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  • 1
    Language: English
    In: Earth-Science Reviews, July 2013, Vol.122, pp.77-102
    Description: Several lines of evidence have previously been used to suggest that ice retreat after the last glacial maximum (LGM) resulted in regionally-increased levels of volcanic activity. It has been proposed that this increase in volcanism was globally significant, forming a substantial component of the post-glacial rise in atmospheric CO , and thereby contributing to climatic warming. However, as yet there has been no detailed investigation of activity in glaciated volcanic arcs following the LGM. Arc volcanism accounts for 90% of present-day subaerial volcanic eruptions. It is therefore important to constrain the impact of deglaciation on arc volcanoes, to understand fully the nature and magnitude of global-scale relationships between volcanism and glaciation. The first part of this paper examines the post-glacial explosive eruption history of the Andean southern volcanic zone (SVZ), a typical arc system, with additional data from the Kamchatka and Cascade arcs. In all cases, eruption rates in the early post-glacial period do not exceed those at later times at a statistically significant level. In part, the recognition and quantification of what may be small (i.e. less than a factor of two) increases in eruption rate is hindered by the size of our datasets. These datasets are limited to eruptions larger than 0.1 km , because deviations from power-law magnitude–frequency relationships indicate strong relative under-sampling at smaller eruption volumes. In the southern SVZ, where ice unloading was greatest, eruption frequency in the early post-glacial period is approximately twice that of the mid post-glacial period (although frequency increases again in the late post-glacial). A comparable pattern occurs in Kamchatka, but is not observed in the Cascade arc. The early post-glacial period also coincides with a small number of very large explosive eruptions from the most active volcanoes in the southern and central SVZ, consistent with enhanced ponding of magma during glaciation and release upon deglaciation. In comparison to non-arc settings, evidence of post-glacial increases in rates of arc volcanism is weak, and there is no need to invoke significantly increased melt production upon ice unloading, as occurred in areas such as Iceland. Non-arc volcanoes may therefore account for a relatively higher proportion of global volcanic emissions in the early post-glacial period than is suggested by the relative contributions of arc and non-arc settings at the present day. The second part of this paper critically examines global eruption records, in an effort to constrain global-scale changes in volcanic output since the LGM. Accurate interpretation of these records relies on correcting both temporal and spatial variability in eruption recording. In particular, very low recording rates, which also vary spatially by over two orders of magnitude, prevent precise, and possibly even accurate, quantitative analysis. For example, if we assume record completeness for the past century, the number of known eruptions (volcanic explosivity index ≥ 2) from some low-latitude regions, such as Indonesia, is approximately 1 in 20,000 (0.005%) for the period 5–20 ka. There is a need for more regional-scale studies of past volcanism in such regions, where current data are extremely sparse. We attempt to correct for recording biases, and suggest a maximum two-fold (but potentially much less) increase in global eruption rates, relative to the present day, between 13 and 7 ka. Although volcanism may have been an important source of CO in the early Holocene, it is unlikely to have been a dominant control on changes in atmospheric CO after the LGM.
    Keywords: Arc Volcanoes ; Glaciation ; Post-Glacial ; Climate Change ; Volcanic Eruption Rates ; Chile ; Geology
    ISSN: 0012-8252
    E-ISSN: 1872-6828
    Source: ScienceDirect Journals (Elsevier)
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  • 2
    Language: English
    In: Quaternary International, 2011, Vol.246(1), pp.324-343
    Description: Late Glacial and Holocene soils and sediments in southern Chile contain an important record of explosive volcanic activity since the end of the last glaciation, and have considerable potential for the development of a regional tephrostratigraphical framework. This paper reports the discovery of several new tephra deposits from the Hualaihue region (∼42° S) of southern Chile. Eruption sizes, constrained from field observations, and ages, constrained by 25 new radiocarbon dates, show that the volcanoes of the Hualaihue peninsula have had relatively few explosive, tephra-generating eruptions during the Holocene. An eruption of Apagado deposited ∼1 km of bedded basaltic scoria at ∼2.6 calibrated (cal) ka BP, and Hornopirén produced a similar, but volumetrically-smaller unit at ∼5.7 cal ka BP. Activity at Yate over the same time period has been predominantly characterised by lava production, although small explosive eruptions, the products of which span a range of compositions, have also occurred, including one at ∼0.9 cal ka BP. The northern part of the regional tephra sequence is dominated by andesitic pumice fall deposits derived from Calbuco volcano. These include deposits from several eruptions during a 3500-year-long period at the start of the Holocene, as well as two large explosive eruptions in the past 2000 years. A distinctive rhyolitic tephra layer that is interbedded with the locally derived tephra sequence is the Cha1 unit, from Chaitén volcano, 108 km south of Hornopirén. This rhyolitic pumice deposit, dated at ∼9.75 cal ka BP, is the largest volumetrically of those described here, with a volume of 3.5 km . This new tephrostratigraphy covers a region whose volcanic history was previously very little known, and contributes to a regional record of large explosive eruptions that now spans a 500 km-long segment of the southern Andean arc, between Calbuco and Hudson volcanoes.
    Keywords: Geology
    ISSN: 1040-6182
    E-ISSN: 1873-4553
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  • 3
    Language: English
    In: Earth and Planetary Science Letters, 2009, Vol.277(3), pp.399-407
    Description: Seismic activity has been postulated as a trigger of volcanic eruption on a range of timescales, but demonstrating the occurrence of triggered eruptions on timescales beyond a few days has proven difficult using global datasets. Here, we use the historic earthquake and eruption records of Chile and the Andean southern volcanic zone to investigate eruption rates following large earthquakes. We show a significant increase in eruption rate following earthquakes of 〉 8, notably in 1906 and 1960, with similar occurrences further back in the record. Eruption rates are enhanced above background levels for ~ 12 months following the 1906 and 1960 earthquakes, with the onset of 3–4 eruptions estimated to have been seismically influenced in each instance. Eruption locations suggest that these effects occur from the near-field to distances of ~ 500 km or more beyond the limits of the earthquake rupture zone. This suggests that both dynamic and static stresses associated with large earthquakes are important in eruption-triggering processes and have the potential to initiate volcanic eruption in arc settings over timescales of several months.
    Keywords: Seismic Triggering ; Volcanic Eruption ; Chile ; Andean Southern Volcanic Zone ; Great Earthquake ; Eruption Rates ; Geology ; Physics
    ISSN: 0012-821X
    E-ISSN: 1385-013X
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  • 4
    Language: English
    In: Environmental Pollution, 2007, Vol.148(1), pp.48-61
    Description: Tree cores ( ssp. ) and leaves ( ) from the flanks of Mount Etna, Sicily were analysed by ICP-MS to investigate whether volcanogenic cations within plant material provide an archive of a volcano's temporal and spatial depositional influence. There is significant compositional variability both within and between trees, but no systematic dendrochemical correlation with periods of effusive, explosive or increased degassing activity. Dendrochemistry does not provide a record of persistent but fluctuating volcanic activity. Foliar levels of bioaccumulated cations correspond to modelled plume transport patterns, and map short-term volcanic fumigation. Around the flanks of the volcano foliar variation is greater for volatile cations (Cs, Cd, Pb) than for lithophilic cations (Ba, Sr), consistent with trace-metal supply from volcanic aerosol during quiescent periods. Dendrochemistry does not provide an archive of persistent volcanic activity.
    Keywords: Mount Etna ; Volcanogenic Cations ; Tree-Rings ; Pinus Nigra ; Castanea Sativa ; Engineering ; Environmental Sciences ; Anatomy & Physiology
    ISSN: 0269-7491
    E-ISSN: 1873-6424
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  • 5
    Language: English
    In: Earth-Science Reviews, November 2014, Vol.138, pp.137-155
    Description: Detailed knowledge of the past history of an active volcano is crucial for the prediction of the timing, frequency and style of future eruptions, and for the identification of potentially at-risk areas. Subaerial volcanic stratigraphies are often incomplete, due to a lack of exposure, or burial and erosion from subsequent eruptions. However, many volcanic eruptions produce widely-dispersed explosive products that are frequently deposited as tephra layers in the sea. Cores of marine sediment therefore have the potential to provide more complete volcanic stratigraphies, at least for explosive eruptions. Nevertheless, problems such as bioturbation and dispersal by currents affect the preservation and subsequent detection of marine tephra deposits. Consequently, cryptotephras, in which tephra grains are not sufficiently concentrated to form layers that are visible to the naked eye, may be the only record of many explosive eruptions. Additionally, thin, reworked deposits of volcanic clasts transported by floods and landslides, or during pyroclastic density currents may be incorrectly interpreted as tephra fallout layers, leading to the construction of inaccurate records of volcanism. This work uses samples from the volcanic island of Montserrat as a case study to test different techniques for generating volcanic eruption records from marine sediment cores, with a particular relevance to cores sampled in relatively proximal settings (i.e. tens of kilometres from the volcanic source) where volcaniclastic material may form a pervasive component of the sedimentary sequence. Visible volcaniclastic deposits identified by sedimentological logging were used to test the effectiveness of potential alternative volcaniclastic-deposit detection techniques, including point counting of grain types (component analysis), glass or mineral chemistry, colour spectrophotometry, grain size measurements, XRF core scanning, magnetic susceptibility and X-radiography. This study demonstrates that a set of time-efficient, non-destructive and high-spatial-resolution analyses (e.g. XRF core-scanning and magnetic susceptibility) can be used effectively to detect potential cryptotephra horizons in marine sediment cores. Once these horizons have been sampled, microscope image analysis of volcaniclastic grains can be used successfully to discriminate between tephra fallout deposits and other volcaniclastic deposits, by using specific criteria related to clast morphology and sorting. Standard practice should be employed when analysing marine sediment cores to accurately identify both visible tephra and cryptotephra deposits, and to distinguish fallout deposits from other volcaniclastic deposits.
    Keywords: Tephrostratigraphy ; Tephrochronology ; Eruption History ; Cryptotephras ; Tephra Fallout ; Reworked Volcaniclastic ; Geology
    ISSN: 0012-8252
    E-ISSN: 1872-6828
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  • 6
    Language: English
    In: Journal of Volcanology and Geothermal Research, 15 March 2017, Vol.333-334, pp.15-35
    Description: Volcanism on Montserrat (Lesser Antilles arc) has migrated southwards since the formation of the Silver Hills ~ 2.5 Ma, and has formed three successively active volcanic centres. The Centre Hills volcano was the focus of volcanism from ~ 1–0.4 Ma, before activity commenced at the currently active Soufrière Hills volcano. The history of activity at these two volcanoes provides an opportunity to investigate the pattern of volcano behaviour on an andesitic arc island over the lifetime of individual volcanoes. Here, we describe the pyroclastic stratigraphy of subaerial exposures around central Montserrat; identifying 11 thick (〉 1 m) pumiceous units derived from sustained explosive eruptions of Centre Hills from ~ 0.8–0.4 Ma. Over 10 other, less well- exposed pumiceous units have also been identified. The pumice-rich units are interbedded with andesite lava breccias derived from effusive, dome-forming eruptions of Centre Hills. The stratigraphy indicates that large (up to magnitude 5) explosive eruptions occurred throughout the history of Centre Hills, alongside effusive activity. This behaviour at Centre Hills contrasts with Soufrière Hills, where deposits from sustained explosive eruptions are much less common and restricted to early stages of activity at the volcano, from ~ 175–130 ka. Subsequent eruptions at Soufriere Hills have been dominated by andesitic effusive eruptions. The bulk composition, petrography and mineral chemistry of volcanic rocks from Centre Hills and Soufrière Hills are similar throughout the history of both volcanoes, except for occasional, transient departures to different magma compositions, which mark shifts in vent location or dominant eruption style. For example, the final recorded eruption of Centre Hills, before the initiation of activity at Soufrière Hills, was more silicic than any other identified eruption on Montserrat; and the basaltic South Soufrière Hills episode marked the transition to the current stage of predominantly effusive Soufrière Hills activity. The compositional stability observed throughout the history of Centre Hills and Soufrière Hills suggests that a predominance towards effusive or explosive eruption styles is not driven by major compositional shifts of magma, but may reflect local changes in long-term magma storage conditions that characterise individual episodes (on 10 year timescales) of volcanism on Montserrat.
    Keywords: Volcanic Evolution ; Explosive Volcanism ; Geology
    ISSN: 0377-0273
    E-ISSN: 1872-6097
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  • 7
    Language: English
    In: Journal of Volcanology and Geothermal Research
    Description: Sector collapses affect volcanic edifices across all tectonic settings and involve a rapid redistribution of mass, comparable in scale to the largest magmatic eruptions. The eruptive behaviour of a volcano following sector collapse provides a test of theoretical relationships between surface loading and magma storage, which imply that collapse-driven unloading may lead to changes in eruption rate and erupted magma compositions. Large sector collapses are infrequent events globally, with all historical examples being relatively small in comparison to many of the events documented in the geological record. As a result, exploration of the impacts of sector collapse on eruptive behaviour requires detailed investigation of prehistoric collapses, but this is often hindered by poorly-resolved stratigraphic relationships and dating uncertainties. Nevertheless, observations from a number of volcanoes indicate sharp changes in activity following sector collapse. Here, a global synthesis of studies from individual volcanoes, in both arc and intraplate settings, is used to demonstrate a number of common processes in post-collapse volcanism. Multiple examples from large (〉5 km ) sector collapses in arc settings show that collapse may be followed by compositionally anomalous, large-volume and often effusive eruptions, interpreted to originate via disruption of a previously stable, upper-crustal reservoir. These anomalous eruptions highlight that magma compositions erupted during periods of typical (i.e. unperturbed by sector collapse) volcanism may not be representative of the range of compositions stored within a vertically extensive crustal reservoir. If eruptible magma is not present, upper-crustal reservoirs may rapidly solidify following collapse, without further eruption, allowing more mafic compositions to ascend to the surface with only limited upper-crustal modification, resulting in edifice regrowth at temporarily elevated eruption rates. Subsequent re-establishment of an upper-crustal reservoir further supports a relationship between surface loading and crustal storage, but long-term chemical and mineralogical differences between pre- and post-collapse evolved magmas imply that a newly-developed reservoir can overprint the influence of a preceding reservoir, forming a spatially and compositionally distinct plumbing system. These broad patterns are replicated in intraplate settings, despite differences in scale and melting processes; current evidence suggests that post-collapse evolution of intraplate volcanoes can be explained by unloading-induced destabilisation of the magma plumbing system, rather than increased melt production. What emerges from an apparently diverse set of observations is a systematic behaviour that strongly supports a coupling between edifice growth and magma ascent, storage and pressurisation. Eruption rates, erupted compositions, and the style of volcanism at any particular system may thus be modulated from the surface, and long-term shifts in surface behaviour may occur without any changes in the deep parts of magmatic systems. Observations of sharp post-collapse changes in erupted compositions, including the ascent of primitive mafic magmas, also require a crystal-dominated mid- to upper-crustal reservoir, consistent with recent models of crustal magmatic systems.
    Keywords: Sector Collapse ; Magma Storage ; Eruptive Behaviour ; Edifice Growth and Destruction ; Debris Avalanche ; Geology
    ISSN: 0377-0273
    E-ISSN: 1872-6097
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  • 8
    Language: English
    In: Geochemistry, Geophysics, Geosystems, 2014, Vol.15(7), pp.3000-3020
    Description: Marine sediments around volcanic islands contain an archive of volcaniclastic deposits, which can be used to reconstruct the volcanic history of an area. Such records hold many advantages over often incomplete terrestrial data sets. This includes the potential for precise and continuous...
    Keywords: Sciences of the Universe ; Earth Sciences ; Geology
    ISSN: 1525-2027
    E-ISSN: 1525-2027
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  • 9
    Language: English
    In: Earth and Planetary Science Letters, 15 September 2019, Vol.522, pp.1-11
    Description: The chalcophile elements are important both in terms of their economic value and as potential tracers of magmatic processes at convergent margins. However, because of analytical difficulties, comprehensive datasets of chalcophile element concentrations for volcanic rocks are rare. Here, we present analyses of a near complete suite of chalcophile elements (S, Cu, Ag, Se, As, Sb, Sn, W, Mo, Pb, Bi, Tl, Zn, Ga, Co) for volcanic rock samples collected from a typical continental arc stratovolcano in southern Chile (Antuco). Enrichment in Pb, Bi, W, Tl, Sb and As relative to Parental-MORB indicates that these elements have been mobilised from the subducting slab into the sub-arc mantle wedge, in contrast to Cu and Ag. Very low Se concentrations suggest that Se, like S, was lost during co-eruptive degassing of the Antuco magmas. Previous studies on oceanic arcs have demonstrated that as higher O subduction-related magmas ascend through the overlying lithosphere, magnetite fractionation may trigger sulfide fractionation during crystallisation. If such a process is extensive and has a sharp onset, this would result in a plummet in the Cu, Se and Ag contents of the residual melt. At Antuco, although a decrease in the Fe O and TiO concentrations at ∼55 wt.% SiO (∼3 wt.% MgO) indicates magnetite fractionation, this is not associated with a corresponding drop in Cu contents. Instead, we observe a general decrease in Cu and a decrease in Cu/Ag with increasing SiO and decreasing MgO. Furthermore, Cu/Ag in the most primitive Antuco rocks are lower than the global MORB array, indicating that the melts were sulfide saturated at an early stage in their crustal evolution. Through modelling fractional crystallisation, we show that only a minor volume (0.5–0.6 vol.%) of fractionating sulfide is needed to produce divergent trends in Cu and Ag, as observed in the Antuco samples. Our results show that sulfide fractionation occurred from an early stage during the crustal evolution of Antuco's magmas. We infer that this was promoted by stalling in the lower crust, which for oxidised magmas at depths 〉20 km is within the sulfide stability field. However, elevated Dy /Yb of the Antuco magmas compared to oceanic island arc magmas provides an additional, or alternate mechanism to inducing sulfide fractionation in the lower crust prior to ascent, through initial garnet fractionation. Fractional crystallisation within this depth range meant that later magnetite fractionation had only a minor impact on the partitioning behaviour of the chalcophile elements. In contrast, arc magmas transiting thinner crust may not experience sulfide saturation until a later stage in their evolution, induced by magnetite fractionation. Our results imply that convergent margin crustal thickness, and therefore the depth range of magmatic differentiation, determines the dominant control on initial magmatic sulfide saturation and therefore the primary distribution of chalcophile elements. This implies that secondary processes are required to explain the transport and concentration of sulfides and chalcophile elements at shallower crustal levels.
    Keywords: Chalcophile Elements ; Sulfide ; Saturation ; Fractionation ; Continental Arc ; Antuco ; Geology ; Physics
    ISSN: 0012-821X
    E-ISSN: 1385-013X
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  • 10
    Language: English
    In: Andean Geology, 01 July 2011, Vol.38(2), pp.335-348
    Description: Huequi, a little-known volcano in the southern part of the Andean southern volcanic zone (SSVZ), shows a regionally unusual eruption style, mineralogy and geochemistry. The volcano comprises multiple highly-eroded lava domes. Past eruptions were accompanied by relatively minor explosive activity, most recently from 1890-1920. The rocks erupted by Huequi range from basaltic andesite to dacite, and are highly distinctive when compared to other volcanoes of the SSVZ, being K-poor and Al-rich, and containing euhedral hornblende phenocrysts. Overall compositions suggest a notably water-rich magma source, evolving through high levels of fractionation and subsequent degassing to produce highly porphyritic dome-forming andesites. The ultimate causes of water-rich magmas at this point in the arc remain unclear.El volcán Huequi es poco conocido, que se ubica en la provincia sur de la zona Volcánica Sur de los Andes (ZVSS). Sus tipos de erupción y características mineralógicas y geoquímicas son poco comunes a nivel regional. El volcán presenta múltiples domos poco erosionados. Las erupciones estuvieron acompañadas por una actividad explosiva secundaria, siendo las más recientes las ocurridas entre los años 1890 y 1920. Los magmas del Huequi son de composición andesítico-basáltica a dacítica. Si se las compara con rocas eruptadas por otros centros volcánicos de la ZVSS de los Andes, las del Huequi se caracterizan por ser pobres en K, ricas en Al y por presentar fenocristales euhedrales de anfíbola. Las composiciones totales sugieren una fuente magmática rica en H2O, que se desarrolla a través de niveles de cristalización fraccionada y desgasificación subsecuente, que producen domos volcánicos andesíticos altamente porfíricos. Sin embargo, la causa última que genera magmas ricos en H2O, en esta parte de los Andes, sigue aún sin explicación.
    Keywords: Volcán Huequi ; Zona Volcánica Sur de Los Andes ; Andesita ; Anfíbola ; Domo Volcánico ; Huequi Volcano ; Andean Southern Volcanic Zone ; Andesite ; Amphibole ; Lava Dome ; Geology
    ISSN: 0718-7092
    E-ISSN: 0718-7106
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