Publication Date:
2017-04-04
Description:
Recent stratigraphic studies at Vesuvius have
revealed that, during the past 4,000 years, long lasting,moderate to low-intensity eruptions, associated with continuous
or pulsating ash emission, have repeatedly occurred. The present work focuses on the AS1a eruption, the first of a series of ash-dominated explosive episodes which
characterized the period between the two Subplinian eruptions of 472 AD and 1631 AD. The deposits of this eruption consist of an alternation of massive and thinly laminated ash layers and minor well sorted lapilli beds, reflecting the pulsatory injection into the atmosphere of variably concentrated ash-plumes alternating with Violent Strombolian stages. Despite its nearly constant chemical composition, the juvenile material shows variable external clast morphologies and groundmass textures, reflecting the fragmentation of a magma body with lateral and/or vertical gradients in both vesicularity and crystal content. Glass
compositions and mineralogical assemblages indicate that the eruption was fed by rather homogeneous phonotephritic magma batches rising from a reservoir located at ~ 4 km
(100 MPa) depth, with fluctuations between magma delivery and magma discharge. Using crystal size distribution (CSD) analyses of plagioclase and leucite microlites, we estimate that the transit time of the magma in the conduit was on the order of ~ 2 days, corresponding to an ascent rate of around 2×
10−2 ms−1. Accordingly, assuming a typical conduit diameter for this type of eruption, the minimum duration of the AS1a event is between about 1.5 and 6 years. Magma fragmentation occurred in an inertially driven regime that, in a magma with low viscosity and surface tension, can act also under conditions of slow ascent.
Description:
In press
Description:
3.5. Geologia e storia dei vulcani ed evoluzione dei magmi
Description:
JCR Journal
Description:
reserved
Keywords:
Ash emission activity
;
Tephrite
;
Vesuvius
;
Stratigraphy
;
Textural analyses
;
04. Solid Earth::04.08. Volcanology::04.08.05. Volcanic rocks
;
04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
Permalink
