Rainfall, infiltration, and groundwater flow in a terraced slope of Valtellina (Northern Italy): field data and modelling

The aim of this work was to understand and reproduce the hydrological dynamics of a slope that is terraced by dry retaining walls. This approach will help to assess the influence of temporary groundwater perched tables, which can form at the area of contact between the backfill of the wall and the bedrock, on the wall’s stability. The study area is located in Valtellina (Northern Italy) near the village of Tresenda, which was affected by three debris flows that caused 18 casualties in 1983. In 2002, another event of the same type affected this area, but that event only caused the interruption of a major transport road. Direct observations of one of the three flows in 1983 and the reconstruction of 2002 indicated that the most probable triggering cause was the collapse of a dry retaining wall after its backfill was saturated. After field work was conducted to discover the principal hydrological and hydrogeological characteristics of the slope, numerical modelling was performed to determine under what conditions the soil will saturate, and therefore, when the collapse of a dry retaining wall might occur. First, a study of the interaction between pluviometric events and groundwater behaviour was conducted; then, modelling was performed using finite element analysis software that permits the calculation of groundwater flow both for completely and partially saturated conditions. The model was calibrated and validated using the hydrographs of the groundwater table recorded on site. It can be used as a predictive instrument for rainfall events of a given duration and return period.     

Terrestrial laser scanning survey in support of unstable slopes analysis: the case of Vulcano Island (Italy)

Natural Hazards - The capability to measure at distance dense cloud of 3D point has improved the relevance of geomatic techniques to support risk assessment analysis related to slope instability....     

Geochemistry of the Adamello massif (northern Italy)

The Tertiary Adamello massif, outcropping over an area of more than 550 km² in the southern Alps (northern Italy) is composed mainly of granitoid rocks (granodiorite, tonalite, quartz diorite) with minor amounts of diorite and gabbro. The major and trace element composition of these rocks is comparable to calc-alkaline volcanic rocks of continental margins. The granitoid rocks display spatial and temporal variations in their composition, particularly in Na, P, Sr, La, Nb and Y contents and ⁸⁷Sr/⁸⁶Sr ratios. The variations were probably produced by concurrent contamination/wall-rock assimilation and fractional crystallization of high-alumina basaltic magma.     

On the tectonics of the Ligurian Apennines (northern Italy)

Four nappes have been recognized in the Ligurian Apennines. In the Lavagna Nappe very low-grade metamorphism is combined with very large, originally W-facing isoclinal folds. In the other nappes, no evidence for metamorphism is found and all eutectonic folding was originally E- to NE-facing. Tectonic transport along the major nappe contacts was in an E- to NE-direction. A tectonic model is presented, which explains the generation of the large, originally W-facing folds as a result of originally E-inclined subduction within a young oceanic basin. Young oceanic lithosphere (maximum age approximately 25 Ma) subducted beneath oceanic lithosphere with a maximum age of approximately 40 Ma, under the influence of horizontally oriented compressional forces. Within the tectonic wedge, associated with the subduction, originally W-facing isoclinal folding and metamorphism occurred. Decrease and/or termination of compression resulted in the cessation of the subduction movements, followed by uplift of the region above the subducted plate by means of buoyancy. This uplift formed a slope from which sequences slid in an E- to NE-direction, causing E- to NE-facing folds. Ultimately, detachment and thrusting of gravitational nappes took place, by which process rock sequences of oceanic origin have been externally transported to attain ensialic (continental) domains. The Triassic-Early Oligocene tectonic events recognized in the Ligurian Apennines correlate quite well with the events that preceded the collision phase of the Alps.     

Tectonics of the Dolomites (southern alps,northern Italy)

In post-Variscan times the Dolomites underwent a number of tectonic events, which may be summarized as follows: Permian and Triassic rifting phases broke the area into NS trending basins with different degrees of subsidence. A Middle Triassic transpressive event then deformed the region along a N70°E axis, generating flower structures within the basement. Volcano-tectonic domal uplift and subsequent caldera formation occurred at the same time as the Late Ladinian magmatism. Early Jurassic rifting also controlled the subsidence which increased eastward. This long period of deformation was followed by a pre-Neogene (Late Cretaceous-Palaeogene ?) EW (ENE-WSW) compression which generated a W-vergent belt, possibly equivalent to the folded foreland of the Dinaric chain. A 70 km EW section of the Dolomites indicates shortening of at least 10 km. During the Neogene the Dolomites, as far north as the Insubric Lineament, were the innermost part of a S-vergent thrust belt: the basement of the Dolomites was thrust southwards along the Valsugana Line onto the sedimentary cover of the Venetian Prealps for at least 10 km. This caused a regional uplift of 3–5 km. The Valsugana Line and its backthrusts on the northern side of the central Dolomites generated a 60 km wide pop-up in the form of a synclinorium within which the sedimentary cover adapted itself mainly by flexural-slip often forming triangle zones. The shortening linked to this folding is about 5 km with Neogene thrusts faulting and folding pre-existing thrust-planes. On the north-eastern side of the Dolomites, Neogene deformation is apparently more strictly controlled by the transpressive effects of the Insubric Lineament and shortening of the sedimentary cover may be greater than in the central Dolomites. Minor deformation linked to the Giudicarie belt is present in the western Dolomites. The present structure of the Dolomites is thus the result of a number of tectonic events of different significance and different strike. Only a 3-dimensional restoration can unravel the true structure of the Dolomites.     

Appraise the structural mitigation of landslide risk via numerical modelling: a case study from the northern Apennines (Italy)

The Ca’ Lita landslide is a large and deep-seated mass movement located in the northern Apennines, about 70 km west of Bologna (Northern Italy). It consists of a composite landslide that affects Cretaceous to Eocene flysch rock masses and chaotic complexes. Many of the sectors making up the landslide have resumed activity between 2002 and 2006, threatening some villages and an important road connecting several key industrial facilities located in the upper watershed. This paper presents the management of the emergency, dealing with the investigation campaigns (geological, geomorphological and LiDAR surveys, borehole drillings, seismic surveys), with the monitoring (in situ instrumentation) and with the design and construction of mitigation measures. The whole process, from landslide reactivation to date, has been modelled on a numerical basis with the finite difference code FLAC 2D, to assess the efficiency of the mitigation system and to propose further countermeasure works in different scenarios.     

Landslide triggers along volcanic rock slopes in eastern Sicily (Italy)

A new dataset of landslides, occurred in a tectonically active region, has been analysed in order to understand the causes of the slope instability. The landslides we have dealt with took place along the volcanic rock cliff of S. Caterina and S. Maria La Scala villages (eastern Sicily, Italy), a densely inhabited area located on the eastern margin of Mt. Etna, where some seismogenic faults, locally named Timpe system, slip during moderate local earthquakes and also move with aseismic creep mechanisms. The results show that landslides are triggered by heavy rainfalls, earthquakes and creep fault episodes. Indeed, they occur along discrete fault segments, exhibiting a combination of both brittle failure, indicated by the earthquake occurrence, and aseismic creep events. The analysis of seismicity occurred on the Timpe fault system has shown that the active Acireale fault, in its southernmost segment, is subject to an aseismic sliding, which increases after the stick–slip motion in the nearby faults. Therefore, aseismic creep seems to concur in the predisposition of a rock to fail, since strains can increase the jointing of rock masses leading to a modification in the slope stability. Understanding the factors concurring to the slope instability is a useful tool for future assessments of the landslide hazard in densely settled areas, located on a volcanic edifice, such as Etna that is slowly sliding seawards, and where active faults, seismicity and heavy rains affect the deeply fractured slopes.     

Dating synmagmatic folds: a case study of Schlingen structures in the Strona-Ceneri Zone (Southern Alps, northern Italy)

The Strona-Ceneri Zone (Southern Alps) contains folds with moderately to steeply inclined axial planes and fold axes, and amplitudes of up to several kilometres (so-called 'Schlingen'). These amphibolite facies folds deform the main schistosity of Late Ordovician metagranitoids and are discordantly overlain by unmetamorphic Permian sedimentary rocks. Mutually cross-cutting relationships between these folds and garnet-bearing leucotonalitic dykes indicate that these dykes were emplaced during folding. Sm–Nd systematics and the strongly peraluminous composition of these dykes point to an anatectic origin. Pb step leaching of magmatic garnet from a leucotonalitic dyke yielded a 321.3±2.3  Ma intrusive age. Rb–Sr ages on muscovites from leucotonalitic dykes range from 307 to 298  Ma, interpreted as cooling ages during retrograde amphibolite facies metamorphism. Conventional U–Pb data of zircons from an older granodioritic dyke that pre-dates the Schlingen folds yielded discordant U–Pb ages ranging from 371 to 294  Ma. These ages reflect a more complicated multi-episodic growth history which is consistent with the observed polyphase structural overprint of this dyke. Schlingen folding was accompanied by prograde amphibolite facies metamorphism, during the thermal peak of which the leucotonalitic dyke material was generated by partial melting in a deeper source region from where these S-type magmas intruded the presently exposed level. Because partial melting may occur in a relatively late stage of a clockwise P–T–t path, or even during decompression on the retrograde path, we do not exclude the possibility that Schlingen folding had already started in Early Carboniferous time. Schlingen folds also occur in Penninic and Austroalpine basement units with a very similar pre-Alpine history, indicating that Variscan folding affected large segments of the future Alpine realm.     

Ductile shear zones on carbonates: the calcaires plaquettés of northern Calabria (Italy)

Field, petrographic and quantitative strain analysis have been performed on highly foliated limestones outcropping in northern Calabria and generally attributed to two distinct units (San Donato and Pollino) on the basis of presence/absence of metamorphism. The deformation, however, is comparable in all the studied outcrops indicating that the widely accepted distinction of units in the area should be revised. Deformation is very localized in narrow ductile shear-zones affecting Tertiary conglomerates and Jurassic oncoidal packstones. The former are more strained because of their closeness to siliciclastic beds. The main deformation mechanism was grain boundary sliding with minor intragranular strain and pressure solution. To cite this article: A. Iannace, S. Vitale, C. R. Geoscience 336 (2004).     

Evaporite karst and sinkholes: a synthesis on the case of Camaiore (Italy)

In 1995 a sinkhole suddenly formed at Camaiore (Tuscany, Italy), causing destruction or heavy damages to several houses and resulting in the evacuation of many people. To understand the causes, for the formation and evolution of the collapse, surface and underground geologic features were investigated and reconstructed on the basis of geologic and geognostic surveys. The sinkhole area is underlain by thick alluvial deposits that cover a bedrock consisting of the Calcare cavernoso formation. This formation results from hydration and dissolution of Triassic evaporites and has a characteristic spongy and vacuolate texture. The bedrock contains karst cavities, generally filled by breccia and/or alluvial materials. Thus, the sinkhole disaster could be ascribed to deep collapse of a cave in the bedrock, and might be considered a distant effect of ancient karst phenomena in evaporites.     

Climate control on stacked paleosols in the Pleistocene of the Po Basin (northern Italy)

Paleosols are recurrent features in alluvial successions and provide information about past sedimentary dynamics and climate change. Through sedimentological analysis on six sediment cores, the mud-dominated succession beneath the medieval ‘Two Towers’ of Bologna was investigated down to 100 m depth. A succession of weakly developed paleosols (Inceptisols) was identified. Four paleosols (P1, P2, P3 and PH) were radiocarbon-dated to 40–10 cal ka bp . Organic matter and CaCO₃ determinations indicate low groundwater levels during soil development, which spanned periods < 5 ka. The development and burial of soils, which occurred synchronously in the Bologna region and in other sectors of the Po Plain, are interpreted to reflect climatic and eustatic variations. Climatic oscillations, at the scale of the Bond cycles, controlled soil development and burial during Marine Isotope Stage (MIS) 3 (P1 and P2). Rapid sea-level oscillations probably induced soil development at the MIS 3/2 transition (P3) and favored burial of PH after 10 ka bp . Weakly developed paleosols in alluvial successions can provide clues to millennial-scale climatic and environmental variations. In particular, the paleosol-bearing succession of the Po Plain represents an unprecedent record of environmental changes across the Late Pleistocene (MIS 3 and 2) in the Mediterranean region.     

Active normal faulting along the Mt. Morrone south-western slopes (central Apennines,Italy)

In the present work we analyse one of the active normal faults affecting the central Apennines, i.e. the Mt. Morrone normal fault system. This tectonic structure, which comprises two parallel, NW-SE trending fault segments, is considered as potentially responsible for earthquakes of magnitude ≥ 6.5 and its last activation probably occurred during the second century AD. Structural observations performed along the fault planes have allowed to define the mainly normal kinematics of the tectonic structure, fitting an approximately N 20° trending extensional deformation. Geological and geomorphological investigations performed along the whole Mt. Morrone south-western slopes permitted us to identify the displacement of alluvial fans, attributed to Middle and Late Pleistocene by means of tephro-stratigraphic analyses and geomorphological correlations with dated lacustrine sequences, along the western fault branch. This allowed to evaluate in 0.4 ± 0.07 mm/year the slip rate of this segment. On the other hand, the lack of synchronous landforms and/or deposits that can be correlated across the eastern fault segment prevented the definition of the slip rate related to this fault branch. Nevertheless, basing on a critical review of the available literature dealing with normal fault systems evolution, we hypothesised a total slip rate of the fault system in the range of 0.4 ± 0.07 to 0.8 ± 0.09 mm/year. Moreover, basing on the length at surface of the Mt. Morrone fault system (i.e. 22–23 km) we estimated the maximum expected magnitude of an earthquake that might originate along this tectonic structure in the order of 6.6–6.7.     

Landslides types controlled by tectonics-induced evolution of valley slopes (Northern Apennines,Italy)

This paper investigates the role played by geomorphological and tectonic processes affecting a portion of an active mountain belt in causing the occurrence of different types of landslides developed in flysch bedrock. The adopted multidisciplinary approach (geomorphology, geology and geophysics) allowed to recognize in a portion of the Northern Apennines of Italy different types of landslides that developed in response to slope dynamics, in turn dependent on broader regional-scale tectonic processes. Sedimentary bed attitude, local tectonic discontinuities and lithology only partially influenced the type of landslides, which have been deeply affected by the activity of regional-scale antiform that controlled the hillslope geomorphic evolution in different ways. The growth of this structure and the tilting of its forelimb produced gently dipping slopes that approached the threshold angle that can cause the occurrence of (mainly) translational rockslides. Conversely, high-angle normal faulting parallel to the antiform axis (related to a later stage of activity of the antiform itself) strongly controlled the stream network evolution and caused the watercourses to deeply incise portions of their valleys. This incision produced younger steep valley slopes and caused the development of complex landslides (roto-translational slides-earth/debris flow). The results of the integrated study presented in this paper allowed to distinguish two main types of landslides whose development reflects the events that led to the geomorphological and geological evolution of the area. In this perspective, within the study area, landslides can be regarded and used as indicators of broader-scale recent tectonic processes.     

Geochemistry and isotope geochemistry of the Monfalcone thermal waters (northern Italy): inference on the deep geothermal reservoir

Geochemical investigations were carried out to define the origin of the low- to moderate-temperature thermal waters feeding the Monfalcone springs in northern Italy. Chemical data indicate that waters approach the composition of seawater. Mixing processes with cold low-salinity waters are highlighted. The δ¹⁸O and δD values are in the range ?5.0 to ?6.4 ‰, and ?33 to ?40 ‰, respectively, suggesting the dilution of the saline reservoir by karst-type freshwaters. A surplus of Ca²⁺ and Sr²⁺ ions with respect to a conservative mixing is ascribed to diagenetic reactions of the thermal waters with Cretaceous carbonates at depth. The measured Sr isotopic composition (⁸⁷Sr/⁸⁶Sr ratio) ranges between 0.70803 and 0.70814; after correction for the surplus Sr, a ⁸⁷Sr/⁸⁶Sr ratio indicating Miocene paleo-seawater is obtained. The dissolved gases indicate long-lasting gas–water interactions with a deep-originated gas phase of crustal origin, dominated by CO₂ and marked by a water TDIC isotopic composition in the range ?5.9 to?8.8 and helium signature with 0.08?<?R/Ra?<?0.27, which is a typical range for the crust. A possible scenario for the Monfalcone thermal reservoir consists of Miocene marine paleowaters which infiltrated through the karstic voids formed within the prevalently Cretaceous carbonates during the upper Eocene emersion of the platform, and which were entrapped by the progressive burial by terrigenous sediments.     

Evidence of dislocations on the southern slope of the nebrodi-madonie mountains (northern Sicily, Italy): Their neotectonics implications

The investigated area is located on the southern slope of the NebrodiMadonie Mts. (northern Sicily, Italy). It was studied in order to obtain neotectonic evidence by means of fracture measurements, morphotectonic and hydrographical patterns, aerial photographs and satellite analysis. The results were compared with the well-known geological structures.This area could be considered an outstanding crustal part of Sicily, as here we find alignments of earthquake foci and a deep gradient of gravity anomalies, testifying to an important isostatic imbalance. This analysis confirms the observed structural picture of surface tectonics. Rose diagrams elaborated from fieldwork and aerial lineations show distinctive E—W trends which conform to the directions of the main faults.From a chronological viewpoint faults breaks, aerial photographs and satellite lineations seem to indicate that the E—W trend is the less dislocated and, therefore, the most recent.     

Volume estimate of flow-type landslides along carbonatic and volcanic slopes in Campania (Southern Italy)

Recent studies on flow-type landslides in pyroclastic deposits have been performed to identify potential source areas and the main depositional mechanisms. Interesting methods for mapping landslide susceptibility have also been proposed. Since the potential volume of flow-type landslides is a measure of event magnitude, hence of considerable use in hazard assessment, we propose a method to estimate the potential volume for the morphometric analysis of 213 flow-like landslides occurred in Campania in recent centuries. First, our data show that the height, H, of the detachment and erosion-transport zones (i.e. the difference in height between the top of source area and a point, the first break at the foot of the slope, where the deposition stars to take place and the landslide loses velocity) and the area, A _f, of the same zones are linked by a mathematical function. Secondly, only part of the entire thickness of the pyroclastic material on the slope is involved. To define the potential volumes of the flow-type landslides, we analysed slopes, both in volcanic and carbonatic contexts, considering both channelled and unchannelled flow-type landslides. The most susceptible areas are identified by using a landslide-triggering susceptibility map, and then in each case the height H was estimated. This height is the difference in level between the point on the slope with highest susceptibility and the first break at the foot of the slope. Using the statistical correlation between H and A _f, both calculated for historical landslides, we evaluate the area of a potential landslide on a slope. Finally, potential volumes are calculated by using A _f and a constant thickness of the pyroclastic cover for the whole slope. This method could represent a useful tool to detect the main areas where risk mitigation works are required.     

Geoarchaeological sea-level proxies from a silted up harbour: A case study of the Roman colony of Luni (northern Tyrrhenian Sea, Italy)

The Luni Plain, which faces the northern Tyrrhenian Sea, underwent major landscape changes over the last 3000 years. The coastline shifted south and west, separating the ruins of the ancient Roman colony of Luni (founded in 177 BC) from the sea by means of a new coastal plain. The precise location of the coastline during the main settlement phase as well as during the city's decline has never been established, although partial and qualitative scenarios have been suggested by various authors. According to these authors, an indentation of the coastline west of the city formed a major water basin, along the shores of which traces of pre-Roman settlements exist; near the city, two minor basins were present, suitable for hosting harbour structures. The city of Luni was famed for its harbour (Portus Lunae), from which the marbles quarried in the Apuan Alps, used to build many of the monuments in Rome, were delivered. The traces of its port, however, are scattered and uncertain.Newly available subsurface data are presented, associated with a revision of unpublished archaeological evidence of the ancient city topography. Progress in palaeoenvironmental reconstructions at Luni has been possible thanks to the collection and analysis of ancient and recent cores, supported by radiocarbon dates, as well as the interpretation of archaeological findings suitable as markers for sea-level recognition. The main environmental changes in the area have been refined: since a few centuries before the colony was founded, the Luni plain had been characterized by a complex architecture of swamps and marshes limited by dune ridges and fluvial sand bars. The positions of these landforms were not fixed, but shifted, mainly depending on the spatial relationship between the coastline and the river mouths.Determining the precise position of the Roman coastline is useful to constrain the area in which archaeological surveys should be concentrated in order to identify the harbour location. Moreover, some of these results have been used to infer altitude constraints on the sea-level position in Roman times: preliminary data are shown for constructing a Late Holocene local sea-level curve in the area.     

Spatial variations in the similarity of earthquake populations: The case of the 1997 Colfiorito–Sellano (northern Apennines, Italy) seismic sequence

The spatial properties of events in the 1997 Colfiorito–Sellano seismic sequence (Northern Apennines, Italy) were investigated using coherence, a parameter derived from seismic moment tensors that quantifies the kinematic similarity between focal mechanisms. The 1997 Colfiorito–Sellano seismic sequence predominantly consists of normal faulting earthquakes, with a few strike-slip and reverse faulting episodes. This kinematic heterogeneity is possibly related to the contemporaneous activity of two different sets of faults: NW–SE normal faults and NNE–SSW sub-vertical faults, the latter inherited from the previous Miocene compressional phase. The study used two independently-derived data sets of the same seismic sequence characterized by a different number of events and by different precision of spatial localisation. Their statistical significances, assessed through a reshuffling procedure, reveal that data sets with at least some hundreds of events and good positional precision are required to obtain significant results through coherence analysis. Results from the better quality data set indicate that this seismic sequence is characterized by a rapid decrease in the kinematic similarity between earthquake pairs within 2 km of separation, particularly along directions sub-perpendicular to the normal fault strike. The decrease rate seems to be controlled by the geometric characteristics of the normal faults, given that the mean along-dip distance between fault segments is 2 km. In proximity to pre-existing tectonic lineaments the relative abundance of strike-slip and reverse faults tends to decrease the kinematic similarity between events but does not influence the coherence decrease rate. The presence of mixed focal mechanisms (normal, reverse and strike-slip) in a single seismic phase implies that mixed fault types are not restricted to polyphase tectonic histories: such heterogeneous kinematics during a single phase may be induced by the presence of inherited discontinuities.