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[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.

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Stromboli, the northernmost island of the Aeolian archipelago, is known for its persistent volcanic activity over the last several centuries and for its cone which, on clear days, is surmounted by a gas plume rising from its summit. The island hosts two settled areas: the village of Stromboli (c. 500 inhabitants) to the NE and that of Ginostra (c. 40 inhabitants) to the SW, both situated along the coast. In summer the number of residents grows considerably, reaching c. 5000 people. This paper provides a description of the present activity and reassesses volcanic hazards on the basis of data from a new monitoring system and from studies on the 2002–2003 and 2007 crises. The normal activity, that of mild Strombolian explosions, is occasionally interrupted by violent eruptions of variable scale (paroxysmal events) and lava flows. Volcanic hazards directly generated by eruptive activity consist of ballistic and tephra fallout, pyroclastic flows, lava flows, wildfires and minor lahars, presenting serious problems to the settled areas only occasionally. In addition to hazards directly related to eruptive phenomena, the Sciara del Fuoco depression has been the site of landslides at various scales, sometimes accompanied by the formation of tsunamis.

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The 5 April 2003 paroxysm of Stromboli occurred during an ongoing effusive episode that initiated on 28 December 2002. It mainly consisted in two, a few seconds apart cannon‐like explosions followed by a vertical gas/pyroclast jet. The HK‐basaltic pumices, that were generated, mainly contain crystals that were drained back from the shallow parts of the plumbing system. Few euhedral to anhedral olivines and their melt inclusions testify to crystal fractionation and possible mixing between HK‐basaltic magmas variable in their volatile content, extent of evolution and volume. The most primitive, volatile‐rich, HK‐basalt term is sizable at micrometer scale, only. We propose that the triggering mechanism of the paroxysm was initiated at moderate pressures (≥240 MPa) and was related to bubble‐driven ascent of magma blobs. The latter rose through and interacted with overlying slightly more evolved melts and, finally mingled with the shallow crystal‐rich magma just before the eruption.

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