Approaches for defining thresholds and return periods for rainfall‐triggered shallow landslides

Probabilistic thresholds for triggering shallow landslides by rainfall are developed using two approaches: a logistic regression model and Iverson's physically based model. Both approaches are applied to a 180 km² area in northern Italy. For the physically based model a Monte Carlo approach is used to obtain probabilities of slope failure associated with differing combinations of rainfall intensity and duration as well as differing topographic settings. For the logistic regression model hourly and daily rainfall data and split‐sample testing are used to explore the effect of antecedent rainfall on triggering thresholds. It is demonstrated that both the statistical and physically based models provide stochastic thresholds that express the probability of landslide triggering. The resulting thresholds are comparable, even though the two approaches are conceptually different. The physically based model also provides an estimate of the percentage of potentially unstable areas in which failure can be triggered with a certain probability. The return period of rainfall responsible for landslide triggering is studied by using a Gumbel scaling model of rainfall intensity–duration–frequency curves. It is demonstrated that antecedent rainfall must be taken into account in landslide forecasting, and a method is proposed to correct the rainfall return period by filtering the rainfall maxima with a fixed threshold of antecedent rainfall. This correction produces an increase of the return periods, especially for rainstorms of short duration. Copyright © 2009 John Wiley & Sons, Ltd.     

A statistical investigation of polar auroras

Summary The magnetosphere depends on the astronomical orientation of the geomagnetic field with respect to the solar wind. The statistical distribution of polar auroras must therefore depend on the orientation of the geomagnetic field with respect to the ecliptic plane. We have investigated this peculiar feature of auroras that we call auroral astronomical geometry. We give here some preliminary results concerning a limited set of pre-IGY auroras. The criteria that we have chosen to prepare the auroral collection are also briefly summarized. The results conform to the hypothesis of the auroral origin from the magnetospheric neutral sheet. Auroral particles are found to impinge over the earth with low angles with respect to the ecliptic plane (40°). Only in a 4-hours interval around midnight they are found to impinge with angles up to 70°. Definite evidence of these facts requires further investigation with a larger amount of data. — We have also prepared a complex code for recording the morphological features of each aurora, namely: standard information, movement. intensity, color, sunlight illumination, period of pulsation, location in the sky among stars and planets, time evolution, duration and general features of the auroral display. It is well known in fact that the auroral morphology affects auroral heights and latitudes, etc.; presumably it should also affect its astronomical geometry, which we will investigate later.Presented at the Inter-Union Symposium on Solar-Terrestrial Physics — Belgrade 1966.     

The evaluation of volcanic risk in the Vesuvian area

Volcanic Risk has been defined as the product: R = Value × Vulnerability × Hazard, where value is the total amount of lives or properties at risk for a volcani eruption, the vulnerability is the percentage of value at risk for a given volcanic event, and the hazard is the probability that a given area may be affected by a certain volcanic phenomenon.We used this definition to evaluate the Risk of loss of human lives for volcanic eruptions of Vesuvius. Value has been determined based on the total number of inhabitants living in areas that could be affected by an eruption. Vulnerability is based on the relative probability of deaths as a result of different volcanic phenomena (tephra fall, pyroclastic flows, etc.). Hazard is evaluated based on the absolute probability of a given phenomenon in a certain area. This last parameter is the most difficult to evaluate.We subdivided the activity of Vesuvius, that produces risk of loss of human lives, into three classes of eruptions, based on the Volcanic Explosivity Index. We assume that the events of each class are distributed according to a poissonian distribution (this is demonstrated for VEI = 3, and inferred for the other classes), so that we can evaluate the absolute probability of an eruption for each class within a given time span. We use a time window of 10 years and evaluate the probabilities of occurrence of at least one eruption for VEI = 3, 4, 5; the probability is respectively: P₃ = 0.09896, P₄ = 0.01748, P₅ = 0.00298We have made a hazard evaluation for the entire Vesuvian area as well as an evaluation of Volcanic Risk.The obtained map shows that the areas with higher risk are on the southern side of Vesuvius, in the coastal region where each town is characterized by an average Risk of 1000 inhabitants/10 years. The risk regularly decreases with increasing distance from the volcano. The risk is mostly due to the events with VEI = 3 and 4, as the most destructive effects of VEI = 5 are counterbalanced by the lower probability of such events.The map of volcanic risk is not intended to predict the loss of human lives of an eruption, but to give a methodology that permits to identify those areas where it is necessary to operate in order to reduce the risk of an eruption before it occurs.     

Volcanic hazard assessment at the restless Campi Flegrei caldera

Eruption forecasting and hazard assessments at the restless Campi Flegrei caldera, within the Neapolitan volcanic area, have been performed using stratigraphical, volcanological, structural and petrological data.On the basis of the reconstructed variation of eruption magnitude through time, we hypothesize that the most probable maximum expected event is a medium-magnitude explosive eruption, fed by trachytic magma. Such an eruption could likely occur in the north-eastern sector of the caldera floor that is under a tensile stress regime, when the ongoing deformation will generate mechanical failure of the rocks. A vent could open also in the western sector, at the intersection of two fault systems contemporaneously activated, as happened in the last eruption at Monte Nuovo. The eruption could likely be preceded by precursors apparent to the population, such as ground deformation, seismicity and increase in gas emissions. It will probably alternate between magmatic and phreatomagmatic phases with the generation of tephra fallout, and dilute and turbulent pyroclastic currents. During and/or after the eruption, the re-mobilization of ash by likely heavy rains, could probably generate mud flows.In order to perform a zoning of the territory in relation to the expected volcanic hazards, we have constructed a comprehensive hazard map. On this map are delimited (I) areas of variable probability of opening of a new vent, (II) areas which could be affected by variable load of fallout deposits, and (III) areas over which pyroclastic currents could flow. The areas in which a vent could likely open have been defined on the basis of the dynamics of the ongoing deformation of the caldera floor. To construct the fallout hazard map we have used the frequency of deposition of fallout beds thicker than 10 cm, the frequency of load on the ground by tephra fallout and the direction of dispersal axes of the deposits of the last 5 ka, and the limit load of collapse for the variable types of roof construction. The pyroclastic-current hazard map is based on the areal distribution and frequency of pyroclastic-current deposits of the last 5 ka.Editorial Responsibility: T. Druitt     

Rare-earth elements in Oligo-Miocenic pelitic sediments from Lagonegro Basin,southern Apennines,Italy: implications for provenance and source area weathering

The Lagonegro Units are a part of the southern Apennines orogenic wedge. The age of the Lagonegro successions ranges from lower–middle Triassic to Oligo-Miocene. During late Cretaceous and Oligocene the deposition of calcareous-clastic sediments occurred interbedded with shales (Flysch Rosso Fm). During Oligocene and early Miocene, in the Mediterranean area, an important variation of the tectonic regime occurred, and siliciclastic sediments of the Numidian Basin unconformably lay on the Meso-Cenozoic units of the Lagonegro Basin. In the Lucanian Apennine, the Aquitanian–Langhian Numidian Flysch Fm overlies the Flysch rosso Fm. The shales of the Flysch rosso Fm have a peculiar geochemical fingerprint relative to typical shales of post-Archean age. The abundance of Ni and Cr is significantly higher and the HREE chondrite-normalized patterns are steep with a (Gd/Yb)_ch>2. A supply of material from the African Archean terranes could be the cause. The palaeo-weathering indices record changes at the source, reflecting variations in the tectonic regime. The oldest samples are derived from an environment in which steady-state weathering conditions prevailed, whereas the youngest samples are related to non-steady-state weathering conditions. This difference could record deformational events that affected the Mediterranean area during the Oligocene and early Miocene. The sample at the top of the studied log has very high silica content and an abundant coarse grain-sized fraction. This suggests that this sample belongs to the Numidian Flysch Fm. The geochemical proxies of this sample are different from those associated with samples from the Flysch rosso Fm, indicating that the source-area of the Numidian Flysch Fm did not include the Archean terranes.     

The use of a non-lethal tool for evaluating toxicological hazard of organochlorine contaminants in Mediterranean cetaceans: new data 10 years after the first paper published in MPB

In the Mediterranean Sea, top predators, and particularly cetacean odontocetes, accumulate high concentrations of organochlorine contaminants and toxic metals, incurring high toxicological risk. In this paper we investigate the use of the skin biopsies as a non-lethal tool for evaluating toxicological hazard of organochlorines in Mediterranean cetaceans, presenting new data 10 years after the paper published by Fossi and co-workers [Mar. Poll. Bull. 24 (9) (1992) 459] in which this new methodology was first presented. Some organochlorine compounds, now with worldwide distribution, are known as endocrine disrupting chemicals (EDCs). Here the unexplored hypothesis that Mediterranean cetaceans are potentially at risk due to organochlorines with endocrine disrupting capacity is investigated. High concentrations of DDT metabolites and PCB congeners (known as EDCs) were found in the different Mediterranean species (Stenella coeruleoalba, Delphinus delphis, Tursiops truncatus and Balaenoptera physalus). In this paper we also propose benzo(a)pyrene monooxygenase (BPMO) activity in marine mammal skin biopsies (non-lethal biomarker) as a potential indicator of exposure to organochlorines, with special reference to the compounds with endocrine disrupting capacity. A statistically significant correlation was found between BPMO activity and organochlorine levels (DDTs, pp(')DDT, op(')DDT, PCBs and PCB99) in skin biopsies of males of B. physalus. Moreover a statistical correlation was also found between BPMO activity and DDT levels in skin biopsies of the endangered Mediterranean population of D. delphis. These results suggest that BPMO induction may be an early sign of exposure to organochlorine EDCs and can be used for periodic monitoring of Mediterranean marine mammal toxicological status.     

Geochemical evidence for mixing of magmatic fluids with seawater,Nisyros hydrothermal system,Greece

The chemical and isotopic compositions (δD_H2O, δ¹⁸O_H2O, δ¹⁸O_CO2, δ¹³C_CO2, δ³⁴S, and He/N₂ and He/Ar ratios) of fumarolic gases from Nisyros, Greece, indicate that both arc-type magmatic water and local seawater feed the hydrothermal system. Isotopic composition of the deep fluid is estimated to be +4.9±0.5‰ for δ¹⁸O and ?11±5‰ for δD corresponding to a magmatic water fraction of 0.7. Interpretation of the stable water isotopes was based on liquid–vapor separation conditions obtained through gas geothermometry. The H₂–Ar, H₂–N₂, and H₂–H₂O geothermometers suggest reservoir temperatures of 345±15 °C, in agreement with temperatures measured in deep geothermal wells, whereas a vapor/liquid separation temperature of 260±30 °C is indicated by gas equilibria in the H₂O–H₂–CO₂–CO–CH₄ system. The largest magmatic inputs seem to occur below the Stephanos–Polybotes Micros crater, whereas the marginal fumarolic areas of Phlegeton–Polybotes Megalos craters receive a smaller contribution of magmatic gases.     

On the application of SAR interferometry to geomorphological studies: estimation of landform attributes and mass movements

This paper presents two examples of application of Synthetic Aperture Radar (SAR) interferometry (InSAR) to typical geomorphological problems. The principles of InSAR are introduced, taking care to clarify the limits and the potential of this technique for geomorphological studies. The application of InSAR to the quantification of landform attributes such as the slope and to the estimation of landform variations is investigated. Two case studies are presented. A first case study focuses on the problem of measuring landform attributes by interferometric SAR data. The interferometric result is compared with the corresponding one obtained by a Digital Elevation Model (DEM). In the second case study, the use of InSAR for the estimation of landform variations caused by a landslide is detailed.