Search

Co-auteur étranger ; This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.; International audience; The eruptive activity of a volcano modifies its surface topography through morphological changes generated by the deposition of emitted volcanic material and resulting gravity-driven processes, which can form accumulation of material in addition to the most common erosional phenomena. Mapping and quantifying such morphological changes allow to derive new data useful to better describe and understand the eruptive history of the volcano itself. Nowadays, one of the mostly used method to identify such morphological changes consists of comparing Digital Elevation Models (DEM) of the volcanic area before and after an eruptive event. If the eruptive event is referred to periods prior to 1980's, the only method to reproduce DEMs consists of elaborating the historical cartography that is often available only in paper format. In this work we aim to prove the reliability of this approach, presenting a study on the morphological changes (from 1876 to 1944) of the summit caldera of the Somma–Vesuvio volcano (Italy). For the first time, we compare DEMs derived from historical maps (1876, 1906 and 1929) and a DEM dated 2012 obtained by remote sensing. The four models of the caldera, digitally reproduced at the same spatial resolution, are morphologically investigated through specific maps derived from the DEMs and a set of height profiles. In addition, further morphometric analyses and accurate quantifications in volume and surface are presented and discussed for a portion of the Somma-Vesuvio summit caldera, represented by the Gran Cono edifice. Considering the different typology of the source data used in this study, it is also provided a discussion on the respective accuracies that, especially for the historical maps, represent a crucial point for obtaining DEMs able to reproduce topographies more realistic as possible. For this reason, despite data source were processed following rigours criteria, the calculations of volume, surface and distance related to the morphological changes of the volcano are associated to an accurate quantification of the error. Following this, the main results obtained in this study are: i) the identification of several past volcanic deposits and the estimation of the related thicknesses, both in good agreement with published literature; ii) the quantification of the morphological changes of the Gran Cono from 1876 to 1944 resulting in a volume and surface growth of 133 × 106 m3 (±5%) and ~0.14 km2, respectively; iii) the identification of a possible migration path of the centroid of the Gran Cono crater along the SW-NE preferential direction during the investigated period.

The Sorrentina Peninsula is a densely populated area with high touristic impact. It is located in a morphologically complex zone of Southern Italy frequently affected by dangerous and calamitous la...

We present the results of a meso-scale systematic structural analysis of fractures, faults and dykes exposed at the Somma-Vesuvius volcano (southern Italy). Observed fractures include: (i) radial and tangential (with respect the caldera axis), sub-metric to metric joints associated with the edifice load and volcano-tectonic activity (i.e. inflation, deflation and caldera collapse stages) and (ii) decameter-scale fractures related to volcano flank instabilities. For the Somma-Vesuvius volcano, preexisting radial joints were commonly reactivated as transfer faults during the caldera formation, allowing different blocks to move toward the center of the collapsing area. Dykes occur with different geometries, including en-echelon structures bounding structural depressions. The orientation analysis of all structures indicates that they are preferentially oriented. Furthermore, we provide a morphological lineament analysis using high-resolution Digital Terrain Models of Somma-Vesuvius. Azimuth and spatial distribution of dykes and morphological lineaments were analyzed for comparison with the old Somma Crater and Gran Cono axes, respectively. Results highlight the overprinting of radial and clustered strain patterns recorded in different volcano-tectonic evolution stages. We suggest a possible deformation evolution model in which structures develop along either radial or preferential trends, highlighting different volcanic conditions: (i) where radial patterns occur, the structures developed during volcanic inflation cycles with a closed magmatic conduit condition whereas (ii) clustered patterns are probably associated with a regional strain field that overcomes the local deformation field, a situation typical in the case of open-conduit activity.

This study presents a new method for producing long-term hazard maps for pyroclastic density currents (PDC) originating at Campi Flegrei caldera. Such method is based on a doubly stochastic approach and is able to combine the uncertainty assessments on the spatial location of the volcanic vent, the size of the flow and the expected time of such an event. The results are obtained by using a Monte Carlo approach and adopting a simplified invasion model based on the box model integral approximation. Temporal assessments are modelled through a Cox-type process including self-excitement effects, based on the eruptive record of the last 15 kyr. Mean and percentile maps of PDC invasion probability are produced, exploring their sensitivity to some sources of uncertainty and to the effects of the dependence between PDC scales and the caldera sector where they originated. Conditional maps representative of PDC originating inside limited zones of the caldera, or of PDC with a limited range of scales are also produced. Finally, the effect of assuming different time windows for the hazard estimates is explored, also including the potential occurrence of a sequence of multiple events. Assuming that the last eruption of Monte Nuovo (A.D. 1538) marked the beginning of a new epoch of activity similar to the previous ones, results of the statistical analysis indicate a mean probability of PDC invasion above 5% in the next 50 years on almost the entire caldera (with a probability peak of ~25% in the central part of the caldera). In contrast, probability values reduce by a factor of about 3 if the entire eruptive record is considered over the last 15 kyr, i.e. including both eruptive epochs and quiescent periods.

Gravity-induced pyroclastic density currents (PDCs) can be produced by the collapse of volcanic crater rims or due to the gravitational instability of materials deposited in proximal areas during explosive activity. These types of PDCs, which are also known as “glowing avalanches”, have been directly observed, and their deposits have been widely identified on the flanks of several volcanoes that are fed by mafic to intermediate magmas. In this research, the suitability of landslide numerical models for simulating gravity-induced PDCs to provide hazard assessments was tested. This work also presents the results of a back-analysis of three events that occurred in 1906, 1930 and 1944 at the Stromboli volcano by applying a depth-averaged 3D numerical code named DAN-3D. The model assumes a frictional internal rheology and a variable basal rheology (i.e., frictional, Voellmy and plastic). The numerical modelling was able to reproduce the gravity-induced PDCs' extension and deposit thicknesses to an order of magnitude of that reported in the literature. The best results when compared with field data were obtained using a Voellmy model with a frictional coefficient of f = 0.19 and a turbulence parameter ξ = 1000 m s − 1 . The results highlight the suitability of this numerical code, which is generally used for landslides, to reproduce the destructive potential of these events in volcanic environments and to obtain information on hazards connected with explosive-related, mass-wasting phenomena in Stromboli Island and at volcanic systems characterized by similar phenomena.

Campi Flegrei (CF) is an example of an active caldera containing densely populated settlements at very high risk of pyroclastic density currents (PDCs). We present here an innovative method for assessing background spatial PDC hazard in a caldera setting with probabilistic invasion maps conditional on the occurrence of an explosive event. The method encompasses the probabilistic assessment of potential vent opening positions, derived in the companion paper, combined with inferences about the spatial density distribution of PDC invasion areas from a simplified flow model, informed by reconstruction of deposits from eruptions in the last 15 ka. The flow model describes the PDC kinematics and accounts for main effects of topography on flow propagation. Structured expert elicitation is used to incorporate certain sources of epistemic uncertainty, and a Monte Carlo approach is adopted to produce a set of probabilistic hazard maps for the whole CF area. Our findings show that, in case of eruption, almost the entire caldera is exposed to invasion with a mean probability of at least 5%, with peaks greater than 50% in some central areas. Some areas outside the caldera are also exposed to this danger, with mean probabilities of invasion of the order of 5-10%. Our analysis suggests that these probability estimates have location-specific uncertainties which can be substantial. The results prove to be robust with respect to alternative elicitation models and allow the influence on hazard mapping of different sources of uncertainty, and of theoretical and numerical assumptions, to be quantified.

Campi Flegrei is an active volcanic area situated in the Campanian Plain (Italy) and dominated by a resurgent caldera. The great majority of past eruptions have been explosive, variable in magnitude, intensity, and in their vent locations. In this hazard assessment study we present a probabilistic analysis using a variety of volcanological data sets to map the background spatial probability of vent opening conditional on the occurrence of an event in the foreseeable future. The analysis focuses on the reconstruction of the location of past eruptive vents in the last 15 ka, including the distribution of faults and surface fractures as being representative of areas of crustal weakness. One of our key objectives was to incorporate some of the main sources of epistemic uncertainty about the volcanic system through a structured expert elicitation, thereby quantifying uncertainties for certain important model parameters and allowing outcomes from different expert weighting models to be evaluated. Results indicate that past vent locations are the most informative factors governing the probabilities of vent opening, followed by the locations of faults and then fractures. Our vent opening probability maps highlight the presence of a sizeable region in the central eastern part of the caldera where the likelihood of new vent opening per kilometer squared is about 6 times higher than the baseline value for the whole caldera. While these probability values have substantial uncertainties associated with them, our findings provide a rational basis for hazard mapping of the next eruption at Campi Flegrei caldera.

In this study, we demonstrate the use of a geo-spatial information system for volume estimation of fallout deposits and for identification of syn-eruptive and post-eruptive depositional mechanisms. For the first time, we present thickness distribution maps, isopachs maps, and fallout deposit volumes for the single stratigraphic units (A-F) of the 122 BC Plinian eruption of Etna, the most powerful eruption of this volcano in historical times. Thickness data collected during the field survey were organized into a geo-referenced database, and several interpolation algorithms were used to calculate the volumes of the six fallout layers of eruption (units A-F). The results are compared with those obtained using the Pyle method, which bases volume calculations on the exponential thickness-decay law of the deposits. Differences in the two methods are analyzed through applying two-dimensional (2D) and 3D geo-statistical analysis to thickness data, with an 'ideal' fallout deposit used as reference. Our approach allowed both identification of stratigraphic sections where the deposits were affected by secondary erosional or accumulation phenomena, and assessment of whether the secondary processes were caused by local morphologic conditions or by variations in eruptive dynamics (e.g., rotation of dispersal axis direction).

With the aim to improve volcaniclastic flows hazard zonation and risk mitigation in volcanic areas, this work presents a GIS-based study on the Sorrentina Peninsula, located southwest of the main Neapolitan volcanoes (Ischia, Procida, Campi Flegrei, and Somma-Vesuvius; Campanian Plain, Southern Italy). This area has beenheavily affected by historical events with more than 200 volcani-clastic flows recorded in the last 500 years. The study here proposed combines different information, including morphometry, geology, volcanology and land use for building a susceptibility index (named VFSI) able to rank the drainage basins potentially prone to generate volcaniclastic flows. The resulting susceptibility map classifies 488 drainage basins into three different classes (low, moderate and high) over an area of about 280 km2. The proposed method allows the rapid ranking of the different drainage basins, and is propaedeutic to detailed investigation on single basins for individuating areas more prone to colluvial cover failure and associated volumes of available material for volcaniclastic flow generation.

Volcaniclastic debris flows are dangerous natural phenomena that originate in volcanic areas not only during or shortly after an eruption but also during a period of volcanic quiescence, when heavy and/or persistent rains remobilize unconsolidated pyroclastic deposits. In Italy, one of the areas most affected by these phenomena is that of the Apennine Mountains which border the southern Campania Plain surrounding the Vesuvius volcano. Historical accounts record in these areas that more than 500 debris flow events occurred during the last five centuries. These events caused very dangerous consequences such as loss of life and serious damage to property. An example is the devastating event of Sarno of 5 May 1998 which caused the death of more than 150 people and considerable damage to villages located at the foot of the Apennine Hills. In order to contribute to the assessment and mitigation of the debris flow risk, we propose a zonation map that identifies the areas more prone to generation and invasion by ...

This paper presents a multidisciplinary study of river migration in alluvial plains. The selected case study is a sector of the Lucca alluvial plain (Tuscany, Central Italy) in which the Serchio River flows. Various types of data were collected, analyzed, and processed using a GIS. In particular, remote sensing imagery of different resolution (aerial orthophotos and satellite images) were processed to enhance buried fluvial features. Detected features were compared with data from stratigraphic investigations, archaeological surveys, geomorphological maps, and previous remote sensing studies. Traces of ancient channels were mapped and compiled in an interactive vector database listing the most important characteristics of each element. Two fluvial channel systems (here called primary and secondary) of differing size (e.g. length and width) were identified. Our analyses confirm the major features of the main paleochannels identified in previous works and enabled the discovery of smaller channels thanks to t...

Easter Island (Chile) is a volcanic island made up entirely of volcanic rocks, which are represented by lava flows and domes as well as cinder and scoria pyroclastic cones, covering the entire compositional range from basalts to peralkaline rhyolites. Apart from representing a cultural heritage of worldwide importance, the megalithic Moai statues of Easter Island are an exquisite example of the utilisation of a variety of volcanic rocks in sculpture. This work illustrates the spectrum of volcanic litho-types available to the islanders through new chemical and petrographic data and presents chemical, mineralogical, petrographic and physical data on the rocks from the same volcanic deposits used for fashioning the megalithic sculptures. The stones used for the statues and their topknots are represented by volcanic rocks with different depositional mechanisms and chemical compositions. They include tuffs deposited in water, subaerial welded scoriae, lava flows and lava domes, with composi- tions ranging from basalt to trachyte. Despite such variations, they all share rather high total porosity, and are all easily workable stones. Their low apparent density seems to be the critical factor in enabling such large statues to be fashioned. The rest of the volcanic rocks on the island were unsuitable for building megalithic sculptures for various reasons: they are either too heavy, as is the case of the basaltic lavas, or too fragile, as the obsidian, or too loose, as the unconsolidated tuff and scoria cones. The rocks used for the platforms and altars are lavas whose compositions vary moderately, from basaltic to mugearitic, but which share similar physical and mechanical properties, well suited to building stable bases for the statues. The results of the study on the Rano Raraku tuff, employed in the great majority of the statues, show that it consists of a hyalotuff, in which volcanic glass was altered by interaction with sea water. The products of alteration vary in composition from nearly amorphous palagonite to crystalline smectite. The magma that erupted at Rano Raraku was originally mugearitic, and the high loss on ignition (LOI) and low alkali content of the rock, as well as its high clay content, are characteristics stemming from glass-sea water interactions during the deposit formation. The samples taken from the base, middle and top of the cone flank hosting the quarries show very similar composition of the bulk rock, the fresh glass and the palagonite products, suggesting homogeneous rock characteristics throughout the quarries.