The Lago di Varano: Hydrologic Characteristics and Sediment Composition

Abstract. The Lago di Varano is situated on the north side of the Gargano National Park (southeast Italy) and covers a surface area of about 65 km². It communicates with the Adriatic Sea through two artificial canals (Foce Capoiale and Foce Varano) located at the two ends of a long and narrow coastal dune. This work presents preliminary results of four seasonal surveys (1999–2000) carried out to measure chemical and physical parameters of the water column (temperature, salinity, dissolved oxygen and pH) and to analyse a number of biogeochemical characteristics of surface sediments (organic matter, total phosphorus, total nitrogen and total Hg, As, Pb, Cd, Cr, Cu and Ni content). Water analysis indicated poor exchange between the coastal pond and the open sea, limited to autumn and winter. Surface sediments were rich in organic matter, whose distribution was influenced by chemical-physical and hydrodynamic variations in the water column. At the sediment level, the highest values of Cd were found in the central zone of the basin, while the highest Cr values were measured in the central and southeastern areas. With the exception of Cd and Pb, the metal content did not indicate anthropogenic pollution, in particular when compared with the Venice Lagoon and the Central Adriatic Sea.     

Estimates of effective permeability for non-Newtonian fluid flow in randomly heterogeneous porous media

An understanding of the interplay between non-Newtonian effects in porous media flow and field-scale domain heterogeneity is of great importance in several engineering and geological applications. Here we present a simplified approach to the derivation of an effective permeability for flow of a purely viscous power–law fluid with flow behavior index n in a randomly heterogeneous porous domain subject to a uniform pressure gradient. A standard form of the flow law generalizing the Darcy’s law to non-Newtonian fluids is adopted, with the permeability coefficient being the only source of randomness. The natural logarithm of the permeability is considered a spatially homogeneous and correlated Gaussian random field. Under the ergodic hypothesis, an effective permeability is first derived for two limit 1-D flow geometries: flow parallel to permeability variation (serial-type layers), and flow transverse to permeability variation (parallel-type layers). The effective permeability of a 2-D or 3-D isotropic domain is conjectured to be a power average of 1-D results, generalizing results valid for Newtonian fluids under the validity of Darcy’s law; the conjecture is validated comparing our results with previous literature findings. The conjecture is then extended, allowing the exponents of the power averaging to be functions of the flow behavior index. For Newtonian flow, novel expressions for the effective permeability reduce to those derived in the past. The effective permeability is shown to be a function of flow dimensionality, domain heterogeneity, and flow behavior index. The impact of heterogeneity is significant, especially for shear-thinning fluids with a low flow behavior index, which tend to exhibit channeling behavior.     

The Ross orogeny of the transantarctic mountains: a northern Victoria Land perspective

Northern Victoria Land (Antarctica) is made up of three terranes of Cambrian–Ordovician rocks: the Wilson (WT), Bowers (BT) and Robertson Bay terranes (RBT). The WT comprises a low- to high-grade metasedimentary sequence intruded by calc-alkaline plutons with magmatic arc affinity; the BT is composed of low-grade metavolcanic and metasedimentary rocks usually interpreted as an intra-oceanic arc; the RBT is a very low-grade flysch-like sequence. Terrane juxtaposition has traditionally been attributed to accretion during the Cambro-ordovician Ross orogeny. We propose a new model in which the WT, BT and RBT are interpreted as an arc/back-arc/trench system, developed in the context of a SW-dipping subduction zone. The subducting plate carried a continent originally located outboard of the turbidite fan of the RBT. Collision between this continent and the East Antarctic craton caused partial subduction of the intervening back-arc basin and, ultimately, the end of Ross-orogenic subduction. The turbidite fan of the RBT originally sedimented above the trench and on the subducting oceanic plate; due to collision it was thrusted on the continent, that constitutes, at least in part, the present basement of the RBT turbidite. The eastern portions of this continental mass were later dissected by the tensile tectonics related to the opening of the of the Southern Ocean.     

A model for eruptive mechanisms of Mt. Etna from the study of seismicity from 1978 to 1983

The papers deals with the seismic activity occurred on Mt. Etna from 1978 to 1983, and special emphasis is given to the seismicity linked to eruptive phenomena that took place during that period.Location of epicentres and hypocentres of all earthquakes occurred during the considered years and in association with each eruption has shown to be a useful tool to investigate relationships between seismicity and characteristics of various eruptions.A preliminary model is proposed to explain seismo-eruptive mechanisms controlling the uprise of magma and subsequent eruptions of Mt. Etna. The complexity of phenomena observed in the Etnean area could be interpreted as the result of the combined effect of regional stress field and local changes of it due to the volcano structural inhomogeneities. Thus, the earthquakes occurring in the studied area may cause either partial intrusion of magma at various depth, or final opening of surface fractures and subsequent output of lava.     

The transfer of Lyman continuum radiation in chromospheric flares

We study the time evolution of a layer of the middle or lower chromosphere being heated by a stream of energetic particles during a solar flare. The region, which is not in LTE, is allowed to cool by the transfer of Lyman continuum radiation, with collisional as well as radiative processes being considered. The resulting time dependence of the electron density and the effective thickness of the layer are in good agreement with values derived from observations. We assume the supply of energetic particles to be cut off when the central electron density of our model layer reaches the peak value of n _e = 4.4 × 10¹³ cm^–3 derived from observations of an importance 3 flare. Depending on the total hydrogen density assumed, the central electron temperature reaches a value ranging from 8000 to 10000 K. These quantities decrease by 20% during the following minute and at a slower rate thereafter.     

Assessment of rockfall susceptibility by integrating statistical and physically-based approaches

In Val di Fassa (Dolomites, Eastern Italian Alps) rockfalls constitute the most significant gravity-induced natural disaster that threatens both the inhabitants of the valley, who are few, and the thousands of tourists who populate the area in summer and winter.To assess rockfall susceptibility, we developed an integrated statistical and physically-based approach that aimed to predict both the susceptibility to onset and the probability that rockfalls will attain specific reaches. Through field checks and multi-temporal aerial photo-interpretation, we prepared a detailed inventory of both rockfall source areas and associated scree-slope deposits. Using an innovative technique based on GIS tools and a 3D rockfall simulation code, grid cells pertaining to the rockfall source-area polygons were classified as active or inactive, based on the state of activity of the associated scree-slope deposits. The simulation code allows one to link each source grid cell with scree deposit polygons by calculating the trajectory of each simulated launch of blocks. By means of discriminant analysis, we then identified the mix of environmental variables that best identifies grid cells with low or high susceptibility to rockfalls. Among these variables, structural setting, land use, and morphology were the most important factors that led to the initiation of rockfalls.We developed 3D simulation models of the runout distance, intensity and frequency of rockfalls, whose source grid cells corresponded either to the geomorphologically-defined source polygons (geomorphological scenario) or to study area grid cells with slope angle greater than an empirically-defined value of 37° (empirical scenario). For each scenario, we assigned to the source grid cells an either fixed or variable onset susceptibility; the latter was derived from the discriminant model group (active/inactive) membership probabilities.Comparison of these four models indicates that the geomorphological scenario with variable onset susceptibility appears to be the most realistic model. Nevertheless, political and legal issues seem to guide local administrators, who tend to select the more conservative empirically-based scenario as a land-planning tool.     

Conceptually-based shot noise modeling of streamflows at short time interval

A conceptual-stochastic approach to short time runoff data modelling is proposed, according to the aim of reproducing the hydrological aspects of the streamflow process and of preserving as much as possible the dynamics of the process itself. This latter task implies preservation of streamflow characteristics at higher scales of aggregation and, within a conceptual framework, involves compatibility with models proposed for the runoff process at those scales. At a daily time scale the watershed response to the effective rainfall is considered as deriving from the response of three linear reservoirs, respectively representing contributions to streamflows of large deep aquifers, with over-year response lag, of aquifers which run dry by the end of the dry season and of subsurface runoff. The surface runoff component is regarded as an uncorrelated point process. Considering the occurrences of effective rainfall events as generated by an independent Poisson process, the output of the linear system represents a conceptually-based multiple shot noise process. Model identification and parameter estimation are supported by information related to the aggregated runoff process, in agreement to the conceptual framework proposed, and this allows parameter parsimony, efficient estimation and effectiveness of the streamflow reproduction. Good performances emerged from the model application and testing made with reference to some daily runoff series from Italian basins.     

Elliptical multi-sun-synchronous orbits for Mars exploration

The multi-sun-synchronous orbits allow cycles of observation of the same area in which solar illumination repetitively changes according to the value of the orbit elements and returns to the initial condition after a temporal interval multiple of the repetition of observation. This paper generalizes the concept of multi-sun-synchronous orbits, whose classical sun-synchronous orbits represent particular solutions, taking into consideration the elliptical case. The feasibility of using this typology of orbits, referred to as elliptical periodic multi-sun-synchronous orbits, has been investigated for the exploration of Mars and particular solutions have been selected. Such solutions considerably reduce the manoeuvre of velocity variation at the end of the interplanetary transfer with respect to the case of a target circular orbit around Mars. They are based on the use of quasi-critical inclinations in order to minimize the apsidal line motion and thus reduce orbit maintenance costs. Moreover, in the case of high eccentricities, the argument of pericentre may be set in order to obtain, around the apocentre, a condition of quasi-synchronism with the planet (the footprint of the probe on the surface presents a small shift with respect to a fixed point on the Martian surface). The low altitude of pericentre allows observation of the planet at a higher spatial resolution, while the orbit arc around the apocentre may be used to observe Mars with a wide spatial coverage in quasi-stationary conditions. This latter characteristic is useful for analysing atmospheric and meteorological phenomena and it allows for most of the orbital period a link between a rover on the surface of Mars and a probe orbiting around the planet.