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  • 1
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    Changes in eruptive style during the A.D. 1538 Monte Nuovo eruption (Phlegrean Fields, Italy): the role of syn-eruptive crystallization (2005)
    Springer
    Details
    Publication Date: 2017-04-04
    Description: The Monte Nuovo eruption is the most recent event that occurred at Phlegrean Fields (Italy) and lasted from 29 September to 6 October 1538. It was characterized by 2 days of quasi-sustained phreatomagmatic activity generating pumice-bearing pyroclastic density currents and forming a 130-m-high tuff cone (Lower Member deposits). The activity resumed after a pause of 2 days with two discrete Vulcanian explosions that emplaced radially distributed, scoria-bearing pyroclastic flows (Upper Member deposits). The juvenile products of Lower and Upper Members are, respectively, phenocryst-poor, light-coloured pumice and dark scoria fragments with K-phonolitic bulk compositions, identical in terms of both major and trace elements. Groundmass is formed by variable proportions of K-feldspar and glass, along with minor sodalite and Fe-Ti oxide present in the most crystallized samples. Investigations of groundmass compositions and textures were performed to assess the mechanisms of magma ascent, degassing and fragmentation along the conduit and implications for the eruptive dynamics. In pumice of the Lower Member groundmass crystal content increases from 13 to 28 vol% from the base to the top of the sequence. Products of the Upper Member consist of clasts with a groundmass crystal content between 30 and 40 vol% and of totally crystallized fragments. Crystal size distributions of groundmass feldspars shift from a single population at the base of the Lower Member to a double population in the remaining part of the sequence. The average size of both populations regularly increases from the Lower to the Upper Member. Crystal number density increases by two orders of magnitude from the Lower to the Upper Member, suggesting that nucleation dominated during the second phase of the eruption. The overall morphological, compositional and textural data suggest that the juvenile components of the Monte Nuovo eruption are likely to record variations of the magma properties within the conduit. The different textures of pumice clasts from the Lower Member possibly reflect horizontal gradients of the physical properties (P, T) of the ascending magma column, while scoriae from the second phase are thought to result from the disruption of a slowly rising plug crystallizing in response to degassing. In particular, crystal size distribution data point to syn-eruptive degassing-induced crystallization as responsible for the transition in eruptive style from the first to the second phase of the eruption. This mechanism not only has been proved to profoundly affect the dynamics of dome-forming calc-alkaline eruptions, but may also have a strong influence in driving the eruption dynamics of alkaline magmas of intermediate to evolved compositions.
    Description: Published
    Description: 601-621
    Description: reserved
    Keywords: Phlegrean Fields ; Vulcanian explosion ; Degassing ; Groundmass crystallization ; Eruption dynamics ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases ; 04. Solid Earth::04.08. Volcanology::04.08.02. Experimental volcanism ; 05. General::05.02. Data dissemination::05.02.03. Volcanic eruptions
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 1175329 bytes
    Format: application/pdf
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  • 2
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    The 512 AD eruption of Vesuvius: complex dynamics of a small scale subplinian event (2012)
    Springer-Verlag, Berlin/Heidelberg
    Details
    Publication Date: 2017-04-04
    Description: We describe the products of the hitherto poorly known 512 AD eruption at Vesuvius, Italy. The deposit records a complex sequence of eruptive events, and it has been subdivided into eight main units, composed of stratified scoria lapilli or thin subordinate ash-rich layers. All the units formed by deposition from tephra fallout, pyroclastic density currents of limited extent being restricted to the initial stages of the eruption (U2). The main part of the deposit (U3 and U5) is characterized by a striking grain size alternation of fine to coarse lapilli, similar to that often described for mid-intensity, explosive eruptions. The erupted products have a phonotephritic composition, with progressively less evolved composition from the base to the top of the stratigraphic sequence. Based on different dispersal, sedimentological and textural features of the products, we identify five phases related to different eruptive styles: opening phase (U1, U2), subplinian phase (U3 to U5), pulsatory phreatomagmatic phase (U6), violent strombolian phase (U7) and final ash-dominated phase (U8). A DRE volume of 0.025 km3 has been calculated for the total fallout deposit. Most of the magma was erupted during the subplinian phase; lithic dispersal data indicate peak column heights of between 10 and 15 km, which correspond to a mass discharge rate (MDR) of 5×106 kg s1. The lower intensity, violent strombolian phase coincided with the eruption of the least evolved magma; a peak column height of 69 km, corresponding to an MDR of 1×106 kg s1, is estimated from field data. Phreatomagmatic activity played a minor role in the eruption, only contributing to the ash-rich deposits of U1, U4, U6 and U8. The two most striking features of the 512 AD eruption are the recurrent shifting of the eruption style and the pulsatory nature of the subplinian phase. Basing on a large set of observational data, we propose a model to explain this complex dynamics, also observed in other eruptions of similar scale from Vesuvius and elsewhere. The inbalance between the rates of magma supply and magma eruption may have caused the frequent changes in the eruptive style. Conversely, the high frequency oscillations of magma discharge recorded by the deposits of the subplinian phase were possibly related to cyclic instabilities in the permeability of the low viscosity magma column, which modulated magma fragmentation and discharge.
    Description: Published
    Description: 789-810
    Description: 3.5. Geologia e storia dei vulcani ed evoluzione dei magmi
    Description: 4.3. TTC - Scenari di pericolosità vulcanica
    Description: JCR Journal
    Description: reserved
    Keywords: Subplinian ; Vesuvius ; Magma fragmentation ; Phreatomagmatism ; Eruption dynamics ; 04. Solid Earth::04.04. Geology::04.04.10. Stratigraphy ; 04. Solid Earth::04.08. Volcanology::04.08.05. Volcanic rocks
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
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    Eruptive scenario of ash-dominated events at Vesuvius: the AP3 eruption (2,710±60 years B.P.) (2012)
    Details
    Publication Date: 2017-04-04
    Description: The deposits of several eruptions dominated by ash emission have been recently described in the stratigraphic record of the last 4000 years of activity of Vesuvius. A peculiarity of this type of eruptions is the persistence of repeated phases dominated by abundant emission of ash and the sporadic occurrence of violent strombolian activity, they are recorded by very thick, massive to laminated, ash layers, interlayered with minor scoria-lapilli beds. These eruptions have a strong impact on the environment and on human and animal health, and their hazard implications assume an important role in the definition of the scenario for a short-term, mid-magnitude, expected event at Vesuvius, in particular when considering their long duration and the large dispersal of the products. These types of events are associated at Vesuvius both with processes of magma-water interaction, or with mechanisms dominated by pure magmatic fragmentation. We discuss here the results of a new morphological and textural study on the juvenile material of the 2700 years old, phreatomagmatic AP3 eruption (Andronico and Cioni 2002). The eruption was produced during discontinuous, explosive events of ash emission (pulsating activity) alternated with minor violent Strombolian activity. Fragments of gas-rich, crystal-poor, magma are ubiquitous, and their presence suggests that the primary fragmentation process was mainly driven by magmatic explosivity. The interaction of external water with magma (phreatomagmatic activity), certainly occurred during the AP3 eruption, acting to increase (but not to trigger) the explosive fragmentation of the magma, due to water vaporization. Textural data on juvenile clasts can be interpreted in terms of episodes of conduit filling, degassing and ash production, and give a time constraint on the total duration of the eruption. All these data provide a useful reference frame to depict the eruption scenario of this type of activity to be used for the definition of contingency plans.
    Description: Published
    Description: 107-122
    Description: 3.5. Geologia e storia dei vulcani ed evoluzione dei magmi
    Description: 4.3. TTC - Scenari di pericolosità vulcanica
    Description: N/A or not JCR
    Description: reserved
    Keywords: Vesuvius ; Ash eruptions ; Clast characterization ; csd ; Eruption dynamics ; 04. Solid Earth::04.04. Geology::04.04.10. Stratigraphy ; 04. Solid Earth::04.08. Volcanology::04.08.05. Volcanic rocks
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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