Publication Date:
2019-04-03
Description:
Since January 2011, Mt. Etna volcano has been affected by more than forty paroxysmal eruptions at the summit
(New South East Crater; NSEC). On the basis of their very variable duration, seven eruptions have been selected
among the twenty-five of 2011–2012 in order to decipher potential differences in their triggering mechanism.
Paroxysms have been investigated through a multidisciplinary approach that integrates data from volcanic
tremor and petrology (textures and micro-analysis on plagioclase crystals). Our results lead to the conclusion
that close relationships exist between the duration of the eruptions and the temporal evolution of the volcanic
tremor amplitude, especially during the Strombolian phase preceding the paroxysmal activity. In this regard,
we distinguished: 1) paroxysms preceded by long-lasting initial Strombolian phases, characterized by low
rate of volcanic tremor amplitude increase; and 2) eruptions preceded by short initial Strombolian phases,
showing high rate of volcanic tremor amplitude increase. Based on the pattern of volcanic tremor amplitude
increase, the former mainly showed a ramp-shaped morphology, while the latter a bell-shaped trend. Location
of the volcanic tremor centroid during the quiescent intervals between the paroxysmal eruptions has
highlighted the presence of a magmatic volume at 1–2 km a.s.l. beneath the North East Crater (NEC). During
the syn-eruptive Strombolian and lava fountaining phases, the centroid of volcanic tremor migrates below the
NSEC. This leads to the consideration that the magma batch residing beneath NEC played an important role in the
volcanic activity at NSEC during the considered period. Also the textures and compositional zoning (anorthite
and iron variations) in selected plagioclase crystals of the analyzed lavas suggest relations between duration of
the paroxysms and dynamics of pre-eruptive magmatic processes at depth. Particularly, two mechanisms have
been accounted for triggering of eruptions at the NSEC on the basis of the concordant or discordant behavior
of anorthite and iron in plagioclase coupled with disequilibrium textures at the rim. Concordant anorthite and
iron increases in plagioclase crystals with sieve-textured rims indicate recharge by more mafic, gas-rich
magma. This textural-compositional behavior has been related to long-lasting eruptions, whose volcanic tremor
amplitude evolution produced ramp-shaped increase of the volcanic tremor amplitude before the paroxysmal
phase. On the contrary, crystalswith sieve-textures at the rim, characterized by increasing iron at rather constant
or decreasing anorthite, suggest the prominent role of gas injections into the residing system. In this instance, the
compositional behavior has been linked with short-lasting eruptions, whose volcanic tremor amplitude evolution
led to a sudden increase of the seismic amplitude before the climax of the eruption. Thus, our work put
forward the idea that the evolution and duration of the Strombolian phase preceding the paroxysmal eruptions
of 2011–2012 at Mt. Etna are strongly controlled by the eruption triggering mechanism, which can be either gas
burst or gas-rich magma recharge.
Description:
Published
Description:
1–13
Description:
3V. Dinamiche e scenari eruttivi
Description:
JCR Journal
Description:
restricted
Keywords:
Etna
;
Volcanic tremor
;
Paroxysmal activity
;
Plagioclase Texture
;
04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
;
04. Solid Earth::04.08. Volcanology::04.08.07. Instruments and techniques
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
Permalink
