A methodology for the evaluation of long-term volcanic risk from pyroclastic flows in Campi Flegrei (Italy)

The volcanological history of Campi Flegrei suggests that the most frequent eruptions are characterized by the emplacement of pyroclastic flow and surge deposits erupted from different vents scattered over a 150-km² caldera. The evaluation of volcanic risk in volcanic fields is complex because of the lack of a central vent. To approach this problem, we subdivided the entire area of Campi Flegrei into a regular grid and evaluated the relative spatial probability of opening of vents based on geological, geophysical and geochemical data. We evaluated the volcanic risk caused by pyroclastic flows based on the formula proposed by UNESCO (1972), R=H×V×Va, where H is the hazard, V is the vulnerability and Va is the value of the elements at risk. The product H×V was obtained by performing simulations of type eruptions centered in each cell of the grid. The simulation is based on the energy cone scheme proposed by Sheridan and Malin [J. Volcanol. Geotherm. Res. 17 (1983) 187–202], hypothesizing a column collapse height of 100 m for eruptions of VEI=3 and 300 m for eruptions of VEI=4 with a slope angle of 6°. Each simulation has been given the relative probability value associated with the corresponding cell. We made use of the GIS software ArcView 3.2 to evaluate the intersection between the energy cone and the topography. The superposition of the areas invaded by pyroclastic flows (124 simulations for VEI=3 and 37 for VEI=4) was used to obtain the relative hazard map of the area. The relative volcanic risk map is obtained by superimposing the urbanization maps.     

Mapping the vulnerability for evacuation of the Campi Flegrei territorial system in case of a volcanic unrest

Over the past few decades, intense urban expansion has occurred over the Campi Flegrei territorial system without considering the volcanic risk. In this active volcanic area, where a short period evacuation could be necessary, the emergency management cannot be based solely on hazard-related information. The territorial and social features must also be considered. In this framework, the main purpose of this research is to point out the seriousness of the present setting of the Campi Flegrei territorial system in case an evacuation is necessary. Following the concept of regional evacuation, the zone to be involved in emergency planning was identified as the whole of the area threatened by the volcanic events of the past 10?ka. Inside this area the spatial relation between the resident distribution and the outflows of roads, railway stations and harbours, to facilitate evacuation, was investigated. A spatial relational GIS-based procedure was used to draw the territorial system vulnerability map, depicting the zones with different capabilities to support the evacuation of residents in case of volcanic activity. Based on the concept that people could leave the dangerous area by the means of transport supplied by Civil Protection, and using the threshold value of over-crowding of 0.70 people/m², we identified the collection areas for residents to be immediately evacuated in case of volcanic unrest, and five macrozones displaying different capabilities to cope with an emergency phase.     

Mapping soil erodibility from composed data set in Sele River Basin, Italy

Evaluation of soil erodibility is an important task for Mediterranean lands, in which fertility and crop yield are significantly affected by soil erosion. The soil physicochemical parameters affecting soil erodibility are highly variable in space and, as for many other environmental variables, sample measurements are generally not enough for assessing its spatial variability with an acceptable level of uncertainty at the scales of practical interest. This study illustrates the procedure applied for estimating the pattern of soil erodibility across the Sele Basin (Southern Italy), where soil properties have been measured on a limited number of sparse samples. Sampled data were integrated with other sparse data estimated by local regression functions, which relate soil erodibility to auxiliary variables, such as terrain attributes and land system class memberships. Sampled and estimated data were merged in a composed data set to assess the spatial pattern of soil erodibility by ordinary kriging. The proposed approach offers effective spatial predictions, and it is exportable to regions where financial costs for soil sampling are not feasible.     

The Late Holocene tephra record of the central Mediterranean Sea: Mapping occurrences and new potential isochrons for the 4.4–2.0 ka time interval

Five cores from the southern Tyrrhenian and Ionian seas were studied for their tephra and cryptotephra content in the 4.4–2.0 ka time interval. The chronological framework for each core was obtained by accelerator mass spectrometry ¹⁴C dating, the occurrence of distinct marker tephra and stratigraphic correlation with adjacent records. Tephrochronology allowed us to correlate the analyzed deposits with tephra markers associated with Somma-Vesuvius (79 ad ), Ischia Island (Cretaio), Mt Etna (FG, FL and FS) and Campi Flegrei (Astroni-Agnano Monte Spina) events. For the first time in the marine setting, a large single glass data set is provided for the Late Holocene Etnean marker beds including the FS tephra (ca. 4.3 ka). Moreover, unknown deposits from Lipari (ca. 2.2–2.0 ka) and Vulcano (3.6–3.3 ka) are also recognized at more distal sites than previously reported. These results contribute to improve the high-resolution tephrostratigraphic framework of the central Mediterranean Sea. They also provide new insights into the chemical composition and dispersal pattern of tephras that can be used as inter-archive tools for regional and ‘local’ stratigraphic correlations and for addressing paleoclimate research.     

Hazard assessment at volcanic fields: the Campi Flegrei case history

Volcanological analysis of the 10 000 yr –1538 explosive activity at Campi Flegrei shows that the most common explosive eruptions are characterized by the emplacement of flow or surge deposits, originating from the interaction between magma and shallow and/or sea water. The minimum volumes of pyroclastic products range between 0.04 and 0.7 km³; the proximal areas covered by these products range from 3–4 to 40–50 km². The pyroclastic flow and surge deposits occurring inside the caldera have been strongly controlled by pre-existent morphology; because of this, the area of present Napoli city was blanketed by approximately 5 m of pyroclastic deposits, during the last 5000 yr.Previous analysis suggests that the presence of even very low topographic obstacles may influence pyroclastic density current run out such that future eruptive deposits would mainly be confined inside the caldera rim. We suggest that a future eruption at Campi Flegrei would not seriously involve the urbanized area of Napoli city located on the hills. On the contrary, the plains located on the eastern side of the caldera (Fuorigrotta, Bagnoli) would be the most damaged area.     

Terrestrial laser scanning survey in support of unstable slopes analysis: the case of Vulcano Island (Italy)

Natural Hazards - The capability to measure at distance dense cloud of 3D point has improved the relevance of geomatic techniques to support risk assessment analysis related to slope instability....     

GEOCITY: a drill-hole database as a tool to assess geological hazard in Napoli urban area

The geological investigations of Napoli city, which represent the basic data source for geological hazard assessment, are characterized by the absence of well exposed and continuous outcrops, mainly due to the development of the urbanized area occurred in the last 50 years. In order to increase the set of available geological information, a database named GEOCITY has been realized on the base of 900 drill holes with stratigraphies reflecting the main drill-hole surveys performed during the last century. The true key moments in its construction were the homogenisation of different data and the identification of the geological formations. A detailed analysis of the drill-hole raw data allowed us to define the database entities, while the features of the deposits, the distribution of products and the reference drill holes were used to identify the geological formation. The analysis performed using the GEOCITY database made it possible to better assess volcanic hazard from Campi Flegrei and Somma-Vesuvio and the hazard related to alluvial phenomena that Napoli city is exposed to.     

Hazard and risk assessment in a complex multi-source volcanic area: the example of the Campania Region, Italy

In order to zone the territory of Campania Region (southern Italy) with regard to the hazard related to future explosive activity of Somma-Vesuvio, Campi Flegrei, and Ischia Island, we drew a multi-source hazard map for tephra and pyroclastic flows. This map, which merges the areas possibly endangered by the three volcanic sources, takes into account a large set of tephra fall and pyroclastic flow events that have occurred in the last 10 ka. In detail, for fall products at Campi Flegrei and Somma-Vesuvio we used the dispersal of past eruption products as deduced by field surveys and their recurrence over the whole area. For pyroclastic flows, the field data were integrated with VEI = 4 simulated events; about 100 simulations sourcing from different points of the area were performed, considering the different probability of vent opening. The spatial recurrence of products of both past eruptions and simulated events was used to assign a weight to the area endangered by the single volcanic sources. The sum of these weights in the areas exposed to the activity of two sources and/or to different kinds of products was used to draw a hazard map, which highlights the spatial trend and the extent of the single equivalent classes at a regional scale. A multi-source risk map was developed for the same areas as the graphic result of the product of volcanic hazard and exposure, assessed in detail from a dasymetric map. The resulting multi-source hazard and risk maps are essential tools for communication among scientists, local authorities, and the public, and may prove highly practical for long-term regional-scale mitigation planning.