1,721,291 research outputs found
Effusive Activity at Mount Etna Volcano (Italy) During the 20th Century: A Contribution to Volcanic Hazard Assessment
No full textMount Etna is an open conduit volcano, characterised by persistent activity, consisting
of degassing and explosive phenomena at summit craters, frequent flank eruptions, and
more rarely, eccentric eruptions. All eruption typologies can give rise to lava flows, which
represent the greatest hazard by the volcano to the inhabited areas. Historical documents and
scientific papers related to the 20th century effusive activity have been examined in detail, and
volcanological parameters have been compiled in a database. The cumulative curve of emitted
lava volume highlights the presence of two main eruptive periods: (a) the 1900–1971 interval,
characterised by a moderate slope of the curve, amounting to 436 · 106 m3 of lava with
average effusion rate of 0.2 m3/s and (b) the 1971–1999 period, in which a significant increase
in eruption frequency is associated with a large issued lava volume (767 · 106 m3) and a higher
effusion rate (0.8 m3/s). The collected data have been plotted to highlight different eruptive
behaviour as a function of eruptive periods and summit vs. flank eruptions. The latter have
been further subdivided into two categories: eruptions characterised by high effusion rates and
short duration, and eruptions dominated by low effusion rate, long duration and larger
volume of erupted lava. Circular zones around the summit area have been drawn for summit
eruptions based on the maximum lava flow length; flank eruptions have been considered by
taking into account the eruptive fracture elevation and combining them with lava flow lengths
of 4 and 6 km. This work highlights that the greatest lava flow hazard at Etna is on the south
and east sectors of the volcano. This should be properly considered in future land-use planning
by local authorities.Published407–4434.3. TTC - Scenari di pericolosità vulcanicaJCR Journalreserve
Clinopyroxene and titanomagnetite cation redistributions at Mt. Etna volcano (Sicily, Italy): Footprints of the final solidification history of lava fountains and lava flows
No full textFor a better understanding of the final solidification history of eruptions at Mt. Etna volcano (Sicily, Italy), we have investigated cation redistributions at the interface between sub-millimetre-sized clinopyroxene and titanomagnetite crystal rims and coexisting melts. The studied products were scoria clasts from lava fountains and rock samples from pahoehoe and aa lava flows. Our data indicate that scoria clasts from lava fountaining were rapidly quenched at the contact with the atmosphere, preserving the original crystal textures and compositions inherited during magma dynamics within the plumbing system. Kinetics and energetics of crystallization were instantaneously frozen-in and post-eruptive effects on mineral chemistry were negligible. The near-equilibrium compositions of clinopyroxene and titanomagnetite indicate that lava fountain episodes were supplied by high-temperature, H2O-rich magmas ascending with velocities of 0.01-0.31 m/s. In contrast, magmas feeding lava flow eruptions underwent a more complex solidification history where the final stage of the crystal growth was mostly influenced by volatile loss and heat dissipation at syn- and post-eruptive conditions. Due to kinetic effects associated with magma undercooling, clinopyroxenes and titanomagnetites formed by crystal attachment and agglomeration mechanisms leading to intricate intergrowth textures. The final compositions of these minerals testify to closure temperatures and melt-water concentrations remarkably lower than those estimated for lava fountains. Kinetically-controlled cation redistributions at the crystal-melt interface suggest that the solidification of magma was driven by degassing and cooling processes proceeding from the uppermost part of the volcanic conduit to the surface. (C) 2015 Elsevier B.V. All rights reserved
Explosive activity and eruption scenarios at Somma-Vesuvius (Italy): Towards a new classification scheme
No full textA new proposal for the classification of Somma-Vesuvius (SV) explosive activity is presented, based on a critical revision of a large set of published and unpublished stratigraphic, compositional, and physical volcanology data on the products of the past 20,000 years of activity. The new database is used to discuss the general behaviour of the volcano in terms of frequency, magnitude and intensity of the events, as well as of the length of the repose time which preceded each eruption. Several different types of eruption are recognized, each characterised by specific physical eruptive parameters: plinian, subplinian (further subdivided in subplinian I and subplinian II), violent strombolian, ash emission events. For each eruption type, a complex scenario is described, with phases of different style, duration, magnitude and intensity occurring during the course of the eruption itself. The name given to each eruption type is derived from the style of the most representative part of the eruption (in terms of duration or volume).
On the whole, the magnitude (expressed as the volume of erupted magma) of the past SV eruptions has been roughly decreasing with time while, starting from 3900 years BP, their frequency has been increasing. The eruption intensity, expressed as the estimated magma discharge rate (MDR) continuously increases with increasing magnitude from strombolian to plinian eruptions, the most voluminous plinian events being, however, characterised by a lower MDR than the smaller ones. The length of the “apparent” repose preceding an eruption (the difference in age between one deposit and that immediately on top of it) appears clearly correlated with magnitude for the most intense eruptions (plinian and subplinian I), while this correlation is poorer for eruptions of intermediate size (from violent strombolian to subplinian II). These exhibit a large variability in magnitude, intensity and eruption style for a range of repose time varying from dozens to hundreds of years, then including the current duration of Vesuvius quiescence.
By reckoning with the whole range of possibilities that a next unrest at Vesuvius implies, the set of presented eruption scenarios can be useful both for developing a probabilistic approach to hazard assessment and depicting a range of impact scenarios. The scenario for high-intensity events had been already well defined since 1995, in order to redact the emergency plan of the National Department of Civil Defence. Conversely, it is now clear that the impact on the territory of long-lasting, although low-intensity, eruptions (subplinian II, violent strombolian, ash emission activity) can be relevant especially in terms of economic costs. A larger consideration of this type of activity at Vesuvius can be important especially for the aspects of emergency planning and risk reduction
Contrasting styles of Mt. Vesuvius activity in the period between the Avellino and Pompeii Plinian eruptions, and some implications for assessment of future hazards.
No full textIntense explosive activity occurred repeatedly
at Vesuvius during the nearly 1,600-year period between
the two Plinian eruptions of Avellino (3.5 ka) and Pompeii
(79 A.D.). By correlating stratigraphic sections from
more than 40 sites around the volcano, we identify the
deposits of six main eruptions (AP1–AP6) and of some
minor intervening events. Several deposits can be traced
up to 20 km from the vent. Their stratigraphic and dispersal
features suggest the prevalence of two main contrasting
eruptive styles, each involving a complex relationship
between magmatic and phreatomagmatic phases.
The two main eruption styles are (1) sub-Plinian to
phreato-Plinian events (AP1 and AP2 members), where
deposits consist of pumice and scoria fall layers alternating
with fine-grained, vesiculated, accretionary lapillibearing
ashes; and (2) mixed, violent Strombolian to
Vulcanian events (AP3–AP6 members), which deposited
a complex sequence of fallout, massive to thinly stratified,
scoria-bearing lapilli layers and fine ash beds. Morphology
and density variations of the juvenile fragments
confirm the important role played by magma–water interaction
in the eruptive dynamics. The mean composition
of the ejected material changes with time, and shows
a strong correlation with vent position and eruption style.
The ranges of intensity and magnitude of these events,
derived by estimations of peak column height and volume
of the ejecta, are significantly smaller than the values
for the better known Plinian and sub-Plinian eruptions
of Vesuvius, enlarging the spectrum of the possible
eruptive scenarios at Vesuvius, useful in the assessment
of its potential hazard.Gruppo Nazionale
di Vulcanologia (GNV) of the Consiglio Nazionale delle
Ricerche (CNR) of ItalyPublished372-3913.5. Geologia e storia dei sistemi vulcaniciJCR Journalreserve
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