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11.
Servando De la Cruz-Reyna Izumi Yokoyama Alicia Martínez-Bringas Esteban Ramos 《Bulletin of Volcanology》2008,70(6):753-767
Popocatépetl Volcano is located in the central Mexican Volcanic Belt, within a densely populated region inhabited by over
20 million people. The eruptive history of this volcano indicates that it is capable of producing a wide range of eruptions,
including Plinian events. After nearly 70 years of quiescence, Popocatépetl reawakened in December 21, 1994. The eruptive
activity has continued up until the date of this submission and has been characterized by a succession of lava dome growth-and-destruction
episodes, similar to events that have apparently been typical for Popocatépetl since the fourteenth century. In this regime,
the episodes of effusive and moderately explosive activity alternate with long periods of almost total quiescence. In this
paper we analyze five years of volcano-tectonic seismicity preceding the initial eruption of the current episode. The evolution
of the V-T seismicity shows four distinct stages, which we interpret in terms of the internal processes which precede an eruption
after a long period of quiescence. The thermal effects of a magma intrusion at depth, the fracturing related to the slow development
of magma-related fluid pathways, the concentration of stress causing a protracted acceleration of this process, and a final
relaxation or redistribution of the stress shortly before the initial eruption are reflected in the rates of V-T seismic energy
release. A hindsight analysis of this activity shows that the acceleration of the seismicity in the third stage asymptotically
forecast the time of the eruption. The total seismic energy release needed to produce an eruption after a long period of quiescence
is related to the volume of rock that must be fractured so imposing a characteristic threshold limit for polygenetic volcanoes,
limit that was reached by Popocatépetl before the eruption. 相似文献
12.
New physical characterization of the Fontana Lapilli basaltic Plinian eruption,Nicaragua 总被引:1,自引:1,他引:0
The Fontana Lapilli deposit was erupted in the late Pleistocene from a vent, or multiple vents, located near Masaya volcano
(Nicaragua) and is the product of one of the largest basaltic Plinian eruptions studied so far. This eruption evolved from
an initial sequence of fluctuating fountain-like events and moderately explosive pulses to a sustained Plinian episode depositing
fall beds of highly vesicular basaltic-andesite scoria (SiO2 > 53 wt%). Samples show unimodal grain size distribution and a moderate sorting that are uniform in time. The juvenile component
predominates (> 96 wt%) and consists of vesicular clasts with both sub-angular and fluidal, elongated shapes. We obtain a
maximum plume height of 32 km and an associated mass eruption rate of 1.4 × 108 kg s−1 for the Plinian phase. Estimates of erupted volume are strongly sensitive to the technique used for the calculation and to
the distribution of field data. Our best estimate for the erupted volume of the majority of the climactic Plinian phase is
between 2.9 and 3.8 km3 and was obtained by applying a power-law fitting technique with different integration limits. The estimated eruption duration
varies between 4 and 6 h. Marine-core data confirm that the tephra thinning is better fitted by a power-law than by an exponential
trend. 相似文献
13.
Detailed facies analysis of hyaloclastites and associated lavas from eight table mountains and similar "hyaloclastite volcanoes"
in the Icelandic rift zone contradict a rapid and continuous, "monogenetic", entirely subglacial evolution of most volcanoes
studied. The majority of the exposed hyaloclastite deposits formed in large, stable lakes as indicated by widespread, up to
300-m-thick, continuous sections of deep water, shallow water and emergent facies. Salient features include extensively layered
or bedded successions comprising mainly debris flow deposits, turbidites, base surge and fallout deposits consisting of texturally
and compositionally variable, slightly altered hyaloclastites, as well as sheet and pillow lavas. In contrast, chaotic assemblages
of coarser-grained, more poorly sorted and more strongly palagonitized hyaloclastite tuffs and breccias, as well as scoria
and lava are interpreted to have formed under sub- or englacial conditions in small, chimney-like ice cavities or ice-bound
lakes. Irregularly shaped and erratically arranged hyaloclastite bodies produced at variable water levels appear to have resulted
mainly from rapid changes of the eruptive environment due to repeated build-up and drainage of ice-bound lakes as well as
the restricted space between the ice walls. We distinguish a "deep water" facies formed during high water levels of the lake,
a hydroclastic shallow water and emergent facies (leakage of the lake or growth of the volcano above the water surface). Our
model implies the temporary existence of large, stable lakes in Iceland probably formed by climatically induced ice melting.
The highly complex edifices of many table mountains and similar volcanoes were constructed during several eruptive periods
in changing environments characterized by contrasting volcanic and sedimentary processes.
Received: 10 June 1997 / Accepted: 28 July 1998 相似文献
14.
吉林省龙岗火山群南龙湾第四纪火山碎屑颗粒特征研究 总被引:2,自引:0,他引:2
爆炸性火山喷发形成的碎屑颗粒的粒度、分选性、表面结构和内部结构等特征与火山喷发的机制、岩浆与水作用的程度、搬运过程等有着重要的联系。本文以此为线索,研究了龙岗火山群南龙湾火山的一个剖面,以探讨其喷发类型和特征。在该剖面上采集了不同层位火山碎屑颗粒样品,然后进行显微形貌观测、粒度分析和扫描电镜形貌观测。显微镜下观测表明,射汽爆发、射汽岩浆爆发和岩浆爆发的碎屑颗粒具有不同的成分和形貌特征。粒度分析结果显示,粒度与喷发类型之间存在很好的对应关系,不同的爆发类型具有不同的分维值D范围。SEM分析可以提供有关火山喷发特征对火山碎屑颗粒的影响。本文的研究结果表明,南龙湾火山喷发为爆炸式喷发,包括早期的射汽岩浆爆发,到岩浆爆发至晚期以射汽爆发为主的射汽岩浆爆发的不同阶段,该区火山喷发的不同时期,水参与喷发的程度不同。 相似文献
15.
长白山天池火山在全新世曾有过几次喷发,其中距今约1000年发生过大规模布里尼式爆炸喷发(即“千年大喷发”),其喷发产物——灰白色碱流质浮岩和喷发柱垮塌形成的火山碎屑流分布范围极广,除长白山区外,在朝鲜半岛和日本北部也有大量浮岩降落和堆积。根据野外较大范围的系统采样、镜下观察和测试分析,在天池火山千年大喷发产物的碱性长石晶屑中发现了两组颜色、形态、化学成分迥异的“火口组”和“圆池组”熔体包裹体,对揭示天池火山千年大喷发的成因具有重要意义。根据电子探针分析结果,“火口组”熔体包裹体成分为英安岩和粗面英安岩,寄主晶多为透长石;“圆池组”熔体包裹体成分为粗面英安岩和流纹岩,寄主晶为歪长石。相对“火口组”熔体包裹体,“圆池组”包裹体具有高SiO2、高H2O和高Cl含量的特点,化学成分也更为演化,可能是天池火山千年大喷发时岩浆结晶分异后期的产物。两组包裹体的存在为千年大喷发前的层状地壳岩浆房和成分并非单一提供了证据,它们可能是在同次大喷发的不同序列中喷出的。由于地幔岩浆注入地壳岩浆房,导致不同层位岩浆的扰动和混合作用,因挥发分出溶在岩浆房最顶部形成挥发分梯度和过饱和,最终触发了天池火山的千年大喷发,对当时的气候环境造成过较大影响。 相似文献
16.
景谷民乐火山灰流型铜矿地质及成因 总被引:2,自引:0,他引:2
民乐浸染状铜矿产于中三叠统灰流型富钠质熔结凝灰岩中。矿区火山岩主体为细碧角斑岩系,矿床的形成与陆内再生地槽海相火山活动及其4后的热液蚀变作用密切相关。矿体分布明显受火山岩岩性、岩相、层位及构造控制,成因上与火山喷发和爆发作用有关。矿床受后期火山热液、次生富集改造后富化明显。 相似文献
17.
硅质岩浆的成因及演化机制研究是认识大陆地壳成分结构演化机制的关键途径。地壳硅质岩浆储库的基本性质及其演化的动力学过程是制约硅质岩浆演化及其多样性的根本原因,也是受到广泛关注的前沿和热点问题。本文总结了硅质岩浆储库的基本性质及其演化机制研究的相关进展,重点探讨了岩浆体系演化的动力学机制,即其物质成分及温度压力条件的动态演化过程,亦即岩浆储库在补给驱动下的存留、活化、分异、喷发过程。经由累积生长的方式形于地壳浅部的硅质岩浆储库以晶粥为主要赋存形式,具有较低的温度压力范围和高硅高结晶度高粘度的特征。岩浆储库的基本性质导致其自身不具有持续演化的能力,只有在基性岩浆补给的驱动下才能长时间存留分异或快速活化喷发。基性岩浆的补给及其携带的热及流体/挥发份深刻地改变了岩浆储库的物质成分及物理条件,是导致硅质岩浆分异演化或喷发的根本原因。本文还结合研究进展探讨了东南沿海地区中生代火山-侵入岩的成因演化机制及相关问题。 相似文献
18.
19.
Batur volcanic field (BVF) in Bali, Indonesia, underwent two successive caldera-forming eruptions, CI and CII (29,300 and 20,150 years b.p., respectively) that resulted in the deposition of dacitic ignimbrites. The respective ignimbrites show contrasted stratigraphies, exemplify the variability of dynamics associated with caldera-forming eruptions and provide insights into the possible controls exerted by caldera collapse mechanisms. The Ubud Ignimbrite is widespread and covers most of southern Bali. The deposits consist dominantly of pyroclastic flow with minor pumice fall deposits. The intra-caldera succession comprises three distinct, partially to densely welded cooling units separated by non-welded pyroclastic flow and fall deposits. The three cooling units consist of pyroclastic flow deposits only and together represent up to 16 distinct flow units, each including a thin, basal, lithic-rich breccia. This eruption was related to a 13.5×10 km caldera (CI) with a minimum collapsed volume of 62 km3. The floor of caldera CI is inferred to have a piecemeal geometry. The Ubud Ignimbrite is interpreted as the product of a relatively long-lasting, pulsating, collapsing fountain that underwent at least two time breaks. A stable column developed during the second time break. Discharge rate was high overall, but oscillatory, and increased toward the end of the eruption. These dynamics are thought to reflect sequential collapse of the CI structure. The Gunungkawi Ignimbrite is of more limited extent outside the source caldera and occurs only in central southern Bali. The Gunungkawi Ignimbrite proximal deposits consist of interbedded accretionary lapilli-bearing ash surge, ash fall, pumice lapilli fall and thin pyroclastic flow deposits, overlain by a thick and massive pyroclastic flow deposit with a thick basal lag breccia. The caldera (CII) is 7.5×6 km in size, with a minimum collapsed volume of 9 km3. The CII eruption included two distinct phases. During the first, eruption intensity was low to moderate and an unstable, essentially phreatomagmatic column developed. During the second phase, the onset of caldera collapse drastically increased the eruption intensity, resulting in column collapse. The caldera floor is believed to have subsided rapidly, producing a single, short-lived burst of high eruption intensity that resulted in the deposition of the uppermost massive pyroclastic flow.Editorial responsibility: T. Druitt 相似文献
20.
Lucia Gurioli Bruce F. Houghton Katherine V. Cashman Raffaello Cioni 《Bulletin of Volcanology》2005,67(2):144-159
The 79 AD eruption of Vesuvius included 8 eruption units (EU1–8) and several complex transitions in eruptive style. This study focuses on two important transitions: (1) the abrupt change from white to gray pumice during the Plinian phase of the eruption (EU2 to EU3) and (2) the shift from sustained Plinian activity to the onset of caldera collapse (EU3 to EU4). Quantification of the textural features within individual pumice clasts reveals important changes in both the vesicles and groundmass crystals across each transition boundary. Clasts from the white Plinian fall deposit (EU2) present a simple story of decompression-driven crystallization followed by continuous bubble nucleation, growth and coalescence in the eruptive conduit. In contrast, pumices from the overlying gray Plinian fall deposit (EU3) are heterogeneous and show a wide range in both bubble and crystal textures. Extensive bubble growth, coalescence, and the onset of bubble collapse in pumices at the base of EU3 suggest that the early EU3 magma experienced protracted vesiculation that began during eruption of the EU2 phase and was modified by the physical effects of syn-eruptive mingling-mixing. Pumice clasts from higher in EU3 show higher bubble and crystal number densities and less evidence of bubble collapse, textural features that are interpreted to reflect more thorough mixing of two magmas by this stage of the eruption, with consequent increases in both vesiculation and crystallization. Pumice clasts from a short-lived, high column at the onset of caldera collapse (EU4) continue the trend of increasing crystallization (enhanced by mixing) but, unexpectedly, the melt in these clasts is more vesicular than in EU3 and, in the extreme, can be classified as reticulite. We suggest that the high melt vesicularity of EU4 reflects strong decompression following the partial collapse of the magma chamber.Editorial responsibility: D.B. Dingwell 相似文献