Structural integrity of Ellisolandia elongata reefs: A mechanical approach to compare tensile strengths in natural and controlled environments

Geniculate coralline algae are oases of biodiversity, providing nursery areas and shelter for the species that live amongst their fronds. The key to their success in the inter‐tidal is the ability to withstand hydrodynamic forces. Under culturing conditions most of the physical and ecological stressors such as intense hydrodynamic forces and grazing are extremely reduced, thus affecting species mechanical properties and their response to external threats. The aim of the present study was to investigate tensile mechanical properties of clusters of fronds of Ellisolandia elongata from natural (sheltered and exposed reef) and culturing conditions (after 1 month of culturing). The tensile test showed that the first failure stress (σ_I) was not significantly different between the natural and culturing conditions, indicating that the two reefs (sheltered and exposed) were characterized by the same distribution of pre‐existing, inherent structural flaws. Interestingly, the σ_max (maximum stress before rupture) was significantly different between the two conditions, with the culturing condition being more resistant to average load compared to the natural conditions. The maximum stress before rupture (σ_max) showed the influence of the environment in reducing the strength and elasticity of the fronds.     

Generalized Laplace coefficients and Newcomb derivatives

It is shown how the generalized Laplace coefficients can be employed to deduce explicit formulas for ordinary and Newcomb derivatives of the Laplace coefficients.      

A perturbative solution of the transfer equations for the Stokes parameters in a magnetic field

The transfer equations for the Stokes parameters, as derived under the assumption of LTE and in the general case of anomalous Zeeman multiplet, are solved by a perturbative method that reduces the system of four coupled linear differential equations to an iterative series of well known linear differential equations. The perturbation parameter turns out to be of the order of magnitude of the ratio of the Larmor frequency to the line Doppler half-width, so that the method appears to be particularly suitable for small magnetic fields.Some qualitative results on the importance of Faraday rotation and the orders of magnitude of the line profiles of the Stokes parameters are obtained.     

Genesis of zeolites in the Neapolitan Yellow Tuff: geological, volcanological and mineralogical evidence

 The study proposes a model by which a thick succession of volcanic tuffs can be zeolitized by alteration of pyroclastic material in the presence of sufficient eruptive water and at temperatures close to water vapour condensation. In the case of phreatomagmatic products, the model simplifies interpretation of problematic deposits that exhibit pronounced vertical and lateral variation in lithification grade. A major feature of the model is that thick zeolitized tuffs can be formed during emplacement of pyroclastic products, in marked contrast to later alteration in an open hydrologic system. Geological, volcanological and mineralogical data for the Neapolitan Yellow Tuff, a widespread trachytic pyroclastic deposit outcropping around Campi Flegrei (Southern Italy), have been used to infer the physico-chemical conditions that determined mineral genesis. This tuff shows a reduction in lithification grade towards the base, top and with distance from the vent and very variable zeolitization within the lithified portion. We suggest that during initial emplacement the erupted products chilled against the ground, inhibiting zeolite crystallization. During rapid deposition of the thick, wet succession thermal insulation allowed the persistence of elevated temperatures for a time sufficient for enhancement of hydration-dissolution processes in the volcanic glass. The highly reactive alkali-trachytic glass quickly buffered the acid pH of the system, favouring phillipsite crystallization followed by chabazite nucleation. The variable zeolite content reflects fluctuating emplacement conditions (e.g. changes in water content and temperature). Cooling of the upper and relatively thin distal deposits inhibited the zeolitization process, thereby preserving the primary unlithified deposit. Received: 25 May 1999 / Accepted: 28 October 1999     

Chemical characterization of fine particulate matter during peak PM10 episodes in Apulia (South Italy)

Some peak PM10 episodes, occurred during PM monitoring campaigns performed on October 2005 and February and June 2006 in Bari town, have been characterized. Moreover back trajectories of air masses and Principal Component Analyses were applied. Three of the peak PM10 episodes investigated were related to local emissions of primary pollutants during poor atmospheric dispersion conditions. The other two peak PM10 episodes considered are related with long range transport air masses toward Apulia region: in one case the chemical characterization and the back trajectories analysis indicate that high PM10 value detected is due to the Saharan dust advection in the Apulia region; in the other case air masses with different origin give rise to high PM10 value.Moreover PM10 daily mean concentrations, presented in this paper collected from January 2005 to August 2007 and obtained by automatic device in six stations of air quality monitoring networks in Bari territory, do not show a seasonal trend for PM10 concentrations, contrary to the PM10 trend shown in the towns of North Italy. This can be explained mostly considering that our region presents generally meteo-climatic conditions that favour pollutants dispersion.     

Shallow earthquakes in a viscoelastic shear zone with depth-dependent friction and rheology

Summary. Most crustal earthquakes of the world are observed to occur within a seismogenic layer which extends from the Earth's surface to a depth of a few tens of kilometres at most. A model is proposed in which the shear zone along a transcurrent plate margin is represented as a viscoelastic medium with depth-dependent power-law rheology. A frictional resistance linearly increasing with depth is assumed on a vertical transcurrent fault within the shear zone. Such a model is able to reproduce a continuous transition from the brittle behaviour of the upper crust to the ductile behaviour at depth. Assuming that the shear zone is subjected to a constant strain rate from the opposite motions of the two adjacent plates, it is found that there exists a maximum depth H below which tectonic stress can never reach the frictional threshold: this may be identified as the maximum depth of earthquake nucleation. The value of H is consistent with observations for plausible values of the model parameters. The stress evolution in the shear zone is calculated in the linear approximation of the constitutive equation. A change in rigidity with depth, which is also introduced in the model, may reproduce the high vertical gradient of shear stress, which has been measured across the San Andreas fault, and the fact that most earthquakes are nucleated at some depth in the seismogenic layer. A crack which drops the ambient stress to the dynamic frictional level is then introduced in the model. To this aim, a crack solution is employed without a stress singularity at its edges, which is compatible with a frictional stress threshold criterion for fracture. A constraint on the vertical friction gradient is obtained if such cracks are assumed to be entirely confined within the seismogenic layer.     

Synergy of multiple geophysical approaches to unravel explosive eruption conduit and source dynamics - A case study from Stromboli

An effective approach to understanding the dynamics of explosive volcanic eruptions and the conduit systems that drive them is through synergy of multiple data sets. Three data sets that lend themselves to ease of integration are seismic, infrasonic and thermal. Although approaches involving these data have been used to record volcanological phenomena since 1862, 1955 and 1965, respectively, their integrated use has only developed since 1999. When combined, these three data sets allow constraint of shallow system geometry and the dynamics of the explosive events that occur within that system. Using Stromboli volcano (Italy) as a case study, we review the complete range of geochemical and geophysical studies that can be applied. In doing so, we aim to show how integration of these diverse studies allows insights into a plumbing system and the dynamics of the eruptive activity that the system feeds. When combined at Stromboli, these data provide constraint of multiple system parameters including chamber depths, gas and magma fluxes, shallow system magma residence times, explosion source depths, and the rise/ejection velocities of ascending gas slugs and ejecta. In turn, these results allow various conduit and eruption dynamic models to be applied and tested.The persistent and repeated mildly explosive events that characterize Stromboli have been modeled in terms of the coalescence of gas within the magma to form large gas slugs that ascend the remaining portion of the conduit to burst at the free surface. Our integrated seismic, infrasonic and thermal data sets indicate that gas coalescence occurs at a depth of ∼260 m, with a typical event frequency of ∼9/h. Infrasonic and thermal data show the explosion source to be located 20-220 m below the vent. Thermal data give emission velocities for the ejected fragments of 8-20 m/s, which converts to gas jet velocities of 23-39 m/s. Tracking these parameters in space and time shows that, although eruptions at Stromboli can be grouped into two characteristic types (simple and complex-each of which characterizes a particular crater, NE and SW, respectively), events within each type show significant short-term variability. The system does, however, appear robust, maintaining its characteristic strombolian eruption style after significant effusive phases and more energetic explosive events.