Publication Date:
2023-02-01
Description:
Low-intensity emission of volcanic ash represents the most frequent eruptive activity
worldwide, spanning the whole range of magma compositions, from basalts to rhyolites.
The associated ash component is typically characterized by heterogeneous texture and
chemical composition, leading to misinterpretation of the role of syn-eruptive processes,
such as cooling and degassing during magma ascent or even magma fragmentation.
Despite their low intensity, the ash emission eruptions can be continuous for enough time
to create problems to health and life networks of the communities all around the volcano.
The lack of geophysical and/or geochemical precursor signals makes the petrological
monitoring of the emitted ash the only instrument we have to understand the leading
mechanisms and their evolution. Formation of low-level plumes related to ash-rich
emissions has increasingly become a common eruptive scenario at Mt. Etna (Italy). In
January–February 2019, an eruptive cycle of ash-rich emissions started. The onset of this
activity was preceded on 24 December 2018 by a powerful Strombolian-like eruption from
a fissure opened at the base of the New Southeast Crater. A lava flow from the same
fissure and an ash-rich plume, 8–9 km high a.s.l., from the crater Bocca Nuova occurred
concurrently. After about 4 weeks of intra-crater strombolian-like activity and strong vent
degassing at summit craters, starting from 23 January 2019, at least four episodes of ash rich emissions were recorded, mainly issued from the Northeast Crater. The episodes were
spaced in time every 4–13 days, each lasting about 3–4 days, with the most intense
phases of few hours. They formed weak plumes, up to 1 km high above the crater, that
were rapidly dispersed toward different directions by dominant winds and recorded up to a
distance of 30 km from the vent. By combining observations on the deposits with data on
textural and chemical features of the ash components, we were able to discriminate
between clasts originated from different crater sources and suggest an interpretive model
for syn-eruptive processes and their evolution. Data indicate the occurrence of scarce (〈10
vol.%) fresh juvenile material, including at least four groups of clasts with marked
differences in microlite content and number density, and matrix glasses and minerals
Moreover, a large amount of non-juvenile clasts has been recognized,
particularly abundant at the beginning of each episode. We propose that the low
amount of juvenile ash results from episodic fast ascent of small magma batches from
shallow reservoirs, traveling within a slow rising magma column subjected to cooling,
degassing, and crystallization. The large number of non-juvenile clasts deriving from the
thick crater infill of variably sealed or thermally altered material at the top of the magma
column is suggested to contribute to the ash generation. The presence of a massive,
granular crater infilling accumulating in the vent area may contribute to buffer the different
geophysical signals associated with the active magma fragmentation process during the
low-energy ash eruptions, as already evidenced at other volcanoes.
Description:
Published
Description:
824872
Description:
5V. Processi eruttivi e post-eruttivi
Description:
JCR Journal
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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