Publication Date:
2023-07-18
Description:
The 4.5 ka trachytic Plinian eruption of Agnano-Monte Spina is the largest magnitude event of the past 5 ka at
Campi Flegrei caldera. The complete eruptive sequence consists of six members, three of which, named A, B and
D, are characterized by the association of fallout and pyroclastic density current (PDC) deposits well preserved at
proximal locations.
In this study, we analyze the textural characteristics of the pumice clasts of the three major fallout deposits
(A1, B1, D1) and of their associated PDC deposits (A2, B2, D2), and link them to the physical properties of
magma in order to investigate conduit fluid dynamics. A combination of data (field work, grain-size and density
measurements, vesicle number densities and size distributions, crystal content, water content) is used to set up
the source term conditions for numerical simulations.
Each fall/PDC transition is accompanied by distinctive changes in textural properties of the juveniles, recognized
by a lowering in vesicle number densities of about one order of magnitude (from 108 to 107 cm−3),
indicating a significant decrease in the magma ascent rate. Melt inclusions show a marked decrease in volatile
content recurrent at each fall/PDC transition and indicate that the three main pulses of the eruption were fed by
distinct and progressively deeper magma batches. Numerical simulations, taking into account magma properties
derived from the textural analyses, and variations in initial water content, show decreases in the exit velocities
and Mass Discharge Rate (MDR) consistent with such fall/PDC transitions. Different initial water contents together
with changes in conduit diameters allow us to simulate the different column heights reconstructed for the
three Plinian phases. The reconstructed scenario for the Agnano-Monte Spina eruption involves a stop-start
behavior and a top-down trigger for the most voluminous and intense eruptive episode D.
Description:
Published
Description:
119301
Description:
4V. Processi pre-eruttivi
Description:
JCR Journal
Keywords:
Campi flegrei
;
Plinian eruptions
;
Textural analysis
;
VSD
;
CSD
;
Numerical modeling
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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