No abstract

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.

[1] Paroxysms at Stromboli are the most violent manifestations of the persistent activity and are related to the emission of small volumes (10 3 -10 5 m 3 ) of nearly aphyric HKbasaltic pumices. They offer the exceptional opportunity to detail the mixingcrystallization-degassing processes that occur in a steady state basaltic arc volcano. We present mineralogy, major, volatile, and trace element geochemistry of olivine-hosted melt inclusions of these pumices. In all the paroxysms, melt inclusions hosted in olivines Fo 88 -91 have recorded the parental melts rich in CaO (up to 14.5 wt %) but low in FeO (6-7 wt %). They demonstrate recurrent variations in the K 2 O content (1.6-1.3 wt %) and S/Cl ratios (1.2-0.8) of the melts that entered the deep system. Dynamic magma mixing between melts slightly distinct by their degree of evolution, rapid crystallization, and entrapment of gas-oversaturated melts during decompression are indicated by (1) the high density of irregular, clear melt inclusions, and embayments in homogeneous olivines (Fo 87±0.5 -Fo 83±0.5 ), (2) the variable ratio between melt and gas bubble, and (3) the variability of melt inclusion compositions in both major (CaO/Al 2 O 3 = 1-0.59) and volatile (3.4-1.8 wt % H 2 O, 1582-1017 ppm CO 2 ) elements. FeO-rich melt inclusions in patchy, reversely zoned olivines also demonstrate interactions between ascending melt blobs and inherited olivine crystals. We propose a model involving a vertically extended dike-like system, where magmas progress and differentiate. On the basis of olivine growth rate calculations the volatile-rich magma blobs may ascend within few hours to few tenths of hours. Finally, we propose that sulfur degassing is possibly initiated during the early stage of magma differentiation.

Stromboli, known worldwide as the ªLight-house of the Mediterraneanº, is commonly believed to have been in a state of persistent activity for the past 2000±2500 years. However, historical sources older than 1000 A.D. are not accurate enough to assess if the activity of the volcano was exactly the same as we see at present. In order to attempt to identify the onset of the present eruptive regime, and assess if it has been maintained with the same characteristics through time, stratigraphic and radiometric studies of the recent tephra deposits were undertaken. Up to 4-m-deep stratigraphic trenches, dug at a height of approximately 500 m on the NE flank of the volcano, exposed a conformable tephra pile containing charcoal fragments. One of the most interesting finds was the discovery of a 7-cm-thick weathered bed rich in organic matter (thin palaeosol) approximately 3 m below the surface. The sequence underneath the palaeosol consists of decimetre-thick lapilli fallout beds alternating with ash deposits bearing small charcoals with calibrated ages of between the fourth century B.C. and the first century A.D. The sequence above the palaeosol is charcoal free and consists of coarseash deposits with discrete, centimetre-thick lapilli fallout beds composed of crystal-poor golden pumice and subordinate crystal-rich black scoriae similar to scoria/ pumice pairs emitted during the more energetic explosions of the present-day activity. The data collected indicate that between the third and seventh centuries A.D., after a period of quiescence, the activity resumed with an eruptive style identical to the present one. We conclude that the ªLighthouse of the Mediterraneanº actually began its activity in a period much later than previously thought.