In‐Situ Sonication for Enhanced Recovery of Aquifer Microbial Communities

Sampling methods for characterization of microbial communities in aquifers should target both suspended and attached microorganisms (biofilms). We investigated the effectiveness and reproducibility of low‐frequency (200 Hz) sonication pulses on improving extraction efficiency and quality of microorganisms from a petroleum‐contaminated aquifer in Studen (Switzerland). Sonication pulses at different power levels (0.65, 0.9, and 1.1 kW) were applied to three different groundwater monitoring wells. Groundwater samples extracted after each pulse were compared with background groundwater samples for cell and adenosine tri‐phosphate concentration. Turbidity values were obtained to assess the release of sediment fines and associated microorganisms. The bacterial community in extracted groundwater samples was analyzed by terminal‐restriction‐fragment‐length polymorphism and compared with communities obtained from background groundwater samples and from sediment cores. Sonication enhanced the extraction efficiency up to 13‐fold, with most of the biomass being associated with the sediment fines extracted with groundwater. Consecutive pulses at constant power were decreasingly effective, while pulses with higher power yielded the best results both in terms of extraction efficiency and quality. Our results indicate that low‐frequency sonication may be a viable and cost‐effective tool to improve the extraction of microorganisms from aquifers, taking advantage of existing groundwater monitoring wells.     

Glacial and post-glacial sedimentary processes in the Irish Rockall Trough from an integrated acoustic analysis of near-seabed sediments

Near-seabed (<50 m) sediments were studied throughout the Irish sector of the Rockall Trough (ca. 123,000 km²) based on a combined analysis of shallow seismic (3.5 kHz) and multibeam swath data acquired by the Irish National Seabed Survey and reprocessed here at higher resolution. The detailed identification of seven acoustic facies served to classify the Rockall Trough into six main sedimentary provinces, incorporating the well-known Feni Drift, Donegal-Barra Fan and Rockall Bank mass flow. In the northern part of the study area, extensive mass transport deposits from both flanks of the trough are the dominant depositional features. Debris flow deposits formed by ice streaming of the British-Irish ice sheet characterise most of the Donegal-Barra Fan, whereas turbidite deposition occurs towards the toe of the fan. On the western margin of the trough, the post-glacial Rockall Bank mass flow deposit displays a rough topography with no acoustic penetration. Several failure scarps are visible on the flank of the bank where the mass flow originated, and pass downslope into large sediment lobes and smaller debris flow deposits. Smaller-scale mass transport deposits were also discovered close to some canyons indenting the eastern slope. High seismic penetration characterises the Feni contourite drift deposit, and precise mapping of its geographical extent shows that it is considerably wider than previously reported. The sediment waves that drape this drift are interpreted as predominantly relict features, and their varied geometry suggests a complex oceanographic regime. In the deeper part of the trough, the data reveal novel evidence of the widespread occurrence (about 12,000 km²) of distinct seismic and backscatter signatures indicating the possible presence of fluid escape structures within fine-grained sediments of mixed contouritic, hemipelagic and turbiditic origin. Sediment overloading and increased pore pressure resulting from extensive mass wasting to the north of the area is a likely cause of dewatering-rooted fluid migration towards the seabed, but further investigations are required to confirm the nature and origin of such fluids in the Rockall Trough.     

A new method for the determination of the specific kinetic energy (SKE) released to pyroclastic particles at magmatic fragmentation: theory and first experimental results

Brittle magmatic fragmentation plays a crucial role in explosive eruptions. It represents the starting point of hazardous explosive events that can affect large areas surrounding erupting volcanoes. Knowing the initial energy released during this fragmentation process is fundamental for the understanding of the subsequent dynamics of the eruptive gas-particle mixture and consequently for the forecasting of the erupting column’s behavior. The specific kinetic energy (SKE) of the particles quantifies the initial velocity shortly after the fragmentation and is therefore a necessary variable to model the gas-particle conduit flow and eruptive column regime. In this paper, we present a new method for its determination based on fragmentation experiments and identification of the timings of energy release. The results obtained on compositions representative for basaltic and phonolitic melts show a direct dependence on magma material properties: poorly vesiculated basaltic melts from Stromboli show the highest SKE values ranging from 7.3 to 11.8 kJ/kg, while experiments with highly vesiculated samples from Stromboli and Vesuvius result in lower SKE values (3.1 to 3.8 kJ/kg). The described methodology presents a useful tool for quantitative estimation of the kinetic energy release of magmatic fragmentation processes, which can contribute to the improvement of hazard assessment.     

Paleomagnetic dating of the most recent silicic eruptive activity at Pantelleria (Strait of Sicily)

We report on the paleomagnetism of ten sites in the products of the most recent silicic eruptive cycle of Pantelleria, Strait of Sicily. Previously radiometrically dated at 5–10 ka, our comparison with proxies for geomagnetic field directions allows us to narrow considerably the time window during which these eruptions occurred. The strongly peralkaline composition causes the magmas to have low viscosities, locally resulting in strong agglutination of proximal fall deposits. This allows successful extraction of paleomagnetic directions from the explosive phases of eruptions. One of our sites was located in the Serra della Fastuca fall deposit, produced by the first explosive event of the eruptive cycle. The other nine sites were located in the most recent explosive (pumice fall and agglutinate from Cuddia del Gallo and Cuddia Randazzo) and effusive (Khaggiar lava) products. The (very similar) paleomagnetic directions gathered from eight internally consistent sites were compared to reference geomagnetic field directions of the last 5–10 ka. Directions from Cuddia del Gallo agglutinate and Khaggiar flows translate into 5.9- to 6.2-ka ages, whereas the Fastuca pumices yield a slightly older age of 6.2–6.8 ka. Hence, the most recent silicic eruptive cycle lasted at most a millennium and as little as a few centuries around 6.0 ka. Paleomagnetically inferred ages are in good agreement with published (and calibrated by us) ¹⁴C dates from paleosols/charcoals sampled below the studied volcanic units, whereas K/Ar data are more scattered and yield ∼30% older ages. Our data show that the time elapsed since the most recent silicic eruptions at Pantelleria is comparable to the quiescence period separating the two latest volcanic cycles.     

Hollow bridge-pier properties for response spectrum analysis

The present paper proposes equivalent stiffness and energy dissipation properties of reinforced concrete hollow bridge piers to be used in the context of response spectrum performance based assessment and design. The work is carried out by performing parametric numerical analysis using a 2D fibre model calibrated against experimental results and by varying the longitudinal steel reinforcement ratio, height over width ratio, normalised axial force, level of confinement and concrete class of a rectangular hollow section reinforced with Tempcore B500C steel. The results of the analysis are given in the form of charts and closed form expressions for the yield curvature and moment, ultimate ductility, post yielding stiffness ratio and energy dissipated of the section, and are translated to the member level through the plastic hinge length approach. Likewise, the parameters of a Takeda model derived from the parametric analysis are given for use in nonlinear time history analysis.     

Understanding the statistical properties of the percent model affinity index can improve biomonitoring related decision making

The percent model affinity (PMA) index is used to measure the similarity of two probability profiles representing, for example, an ideal profile (i.e. reference condition) and a monitored profile (i.e. possibly impacted condition). The goal of this work is to study the effects of sample size, evenness, true value of the index and number of classes on the statistical properties of the estimator of the PMA index. We derive and extend previous formulas of the expectation and variance of the estimator for estimated monitored profile and fixed reference profile. Using the obtained extension, we find that the estimator is asymptotically unbiased, converging faster when the profiles differ. When both profiles are estimated, we calculate the expectation using transformation rules for expectation and in addition derive the formula for the estimator’s variance. Since the computation of the probabilities in the variance formula is slow, we study the behavior of the variance with simulation experiments and assess whether it could be approximated with the variance for the fixed reference profile. Finally, we provide a set of recommendations for the users of the PMA index to avoid the most common caveats of the index.     

ESEEM of industrial quartz powders: insights into crystal chemistry of Al defects

A set of raw industrial materials, that is, pure quartz and quartz-rich mixtures, were investigated through electron paramagnetic resonance and electron spin echo-envelope modulation spectroscopies, with the aim of evaluating the effective role played by defect centres and of assessing whether they can be used to monitor changes in the physical properties of quartz powders with reference to their health effects. The obtained results point to two interactions of the Al defect centres with H⁺, hosted in sites within the channels parallel and perpendicular to the c axis of quartz, respectively. These two Al/H⁺ (h_Al) centres exhibit a weak chemical bond, and their relative amounts appear to be modified/controlled by the thermo-mechanical processes underwent by powders. Indeed, a mechanically promoted inter-conversion between the two kinds of site is suggested. As a consequence, the h_Al centres are effective in monitoring even modest activations of powders, through thermal or mechanical processes, and they are also supposed to play a specific, relevant role in quartz reactivity during the considered industrial processes.     

Rockfall risk assessment to persons travelling in vehicles along a road: the case study of the Amalfi coastal road (southern Italy)

The paper deals with the assessment of rockfall risk to persons travelling in vehicles along the SS163 road, an important transportation corridor supporting a high vehicle traffic within the well-known tourist area of the Amalfi Coast (southern Italy). To this aim, the Rockfall Hazard Rating System (RHRS) and quantitative risk assessment (QRA) procedures, in this latter case for three rockfall risk scenarios, are applied. With reference to a large portion (33.820 out of a total of 50.365 km) of the SS163 road, the obtained QRA results highlight that, although the estimated individual risk to life satisfies the adopted tolerable risk criterion, the computed societal risk cannot be tolerated. Starting from this result, site-specific QRA analyses—carried out with reference to some road sections chosen on the basis of the RHRS results—allow the detection of the SS163 portions where the individual risk to life exceeds the tolerable risk threshold and, then, the recourse to mitigation measures could reveal necessary. In this regard, RHRS and QRA methods can be considered complementary tools in prioritizing the road sections where construction funds can be profitably spent in order to mitigate the rockfall risk with reference to both direct consequences (life loss) and indirect ones (traffic delay and diversions).     

Identifying rift zones on volcanoes: an example from La Réunion island,Indian Ocean

We describe a methodology for identifying complex rift zones on recent or active volcanoes, where structures hidden by recent deposits and logistical conditions might prevent carrying out detailed fieldwork. La Réunion island was chosen as a test-site. We used georeferenced topographic maps, aerial photos and digital terrain models to perform a statistical analysis of several morphometric parameters of pyroclastic cones. This provides a great deal of geometric information that can help in distinguishing the localisation and orientation of buried magma-feeding fractures, which constitute the surface expression of rift zones. It also allowed the construction of a complete GIS database of the pyroclastic cones. La Réunion is a perfect example where past and active volcanic rift zones are mostly expressed by clusters of monogenic centres. The data has been validated in the field and compared and integrated with the distribution and geometry of dyke swarms. Results show the presence of several main and secondary rift segments of different ages, locations and orientations, whose origin is discussed considering regional tectonics, local geomorphology, and volcano deformation.