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Ischia Island is an active volcano representing the emerged sector of an E -W trending volcanic ridge largely extending undersea. Its collapsing behaviour, mainly in the form of fast-moving, terrestrial and submarine debris avalanches, has been recognized during the Holocene, but much less is known about previous gravity-driven processes. Using high-resolution multibeam bathymetric data and seismic reflection profiles, we provide evidence that the Island's southwestern flank has been involved in a slow-moving, deep-seated slope deformation that has displaced large volumes of its apron since the Late Pleistocene and until very recent or contemporary times. A long tongue of deformed seafloor, spreading up to 45 km from the Island over an area of 330 km2, between 500 and 1300 m water depths, has been detected along its southwestern slope. Different types of mass movements, genetically associated with each other, characterize this landslide: 1) a basal slump anticline, corresponding to a bulge on the bathymetry detaching at about 400 m sub-bottom depth; 2) an intermediate-mass movement chiefly consisting of debris avalanches and debris/turbiditic flows; 3) an upper mass movement consisting of hundred-metre size slumps detaching at relatively shallow depths. Conservative estimates indicate that at least 50 km3 of volcano-clastic and hemipelagic deposits have been mobilized, most of which comprise the basal slump anticline. This submarine landslide can be explained as a gravity failure of the continental slope unrelated to volcanism or rather as a process related to the dynamics of the volcanic edifice, which would imply volcano-spreading. • Oceanic and continental volcanic edifices may undergo slow collapse, named spreading • Ischia is an active volcano suspected to undergo long-term subsidence along with seismicity • Its southern, undersea section is affected by fast and long-term landslide phenomena • This long-term gravity instability can be viewed within the concept of volcano-spreading. [ABSTRACT FROM AUTHOR]

Geochemical and isotopic ( 87 Sr/ 86 Sr and 18 O/ 16 O) data have been acquired on whole rock and separated mineral samples from volcanic products of the 1302 AD Arso eruption, Ischia volcanic island (Gulf of Naples, Southern Italy), to investigate magmatic processes. Our results highlight petrographic and isotopic disequilibria between phenocrysts and their host rocks. Similar disequilibria are observed also for more mafic volcanic rocks from Ischia and in the Phlegraean Volcanic District in general. Moreover, 87 Sr/ 86 Sr and 18 O/ 16 O values suggest mixing between chemically and isotopically distinct batches of magma, and crystals cargo from an earlier magmatic phase. The radiogenic Sr isotope composition suggests that the mantle source was enriched by subduction-derived sediments. Furthermore, magmas extruded during the Arso eruption were affected by crustal contamination as suggested by high oxygen isotope ratios. Assimilation and fractional crystallization modelling of the Sr-O isotope compositions indicates that not more than ~ 7% of granodioritic rocks from the continental crust have been assimilated by a mantle-derived mafic magma. Hence the recent volcanic activity of Ischia has been fed by distinct batches of magma, variably contaminated by continental crust, that mixed during their ascent towards the surface and remobilized phenocrysts left from earlier magmatic phases. [ABSTRACT FROM AUTHOR]

Abstract: The lithological and compositional characteristics of eighteen different pyroclastic deposits of Campanian origin, dated between 125 cal ky BP and 22 cal ky BP, were described. The pyroclastic deposits were correlated among different outcrops mainly located on the Apennine slopes that border the southern Campanian Plain. They were grouped in two main stratigraphic and chronologic intervals of regional significance: a) between Pomici di Base (22.03 cal ky BP; Somma–Vesuvius) and Campanian Ignimbrite (39 cal ky BP; Campi Flegrei) eruptions; and b) older than Campanian Ignimbrite eruption. Three new 14C AMS datings support the proposed correlations. Six eruptions were attributed to the Pomici di Base-Campanian Ignimbrite stratigraphic interval, while twelve eruptions are older than Campanian Ignimbrite. Of the studied deposits two originated from Ischia island, five are related to Campi Flegrei, and three to Somma–Vesuvius. Two eruptions have an uncertain correlation with Somma–Vesuvius or Campi Flegrei, while six eruptions remain of uncertain source. Minimum volumes of five eruptions were assessed, ranging between 0.5 km3 and 4 km3. Two of the studied deposits were correlated with Y-3 and X-5 tephra layers, which are widely dispersed in the central Mediterranean area. The new stratigraphic and chronologic data provide an upgraded chrono-stratigraphy for the explosive activity of Neapolitan volcanoes in the period between 125 and 22 cal ky BP. [Copyright &y& Elsevier]

Abstract: The areas exposed to pyroclastic flow invasion in case of explosive eruptions at Ischia island (Italy) have been evaluated, together with the related volcanic hazard and risk. Ischia island lacks a central vent so, for the evaluation of volcanic hazard, it is necessary to forecast where a future explosive event might occur. At this purpose, we have evaluated the Vent Opening Probability by taking into account all the relevant geological information and processing them through spatial analysis. The whole Ischia island has been subdivided into 358 cells, in which we take into account the contribution of volcanological, geophysical and geochemical data to define the probability of opening of the vents. As a result, the highest spatial probability is found on the eastern sector of the island. Two series of simulations, by using the “energy cone” model [Malin, M.C., Sheridan, M.F., 1982. Computer-assisted mapping of pyroclastic surges. Science 217, 637–640] and assuming column collapse heights of 100 m, for eruptions of Volcanic Explosivity Index (VEI)=3, and of 300 m for eruptions of VEI=4, with Heim coefficient equal to 0.1, were performed. Through the overlay of the energy cone to the Digital Elevation Model of Ischia, it has been possible to automatically detect the invaded areas for each hypothesized vent. The intersection of this areas made it possible to define the different spatial probabilities of invasion by pyroclastic flow (PyF) for each point of the Ischia territory. Two different types of hazard maps have been derived: an equi-probability hazard map, sensitive to the distance from the vents and the presence of topographic obstacles, and a weighted hazard map, in which the probability of vent opening has also been taken into account. For both types of eruptions, the highest spatial probability of invasion are the so-called “graben of Ischia”, and the coastal plain between Monte Vico and Ischia Porto. Finally, by intersecting the exposed value map with the weighted hazard maps, the classification of the Ischia territory into three risk classes has been performed. The villages located in the Ischia graben and in the northern sector of the island have resulted to be exposed to the highest risk. [Copyright &y& Elsevier]

The correlation between onshore and offshore of the volcanic features in a complex volcanic field area is a difficult task, however, it is a fundamental step in order to better understand the geological evolution of such a complex area and for an assessment of geologic hazards. Ischia is a well exposed and densely populated volcanic field located in the Campania volcanic province of Italy. In order to improve our understanding of the recent volcanic history of Ischia Island, high-resolution seismic reflection profiles were used to identify volcanic and sedimentary features in the northern offshore. The volcano stratigraphy interpretation permitted us to recognize seismic units with a reflection-free/chaotic facies. These latter units have been associated with volcanic deposits and correlated to the main volcanic units outcropping on the northern coast of Ischia Island. They are limited in extent and interlayered with eight seismic units with continuous reflectors corresponding to clastic sedimentary units that were deposited during inter-eruptive phases. The main result of this work is the documentation of volcanic activity during the Holocene in the area offshore between Castello d'Ischia, Ischia Porto (mainly effusive products) and Punta della Scrofa (mainly shallow lava domes and dykes). The key volcanic units were mapped and 3D geological models were reconstructed. The reconstruction of the stratigraphic framework offshore a volcanic coast provides a pathway to the investigation of the stratigraphic relationships between inter-eruptive sedimentary deposits and volcanic units, and permits the assessment of a wide and continuous chronostratigraphic framework in a complex area. Furthermore, the onshore-offshore correlation of the main Holocene volcanic units allows us to better estimate their areal distribution, a critical factor in the hazard evaluation of a coastal volcanic area. The application of seismic volcano stratigraphy illustrates the remarkable possibilities that the study of submarine volcanic fields offers. • The goal of the paper is the stratigraphic analysis of an offshore volcanic field using seismic reflection profiles • The stratigraphic relationships between eruptive and inter-eruptive deposits have been reconstructed • We built 3D geologic surfaces of the main Holocene volcanoes offshore Ischia (Italy) • The onshore-offshore correlation of the volcanic unit permits to establish a geologic continuity across the coast • The application of seismic volcano stratigraphy proves the remarkable capabilities for the study of submarine volcanoes [ABSTRACT FROM AUTHOR]

• A study of the seismic noise at Ischia Island shows two persistent sources. • The principal source is related to the hydrothermal activity. • The fluid-solid interaction mechanism is modelled using organ-pipe theory. This work is devoted to the study of the background seismic noise at Ischia Island. We highlight two persistent independent signals, with dominant frequency peaks in the range 1−2 Hz and 3−4 Hz, respectively. The first signal is the most energetic and persistent and its polarization properties are well defined, revealing a shallow propagation likely controlled by both tectonic/volcanic structures and morphological features. This signal is well correlated at all the stations in the Casamicciola area and its group velocity is estimated as 500−600 m/s. The second signal shows similar polarization properties but the temporal pattern of its amplitude is strongly affected by anthropogenic noise, revealing a modulation on a diurnal scale. On the investigated spatial scales, any clearly correlated signal is not evidenced. We interpret the 1−2 Hz correlated wave-packets as the persistent whisper of the shallow circulation of fluids, which are a mixing of sea and meteoric water and thermal fluids of the hydrothermal reservoir. In the conceptual scheme of the self-sustained musical instruments, we hypothesize that the solid structure of the shallow hydrothermal system of Ischia is formed by a network of channels, continuously excited by the circulating hydrothermal fluids, which produce a whispered sound (i.e. the seismic noise). This mechanism is able to produce persistent self-sustained oscillations that we observe as the 1−2 Hz seismic signal and, eventually, higher modes. [ABSTRACT FROM AUTHOR]