Geometric constraints on composition of sediment derived from erosional landscapes

Although unroofing sequences are well known in the stratigraphic record, there is no general theory for estimating relevant basic quantities such as the time history of sediment production from a particular unit or the degree of mixing between successive units. Here we investigate the production of sediment from layered source rocks that are milled off by steady-state erosional topography. The shape of the sediment-production function for milling off a thin horizontal layer is given by the derivative of the hypsometric function, in the form of area contained within contours as a function of contour altitude. The time-scale for the production function, the ‘topographic mixing time’, is set by the topographic relief divided by the uplift rate. The production function for a sharp transition from one unit to another is given directly by the hypsometric function. The effects of stratal dip parallel to the mean slope of the erosional topography and finite layer thickness can be accounted for to a first approximation by simple geometric corrections to the mixing time. Finite layer thickness also has the effect of smoothing the production function although most natural hypsometric functions are smooth enough that this effect is relatively weak. The quality of an unroofing sequence can be measured in terms of the ‘sharpness’ of separation of successive peaks in sediment production produced by milling off a sequence of geometrically similar layers. This peak sharpness can be parameterized by a ratio of the interval between successive peaks in sediment production to topographic mixing time. By this measure, the quality of unroofing sequences is controlled by two parameters: the ratio of layer thickness to topographic relief, and the dip angle. The dip angle in concert with topographic mixing exerts a strong control on the degree of signal segregation; in particular, production of cleanly segregated signals for dip angles greater than about 15° requires very high ratios of layer thickness to relief. Hence identification of distinct unroofing sequences may place significant and useful constraints on the attitude and/or thickness of units in the eroding stratigraphy.     

Volcanology and petrology of Nisyros Island (Dodecanese,Greece)

Nisyros is a totally volcanic island located at the eastern limit of the quaternary calc-alkaline island arc system of the South Aegean Sea. Its age is rather young since K/Ar dating has given an age of 0.2 m.y. B.P. for one of the oldest outcropping products of this volcano. The volcanological evolution of Nisyros has tentatively been reconstructed as follows:

1. after a period (from 3.0? to 0.2 m.y. B.P.) of submarine activity, evidenced by the presence of pillow-lavas and hyaloclastites, the volcano grew above sea level;
2. effusive and explosive subaerial activity from different vents built up a complex stratovolcano, probably around 0.2 m.y. B. P.;
3. at the end of an intense explosive activity (between 0.2 m.y. B.P. and Present) the top of the volcano collapsed forming a caldera which is still perfectly preserved. A post-caldera activity with eruptions of huge and viscous domes and lava flows of uniform composition, both inside and outside the caldera, concluded this stage of the volcano evolution;
4. in historical times, spectacular phreatic explosion craters formed on the caldera floor;
5. presently, a large area of the caldera floor is affected by a considerable hydrothermal activity. The hypothesis is formed that Nisyros volcano is not yet extinct.

Four small volcanic islets — Yali, Stronjili, Pakia and Perigusa — located a few miles on the North and West of Nisyros, although volcanologically independent of one another, are composed of products which are attributable, from the petrologic point of view, to the Nisyros magma. The volcanic rocks of Nisyros and of its neighbouring minor islands as well as the volcanics of the coeval volcanoes of the South Aegean Sea arc (Aegina, Milos, Santorini, etc.) belong to a typical orogenic calc-alkaline series (from basic andesites through andesites-dacites-rhyodacites to strongly silicic rhyolites) with normal K₂O contents. The potassium contents of these rocks are compatible with the depth of 150 km (as inferred from geophysical data) for the inclined seismic zone underneath the active volcanic arc. The existence of a top-caldera as well as the occurrence of a huge amount of xenoliths (hornblende-rich cumulates and contact-metamorphic calcareous rock derivatives) suggest the presence of a magma chamber at a relatively shallow depth beneath the volcano. The rhyolitic obsidians of Yali can be considered as residual liquids from the Nisyros rhyodacites, thus representing the end-members of a fractionation process. Volcanological and petrological arguments are in favour of fractional crystallization as the most probable genetic process for the calc-alkaline differentiation series of Nisyros and of its neighbouring minor islands. However, the lack of any rock with a high alumina basalt composition makes it difficult to define exactly the nature of the parent magma. According to recent geophysical data, continental collision is already in progress at the Hellenic trench. Therefore, Nisyros and the other active volcanoes of the South Aegean Sea arc are approaching the senile stage. What would follow could be a transition to shoshonitic magmatism as a consequence of the deepening of the lithospheric slab under the Aegean microplate. The limited extension and the relatively short-lived calc-alkaline activity of the South Aegean Sea arc could be related to the particular geodynamic pattern of the Mediterranean area which is characterized by a microplates mosaic between the two converging African and Eurasian major plates.     

Depth profiles of bacterioplankton assemblages and their activities in the Ross Sea

The identification of bacterial community structure has led, since the beginning of the 1990s, to the idea that bacterioplankton populations are stratified in the water column and that diverse lineages with mostly unknown phenotypes dominate marine microbial communities. The diversity of depth-related assemblages is also reflected in their patterns of activities, as bacteria affiliated to different groups can express different activities in a given ecosystem. We analysed bacterial assemblages (DGGE fingerprinting) and their activities (prokaryotic carbon production, protease, phosphatase, chitinase, beta-glucosidase and lipase activities) in two areas in the Ross Sea, differing mainly in their productivity regime: two stations are located in the Terra Nova Bay polynya area (highly productive during summer) and two close to Cape Adare (low phytoplankton biomass and activity). At every station a pronounced stratification of bacterial assemblages was identified, highlighting epipelagic communities differing substantially from the mesopelagic and the bathypelagic communities. Multivariate analysis suggested that pressure and indirectly light-affected variables (i.e. oxygen and fluorescence) had a great effect on the bacterial communities outcompeting the possible influences of temperature and dissolved organic carbon concentration. Generally activities decreased with depth even though a signal of the Circumpolar Deep Water (CDW) at one of the northern stations corresponded to an increase in some of the degradative activities, generating some ‘hot spots’ in the profile. We also found that similar assemblages express similar metabolic requirements reflected in analogous patterns of activity (similar degradative potential and leucine uptake rate). Furthermore, the presence of eukaryotic chloroplasts’ 16S rDNA in deep samples highlighted how in some cases the dense surface-water formation (in this case High Salinity Shelf Water—HSSW) and downwelling can affect, at least for some phylotypes, the bacterial (16S rDNA based) community structure of the dark ocean.     

Web-based macroseismic survey in Italy: method validation and results

A new method of macroseismic surveys, based on voluntary collaboration through the Internet, has been running at the Istituto Nazionale di Geofisica e Vulcanologia (INGV) since July 2007. The macroseismic questionnaire is addressed to a single non-specialist; reported effects are statistically analysed to extrapolate a probabilistic estimate of Mercalli Cancani Sieberg and European Macroseismic Scale intensities for that observer. Maps of macroseismic intensity are displayed online in almost real time and are continuously updated when new data are made available. For densely inhabited zones, we have received reports of felt effects for even very small events (M = 2). Six earthquakes are presented here, showing the ability of the method to give fast and interesting results. The effects reported in questionnaires coming from three towns are carefully analysed and assigned intensities are compared with those derived from traditional macroseismic surveys, showing the reliability of our web-based method.     

Research progress in volcanology in the Neapolitan area, southern Italy: a review and some alternative views

Comprehensive reviews are given for the major volcanic systems that occur in the greater metropolitan area of Naples, southern Italy; Mt. Somma-Vesuvius to the east and the Campi Flegrei volcanic system to the west. Also included in the review is a detailed discussion of the large, highly explosive Campania Volcanic Zone (CVZ) ignimbrite events. These volcanic areas have been studied for more than 100 years, yet significant differences of opinion exist related to fundamental issues of origin and distribution. We present some alternative views related to petrogenesis on some issues based on more than 25 years of research. The relationship between risk assessment and management that impacts the threatened society or culture and the past and ongoing fundamental volcanological research is an essential part of the science. Countries with limited resources may be forced to accept an increased risk but even highly industrialized societies may not be able to completely eliminate deaths from volcanic eruptions. Scientific studies of the hazardous regions should be comprehensive and include reasonable alternative interpretations as this information reveals the level of confidence that must be conveyed to the public officials. The authors review the state of the art of risk assessment and management of the volcanic hazards in the Neapolitan region in light of the review of research.     

An empirical equation for tunnel inflow assessment: application to sedimentary rock masses

Groundwater inflow assessment is essential for the design of tunnel drainage systems, as well as for assessment of the environmental impact of the associated drainage. Analytical and empirical methods used in current engineering practice do not adequately account for the effect of the jointed-rock-mass anisotropy and heterogeneity. The impact of geo-structural anisotropy of fractured rocks on tunnel inflows is addressed and the limitations of analytical solutions assuming isotropic hydraulic conductivity are discussed. In particular, the study develops an empirical correction to the analytical formula frequently used to predict groundwater tunnel inflow. In order to obtain this, a discrete network flow modelling study was carried out. Numerical simulation results provided a dataset useful for the calibration of some empirical coefficient to correct the well-known Goodman’s equation. This correction accounts for geo-structural parameters of the rock masses such as joint orientation, aperture, spacing and persistence. The obtained empirical equation was then applied to a medium-depth open tunnel in Bergamo District, northern Italy. The results, compared with the monitoring data, showed that the traditional analytical equations give the highest overestimation where the hydraulic conductivity shows great anisotropy. On the other hand, the empirical relation allows a better estimation of the tunnel inflow.     

Venomous snakes and climate change: ophidism as a dynamic problem

Snakebite envenoming is an important public health problem worldwide and addressing this issue has turned into a challenge for applied science. In this sense, the study of the distributional patterns of problematic snakes is central in terms of public health. Global Climate Change is affecting the distributional ranges of snakes, so that decisions regarding treatment of ophidism (poisoning by snake venom) may also change spatially and/or temporally. Here, we assessed suitable climate spaces at present conditions and estimated potential future changes in the distributions of the five southernmost venomous snakes, responsible for almost 99 % of accidents in Argentina, by implementing an ensemble of forecasts between different algorithms and scenarios for 2030 and 2080. Present suitable climate spaces showed high concordance with known distribution of the species. Future projections show moderate “north to south” displacements of the snakes’ suitable climate spaces, implying potential increments of suitable spaces in human populated areas in Argentina. Our results suggest the necessity of considering ophidism as a dynamic problem. In this regard, the analyses implemented here are useful tools in improving the assessment of snakebite envenoming in light of global climate change.     

The effect of cation ordering and temperature on the high-pressure behaviour of dolomite

Synchrotron single-crystal X-ray diffraction experiments at high-pressure and high-temperature conditions were performed up to 20 GPa and 573.0(2) K on a fully ordered stoichiometric dolomite and a partially disordered stoichiometric dolomite [order parameter, s = 0.26(6)]. The ordered dolomite was found to be stable up to approximately 14 GPa at ambient temperature and up to approximately 17 GPa at T = 573.0(2) K. The P–V data from the ambient temperature experiments were analysed by a second-order Birch–Murnaghan equation-of-state giving K ₀ = 92.7(9) GPa for the ordered dolomite and K ₀ = 92.5(8) GPa for the disordered dolomite. The high-temperature data, collected for the ordered sample, were fitted by a third-order Birch–Murnaghan equation-of-state resulting in K ₀ = 95(6) GPa and K′ = 2.6(7). In order to compare the three experiments results, a third-order Birch–Murnaghan equation-of-state was also calculated for the ambient temperature experiments giving K ₀ = 93(3) GPa, K′ = 3.9(6) for the ordered dolomite and K ₀ = 92(3) GPa, K′ = 4.0(4) for the disordered dolomite. The derived axial moduli show that dolomite compresses very anisotropically, being the c-axis approximately three times more compressible than the a-axis. The axial compressibility increases as T increases, and the a-axis is the most temperature-influenced axis. On the contrary, axial compressibility is not influenced by disordering. Structural refinements at different pressures show that Ca and Mg octahedra are almost equally compressible in the ordered dolomite with K(CaO₆) = 109(4) GPa and K(MgO₆) = 103(3) GPa. On the contrary, CaO₆ compressibility is reduced and MgO₆ compressibility is increased in the disordered crystal structure where K(CaO₆) = 139(4) GPa and K(MgO₆) = 89(4) GPa. Disordering is found to increase CaO₆ and to decrease MgO₆ bond strengths, thus making stiffer the Ca octahedron and softer the Mg octahedron. Cation polyhedra are distorted in both ordered and disordered dolomites and they increase in regularity as P increases. Ordered dolomite approaches regularity at approximately 14 GPa. The increase in regularity of octahedra in the disordered dolomite is strongly affected by the very slow regularization of MgO₆ with respect to CaO₆. The phase transition to the high-pressure polymorph of dolomite (dolomite-II), which is driven by a significant increase in the regularity of both cations polyhedra and mineral crystal structure, occurs in the ordered dolomite at ambient temperature at approximately 14 GPa; whereas no clear evidences of phase transition were observed as regards the disordered crystal structure.     

Coastal vulnerability to wave storms of Sele littoral plain (southern Italy)

This paper presents a new method for coastal vulnerability assessment (CVA), which relies upon three indicators: run-up distance (as a measurement of coastal inundation), beach retreat (as a measurement of potential erosion), and beach erosion rate (obtained through the shoreline positions in different periods). The coastal vulnerability analysis of Sele Coastal Plain to storm impacts is examined along a number of beach profiles realized between 2008 and 2009. This particular study area has been selected due to its low-lying topography and high erosion propensity. Results are given in terms of an impact index, performed by combining the response due to coastal inundation, storm erosion, and beach erosion rate. This analysis is implemented on the basis of morphosedimentary characteristics of the beach, wave climate evaluation, and examination of multitemporal aerial photographs and topographic maps. The analysis of the final results evidences different coastal responses as a function of the beach width and slope, which in turn depend on the local anthropization level. The comparison of this method with a Coastal Vulnerability Index method evidences the better attitude of CVA index to take into account the different beach features to explain the experienced damages in specific stretches of the coastline considered.