TY - JOUR
T1 - Discriminating the long distance dispersal of fine ash from sustained columns or near ground ash clouds
T2 - The example of the Pomici di Avellino eruption (Somma-Vesuvius, Italy)
AU - Sulpizio, Roberto
AU - Bonasia, Rosanna
AU - Dellino, Pierfrancesco
AU - Di Vito, Mauro A.
AU - La Volpe, Luigi
AU - Mele, Daniela
AU - Zanchetta, Giovanni
AU - Sadori, Laura
N1 - Funding Information:
This work is part of the ongoing research on explosive volcanic activity of Italian volcanoes funded by Dipartimento della Protezione Civile and Istituto Nazionale di Geofisica e Vulcanologia of Italy (DPC-INGV sub-project V3-4). Daniela Pantosti is acknowledged for helpful discussions and for providing samples of the Pian di Pecore site. David Pyle, Gianluca Sottili and an anonymous reviewer are acknowledged fro the useful review of the manuscript.
PY - 2008/10/20
Y1 - 2008/10/20
N2 - Ash samples from tephra layers correlated with the Pomici di Avellino (Avellino Pumice) eruption of Somma-Vesuvius were collected in distal archives and their composition and particle morphology investigated in order to infer their behaviour of transportation and deposition. Differences in composition and particle morphologies were recognised for ash particles belonging to the magmatic Plinian and final phreatomagmatic phases of the eruption. The ash particles were dispersed in opposite directions during the two different phases of the eruption, and these directions are also different from that of coarse-grained fallout deposits. In particular, ash generated during magmatic phase and injected in the atmosphere to form a sustained column shows a prevailing SE dispersion, while ash particles generated during the final phreatomagmatic phase and carried by pyroclastic density currents show a general NW dispersion. These opposite dispersions indicate an ash dispersal influenced by both high and low atmosphere dynamics. In particular, the magmatic ash dispersal was first driven by stratospheric wind towards NE and then the falling particles encountered a variable wind field during their settling, which produced the observed preferential SE dispersal. The wind field encountered by the rising ash clouds that accompanied the pyroclastic density currents of the final phreatomagmatic phase was different with respect to that encountered by the magmatic ash, and produced a NW dispersal. These data demonstrate how ash transportation and deposition are greatly influenced by both high and low atmosphere dynamics. In particular, fine-grained particles transported in ash clouds of small-scale pyroclastic density currents may be dispersed over distances and cover areas comparable with those injected into the stratosphere by Plinian, sustained columns. This is a point not completely addressed by present day mitigation plans in case of renewal of activity at Somma-Vesuvius, and can yield important information also for other volcanoes potentially characterised by explosive activity.
AB - Ash samples from tephra layers correlated with the Pomici di Avellino (Avellino Pumice) eruption of Somma-Vesuvius were collected in distal archives and their composition and particle morphology investigated in order to infer their behaviour of transportation and deposition. Differences in composition and particle morphologies were recognised for ash particles belonging to the magmatic Plinian and final phreatomagmatic phases of the eruption. The ash particles were dispersed in opposite directions during the two different phases of the eruption, and these directions are also different from that of coarse-grained fallout deposits. In particular, ash generated during magmatic phase and injected in the atmosphere to form a sustained column shows a prevailing SE dispersion, while ash particles generated during the final phreatomagmatic phase and carried by pyroclastic density currents show a general NW dispersion. These opposite dispersions indicate an ash dispersal influenced by both high and low atmosphere dynamics. In particular, the magmatic ash dispersal was first driven by stratospheric wind towards NE and then the falling particles encountered a variable wind field during their settling, which produced the observed preferential SE dispersal. The wind field encountered by the rising ash clouds that accompanied the pyroclastic density currents of the final phreatomagmatic phase was different with respect to that encountered by the magmatic ash, and produced a NW dispersal. These data demonstrate how ash transportation and deposition are greatly influenced by both high and low atmosphere dynamics. In particular, fine-grained particles transported in ash clouds of small-scale pyroclastic density currents may be dispersed over distances and cover areas comparable with those injected into the stratosphere by Plinian, sustained columns. This is a point not completely addressed by present day mitigation plans in case of renewal of activity at Somma-Vesuvius, and can yield important information also for other volcanoes potentially characterised by explosive activity.
KW - Pomici di Avellino eruption
KW - ash dispersal
KW - atmosphere dynamics
KW - tephra layers
KW - volcanic hazard
UR - http://www.scopus.com/inward/record.url?scp=53949085752&partnerID=8YFLogxK
U2 - 10.1016/j.jvolgeores.2007.11.012
DO - 10.1016/j.jvolgeores.2007.11.012
M3 - Artículo
SN - 0377-0273
VL - 177
SP - 263
EP - 276
JO - Journal of Volcanology and Geothermal Research
JF - Journal of Volcanology and Geothermal Research
IS - 1
ER -