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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
    Late Pleistocene to Holocene eruptive activity of Pico de Orizaba, Eastern Mexico (1993)
    Springer
    Bulletin of volcanology 55 (1993), S. 571-587 
    Details
    ISSN: 1432-0819
    Keywords: Volcanism ; Mexico ; Holocene ; History ; Pico ; Citlaltepetl ; Volcano
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The Late Pleistocene to Holocene eruptive history of Pico de Orizaba can be divided into 11 eurptive episodes. Each eruptive episode lasted several hundred years, the longest recorded being about 1000 years (the Xilomich episode). Intervals of dormancy range from millenia during the late Pleistocene to about 500 years, the shortest interval recorded in the Holocene. This difference could reflect either changes in the volcano's activity or that the older stratigraphic record is less complete than the younger. Eruptive mechanisms during the late Pleistocene were characterized by dome extrusions, lava flows and ash-and-scoria-flow generating eruptive columns. However, in Holocene time plinian activity became increasingly important. The increase in dacitic plinian eruptions over time is related to increased volumes of dacitic magma beneath Pico de Orizaba. We suggest that the magma reservoir under Pico de Orizaba is stratified. The last eruptive episode, which lasted from about 690 years bp until ad 1687, was initiated by a dacitic plinian eruption and was followed by effusive lava-forming eruptions. For the last 5,000 years the activity of the volcano has been gradually evolving towards such a trend, underlining the increasing importance of dacitic magma and stratification of the magma reservoir. Independent observations of Pico de Orizaba's glacier early this century indicate that some increase in volcanic activity occurred between 1906 and 1947, and that it was probably fumarolic.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00301810
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  • 3
    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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  • 4
    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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  • 5
    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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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    Mixed-magma pyroclastic surge deposits associated with debris avalanche deposits at Colima volcanoes, Mexico (1990)
    Springer
    Bulletin of volcanology 52 (1990), S. 391-403 
    Details
    ISSN: 1432-0819
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The transition between the terminal cones and the ancestral edifices of Nevado de Colima and Fuego de Colima volcanoes is marked by the deposits of gigantic volcanic debris avalanches of the Mount St. Helens (MSH) or Bezymianny type. Unusual mafic juvenile fragments and cauliflower bombs as well as juvenile fragments of mixed and more evolved composition are abundant in dune-bedded pyroclastic-surge deposits directly associated with these catastrophic events at both volcanoes. At Nevado, these mafic juvenile fragments represent the most primitive magma ever erupted by the volcano (SiO2∼52.50%). The lavas directly preceding and following the debris-avalanche event are silicic andesites (SiO2∼59%). At Fuego these juvenile fregments have ∼56% SiO2. The lavas from the upper parts of the caldera wall are dacites (∼65% SiO2), whereas the terminal cone is composed of andesites (57% to 62% SiO2). At Nevado, petrologic evidence for interaction of mafic magma with andesitic or dacitic magma in a high-level magma chamber, just before the eruption of pyroclastic surge deposits, consists of: (1) banded juvenile bombs of intermediate composition; (2) the range of composition of these bombs from SiO2∼52% to ∼58%; (3) the presence of highly magnesian olivine with reaction rims; (4) inverse zoning in clinopyroxene with strong Mg enrichment towards the rim; (5) resorption of plagioclase; and (6) significant compositional heterogeneity in the vitric phase. Volcanic debris-avalanche events at Nevado and Fuego de Colima may thus correspond with major breaks in the petrological evolution of the volcanoes and the start of a new magmatic cycle. Injection of mafic magma into the presently perched viscous surface dome of the active Fuego cone, as occurred in 1818 and 1913, could enhance the likelihood of southward collapse of the flank of an already unstable edifice, and it must be considered in future hazard assessment of this active volcano. Risk to life and property for the entire Colima region associated with such catastrophic phenomena would be immeasurably greater in comparison with hazards related to the last explosive outburst in 1913, which resulted in emplacement of pyroclastic flows over uninhabited areas of the upper flanks of the volcano.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00302051
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  • 8
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    Seismic-stratigraphic record of a deglaciation sequence: from the marine Laflamme Gulf to Lake Saint-Jean (late Quaternary, Québec, Canada) (2013)
    Wiley
    In: Boreas
    Details
    Publication Date: 2013-09-04
    Description: The stratigraphy of the last deglaciation sequence is investigated in Lake Saint-Jean (Québec Province, Canada) based on 300 km of echo-sounder two dimensional seismic profiles. The sedimentary archive of this basin is documented from the Late Pleistocene Laurentidian ice-front recession to the present-day situation. Ten seismic units have been identified that reflect spatio-temporal variations in depositional processes characterizing different periods of the Saint-Jean basin evolution. During the postglacial marine flooding, a high deposition rate of mud settling, from proglacial glacimarine and then prodeltaic plumes in the Laflamme Gulf, produced an extensive, up to 50 m thick mud sheet draping the isostatically depressed marine basin floor. Subsequently, a closing of the water body due to glacio-isostatic rebound occurred at 8.5 cal. ka BP, drastically modifying the hydrodynamics. Hyperpycnal flows appeared because fresh lake water replaced dense marine water. River sediments were transferred towards the deeper part of the lake into river-related sediment drifts and confined lobes. The closing of the water body is also marked by the onset of a wind-driven internal circulation associating coastal hydrodynamics and bottom currents with sedimentary features including shoreface deposits, sediment drifts and a prograding shelf-type body. The fingerprints of a forced regression are well expressed by mouth-bar systems and by the shoreface–shelf system, the latter unexpected in such a lacustrine setting. In both cases, a regressive surface of lacustrine erosion (RSLE) has been identified, separating sandy mouth-bar from glaciomarine to prodeltaic muds, and sandy shoreface wedges from the heterolithic shelf-type body, respectively. The Lake Saint-Jean record is an example of a regressive succession driven by a glacio-isostatic rebound and showing the transition from late-glacial to post-glacial depositional systems.
    Print ISSN: 0300-9483
    Electronic ISSN: 1502-3885
    Topics: Geography , Geosciences
    Published by Wiley
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  • 9
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    Temporal magma source changes at Gaua volcano, Vanuatu island arc (2016)
    Elsevier
    Details
    Publication Date: 2016-08-01
    Print ISSN: 0377-0273
    Electronic ISSN: 1872-6097
    Topics: Geosciences
    Published by Elsevier
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  • 10
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    Holocene recurrent explosive activity at Chimborazo volcano (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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