Publication Date:
2021-12-16
Description:
Pyroclastic density currents (PDCs) generated
during the Plinian eruption of the Pomici di Avellino (PdA)
of Somma–Vesuvius were investigated through field and
laboratory studies, which allowed the detailed reconstruction
of their eruptive and transportation dynamics and the
calculation of key physical parameters of the currents. PDCs
were generated during all the three phases that characterised
the eruption, with eruptive dynamics driven by both magmatic
and phreatomagmatic fragmentation. Flows generated during
phases 1 and 2 (EU1 and EU3pf, magmatic fragmentation)
have small dispersal areas and affected only part of the
volcano slopes. Lithofacies analysis demonstrates that the
flow-boundary zones were dominated by granular-flow
regimes, which sometimes show transitions to traction
regimes. PDCs generated during eruptive phase 3 (EU5,
phreatomagmatic fragmentation) were the most voluminous
and widespread in the whole of Somma–Vesuvius’ eruptive
history, and affected a wide area around the volcano with
deposit thicknesses of a few centimetres up to more than
25 km from source. Lithofacies analysis shows that the flowboundary
zones of EU5 PDCs were dominated by granular
flows and traction regimes. Deposits of EU5 PDC show
strong lithofacies variation northwards, from proximally
thick, massive to stratified beds towards dominantly alternating
beds of coarse and fine ash in distal reaches. The EU5
lithofacies also show strong lateral variability in proximal
areas, passing fromthe western and northern to the eastern and
southern volcano slopes, where the deposits are stacked beds
of massive, accretionary lapilli-bearing fine ash. The sedimentological
model developed for the PDCs of the PdA
eruption explains these strong lithofacies variations in the
light of the volcano’s morphology at the time of the eruption.
In particular, the EU5 PDCs survived to pass over the break in
slope between the volcano sides and the surrounding
volcaniclastic apron–alluvial plain, with development of new
flows from the previously suspended load. Pulses were
developed within individual currents, leading to stepwise
deposition on both the volcano slopes and the surrounding
volcaniclastic apron and alluvial plain. Physical parameters
including velocity, density and concentration profile with
height were calculated for a flow of the phreatomagmatic
phase of the eruption by applying a sedimentological method,
and the values of the dynamic pressure were derived. Some
hazard considerations are summarised on the assumption that,
although not very probable, similar PDCs could develop
during future eruptions of Somma–Vesuvius
Description:
Published
Description:
559–577
Description:
2.3. TTC - Laboratori di chimica e fisica delle rocce
Description:
3.5. Geologia e storia dei vulcani ed evoluzione dei magmi
Description:
3.6. Fisica del vulcanismo
Description:
JCR Journal
Description:
reserved
Keywords:
Pyroclastic density currents
;
Pomici diAvellino
;
Somma–Vesuvius
;
Dynamic pressure
;
04. Solid Earth::04.04. Geology::04.04.10. Stratigraphy
;
04. Solid Earth::04.08. Volcanology::04.08.05. Volcanic rocks
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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