Publication Date:
2017-04-04
Description:
During the last two decades Mt. Etna experienced many summit and flank eruptions with different styles of
activity, ranging from quiet lava effusion to explosive activity consisting of Strombolian explosions and/or
spectacular fire fountains. This complex picture entails the presence of a complex plumbing system where magma
dynamics strongly controls both the eruptive style and magma differentiation.
All these eruptive events have furnished volcanic products on which systematic petrographic and geochemical
analyses have been carried out since the mid 1990s. In particular, the content of major and trace elements of lavas
is a key-point to characterize the composition of a magma emitted during an eruption. Petrologic investigations are
traditionally based on the interpretation of compositional patterns described by selected oxides and/or elements
in binary and ternary petrologic systems. This kind of analysis provides useful information about the magmatic
processes occurring in the plumbing system. In this presentation we investigate whether the quality of petrologic
investigations is improved by the application of more sophisticated analytical techniques based on the use of a
relatively large number of parameters. To this purpose, we selected 13 components, i.e., SiO2, K2O, CaO/Al2O3,
Mg#, Th, La, Nb, Nd, Sr, Tb, Cr, Ni and Rb/Nb. This choice brings along the problem of designing a suitable
statistics and a convenient visualization of the results. As a way out, we propose advanced concepts of multivariate
classification based on a synopsis of Kohonen Maps and Fuzzy Clustering, and apply them to the study of
volcanics erupted from Mt. Etna between 1995 and 2005.
Lavas erupted during the fire fountains (in 2000) and during the flank eruptions (2001, 2002-03) represent the
most primitive products erupted from Mt. Etna in the investigated period. The literature data suggest that during
the 2001 and 2002-03 eruptions two magmas with different geochemical characteristics were contemporaneously
erupted. One magma type ascended from a deep portion of the plumbing system (〉 5 km), and was emitted from
the so called “Lower” (2001) and “Southern” vents (2002-03). Another one rose from a shallower reservoir (〈5
km) and was erupted from the so called “Upper” (in 2001) and “Northern” vents (in 2002-03).
In our analysis the “Lower” and “Southern” vent lavas are assigned to the same cluster ID and are grouped
together also in the Kohonen Map. On the other hand, “Upper” vent lavas and “Northern “ vent lavas are clearly
distinguished from each other as well as from the afore mentioned products. Volcanics emitted by the South-East
crater during the fire fountains in 2000 belong to the same fuzzy cluster as the “Lower” and “Southern” vent
lavas, however, a neat distinction with respect to 2001 and 2002-03 lavas becomes evident in the Kohonen Map.
Besides this we observe differences in the seismic signal characteristics between the fire fountain events and flank
eruptions, supporting the hypothesis that various eruptive sources were active on Mt Etna in 2000, 2001 and
2002-03.
The relation of the products to eruptive sources is less clear in the time span between 1995 and 1999, when
essentially only the summit craters were active.
Description:
Published
Description:
Vienna, Austria
Description:
1.2. TTC - Sorveglianza geochimica delle aree vulcaniche attive
Description:
open
Keywords:
Patterns Classification
;
volcanic products
;
Mt. Etna
;
04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
Poster session
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