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  • 1
    Electronic Resource
    Electronic Resource
    Mafic pyroclastic flows at Santa Maria (Gaua) Volcano, Vanuatu: the caldera formation problem in mainly mafic island arc volcanoes (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Terra nova 7 (1995), S. 0 
    Details
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: At Santa Maria Volcano (New Hebrides island arc), extensive ash and scoria flow deposits overlie the mainly effusive, pre-caldera cone. Hydromagmatic features characterize these deposits, the composition of juvenile clasts ranges from basalt to acid andesite/dacite (SiO2= 51–63.6%) with a dominant basaltic composition. The stratigraphic position of this pyroclastic series and its spatial distribution around a 8.5 km × 6 km wide caldera provide evidence of a relationship between this series and the caldera formation. In addition, these pyroclastic deposits are co-genetic to parasitic cones and lava flows developed along faults concentric to the caldera. Both series result from a compositionally layered magma reservoir, the subordinate differentiated magmas being the result of fractional crystallization from the basalts. A model of caldera formation which implies a large hydromagmatic eruption at the central vent and minor magma withdrawal by flank eruptions is proposed. This model emphasizes the importance of mafic hydroclastic eruptions in the caldera forming event and contradicts a model implying only quiet subsidence, a process often proposed for the formation of calderas in island are volcanoes of mainly mafic composition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3121.1995.tb00539.x
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  • 2
    Electronic Resource
    Electronic Resource
    Ignimbrites of basaltic andesite and andesite compositions from Tanna, New Hebrides Arc (1994)
    Springer
    Bulletin of volcanology 56 (1994), S. 10-22 
    Details
    ISSN: 1432-0819
    Keywords: Island arc volcanism ; New Hebrides ; Ignimbrite ; Phreatomagmatic deposits ; Basaltic andesite ; Glass composition ; Crystal fractionation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Tanna island is part of a large volcanic complex mainly subsided below sea-level. On-land, two series of hydroclastic deposits and ignimbrites overlie the subaerial remains of a basal, mainly effusive volcano. The ‘Older’ Tanna Ignimbrite series (OTI), Late Pliocene or Pleistocene in age, consists of ash flows and ash- and scoria-flow deposits associated with fallout tephra layers, overlain by indurated pumice-flow deposits. Phreatomagmatic features are a constant characteristic of these tuffs. The ‘younger’ Late Pleistocene pyroclastics, the Siwi sequence, show basal phreatomagmatic deposits overlain by two successive flow units, each comprising a densely welded layer and a nonwelded ash-flow deposit. Whole-rock analyses of 17 juvenile clasts from the two sequences (vitric blocks from the phreatomagmatic deposits, welded blocks, scoriaceous bombs and pumices from the ignimbrites) show basaltic andesite and andesite compositions (SiO2=53–60%). In addition, 296 microprobe analyses of glasses in these clasts show a wide compositional range from 51 to 69% SiO2. Dominant compositions at ∼54, 56, 58.5 and 61–62% SiO2 characterize the glass from the OTI. Glass compositions in the lower — phreatomagmatic — deposits from the Siwi sequence also show multimodal distribution, with peaks at SiO2=55, 57.5, 61–62 and 64% whereas the upper ignimbrite has a predominant composition at 61–62% SiO2. In both cases, mineralogical data and crystal fractionation models suggest that these compositions represent the magmatic signature of a voluminous layered chamber, the compositional gradient of which is the result of fractional crystallization. During two major eruptive stages, probably related to two caldera collapses, the OTI and Siwi ignimbrites represent large outpourings from these magmatic reservoirs. The successive eruptive dynamics, from phreatomagmatic to Plinian, emphasize the role of water in initiating the eruptions, without which the mafic and intermediate magmas probably would not have erupted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00279725
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  • 3
    Electronic Resource
    Electronic Resource
    Formation of the mid-fifteenth century Kuwae caldera (Vanuatu) by an initial hydroclastic and subsequent ignimbritic eruption (1994)
    Springer
    Bulletin of volcanology 56 (1994), S. 170-183 
    Details
    ISSN: 1432-0819
    Keywords: caldera ; caldera-forming event ; island arc volcanism ; pyroclastic flows ; welded tuffs ; hydromagmatism ; basalts ; dacites ; Vanuatu
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract In the mid-fifteenth century, one of the largest eruptions of the last 10 000 years occurred in the Central New Hebrides arc, forming the Kuwae caldera (12x6 km). This eruption followed a late maar phase in the pre-caldera edifice, responsible for a series of alternating hydromagmatic deposits and airfall lapilli layers. Tuffs related to caldera formation (≈ 120 m of deposits on a composite section from the caldera wall) were emitted during two main ignimbritic phases associated with two additional hydromagmatic episodes. The lower hydromagmatic tuffs from the precaldera maar phase are mainly basaltic andesite in composition, but clasts show compositions ranging from 48 to 60% SiO2. The unwelded and welded ashflow deposits from the ignimbritic phases and the associated intermediate and upper hydromagmatic deposits also show a wide compositional range (60–73% SiO2), but are dominantly dacitic. This broad compositional range is thought to be due to crystal fractionation. The striking evolution from one eruptive style (hydromagmatic) to the other (magmatic with emission of a large volume of ignimbrites) which occurred either over the tuff series as a whole, or at the beginning of each ignimbritic phase, is the most impressive characteristic of the caldera-forming event. This strongly suggests triggering of the main eruptive phases by magma-water interaction. A three-step model of caldera formation is presented: (1) moderate hydromagmatic (sequences HD 1–4) and magmatic (fallout deposits) activity from a central vent, probably over a period of months or years, affected an area slightly wider than the present caldera. At the end of this stage, intense seismic activity and extrusion of differentiated magma outside the caldera area occurred; (2) unhomogenized dacite was released during a hydromagmatic episode (HD 5). This was immediately followed by two major pyroclastic flows (PFD 1 and 2). The vents spread and intense magma-water interaction at the beginning of this stage decreased rapidly as magma discharge increased. Subsequent collapse of the caldera probably commenced in the southeastern sector of the caldera; (3) dacitic welded tuffs were emplaced during a second main phase (WFD 1–5). At the beginning of this phase, magma-water interaction continued, producing typical hydromagmatic deposits (HD 6). Caldera collapse extended to the northern part of the caldera. Previous C14 dates and records of explosive volcanism in ice from the south Pole show that the climactic phase of this event occurred in 1452 A.D.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00279602
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  • 4
    Electronic Resource
    Electronic Resource
    Ignimbrites of basaltic andesite and andesite compositions from Tanna, New Hebrides Arc (1994)
    Springer
    Bulletin of volcanology 56 (1994), S. 10-22 
    Details
    ISSN: 1432-0819
    Keywords: Key words: Island arc volcanism – New Hebrides – Ignimbrite – Phreatomagmatic deposits – Basaltic andesite – Glass composition – Crystal fractionation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract. Tanna island is part of a large volcanic complex mainly subsided below sea-level. On-land, two series of hydroclastic deposits and ignimbrites overlie the subaerial remains of a basal, mainly effusive volcano. The ‘Older’ Tanna Ignimbrite series (OTI), Late Pliocene or Pleistocene in age, consists of ash flows and ash- and scoria-flow deposits associated with fallout tephra layers, overlain by indurated pumice-flow deposits. Phreatomagmatic features are a constant characteristic of these tuffs. The ‘younger’ Late Pleistocene pyroclastics, the Siwi sequence, show basal phreatomagmatic deposits overlain by two successive flow units, each comprising a densely welded layer and a nonwelded ash-flow deposit. Whole-rock analyses of 17 juvenile clasts from the two sequences (vitric blocks from the phreatomagmatic deposits, welded blocks, scoriaceous bombs and pumices from the ignimbrites) show basaltic andesite and andesite compositions (SiO2=53–60%). In addition, 296 microprobe analyses of glasses in these clasts show a wide compositional range from 51 to 69% SiO2. Dominant compositions at ∼54, 56, 58.5 and 61–62% SiO2 characterize the glass from the OTI. Glass compositions in the lower – phreatomagmatic – deposits from the Siwi sequence also show multimodal distribution, with peaks at SiO2=55, 57.5, 61–62 and 64% whereas the upper ignimbrite has a predominant composition at 61–62% SiO2. In both cases, mineralogical data and crystal fractionation models suggest that these compositions represent the magmatic signature of a voluminous layered chamber, the compositional gradient of which is the result of fractional crystallization. During two major eruptive stages, probably related to two caldera collapses, the OTI and Siwi ignimbrites represent large outpourings from these magmatic reservoirs. The successive eruptive dynamics, from phreatomagmatic to Plinian, emphasize the role of water in initiating the eruptions, without which the mafic and intermediate magmas probably would not have erupted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004450050013
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  • 5
    Electronic Resource
    Electronic Resource
    Formation of the mid-fifteenth century Kuwae caldera (Vanuatu) by an initial hydroclastic and subsequent ignimbritic eruption (1994)
    Springer
    Bulletin of volcanology 56 (1994), S. 170-183 
    Details
    ISSN: 1432-0819
    Keywords: Key words: caldera ; caldera-forming event ; island arc volcanism ; pyroclastic flows ; welded tuffs ; hydromagmatism ; basalts ; dacites ; Vanuatu
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: 2 . The unwelded and welded ash-flow deposits from the ignimbritic phases and the associated intermediate and upper hydromagmatic deposits also show a wide compositional range (60–73% SiO2), but are dominantly dacitic. This broad compositional range is thought to be due to crystal fractionation. The striking evolution from one eruptive style (hydromagmatic) to the other (magmatic with emission of a large volume of ignimbrites) which occurred either over the tuff series as a whole, or at the beginning of each ignimbritic phase, is the most impressive characteristic of the caldera-forming event. This strongly suggests triggering of the main eruptive phases by magma–water interaction. A three-step model of caldera formation is presented: (1) moderate hydromagmatic (sequences HD 1–4) and magmatic (fallout deposits) activity from a central vent, probably over a period of months or years, affected an area slightly wider than the present caldera. At the end of this stage, intense seismic activity and extrusion of differentiated magma outside the caldera area occurred; (2) unhomogenized dacite was released during a hydromagmatic episode (HD 5). This was immediately followed by two major pyroclastic flows (PFD 1 and 2). The vents spread and intense magma–water interaction at the beginning of this stage decreased rapidly as magma discharge increased. Subsequent collapse of the caldera probably commenced in the southeastern sector of the caldera; (3) dacitic welded tuffs were emplaced during a second main phase (WFD 1–5). At the beginning of this phase, magma–water interaction continued, producing typical hydromagmatic deposits (HD 6). Caldera collapse extended to the northern part of the caldera. Previous C14 dates and records of explosive volcanism in ice from the south Pole show that the climactic phase of this event occurred in 1452 A.D.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004450050026
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  • 6
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    Geochemistry vs. seismo-tectonics along the volcanic New Hebrides Central Chain (Southwest Pacific) (1997)
    Elsevier
    Details
    Publication Date: 1997-06-01
    Print ISSN: 0377-0273
    Electronic ISSN: 1872-6097
    Topics: Geosciences
    Published by Elsevier
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  • 7
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    Giant tuff cone and 12-km-wide associated caldera at Ambrym Volcano (Vanuatu, New Hebrides Arc) (1993)
    Elsevier
    Details
    Publication Date: 1993-03-01
    Print ISSN: 0377-0273
    Electronic ISSN: 1872-6097
    Topics: Geosciences
    Published by Elsevier
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  • 8
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    Late Pleistocene and Holocene activity of the Atacazo–Ninahuilca Volcanic Complex (Ecuador) (2008)
    Elsevier
    Details
    Publication Date: 2008-09-01
    Print ISSN: 0377-0273
    Electronic ISSN: 1872-6097
    Topics: Geosciences
    Published by Elsevier
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  • 9
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    Seismic, petrologic, and geodetic analyses of the 1999 dome-forming eruption of Guagua Pichincha volcano, Ecuador (2007)
    Elsevier
    Details
    Publication Date: 2007-04-01
    Print ISSN: 0377-0273
    Electronic ISSN: 1872-6097
    Topics: Geosciences
    Published by Elsevier
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  • 10
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    Adakitic magmas in the Ecuadorian Volcanic Front: Petrogenesis of the Iliniza Volcanic Complex (Ecuador) (2007)
    Elsevier
    Details
    Publication Date: 2007-01-01
    Print ISSN: 0377-0273
    Electronic ISSN: 1872-6097
    Topics: Geosciences
    Published by Elsevier
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