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  • Calbuco  (1)
  • VOLCANIC ASH AGGREGATION, PHREATOMAGMATIC DEPOSIT  (1)
  • 1
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    Volcanic ash aggregation enhanced by seawater interaction: the case of Secche di Lazzaro phreatomagmatic deposit (Stromboli) (2019)
    INGV
    Details
    Publication Date: 2019-12-04
    Description: The Secche di Lazzaro formation (ca. 6.2-7 kys BP) is a phreatomagmatic deposit situated in the southwestern part of the island of Stromboli (Aeolian Archipelago, Italy). The volcanic sequence is comprised of three main units. In the lower unit accretionary lapilli are particularly abundant and are characterized by strong cementation between the particles and an uncommon resistance to breakage. To understand the processes behind the formation of the Secche di Lazzaro (SdL) accretionary lapilli a multi-analytical approach was used on the lapilli Aggregate Tuff (AT), and on single Accretionary Lapilli (AL). We carried out granulometric analysis, Field Emission – Scanning Electron Microscopy (FE-SEM), Electron Microprobe Analysis (EMPA), X-ray powder diffraction (XRPD) and 3D imaging by X-ray micro-tomography (X-mCT). The granulometric data show that most particles in the AT have a diameter equal to Φ -1 corresponding to 2 mm. The EMPA, FE-SEM and XRPD analyses reveal the presence of different mineral phases, mainly plagioclase, K-feldspar, halite, and clinopyroxene, together with volcanic glass. From the X-mCT analysis, we constrained the particle distribution and estimated the porosity of AL. The results of the FE-SEM images provided the chemical distribution within individual lapilli allowing the identification of rim and core zoning as well as the presence of halite located both on the border of single lapilli and on the juncture between different lapilli. Moreover, halite occurs among different aggregates in single AL, thus acting as a binding agent, as well as within rim pores. The results of this work shed new light into the formation of accretionary lapilli in phreatomagmatic eruption a t volcanic island involving marine water.
    Description: University of Perugia (Progetti Ricerca di Base MORGABASE2015). European Research Council with the Consolidator grant CHRONOS (612776). European project EUROVOLC (grant agreement number 731070). MIUR project Premiale Ash-RESILIENCE.
    Description: Published
    Description: VO674
    Description: 5V. Processi eruttivi e post-eruttivi
    Description: JCR Journal
    Keywords: Accretionary Lapilli ; Stromboli ; X-ray microtomography ; Salt ; VOLCANIC ASH AGGREGATION, PHREATOMAGMATIC DEPOSIT
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
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    The unexpected explosive sub-Plinian eruption of Calbuco volcano (22–23 April 2015; southern Chile): Triggering mechanism implications (2020)
    Details
    Publication Date: 2020-02-24
    Description: Plinian-type eruptions are extremely hazardous, producing pyroclastic fallout and flows extending many kilometres from the vent. The most commonly invoked eruption trigger for Plinian-type eruptions is the intrusion of fresh magma, generally associated with precursory ground deformation and seismicity days/weeks before eruption. Closed-system internal triggering has also been proposed, such as protracted crystallisation of magma, which can produce a build-up of exsolved volatiles and thus pressurise the system prior to eruption. On 22–23 April 2015 Calbuco volcano, Chile, produced a sub-Plinian eruption with 〈3 h seismic precursory activity and no clear deformation signals in the preceding months. Here, we show that petrological and geochemical evidence do not support a hypothesis of eruption triggering due to pre-eruptive intrusion of fresh magma, but instead are consistent with an internal trigger. We found that basaltic andesitic magma was stored at depths between 8 and 12 km (i.e. 230–320 MPa) beneath Calbuco volcano before the 2015 eruption. The stored magma had an initial temperature of 900–950 °C, was water-saturated (5.5–6.5 wt% H2O) and formed phenocrysts of titanomagnetite, orthopyroxene, clinopyroxene and plagioclase cores (An78–93). Gradual cooling of the magma chamber produced thermal gradients and magma convection, evidenced by plagioclase overgrowth rims (An58–77) and blocky microlites (25–250 μm). Our interpretation is that this continuing crystallisation induced second boiling and an over-pressurisation of the system, leading to the rapid onset of the 2015 eruption. Petrological and geochemical evidence therefore shows that a closed-system magma chamber can evolve into a highly explosive eruption with very little precursory warning, posing a challenge for current volcano monitoring paradigms. We propose that internal triggering should be carefully considered as a mechanism for unexpected sub-Plinian eruptions, prompting a potential revision of existing hazard management strategies.
    Description: Published
    Description: 35-50
    Description: 4V. Processi pre-eruttivi
    Description: JCR Journal
    Keywords: Calbuco ; Sub-Plinian eruption ; Internal trigger ; Crystallisation ; Volcanic hazard ; 04.08. Volcanology ; Petrology ; 04.06. Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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