Publication Date:
2017-04-04
Description:
On 28 December 2002, the persistent Strombolian activity at Stromboli was interrupted by the sudden onset of lava emission
onto the Sciara del Fuoco slope, a horseshoe-shaped depression on the NW flank of the volcano. The effusive episode went on until
22 July 2003 and produced a cumulative volume of lavas of 11×106 m3 ranking the event as the largest occurred in the past
30 years. The eruptive vents were mainly located in the NE sector of the Sciara del Fuoco depression, at an elevation of 550–600 m
a.s.l. On 30 December, the eastern portion of the Sciara del Fuoco collapsed producing a tsunamigenic landslide. On 5 April 2003,
a paroxysmal eruption occurred at the summit craters during which crystal-poor pumiceous products were emitted. The paroxysm
did not interrupt the lava emission. The Strombolian activity at the summit craters gradually resumed starting from March 2003 and
fully recovered by the end of July.
Periodic sampling of the lava at the active vents was carried out during the entire effusive event. All the analysed samples are
shoshonitic basalts (SiO2 48.5–50.4 wt.%; K2O 2.1–2.4 wt.%) in the range of composition observed in the products erupted during
the past 20 years. They bear about 50 vol.% zoned crystals of plagioclase An90–60, diopside–augite and olivine Fo70–73 in a
compositionally homogeneous shoshonitic groundmass. Bulk rock major and trace element contents measured with different
methodologies at different laboratories show only minor variations. Sr and Nd isotope ratios are close to those of the crystal-rich
scoriae erupted in the previous years.
Despite of small compositional variations related to the emptying of the zoned topmost portion of the conduit, the data show
that the switch from Strombolian explosive to effusive activity is not associated with changes of the textures and composition of the
erupted products. Slight but somehow systematic variation of trace elements and isotope ratios between products erupted before
and after the 5 April eruption are likely accounted by limited mixing between the fresh, volatile-rich, crystal-poor, magma erupted
as pumice during the paroxysm, and the volatile-poor, crystal-rich magma feeding the lava flow. The uniform composition of the
erupted lava indicates the presence of a large volume of well-mixed, crystal-rich, homogeneous magma residing in the shallow
plumbing system of the volcano.
Two possible trigger mechanism of the effusive event are here proposed: (i) a discrete input of fresh magma into the lower part
of the shallow magmatic system occurred some months before the eruption and was followed by crystallisation, degassing and mixing with the crystal-rich shallow magma which re-homogenised the system. These processes eventually led to the rise of the
magma at a higher level and failure of the conduit walls. (ii) The onset of the effusion may represent the consequence of a gradual
rise of the magma level in the conduits occurred in the past two decades. The process of progressive refilling, initiated after the
1985 effusive eruption, ultimately culminated on 28 December 2002 with the failure of the conduit wall and the opening of vents
100–150 m below the summit craters
Description:
Published
Description:
263-284
Description:
JCR Journal
Description:
reserved
Keywords:
Stromboli volcano
;
Aeolian Islands
;
2002–2003 eruption
;
Mineralogy
;
Geochemistry
;
Sr isotope
;
04. Solid Earth::04.08. Volcanology::04.08.03. Magmas
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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