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Results are presented for a paleodirectional and paleointensity study of 16 Popocatepetl lava flows. Popocatepetl is a tall, active, dacitic-andesitic stratovolcano; it forms the southern end of a N-S-trending Quaternary volcanic range at the eastern edge of the Basin of Mexico. Studied units are mainly andesites and one trachyandestite, and all possess similar trace- and rare-earth-element compositions. Rock-magnetic experiments show that remanence is carried in most cases by Ti-poor titanomagnetite, resulting from oxy-exsolution of original titanomagnetite during flow cooling. Unblocking temperature spectra and high coercivities point to "small" pseudo-single domain magnetic grains for these (titano)magnetites. Single-component, linear demagnetization plots were observed in most cases. A strong, lightning-produced magnetization overprint was detected for one site. Combining the new paleomagnetic data provides a mean paleodirection of I = 35.4degrees, D = 345.7degrees, k = 21, alpha(95) = 8.5degrees, N = 15 for the Popocatepetl volcano region. All studied flows yield normal polarity magnetization, which supports a maximum age within the Brunhes chron.

Detailed paleomagnetic and rock magnetic studies of 14 previously undated lava flows from the Somma-Vesuvius volcanic complex were undertaken. The magnetic carriers consist of Ti-poor titanomagnetites typified by pseudo-single domains. Characteristic magnetization directions determined from detailed stepwise alternating field and thermal demagnetizations gave well-defined mean directions for each flow unit. Paleodirectioris for 10 of the 14 lavas appear to be related to the early 17(th) century segment of the Italian paleosecular variation reference curve; thus their ages are easily retrieved. The remaining four sites yielded distinct mean directions. which cannot be simply cor-related to any given sector of the reference curve. within the little frame expected for the activity. The paleomagnetic directions for these lavas may correspond to little intervals outside the period covered by the reference secular variation curve, or they may reflect local structural disturbance and have no geomagnetic significance.

SUMMARY A palaeomagnetic study on Vesuvius lava flows, emplaced after the 79 AD event, has been carried out in order to correlate and/or discriminate deposits and to verify their age of emplacement using the new SISVC (Southern Italy secular variation curve). Results from 18 sites located on the W, S and E slopes of the volcano, are presented. IRM (isothermal remanent magnetization), along three orthogonal directions, ARM (anhysteretic remanent magnetization), low field susceptibilities measurements and coercivity analyses have been carried out on three pilot specimens per each site in order to both identify the magnetic carriers and determine the magnetic grain sizes. The study of TRM (thermal remanent magnetization) of each investigated lava flow was carried out by subjecting each specimen to complete PTD (progressive thermal demagnetization). The primary directions were defined by linearity analysis following very stringent criteria. It is shown that three of the investigated lava flows, outcropping on the W–S slopes of the volcano, must be associated to the 1631 AD big eruption. This result widens the number of sites to be associated to this eruption, in accordance with previous palaeomagnetic works. The site mean direction of 1906 lava flow is anomalous with reference to the SISVC and further investigations are needed to clarify this point.

The Campi Flegrei volcanic field, Southern Italy, is composed of a large variety of pyroclastic deposits related to both magmatic and hydromagmatic activity. In spite of similarities of composition, grain size, age and pre-eruptive environment, the various deposits exhibit great differences in terms of degree and type of alteration of the juvenile components. In particular, detailed analyses of pyroclasts collected in the numerous monogenetic volcanic cones show the broad range of alteration, from fresh glass to complete replacement of the glass by the zeolites. The comparative analysis of 17 different deposits has allowed us to conclude that the eruptive and emplacement conditions were the major controls on the zeolitization processes. The relationships between volcanological features of deposits and secondary mineralization are consistent with the glass-fluid phase reaction in a near-closed post-depositional system. Eruptions characterised by separation of water vapour from the pyroclastic particles produce unaltered or poorly altered deposits. In contrast, eruptions characterised by mechanisms that permit the capture and retention of pore water and water vapour produce zeolitized deposits. According to these lines of evidence the zeolitization of pyroclastic products of Campi Flegrei took place immediately after emplacement, during the cooling of wet deposits.

The eruption's first surge instantly killed some people sheltering from the impact. The town of Herculaneum, lying at the foot of Mount Vesuvius on a cliff overlooking the sea, was buried by a succession of pyroclastic surges and flows (currents of volcanic ash and hot gases generated by collapse of the eruptive column) during the plinian eruption of ad 79. The skeletons of 80 of 300 people who had taken refuge in 12 boat chambers along the beach have now been unearthed from the first surge deposit. We have investigated how these people were killed by this surge, despite being sheltered from direct impact, after its abrupt collapse (emplacement) at about 500 °C on the beach. The victims' postures indicate that they died instantly, suggesting that the cause of death was thermally induced fulminant shock1 and not suffocation, which is believed to have killed many of the inhabitants of Pompeii and of Herculaneum itself.