Predictive Power Evaluation of a Physically Based Model for Shallow Landslides in the Area of Oltrepò Pavese,Northern Italy

The use of real-time landslide early warning systems is attracting the attention of the scientific community, since it allows to assess “where” and “when” a shallow rainfall-induced landslide might occur by coupling rainfall amounts, hydrological models and slope-stability analysis. The paper deals with the main results of a back analysis, which refers to the application of a physically based stability model [Shallow Landslides Instability Prediction (SLIP)] on regional scale. The analysis concerns the occurrence of some recent rainfall-induced shallow landslides in the municipal territory of Broni, in the area of Oltrepò Pavese (Northern Italy). The study area is a hilly region 2.4 km² wide, where more than 40 % of the territory has slopes steeper than 15° and altitudes are between 90 and 250 m a.s.l. As regards the geologic setting, clayey-silty shallow colluvial deposits, with a maximum thickness of about 3 m, overlap a bedrock made of clayey shales, calcareous flysch and marls. The SLIP model is based on the limit equilibrium method applied to an infinite slope and on the Mohr–Coulomb strength criterion for the soil. By assuming that the main hydro-geotechnical process that leads to failure is the saturation of parts of the soil, the model allows to take into account the condition of partial saturation of the soil. The safety factor (F _S ) of a slope is also function of previous rainfalls. After the implementation of the model at territory scale, the input data have been introduced through a geographic information systems platform. In the current paper we mainly intend to evaluate the performance of SLIP at catchment scale, by comparison to (1) observed landslide events and (2) another well-established physically based model (TRIGRS). Further, we want to assess the suitability of the model as early warning tool. The results produced by the model are analyzed both in terms of safety factor maps, corresponding to some particular rainfall events, and in terms of the time-varying percentage of unstable areas over a 2-year span period. The paper shows the comparison between observed landslide localizations and model predictions. A quantitative comparison between the SLIP model and TRIGRS is presented, only for the most important event that occurred during the analyzed period. Overall, the results of the stability analyses based on observed rainfalls show the capability of the SLIP model to predict, in real-time and on a wide area, the occurrence of the analyzed phenomena.     

Rainfall-induced shallow landslides: a model for the triggering mechanism of some case studies in Northern Italy

The article relates the main findings of a recent investigation aimed at modeling the triggering of shallow landslides. A simplified model for assessing the safety factor of potentially unstable slopes, directly related with rainfall trends, was developed. Based on the geometric characteristics of the slope, the geotechnical properties, and strength parameters of the soil, the model makes it possible to define a safety factor of a slope as a function of time. The model is based on the limit equilibrium method and takes into account the seepage of underground water. The safety factor is, in turn, related to the seasonal rainfall. The model was applied on a local scale to some historical cases which had occurred recently in Northern Italy. The paper shows how the results of the application of the model on a local scale achieve a good agreement between the instability condition and the real date of each considered event.     

Experimental Analysis and Micromechanical Modelling of Dry Granular Flow and Impacts in Laboratory Flume Tests

Summary. The paper presents the results of a numerical analysis, carried out by using the Discrete Element Method (DEM) and aimed at reproducing a series of tests on a small-scale laboratory model of a slope. Particular attention is devoted to the validation of DEM when used for the prediction of the run-out distance and of the impact force on obstacles. The soil used for the small-scale model is a mono-granular medium sand, which revealed to be particularly suitable to simulate flows like debris or rock avalanches. The experimental set-up comprises a flume equipped with a system of differently sized instrumented obstacles. The numerical model of the granular flow has been calibrated on the basis of the displacement measurements, obtained through a photogrammetric technique. Author’s address: Roberto Valentino, Department of Civil, Environmental, Territorial Engineering and Architecture, Università degli Studi di Parma, Parma, Italy     

Two geologic systems providing terrestrial analogues for the exploration of sulfate deposits on Mars: Initial spectral characterization

We present the Messinian evaporite suite (Mediterranean region) and the Solfatara hydrothermal system (Phlegraean Fields volcanic province, Italy), discuss their implications for understanding the origin of sulfates on Mars and show preliminary sets of VNIR laboratory and in situ reflectance spectra of rocks from these geologic systems. The choice was based on a number of evidence relative to Mars: (1) the chemistry of the Martian sulfates, suggesting fluid interactions with possibly alkali-basaltic rocks and/or regolith; (2) close range evidence of sulfates within sedimentary formations on Mars; (3) sulfate spectral signatures associated to large-scale layered patterns interpreted as thick depositional systems on Mars. The Messinian evaporites comprise three units: primary shallow-water sulfates (primary lower gypsum: PLG), shallow- to deep-water mixed sulfates and clastic terrigenous deposits (resedimented lower gypsum: RLG), and shallow-water associations of primary sulfates and clastic fluvio-deltaic deposits (upper evaporites: UE). The onset of the Messinian evaporites records the transition to negative hydrologic budget conditions associated with the Messinian Salinity Crisis, which affected the entire Mediterranean basin and lasted about 640 kyr. The Solfatara is a still evolving hydrothermal system that provides epithermal deposits precipitated from the interaction of fluids and trachybasaltic to phonolitic rocks. Thermal waters include alkali-chloride, alkali-carbonate and alkali-sulfate endmembers.The wide spectrum of sedimentary gypsum facies within the Messinian formation includes some of the depositional environments hitherto identified on Mars and others not found on Mars. The PLG unit includes facies associations correlated over long distances, that could be a possible analog of the stratified rock units exposed from Arabia Terra at least as far as Valles Marineris. The facies cycles within the UE unit can be compared to the sequences of strata observed in craters such as Holden and Eberswalden. The UE unit records paleoenvironmental changes which are ultimately controlled by terrestrial climatic variations. They can be considered as a reliable climatic proxy and may be useful for the reconstruction of climatic events on Mars. The intermediate Messinian RLG unit has not, at present, a well-defined depositional counterpart on Mars, although there are some similarities with the northern lowlands and Vastitas Borealis Formation. The dramatic variation of hydrologic budget conditions at the onset of the Messinian evaporites may provide criteria for the interpretation of similar variations on Mars.The volcanic rocks at the Solfatara bear some similarities with the “alkaline magmatic province” observed at the Gusev crater on Mars, and the assemblages of hydrothermal phases resulting from the Solfatara's parent rocks could be analogues for processes involving Gusev-type rocks.The Messinian sulfates have a prevalent Ca-sulfatic composition and wide textural variability. Preliminary laboratory reflectance spectra of rock samples in the VNIR region reveal the signature of sulfates and mixtures of several Fe-bearing phases. At the Solfatara, in situ reflectance measurements of epithermal minerals close to active fumaroles showed the presence of Fe-bearing sulfates, hematite, Al- and K-sulfates and abundant amorphous fraction. XRD analysis supported this interpretation.The range of depositional facies observed in the Messinian units and the variety of minerals detected in the Solfatara will be useful for the interpretation of close range data of Mars. The spectral characterization at various scales of the Messinian sedimentary facies and the Solfatara hydrothermal minerals will both help in the exploration of Mars from orbit and with close range inspection.     

Oiled birds' bibliography

Mussels collected from hydrocarbon polluted areas of the Lagoon of Venice were transferred to the relatively unpolluted port entrance of Malamocco. Hydrocarbon elimination was quite rapid in the first 10–15 days but then slow and incomplete: 12% of the initial content persisted in the tissues for 8 weeks. Elimination of hydrocarbons was almost independent of water temperature between 7.5–26.0°C but virtually ceased in one lot when the temperature abruptly dropped from about 11°C to 4.5–6.0°C. The biological half-life of hydrocarbons in the mussels was calculated to be a little over $\text{3}\text{1}\text{2}$ days, but this relates only to the initial rapid phase of elimination.     

Alleghanian orogenic-float on the Martic thrust during dextal transpression, central Appalachian Piedmont

During the Late Paleozoic Alleghanian orogeny, the mid-Atlantic Piedmont experienced transpressional deformation dominated by dextral strke-slip shear zones. The dextral displacement on these shear zones greatly influenced the geographic distribution of lithotectonic units. Transpressional deformation is evident in the Piedmont with the cogenetic development of domes and en-echelon antiforms between many of the shear zones. In the core of the Pennsylvania reentrant, major Alleghanian structures include the dextral Pleasant Grove shear zone and Tucquan-Mine Ridge antiform. Recent field mapping coupled with detailed metamorphic and deformation fabric studies have revealed that a major thrust, the Martic thrust, was also active during this time. Shear bands were identified during petrofabric analysis of the hanging wall rocks to the Martic thrust. The direction of displacement on these shear bands was parallel to the orogen, a direction contrary to earlier studies. Metamorphic mineral assemblages and ceased reaction textures, associated with ductile shear fabrics in the hangingwall rocks, are consistent with lower greenshist facies deformation. This low grade metamorphism, which is generally confined to sheared rocks, overprints the regional upper greenshist- to lower amphibolite-facies assemblages. Structural and magnetic modeling of the hangingwall block has revealed a complex geometry. A model of orogen parallel structural escape, or orogenic float, related to late Paleozoic dextral transpression is employed to explain the late reactivation on this important central Appalachian structure.     

Exhumed Himalayan-type syntaxis in the Grenville orogen, northeastern Laurentia

A deep-seated analog of the syntaxis developed in the Tibetan Plateau occurs in the Grenville Orogen of eastern Laurentia. During the final assembly of Rodinia, Amazonia collided with Laurentia and produced a series of large, conjugate, transcurrent, shear systems and pervasive strike-slip deformation that overprinted compressional structures related to the Ottawan Orogeny (the last orogenic phase of what is considered Grenvillian). A northeast-striking dextral system at least 35-km wide developed in the Reading Prong of New York (locally known as the Hudson Highlands), New Jersey, and Pennsylvania. U-Pb SHRIMP zircon geochronology and Ar/Ar thermochronology on the lowest grade cataclasites constrain the age of movement between 1008 and 876 Ma. A 60-km-wide, east-west striking, sinistral shear system developed across the central Adirondack Highlands. This system overprints rocks with granulite-facies metamorphic assemblages containing ca. 1050 Ma metamorphic zircons and is cut by a swarm of 950 Ma leucogranites. The timing, geometric relationships, and shear sense of the Adirondacks and Reading Prong shear systems suggest a conjugate system within a syntaxis with bulk compression directed ENE–WSW. This tectonic scenario invokes a component of strike-parallel deformation during the Ottawan Orogeny and provides a kinematic mechanism for an otherwise enigmatic, synchronous, late (ca. 930 Ma) extensional event including the Carthage–Colton mylonite zone in the northwest Adirondacks and Canada.     

Ultraphyllonite origin for slate,mid-Atlantic Piedmont,USA

Structural, petrographic, and geochemical criteria are applied in combination to determine the petrologic origins of slaty rocks in polydeformed metasedimentary terranes. Multiple lines of evidence suggest that the Peach Bottom slate (PBs), mined over several centuries, is an ultraphyllonite. It occurs within an Alleghanian dextral retraining bend within the Appalachian Piedmont, as a segment of the Pleasant Grove-Huntington Valley shear zone system (>200 km long). The PBs differs markedly from other slates, in that, it contains abundant, micro-scale remnant porphyroclasts of higher-grade minerals. The PBs has major, trace and rare earth element geochemistry and ¹⁴⁷Sm/¹⁴³Nd ratios that are similar to the surrounding pelitic rocks. When compared to average slates, the geochemistry of the PBs exhibits depletion in alkali earth and alkali elements.