition to landslide events was strongly characterized by the disastrous earthquake occurred in 1973, which generated fractures and considerable masses dislocated over the whole slope. As a consequence, the seep rains feed a powerful aquifer localized in the permeable layers of deposits. Due to the almost verticality of the cracks, the outflow occurs with a high gradient (about 10%) which, in case of abundant infiltrations, can generate a real “underground torrent”. The landslide of February 15th 2010 was preceded by a long phase of deformation that later produced the collapsed of slope. The elevation speed of the phenomenon seems to suggest that the movement has developed on a completely fluidized substrate, allowing to the ancient landslide debris to mobilize with great energy. The water level has generated pressures in order to cancel the effective stress, inducing a real liquefaction. The conditions favored a collapse in according to a mechanism of multiple rotational sliding, followed by a deep “disarticulation” of the landslide. It could be considered as a “debris flow with rock blocks”. The landslide movement has a main scarp with a development of approximately 1.1 km and with a maximum depth about 50 m. The average depth of the landslide body was estimated at 25-30 m, with a volume that exceeds 8 million m3.

The area affected by instability is located in Gimigliano, in the “Sila Piccola’s” southern sector, located to 8,5 km from Catanzaro town, Calabria, Italy. The area’s geomorphological context is strongly influenced by the geological structure. Therefore, in the analysis is appropriate to consider the topographic, geologic-structural and hydrogeological influence due to the presence of fractured rocks and the underground water circulation. The stratigraphic reconstruction is very complex, regarding these units as have undergone multiple deformation phases. The presence of fault systems generates many areas covered by strongly fractured and altered rocks that often are the expression of real shear zone. Surveys and superficial and deep (inclinometers) monitoring data gave information on the deformation evolution. The phenomena occurred are characterized not only by different types of mechanisms but also by different states, distributions and activity styles (WP / WLI, 1995), as a consequence of an extremely complex geological context. In the area considered there are three main landslides, on which innumerable superficial phenomena develop. One of these is located at north-west of Gimigliano Superiore, one at South and other at East of the town (characterized by major cracks and fissures). Some of these landslides show translational sliding mechanisms and in some situations a rotational component. The multiplicity of landslides classifies the instability as a complex mechanism. Moreover, the results define the landslide of Gimigliano as a deep landslide with a well identified sliding surface around the depth of 50 meters in the central area of the landslide body. The landslide is active and the movements have a moderated speed, therefore the phenomenon is classified as a slow mechanism. Due to the presence of an active landslide body, of considerable size, joined with various degradation phenomena of the slope, this area is considered with a very high landslide risk.

The Xinmo rock avalanche occurred at 5:38 AM on the 24th June, 2017, destroyed the whole village of Xinmo, in Maoxian County, Sichuan Province, China. About 4.3 million m3 of rock detached from the crest of the mountain, gained momentum along a steep hillslope, entrained a large amount of pre-existing deposits, and hit the village at a velocity of 250 km/h. The impact produced a seismic shaking of ML = 2.3 magnitude. The sliding mass dammed the Songping gully with an accumulation body of 13 million m3. The avalanche buried 64 houses; 10 people were killed and 73 were reported missing. Source: Fan, X., Xu, Q., Scaringi, G. et al. Landslides (2017) 14: 2129. https://doi.org/10.1007/s10346-017-0907-7

The Congo DR landslide of August 16, 2017, occurred at the Toro Village on the Western Bank of Lake Albert. Lake Albert is an elongated lake formed within the rift structures of the Western or Albertine branch of the East African Rift Valley System. The rift valley which is filled by Lake Albert is an asymmetric half-graben with the main fault on the western side of the Lake dipping to the east (Chorowicz, 2005). This fault is manifested as a 2200m high scrap which slopes down directly to the lake. The rifted rocks are Precambrian Basement Rocks of the Tanzanian Craton overlain by Neogene to recent volcanic rocks .

The Sierra Leone mudslide of August 14, 2017, took place in the Regent area of Freetown on the steep slopes of Mount Sugar Loaf. Sugar Loaf forms a part of extensive and forested highlands south of the the city. The city of Freetown and its suburbs have grown in recent times to almost encircle this roughly elliptical highland region. Intruding these rocks are isolated basic intrusives of Triassic to Early Jurassic age. The most prominent of this is the Freetown Layered complex which forms the extensive highlands which Freetown surrounds and which Mount Sugar Loaf is a part of. The Freetown layered complex consists of troctolitic gabbro and anorthositic rocks dated 193 Ma. This intrusion formed part of the basic volcanism associated with the initial rifting stage of the opening of the Atlantic Ocean. The hills of the Freetown Layered Complex show major NE-SW and minor NW-SE trending lineaments. These lineaments are most likes fracture zones within the rocks of the Freetown complex. The lineaments clearly control the drainage and the erosion of the hills in the region. One of these structurally controlled NE-SW streams cuts through the Regent area where the mudslide occurred.

Rock-debris Avalanche that occurred on in the Bamenda massif area on the Nigeria-Cameroon Border. The slide occurred on steep hillslopes with a thin veneer of clay-rich soils weathered from Precambrian Basement migmatites, gneisses and granites, forming a complex of mud and rock boulder debris. The slide occurred after an extended period of heavy rainfall in the area. It led to the loss of 3 lives as well as substantial damage to surrounding farmland and pastureland.

In the early morning on May 19, 2010, a large deep-seated landslide occurred at Gírová Mountain, Outer West Carpathians, Czech Republic. The area where this landslide happens is the region of pre-existing deep-seated gravitational deformation. The size of the landslide is approximately 1060 meters long and 200 meters wide. The thickness of the landslide ranges from around 10 meters in the lower part to around 30 meters in the upper area. The entire sliding mass has a volume of roughly 2.8 million cubic meters and the estimated displacement varies from about 75 meters to 253 meters. No-one was injured and no properties were damaged. The precipitation fell from May 15th to 18th (few hours before the initiation of the landslide) is considered as the main factor inducing the landslide. The total amount of the rainfall was 244.6 mm with the maximum daily precipitation was 115.1 mm and the minimum daily precipitation was 12.4 mm. The Gírová landslide is a good case study on inducing factors and process of liquefaction at mountain slopes. This case study also confirms the theory that large active landslide often progresses inside existing unstable regions. This report referred the research in the paper: Ivo Baroň,Tomáš Řehánek, Jiří Vošmik, Vítězslav Musel, Lucie Kondrová (2011) Report on a recent deep-seated landslide at Gírová Mt., Czech Republic, triggered by a heavy rainfall: The Gírová Mt., Outer West Carpathians; Czech Republic. Landslides 8:355–361

A large block slide occurred on the south face of the Cerro La Pera, in the locality of Juan Grijalva (JG), municipality of Ostuacan, northwest Chiapas (Mexico). The JG landslide (1.11 km2 / 50 Mm3) created a dam over 80 m high and 1,170 m wide across the Grijalva River (the second largest river in Mexico), backing up the water and forming a 49 km2 lake. Landslide-generated tsunamis up to 15 m high destroyed the village of JG and killed 16 people. The newly formed lake flooded 21 villages located upstream and around 3,600 people to be evacuated with incalculable economic losses. Further, the probable dam-landslide collapse put at risk the Peñitas dam and the city of Villa Hermosa (Tabasco) located downstream 14 km and 120 km, respectively. It was perhaps the most catastrophic landslide in the history of Mexico. The probable trigger of the landslide was cumulative precipitation of about 67% of the average annual rainfall over the preceding 30 days, and a water-level drawdown at the Grijalva River generated by the release of water from the Peñitas dam. After works carried out by the Comisión Federal de Electricidad to join the river and stabilize the slope, the landslide is motionless.