Geological, geomechanical and geostatistical assessment of rockfall hazard in San Quirico Village (Abruzzo, Italy)

This paper describes the results of a rockfall hazard assessment for the village of San Quirico (Abruzzo region, Italy) based on an engineering-geological model. After the collection of geological, geomechanical, and geomorphological data, the rockfall hazard assessment was performed based on two separate approaches: i) simulation of detachment of rock blocks and their downhill movement using a GIS; and ii) application of geostatistical techniques to the analysis of georeferenced observations of previously fallen blocks, in order to assess the probability of arrival of blocks due to potential future collapses. The results show that the trajectographic analysis is significantly influenced by the input parameters, with particular reference to the coefficients of restitution values. In order to solve this problem, the model was calibrated based on repeated field observations. The geostatistical approach is useful because it gives the best estimation of point-source phenomena such as rockfalls; however, the sensitivity of results to basic assumptions, e.g. assessment of variograms and choice of a threshold value, may be problematic. Consequently, interpolations derived from different variograms have been used and compared among them; hence, those showing the lowest errors were adopted. The data sets which were statistically analysed are relevant to both kinetic energy and surveyed rock blocks in the accumulation area. The obtained maps highlight areas susceptible to rock block arrivals, and show that the area accommodating the new settlement of S. Quirico Village has the highest level of hazard according to both probabilistic and deterministic methods. (C) 2010 Elsevier B.V. All rights reserved

Il vulcanismo monogenico medio-pleistocenico della conca di Carsoli (L’Aquila).

The volcanic field is comprised of several Upper Pleistocene small tuff cones, tuff rings and maars (531 ka), aligned along a NNW-SSE normal fault of regional meaning. Most of the deposits are directly related to vent structures and preserve signs of primary proximal origin consisting of high-energy structures, welded lapilli and ballistic impacts. Characteristic sequences of vent coring eterolithic breccias, dry lapilli-ash surges of high-temperature and wet surges of ash-lapilli tuff are exposed and found in well coring. Juvenile fragments consist of plastically moulded lapilli, essentially composed of diopside, phlogopite, leucite, K-feldspar, apatite and immersed in a turbid micro-cryptocrystalline matrix of Ca-carbonate. Lapilli shape indicates that they agglutinated and quenched when still hot plastic. Silicate glass shards are present and have typical cuspate wedges produced by bubbles expansion and disruption during magmatic activity sustained by juvenile gases. A late phreato-strombolian phase builted several tuff-rings and cones. At Oricola - Carsoli - Rocca di Botte - Camerata Nuova volcanic field, juvenile fragments and tuffs range from phonolitic-foidite to foiditic-carbonatitic to carbonatite s.s. The latter forms small pyroclastic flows and surge deposits. Geological context, age, mineralogy and petrology are germane with the near Grotta del Cervo occurrence and are consistent with the carbonatitic-kamafugitic suite of Italy. This new carbonatitic outcrop, that joins the increasing number of Italian carbonatites, puts Italy in a relevant place for what concerns carbon-rich mantle magmatism occurrences. Actually, the six extrusive carbonatites and the intrusive one so far reported, represent one of the largest concentrations of such a kind of rocks all over the world

U/Th dating of a tufa deposit from the Carsoli intramontane basin (Abruzzo, Italy)

A few km far from the confluence of the Fioi valley into the Carsoli basin, some hundreds m2 wide and ca. 1.5 m thick carbonatic deposit is present, embedded within late Middle Pleistocene alluvial gravel. The deposit formation might be related to sub-aerial deposition of CaCO3 (tufa) from emerging groundwater. A U/Th dating to 46 ± 6 ka BP constrains the deposit within the MIS 3, corresponding to a phase of warming between the MIS 4 and 2

Evoluzione geomorfologica quaternaria della conca intermontana di Carsoli (Aq)

In the present work the results of a geological and geomorphological study are presented. The study has been carried out in the Carsoli intermontane basin (AQ), a wide depression of tectonic origin, located between Abruzzo and Lazio regions, at the boundary of two different palaeogeographic domains, separated by the “Olevano-Antrodoco” tectonic line. The Carsoli basin is filled with a continental sedimentary succession of considerable thickness and extent, which has been classified into several lithostratigraphic units, mainly on the basis of their lithological, morphological and geochronological characteristics. The oldest continental sediments outcropping within the study area are of lacustrine origin (Bosco di Oricola silts, clays and sands). These sediments, whose deposition has probably occurred in the Lower – Middle Pleistocene, are characterized by a maximum thickness of about 200 m. They are widespread in the north-western and central parts of the basin (Bosco di Oricola) and are locally present on the eastern edge of the basin. The lacustrine deposits are cut across by an ancient sub-horizontal erosion surface, and at present, only some remnants remain. The lacustrine sediments are covered, on the north-eastern edge of the basin, by coarse fluvial sediments suspended on the present plain, originally deposited by the paleo-Turano River (Madonna delle Grazie gravels). In the central-western and southern part of the study area, a significant sequence of local volcanic deposits, dated around 530 – 540 kyears BP, outcrops. The volcanic sequence abruptly begins from an articulated erosive surface shaped in lacustrine deposits and Meso-Cenozoic carbonatic bedrock. Three main pyroclastic units are distinguished in the following members: 1) Oricola scalo opening–vent breccias, 2) Oricola Scalo grey tuffs, 3) S. Giovanni red tuffs. Only the last two units widely outcrops in the study area. The Oricola Scalo opening-vent breccias are relative to the early opening phase of the conduit. They consist of a massive structure connected to the depositional mechanisms of airfall and/or debris flow, separated by tuff layers related to base surge phenomena. The Oricola Scalo grey tuffs unit mainly consists of grey ash-lapilli tuffs with surge cross-laminations, and grey lapilli tuffs with a massive structure of pyroclastic flow. The overlying S. Giovanni red tuffs are characterized, instead, by a thickness and distribution greater than that of underlying grey tuffs. The unit is mainly composed of red lapilli tuffs, with dune structures or a parallel lamination of surge and airfall. After the lacustrine sedimentation and the volcanic episodes, the examined area underwent intense fluvial dynamics. This led to the sedimentation, in the central-southern and eastern part of the basin, of a sequence of alluvial deposits belonging to different depositional events. The morpho-litho-stratigraphic analysis of these fluvial deposits, in addition with radiometric ages, allowed for their classification into four units (Prati gravels, sands and silts, Fioio Stream conglomerates, Immagine gravels, sands and silts, Turano River gravels, sands and silts) progressively embedded into each other and ranging in age between the late Middle Pleistocene and the Present. Entrenched in the late Middle Pleistocene alluvial unit, in the southern sector of the basin (Fonte Bosco), a few hundred meters long and 1.5 meters thick calcareous tufa layer, dated by U-series method at 46,000 ± 6,000 years BP outcrops. With regard to the most recent depositional phases, great relevance has to be ascribed to the stratigraphic study carried out on the Fosso Luisa fan (Camerata Nuova) and the radiometric dating of colluvial horizon, there present. This dating, providing a calibrated 14C age of 3,550-3,400 years BP, has allowed for a temporal definition of some sedimentary and erosive events that marked the upper part of the fan during the final part of Holocene

Palaeogeographic reconstruction of northern Tyrrhenian coast using archaeological and geomorphological markers at Pianosa island(Italy)

This paper provides new data and interpretations on the relative sea level change occurred at Pianosa island (Italy) since the last w125 ka, where the recent relative sea level changes have not yet been adequately constrained, based on geomorphological and archaeological research of tectonic movements. The MIS 5.5 deposits are characterized by a 2 m thick sandstone, cropping out at a maximum altitude of 4 m a.s.l. containing Strombus bubonius, and are associated with an abrasion platforms carved by lith- odome holes. These deposits, considered one of the best long term sea level markers, establish that Pianosa was a stable area since 125 ka. Archaeological remains provide evidence of sea level change for the last w8 ka. Particularly useful are some fishtanks and a quarry cut around 2 ka BP (Roman age). The measurements, compared with predicted sea level curves, have established that Pianosa has remained stable during the last millennia. Based on this assumption, palaeomorphology variations since Palae- olithic age for this portion of the Tuscan Archipelago are reconstructed