Non-explosive silicic volcanism

Eichelberger, J. C.; Carrigan, Charles R.; Westrich, Henry R.; Price, R.H.

doi:10.1038/323598a0

Cited by 565 publications

(414 citation statements)

References 13 publications

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“…(2) Magma discharge rate is certainly influenced by conduit dimensions, but there need be no simple relationship; the influence of non-explosive degassing history on viscosity during gradual decompression (Eichelberger et al 1986) can impose a stronger control. At Quizapu, similar volumes of otherwise identical dacite magma erupted through approximately the same conduit twice, in 1932 at > 108 kg/s and in 1846-47 at a rate at least two orders of magnitude slower.…”

Section: Discussionmentioning

confidence: 99%

Volc�n Quizapu, Chilean Andes

1992

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Abstract. Quizapu is a flank vent of the basalt-to-rhyodacite Holocene stratocone, Cerro Azul, and lies at the focus of a complex Quaternary volcanic field on the Andean volcanic front. The Quizapu vent originated in 1846 when 5 km 3 of hornblende-dacite magma erupted effusively with little accompanying tephra. Between 1907 and 1932, phreatic and strombolian activity reamed out a deep crater, from which 4 km 3 of dacite magma identical to that of 1846 fed the great plinian event of 10-11 April 1932. Although a total of > 9 km 3 of magma was thus released in 86 years, there is no discernible subsidence. As the pre-plinian crater was lined by massive lavas, 1932 enlargement was limited and the total plinian deposi t contains only ~ 0.4 wt % lithics. Areas of 5-cm and 1-cm isopachs for compacted 1932 fallout are about half of those estimated in the 1930's, yielding a revised ejecta volume of -9.5 km 3. A strong inflection near the 10-cm isopach (downwind -1 1 0 km) on a plot of log Thickness vs Area 1/2 reflects slow settling of fine plinian ash -not of coignimbrite ash, as the volume of pyroclastic flows was trivial (<0.01 km3). About 17 vol.% of the fallout lies beyond the 1-cm isopach, and ~ 82 wt% of the ejecta are finer than 1 mm. At least 18 hours of steady plinian activity produced an exceptionally uniform fall deposit. Observed column height (27-30 km) and average mass eruption rate (1.5 x 108 kg/s) compare well with values for height and peak intensity calculated from published eruption models. The progressive "aeolian fractionation" of downwind ash (for which Quizapu is widely cited) is complicated by the large compositional range of 1932 juvenile pumice (52-70% SiO2). The eruption began with andesitic scoria and ended with basaltic scoria, but > 95% of the ejecta are dacitic pumice (67-68% SiO2); minor andesitic scoria and frothier rhyodacite pumice (70% SiO2) accompanied the dominant dacite. Phenocrysts (pl > hb -opx > mt > ilm ~ cpx) are similar in both abundance and composition in the 1846 (effusive) and 1932 (plinian) dacites. Despite the contrast in mode of eruption, bulk compositions are also indistinguishable. The only difference so far identified is a lower range of ~D values for 1846 hornblende, consistent with pre-emptive degassing of the effusive batch.

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Section: Discussionmentioning

confidence: 99%

Volc�n Quizapu, Chilean Andes

1992

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“…The weakly explosive character of TVG volcanism can be explained by syneruptive non-explosive degassing of magma (Eichelberger et al, 1986;Eichelberger, 1995). In the case of the TVG, loss of volatiles probably occurred though country rocks, which were initially extensively fractured by the very active tectonic processes operating in Taiwan.…”

Section: Styles and Mechanisms Of Past And Future Eruptions Of Tvgmentioning

confidence: 99%

“…This observation cannot be explained by simply assuming that magmas of the TVG at depth had initially a low content of dissolved volatiles. Although we did not measure volatile content in TVG magmas, abundant presence of hornblende in all products of the E-W volcanic ridge clearly indicates that initially (at depth), magmas of the TVG had a significant proportion of dissolved water (at least 3% according to Eichelberger et al, 1986). Such magmas are potentially very explosive.…”

Section: Styles and Mechanisms Of Past And Future Eruptions Of Tvgmentioning

confidence: 99%

Deposits, character and timing of recent eruptions and gravitational collapses in Tatun Volcanic Group, Northern Taiwan: Hazard-related issues

Belousov

Belousova

Chen

et al. 2010

Journal of Volcanology and Geothermal Research

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Keywords:extrusive eruption explosive eruption pyroclastic edifice collapse volcanic hazard Taiwan Taipei City, with a population of around 8 million, as well as two nuclear power plants is located in close proximity to the Quaternary, dominantly andesitic Tatun Volcanic Group (TVG) of Northern Taiwan. We have investigated the stratigraphy of the youngest volcaniclastic deposits, as well as the morphology of lava flows and domes of the TVG in order to reconstruct the character and timing of the most recent eruptions and related hazardous events in the area. Our data indicate that recent eruptions of the group were dominated by long-term, voluminous extrusions of crystal-rich, very viscous lavas. These eruptions formed closely spaced monogenetic domes and lava flows. Based on morphological parameters of the lava flows (thicknesses 80-150 m, lengths up to 5.6 km, and volumes up to 0.6 km 3 ), average rates of magma effusion ranged from 1 to 10 m 3 /s, eruption durations from 500 to 1800 days, and lava front speeds from 0.5 to 6 m/h. Explosive activity of TVG was diverse, ranging from weak phreatic to highly explosive (VEI 4) Plinian eruptions; vulcanian activity with deposition of lithic ashes was most common. Interaction of rising magma with ground water frequently occurred during the eruptions. This study presents the first radiocarbon dates of various volcaniclastic deposits of the TVG, which indicate that Cising, Siaoguanyin, and possibly Huangzuei volcanoes had magmatic eruptions in the period 13,000-23,000 years ago. In addition, Mt. Cising had a phreatic eruption 6000 years ago, and possibly an effusive eruption just before that. Gravitational collapses of volcanic edifices with volumes 0.01-0.1 km 3 and H/L 0.16-0.25 were also common. They occurred on intersections with tectonic faults and may have been triggered by seismic activity. The youngest collapses occurred at Mt. Siaoguanyin (23,000 BP) and Mt. Cising (6000 BP). It is concluded that the TVG should be considered volcanically active. The results of this study provide a basis for volcanic hazard assessment and mitigation in the area.

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“…In contrast, other volcanoes have conduit systems that activate only when gas and magma are available in sufficient quantity to force the system open. If volatiles are unable to escape from magma through passive degassing, the result can be an explosive eruption [Eichelberger et al, 1986]. Both styles of volatile release have occurred at Mt.…”

Section: Introductionmentioning

confidence: 99%

Fluid ascent during the 2004–2005 unrest at Mt. Spurr inferred from seismic tomography

Koulakov

West²,

Izbekov³

2013

Geophysical Research Letters

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We present a seismic model of the crust beneath Mt. Spurr Volcano in Alaska based on tomographic inversion of local earthquake data recorded by temporary seismic network during the unrest of Mt. Spurr in 2004–2005. Beneath the northern vent of Mt. Spurr, where the most intensive fumarolic activity was observed during the last unrest, we observe a finger‐shaped anomaly with a higher P and lower S velocity, which corresponds to high Vp/Vs ratio. Another anomaly is located to the south of Crater Peak approximately beneath the same location where an explosive eruption occurred in 1992. We propose that these two finger anomalies represent separated conduits of magma and volatiles. The NE conduit extends to the surface and enables free volatile flux. The SE conduit seems to be blocked at a ca. 20 km depth and in case of continuous pressure build up may become a source of an explosive eruption.

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Non-explosive silicic volcanism

Cited by 565 publications

References 13 publications

Volc�n Quizapu, Chilean Andes

Volc�n Quizapu, Chilean Andes

Deposits, character and timing of recent eruptions and gravitational collapses in Tatun Volcanic Group, Northern Taiwan: Hazard-related issues

Fluid ascent during the 2004–2005 unrest at Mt. Spurr inferred from seismic tomography

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