The combined use of field investigation and laboratory analyses allowed the detailed stratigraphic reconstruction of the Pollena eruption (472 AD) of Somma-Vesuvius. Three main eruptive phases were recognized, related either to changes in the eruptive processes and/or to relative changes of melt composition. The eruption shows a pulsating behavior with deposition of pyroclastic fall beds and generation of dilute and dense pyroclastic density currents (PDC). The eruptive mechanisms and transportation dynamics were reconstructed for the whole eruption. Column heights were between 12 and 20 km, corresponding to mass discharge rates (MDR) of 7x10(6) kg/s and 3.4x10(7) kg/s. Eruptive dynamics were driven by magmatic fragmentation of a phono-tephritic to tephri-phonolitic magma during Phases I and II, whereas phreatomagmatic fragmentation dominated Phase III. Magma composition varies between phonolitic and tephritic-phonolitic, with melt viscosity likely not in excess of 10(3) Pa s. The volume of the pyroclastic fall deposits, calculated by using of proximal isopachs, is 0.44 km(3). This increases to 1.38 km(3) if ash volumes are extrapolated on a log thickness vs. square root area diagram using one distal isopach and column height.
A complex Subplinian-type eruption from low viscosity, phonolitic to tephri-phonolitic magma: the Pollena eruption of Somma-Vesuvius (Italy)
SULPIZIO, ROBERTO;Mele D;DELLINO, Pierfrancesco;
2005-01-01
Abstract
The combined use of field investigation and laboratory analyses allowed the detailed stratigraphic reconstruction of the Pollena eruption (472 AD) of Somma-Vesuvius. Three main eruptive phases were recognized, related either to changes in the eruptive processes and/or to relative changes of melt composition. The eruption shows a pulsating behavior with deposition of pyroclastic fall beds and generation of dilute and dense pyroclastic density currents (PDC). The eruptive mechanisms and transportation dynamics were reconstructed for the whole eruption. Column heights were between 12 and 20 km, corresponding to mass discharge rates (MDR) of 7x10(6) kg/s and 3.4x10(7) kg/s. Eruptive dynamics were driven by magmatic fragmentation of a phono-tephritic to tephri-phonolitic magma during Phases I and II, whereas phreatomagmatic fragmentation dominated Phase III. Magma composition varies between phonolitic and tephritic-phonolitic, with melt viscosity likely not in excess of 10(3) Pa s. The volume of the pyroclastic fall deposits, calculated by using of proximal isopachs, is 0.44 km(3). This increases to 1.38 km(3) if ash volumes are extrapolated on a log thickness vs. square root area diagram using one distal isopach and column height.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
