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Nephelines from the Somma-Vesuvius volcanic complex (Southern Italy): crystal-chemical, structural and genetic investigations
No full textSixteen nephelines from different geological occurrences
were sampled at the type-locality, the Somma-
Vesuvius volcanic complex (southern Italy), and investigated
for their chemistry and crystal structure obtained by both
single-crystal and powder X-ray diffraction. Nephelinebearing
samples are metamorphic or from magmatic ejecta
and pumice deposits. The lower K contents characterize the
pumice- and some metamorphic-derived nephelines, whereas
the higher ones are found in some samples from magmatic
nodules. The amount of the anorthite molecule, quite
low on average, can be more variable in the metamorphic
nephelines. The crystal-structure investigations on Somma-
Vesuvius samples compare well with previous studies of
natural nephelines. All 16 nepheline samples adopt space
group P63. The observed lattice parameters vary between
9.9768–9.9946 Å (for a) and 8.3614–8.3777 Å (for c), respectively.
Furthermore, chemical analysis revealed that all specimens
exhibit an excess of Si relative the ideal Si:Al ratio of 1:1.
The analysis of the T-O distances in our samples clearly
indicates a distinct ordering process of aluminium and silicon
on the tetrahedral sites which is an agreement with
Loewenstein’s rule. A linear correlation between the distance
of symmetry equivalent split atoms O(1)-O(1)’ and the T(1)-
O(1)-T(2) tilt angle was observed. The average (B =
Na) distances of all crystals are very similar which is consistent
with the outcome of the site population refinement indicating
full occupancy with sodium. Oriented precession-type
sections of reciprocal space indicated the presence of at least
the most intense family of satellite peaks, demonstrating that
this group of satellite reflections can occur not only in nephelines
from pegmatites and ijolites but also in rocks from
completely different petrological settings
Pre-caldera lateral activity at Somma – Vesuvius
No full textS01.14 - Volcano geology and field observations aimed at validation of numerical models
Pre-caldera lateral activity at Somma- Vesuvius
Claudio Scarpati, Domenico Sparice, Annamaria Perrotta
Dipartimento di Scienze della Terra, dell'Ambiente e delle Risorse (DiSTAR), Università di Napoli Federico II, Italy
Five pre-caldera, scoria- and spatter-cones at Somma-Vesuvius were produced by alternative pulses of Strombolian and Hawaiian activity that emplaced scoria and welded spatter fall deposits, several meters thick. These vents cover a wide azimuth around the volcano. A persistent feature throughout the exposed stratigraphy of the studied parasitic cones is the abundance of coarse, juvenile material (97–100 wt%), a feature suggesting an overall magmatic style during these eruptive episodes. Most of the observed eruptive units show an alternation of unwelded scoria and welded spatter suggesting a repeated variation of the eruptive style. A dominant Strombolian style of fragmentation, with bubble coalescent and rhythmic outbursts, emplaced thick scoriaceous succession; episodically, lava fountaining activity ejected coarse clots of magma which fell near the vent producing spatter horizons. The fragmentary nature (spatter-fed) of lavalike
facies strictly associated (transitional) to less welded to agglutinated facies, as well as the plastic deformation (flattening) of spatter fragments indicate the continuous fall deposition from Hawaiian firefountain episodes alternated with Strombolian phases emplacing loose scoria deposits. The remnants of two
cones show a continuous sequence (no breaks) of pyroclastic beds emplaced as a result of a single coneforming eruptions. This allows us to define them “monogenetic”. Conversely, the presence of thick paleosols, reworked material, exotic tephras and deep erosional surfaces in the pyroclastic succession of the
other three cones has to be regarded as clear, well developed and laterally traceable breaks in the pyroclastic sequence of these small parasitic volcanoes. In light of this, we define such edifices as the result of a polygenetic (multi-phase) evolution. These evidences indicate resumption of activity after a quite long, nonquantifiable period of quiescence. This behaviour should suggest more caution when considering the parasitic volcanoes that erupted in historical time, completely extinct.
S01.1
A time-distance reconstruction of the Campanian Ignimbrite pyroclastic current based on lithofacies architecture
No full textS01.36 - Hazard assessment of pyroclastic density currents and lahars current capabilities
and new strategies for comprehensive uncertainty quantification
A time-distance reconstruction of the Campanian Ignimbrite pyroclastic current
based on lithofacies architecture
Claudio Scarpati, Domenico Sparice, Annamaria Perrotta
Dipartimento di Scienze della Terra, dell'Ambiente e delle Risorse (DiSTAR), Università di Napoli Federico II, Italy
Large ignimbrites are the product of high-temperature pyroclastic density currents (PDCs) spreading over huge regions. Understanding the behaviour of these volcanic events is critical to assess the hazard posed to millions of peoples living near volcanoes producing this type of activity. Here we present a detailed examination of the medial (from 30 to 80 km from the source area) ignimbrite sequence of the Campanian Ignimbrite eruption (Campanian Ignimbrite s.s., CI), a caldera-forming Plinian event, occurred 39 ka ago,
whose PDC spread over a huge area from Campi Flegrei (Italy). Ignimbrite deposits have a mass of 1.74*1014 kg and a tephra volume of 54 km3 (25 km3 DRE). We describe CI lithofacies and their vertical and lateral variations. The eruption started with a fluctuating Plinian phase that collapsed irreversibly spreading a pyroclastic density current over a rugged region. Vertical facies variations reflect a temporal evolution of
depositional mechanisms, from traction- to granular- or fluid escape-dominated, that records unsteady conditions and contrast with persistent lateral facies reflecting an overall uniform spatial behaviour of the current. Our lithofacies investigation illustrates how the CI PDC evolved in time and space and the role of internal (eruptive and transport mechanisms) and external (topography, surficial water and rain) factors in
governing its behaviour. Our study may have important implications for assessing the hazards related to the reactivation of the Campi Flegrei caldera with a large ignimbrite-forming Plinian event, like the Campanian Ignimbrite eruption, on the densely populated Campania region
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Lateral facies variations in the 79 AD deposits at Pompeii
No full textS03.06 - Volcanoes and Human History
Lateral facies variations in the 79 AD deposits at Pompeii
Andrea Montanaro1, Claudio Scarpati1, Annamaria Perrotta1, Domenico Sparice1, Alberta Martellone2, Arianna Spinosa2, Massimo Osanna2
1Dipartimento di Scienze della Terra, dell’Ambiente e delle Risorse, Università di Napoli Federico II, Italy
2Parco Archeologico di Pompei, Italy
The 79 AD eruption destroyed Pompeii and buried the town under almost six metres of pyroclastic materials. Pompeii was excavated in the last 270 years and most of the volcanic material was removed without any geological descriptions. For this reason, most of the recent (last 30 years) illustrations of the tephra succession refer to outcrops located outside the town walls. Almost one-third of the Pompeii area is still
unexcavated. The boundary between excavated and unexcavated areas cut throughout the town and a 2.5 km thick front looms over the unburied buildings. To secure the excavation front a re-profiling of this front with gentle slopes is in progress. Excavations in the Regio V exposed several new astonishingly well preserved stratigraphic successions of the 79 AD deposits. Most of these logs are ephemeral and last few days to allow
archaeologists to exhume roman artefacts. A systematic survey of all exposed pyroclastic sequence allowed us to study in detail the distribution and lateral facies variations of the different 79 AD stratigraphic units. The basal lapilli fall deposit shows a remarkable thickness variation ranging from 2.7 m to 4.5 m. Local overthickening are observed where pumice lapilli rolled on sloping roofs and accumulated in the alleys around the buildings. Even more pronounced lateral variations are observed in the upper part of the
sequence, a mainly pyroclastic density current (PDC), stratified ash deposit, that ranges in thickness from few tens of centimetres to two metres. In this case thin, massive ash layers can be traced laterally into thick, poorly sorted, ash and lapilli layers, with well-developed sedimentary structures. Lateral facies distribution of the PDC deposits within Pompeii are influenced by urban structures (e.g. height, direction)
Recent excavations at Pompeii: new findings and their volcanological implications
No full textS03.06 - Volcanoes and Human History
Recent excavations at Pompeii: new findings and their volcanological implications
Claudio Scarpati1, Annamaria Perrotta1, Andrea Montanaro1, Domenico Sparice1, Alberta Martellone2,
Arianna Spinosa2, Massimo Osanna2
1Dipartimento di Scienze della Terra, dell’Ambiente e delle Risorse, Università di Napoli “Federico II”, Italy
2Parco Archeologico di Pompei, Italy
Detailed descriptions of the effects of Plinian explosive eruptions on urban settlements are rare. For this reason, volcanologists spent considerable time studing the destruction of the roman towns around Vesuvius occurred during the 79 AD eruption. At Pompeii, during the eruption accumulated about three metres of pumice lapilli from the eruptive cloud and successively one to three metres of stratified ash aggraded from pyroclastic currents. Both phases caused hundreds of victims. All reconstructions followed the chronology of Pliny the Younger, who witnessed the eruption and wrote two famous epistulae to the historian Tacitus. In these letters the eruption is described as a continuous event that lasted about nineteen hours. New stratigraphic data collected during recent excavations in the Schola Armaturarum, a famous building located
in the central part of the Pompeii archaeological site, seems to contradict the never discussed before continuity of the eruption. Inside this building a large quantity of debris from walls and roofs was found lying through the whole pyroclastic sequence. Roofing tiles were found in the lapilli fall deposits, while eastwest trending walls were partly demolished in the ashy deposit accumulated during the flowage of the pyroclastic currents. A relevant observation is the presence of an erosive surface, 55 cm depth and 320 cm wide, covered with a few cm thick lens of reworked material cut into the middle part of the pyroclastic succession. The finding of this structure suggests a time gap in the eruptive phenomena affecting the city of Pompeii; this pause could have pushed the inhabitants, recovered indoor during the fallout phase, to leave their homes trying to reach safer places
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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