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A dynamic model for the 1631 Vesuvius eruption
Abstract
The 1631 eruption has been selected by the Italian Civil Defence as the
maximum expected event upon short-medium term reactivation of Vesuvius.
Therefore, reconstruction of 1631 eruptive dynamic (Rosi et al., 1993)
is an important task for forecasting future eruptive behaviours. To
obtain a fully constrained dynamic model of the 1631 eruption, all the
deposits of this eruption have been investigated by a number of
different perspectives, including the stratigraphical, physical and
petro-chemical points of view. The geometry of the magma chamber walls
has been constrained by means of volcanological, stratigraphical, and
mineralogical data, with special emphasis on phase equilibria for the
peculiar lithics contained in pyroclastic deposits. Distribution,
granulometry, componentry, vescicularity of the fallout and nuée
ardentes deposits give reason of the volatiles distribution before and
during the eruption, as evidentiated by chemical and isotopic data. In
the resulting dynamic model the magma chamber of 1631 is a shallow,
closed, and slowly cooling magma chamber, with a continuous variation
from top to botton (fallout layers b, c, d, ei) of all relevant physical
and chemical parameters. At the margins of the magma chamber, cooling
and thermometasomatic reactions involving Mesozoic limestones originated
a skarn and cumulite carapax. The internal pressure was relatively high
during the plinian stage of the eruption (December 16th), when the
eruptive column reached a height of 13 km (fallout layer b), but
afterwards it became lower than external fluid pressure, which was
largely controlled by the CO2 produced all around the magma body by
thermometasomatic reactions. For this reason the chamber walls
collapsed, CO2 entered the system and expanded, giving new energy to the
plinian column, that became 19-km-high during the emission phase of the
es fallout layer. This new external motor dragged inside the plinian
column a huge quantity of skarn and cumulate fragments as well as the
poorly vesciculated magma (vescicularity close to 25%) positioned near
the chamber walls (layer f). After the end of the plinian phase, on
December 17th, the Vesuvian cone collapsed, the pressure inside the
magmatic system decreased further on, causing expulsion of the remaining
magma as nuée ardentes and allowing interaction between the magma
and the fluids coming from the nearby carbonate aquifers (mainly H2O).
This magma-water interaction was responsible of the final
phreatomagmatic phases of the eruption. Rosi M, Principe C, Vecci R
(1993): The 1631 vesuvius eruption - A reconstruction based on
historical and stratigraphical data. JVGR, 58:151-182.
Supplementary resource (1)
Data
January 2014
... Sulfur isotopes of the 1631 eruption products suggest that preeruptive degassing was more important than syn-eruptive degassing (Principe et al., 2003), although the quantitative interpretation of these data requires a sufficiently precise evaluation of the temperature-pressure-redox conditions present in the different parts of the magma chamber which are not available yet. ...
... In contrast, these gas mixtures are very unlikely to be present in active volcanic areas, where discharged gases are typically rich in H 2 O and CO 2 and the amounts of reduced species are small or comparatively small and insufficient to sustain combustion. In particular, these H 2 O-CO 2 -rich compositions can be expected for the fumarolic gases emitted from the Vesuvius crater prior to the 1631 eruption, owing to the important production of both volatiles through thermometamorphic/metasomatic reactions between magma and carbonate wall rocks (Principe et al., 2003;Pascal et al., 2006, submitted for publication). ...
... Besides, the Ligorio's description indicates that a fumarolic field was present at that time inside the Vesuvius crater. The fumarolic activity was continuous and sustained by a large flux of gases, in line with the important pre-eruptive degassing from the magma chamber, as indicated by sulfur isotopes (Principe et al., 2003). From time to time, small explosions occurred, caused by either vaporization of rain water soaking sediments in the crater bottom or pressurization of the underlying hydrothermal system. ...
In a recently published manuscript [Guidoboni, E., Boschi, E., 2006. Vesuvius before the 1631 eruption, EOS, 87(40), 417 and 423]; [Guidoboni, E. (Ed.), 2006. Pirro Ligorio, Libro di diversi terremoti (1571), volume 28, codex Ja II 15, Archivio di Stato di Torino, Edizione Nazionale delle Opere di Pirro Ligorio, Roma, De Luca, 261 pp], Pirro Ligorio gives a detailed description of the phenomena occurring in the crater area of Vesuvius volcano, in 1570–1571 and previous years. Here, these phenomena are interpreted as the first clearly documented signals of unrest of this volcanic system caused by the shallow emplacement of a magma batch and leading to the 1631 eruption. Our interpretation is mainly based on the present understanding of the fluid geochemistry of magmatic-hydrothermal systems. In this way, it is possible to conclude that: (i) incandescent rocks were present at the surface, with temperatures > 500 °C approximately and (ii) either a magmatic-dominated or a magmatic-hydrothermal-type of conceptual geochemical model applies to Vesuvius in 1570–1571 and preceding years.The Ligorio's picture represents the first clear evidence that the magma involved in the 1631 eruption was present under the volcano more than sixty years before the eruption. Moreover, its emplacement produced a series of phenomena which were clearly observed although not understood at that time. A similar phenomenological pattern should be easily detected and correctly interpreted at present or in the future.
... The large compositional range displayed by these minerals at Vesuvius, in addition to providing data on the ternary miscibility-gap, sheds light on the genesis, which involves fluid-rock interactions recorded by the carbonate host-rocks (Brocchini et al. 2001) of the Vesuvius magma chamber(s). The present study forms part of a continuing study of these interaction processes (Pascal et al. 2006(Pascal et al. , 2009 and their influence on the pre-eruption conditions of the 1631 AD eruption, especially as regards the gas pressures (CO 2 , H 2 O) and, therefore, on the eruption dynamics (Giosa 2002, Principe et al. 2003. ...
... The large compositional range displayed by these minerals at Vesuvius, in addition to providing data on the ternary miscibility-gap, sheds light on the genesis, which involves fluid-rock interactions recorded by the carbonate host-rocks (Brocchini et al. 2001) of the Vesuvius magma chamber(s). The present study forms part of a continuing study of these interaction processes (Pascal et al. 2006(Pascal et al. , 2009 and their influence on the pre-eruption conditions of the 1631 AD eruption, especially as regards the gas pressures (CO 2 , H 2 O) and, therefore, on the eruption dynamics (Giosa 2002, Principe et al. 2003. ...
Qandilite (Mg(2)TiO(4)) and magnesioferrite occur in forsterite - spinel - calcite skarn ejecta from Mt. Vesuvius, Italy, with an exceptionally large compositional range that outlines the miscibility gap in the system spinel - qandilite - magnesioferrite (with a small amount of Fe(2+)), at present solely determined on the spinel-qandilite binary at T > 1000 degrees C. The analyzed spinel-qandilite and spinel-magnesioferrite pairs are consistent with the solvus and tie-lines (except for a temperature offset) derived from the thermochemical model of spinel solid-solutions. Temperatures of formation in the range 650-700 degrees C are inferred from the petrological study of the skarn-forming processes involved, which typically include two types of metasomatic reactions, i.e., formation of spinel - forsterite - calcite endoskarns by desilication of aluminosilicate bodies at the contact of dolostone wallrocks, and reaction of such pre-existing endoskarns with new influxes of magma +/- fluid. Calculated phase-relations among qandilite, perovskite and geikielite show that qandilite with moderate magnesioferrite contents is the high-temperature Ti mineral stable in magnesian and extremely silica-deficient surroundings under oxidized conditions.
... The question then arises of the quantitative importance of skarns remaining within the carbonate sequence, that may be thought (1) to have experienced one or several phases of reworking such as observed on skarns in plutonic settings, and (2) to represent host rocks different from the original limestones/dolostones and therefore susceptible to different reactions with magmas forming new reservoirs. This paper forms part of a continuing study of the magmawallrock interaction processes at Somma- Vesuvius (Pascal et al., 2006Pascal et al., , 2008) which is focusing on the construction of the pre-eruptive conditions of the 1631 AD magma chamber and their implications for the eruptive dynamics of the tephritic phonolite 1631 eruption (Giosa, 2002; Principe et al., 2003). The skarns from this especially skarn-rich eruption (Rosi et al., 1993, Crocetti 1996), are extremely variable in texture and mineralogy and provide evidence for complex, multi-fold genetic processes. ...
Two Ca-Zr-Ti oxides, zirconolite CaZrTi2O7 and calzirtite Ca2Zr5Ti2O16, occur as minute interstitial crystals in skarn (forsterite-spinel-calcite, with rhythmic banding) ejecta from the 1631 eruption of Vesuvius. The substitutions in zirconolite observed here mainly include Nb-for-Ti (typical for zirconolites in alkaline magmatic surroundings) and (Th,U)-for-Ca, and produce a crystal-chemical formula Ca0.9–1Th0.04–0.12U0.04–0.10ZrTi1.36–1.61Nb0.09–0.22(Fe,Mg,Al)0.29–0.47O7. The skarn, which occurs in contact with a pyroxenite of magmatic origin, displays a mineralogical zoning with Zr-, Ti-, Nb- and (U,Th)-rich oxides (e.g. Nb-perovskite and zirconolite) close to the pyroxenite (1 cm) are richer still in Zr but (Ti, Nb, U, Th)-poor or free (e.g. calzirtite and baddeleyite ZrO2). Textural relationships between minerals provide evidence for a metasomatic development of the skarn at the expense of the pyroxenite, through drastic leaching of Na, K, Si, Fe. The same process is responsible for the zoning in the skarn (leaching of Fe, Si, Ti, Nb, U and Th), in which Zr was less mobilized than other HFSE. This process, related to the circulation of fluids equilibrated with carbonates, is responsible for those forsterite-spinel (± calcite) skarns which can be observed as remnants in a large part of the 1631 ejecta. Such endoskarns probably formed repeatedly during at least the last millennia of Vesuvius' history, and existed prior to the emplacement at shallow depth of the 1631 magma whose chamber walls were different from the limestone/dolostone classically assumed to host the Vesuvius magmas (Fulignati et al., 2005).
... Recently, Rolandi & Russo (1989) ascribed both the lava under Masseria Donna Chiara and the lava cropping out along the coast near Torre Annunziata between Cantiere la Perla and Palazzo Monteleone to the 1631 eruption. Finally, although the emission of lavas during the 1631 eruption can be ruled out, based on volcanological evidence (Principe et al., 2003) and historical documents (Rosi et al., 1993), most of the lavas cropping out along4 a-b Sector II. (a) Aerial photograph of Torre del Greco as it appears today. ...
The activity of Vesuvius between A.D. 79 and 1631 has been investigated by means of precise archaeomagnetic dating of primary volcanic deposits and taking into account the stratigraphy of lavas and tephra, historical written accounts, archaeological evidence related to the developing urbanisation, and radiocarbon ages. We found that the historical records are highly useful in constraining the timing of the main events, even if the data are often too scarce and imprecise for ascertaining the details of all phases of activity, especially their magnitude and emplacement of all the deposit types. In addition, some eruptions that took place in the 9th and 10th centuries appear to be unnoticed by historians. The archaeomagnetic study involved 26 sites of different lavas and 2 pyroclastic deposits. It shows that within the 15 centuries which elapsed between A.D. 79 and 1631, the effusive activity of Vesuvius clustered in the relatively short period of time between A.D. 787 and 1139 and was followed by a 5-century-long repose period. During this time Vesuvius prepared itself for the violent explosive eruption of 1631. The huge lavas shaping the morphology of the coast occurred largely through parasitic vents located outside the Mount Somma caldera. One of these parasitic vents is located at low elevation, very close to the densely inhabited town of Torre Annunziata. Among the various investigated lavas, a number of which were previously attributed to the 1631 eruption, none is actually younger than the 12th century. Therefore it is definitively concluded that the destructive 1631 event was exclusively explosive.
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