Plinian eruptions are short-lived events that can have long-lasting consequences. They produce high eruptive columns by injecting huge volumes of pyroclastic fragments and gases into the stratosphere. Pyroclastic clasts fall back to the ground forming widespread tephra sheets in which three different components are distinguished: juvenile clasts, lithic clasts and crystals. Frothy, well-vesiculated (pumice) juvenile clasts, produced during magma fragmentation in the volcanic conduit, are the main component of these deposits. This ‘classical’ behavior is well represented by the AD 79 Vesuvius eruption that produced a sustained column phase, which deposited a thick pumice lapilli deposit consisting of a white, phonolitic layer A overlain by a gray, tephriphonolitic layer B. New field and laboratory data define the reprise of the sustained column during the second phase of the eruption, characterized by a prevalence of collapsing column phases, that produced numerous pyroclastic density currents. Five lithic-rich fall layers have been recognized in the pyroclastic density currents post-Plinian sequences of the Vesuvius AD 79 eruption cropping out at various locations from the Vesuvius slopes to the edge of the Campanian Plain, 20 km from the source. These lithic-rich horizons, named D, G1, G3, I and X2 from base to top, exhibit mantling structures, are massive and generally well sorted (sf = 1.05- 1.55). Lithic-rich layers show the same dispersal direction as the basal lapilli Plinian deposit, with their axes trending between N130°E and N140°E. The relative abundance of the components for all samples has been plotted on a triangular diagram (Fig. 1). Plotted fields for each layer are only partially overlapping. Layers A and B are rich in juvenile clasts (average 77-82 and 64-66 wt%, respectively), while layer D has 63-70 wt% of lithics and 24 wt% of juvenile clasts. The upper layers show 82-94 wt% of lithics and less than 5 wt% of juvenile material. The main difference with the basal pumice lapilli deposit is the strong enrichment in lithic clasts, possibly associated with an instability in the conduit-vent system.
Components Evolution During the Sustained Phases of the AD 79 Vesuvius Eruption / Chiominto, G.; Scarpati, C.; Perrotta, A.; Fedele, L.; Santangelo, I.. - (2021). (Intervento presentato al convegno AGU Fall Meeting tenutosi a New Orleans, LA & Everywhere nel 13-17 December 2021).
Components Evolution During the Sustained Phases of the AD 79 Vesuvius Eruption
Chiominto G.;Scarpati C.;Fedele L.;Santangelo I.
2021
Abstract
Plinian eruptions are short-lived events that can have long-lasting consequences. They produce high eruptive columns by injecting huge volumes of pyroclastic fragments and gases into the stratosphere. Pyroclastic clasts fall back to the ground forming widespread tephra sheets in which three different components are distinguished: juvenile clasts, lithic clasts and crystals. Frothy, well-vesiculated (pumice) juvenile clasts, produced during magma fragmentation in the volcanic conduit, are the main component of these deposits. This ‘classical’ behavior is well represented by the AD 79 Vesuvius eruption that produced a sustained column phase, which deposited a thick pumice lapilli deposit consisting of a white, phonolitic layer A overlain by a gray, tephriphonolitic layer B. New field and laboratory data define the reprise of the sustained column during the second phase of the eruption, characterized by a prevalence of collapsing column phases, that produced numerous pyroclastic density currents. Five lithic-rich fall layers have been recognized in the pyroclastic density currents post-Plinian sequences of the Vesuvius AD 79 eruption cropping out at various locations from the Vesuvius slopes to the edge of the Campanian Plain, 20 km from the source. These lithic-rich horizons, named D, G1, G3, I and X2 from base to top, exhibit mantling structures, are massive and generally well sorted (sf = 1.05- 1.55). Lithic-rich layers show the same dispersal direction as the basal lapilli Plinian deposit, with their axes trending between N130°E and N140°E. The relative abundance of the components for all samples has been plotted on a triangular diagram (Fig. 1). Plotted fields for each layer are only partially overlapping. Layers A and B are rich in juvenile clasts (average 77-82 and 64-66 wt%, respectively), while layer D has 63-70 wt% of lithics and 24 wt% of juvenile clasts. The upper layers show 82-94 wt% of lithics and less than 5 wt% of juvenile material. The main difference with the basal pumice lapilli deposit is the strong enrichment in lithic clasts, possibly associated with an instability in the conduit-vent system.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
