HR: 1340h
AN: V53B-1548    [Abstracts]
TI: Estimate Of Deposition Temperature Of The PDC Deposits Of The AD 472 Pollena Eruption Of Somma-Vesuvius, Italy.
AU: Zanella, E
EM: elena.zanella@unito.it
AF: Dipartimento Scienze della Terra, universita di Torino, Via Valperga Caluso 35, Torino, 10125 Italy
AU: Sulpizio, R
EM: sulpizio@dst.unipi.it
AF: Dipartimento Geomineralogico, Universita' di Bari, Via Orabona 4, Bari, 70125 Italy
AU: Lanza, R
EM: roberto.lanza@unito.it
AF: Dipartimento Scienze della Terra, universita di Torino, Via Valperga Caluso 35, Torino, 10125 Italy
AU: * Gurioli, L
EM: gurioli@hawaii.edu
AF: G&G/SOEST University of Hawaii, 1680 East-West Rd., Honolulu, HI 96822 United States
AU: Bontempi, M
EM: manubont@yahoo.it
AF: Dipartimento Scienze della Terra, universita di Torino, Via Valperga Caluso 35, Torino, 10125 Italy
AB: The AD 472 Pollena eruption of Somma Vesuvius, Italy, was a complex subplinian event which generated several pyroclastic density currents (PDCs). PDC deposits were emplaced by dilute-to-highly concentrated stratified currents both during the magmatic and phreatomagmatic phases of the eruption. PDCs are the most devastating of all volcanic phenomena, due to their high velocity, temperature, ash concentration and missels content. A key piece of information in understanding PDC dynamics and their hazard is given by the temperatures at which they are emplaced (Tdep). Because the Pollena eruption is considered to have a size and style similar to that of the Maximum Expected Event defined for Somma-Vesuvius, knowledge of the PDC deposits and their temperatures is very important in terms of hazard evaluation and physical modelling. In this research we completed a thermal analysis of the magnetic remanence carried by lithic clasts embedded within the deposits to infer the Tdep of the PDC deposits allowing us to develop a detailed picture of the depositional history of the entire pyroclastic sequence of Pollena eruption. Sampling of the lithic clasts embedded within the deposits was done both vertically through the stratigraphic sequence, as well as within single flow units along transects extending radially from the vent. Clasts, ranging in volume from 2 to 100 cm³, were collected from twelve sites. The clasts were subjected to stepwise thermal demagnetization at temperature steps of 20-40 °C. This procedure allowed to separate two remanence components in each individual clast: the primary, high blocking-temperature component and the secondary, low blocking temperature component acquired because of reheating during the PDC emplacement. The Tdep at a particular site was then estimated from the overlapping of the reheating temperature range for all invididual lithic clasts collected at that site. Preliminary results show that the Tdep values vary between 260 and 320 °C in most PDC units and reach in one unit the highest value of 340 °C.
DE: 8414 Eruption mechanisms and flow emplacement
DE: 8428 Explosive volcanism
DE: 8486 Field relationships (1090, 3690)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005