腾冲马鞍山、打鹰山、黑空山火山岩浆来源与演化

本文对马鞍山、打鹰山、黑空山火山岩主微量和Sr、Nd、Pd同位素地球化学研究认为,腾冲火山岩浆源区具有MORB与富集地幔混合之特征,推测为新特提斯俯冲洋壳重新熔融,导致腾冲地区的高钾钙碱性岩浆的火山活动,解释了腾冲在新生代大陆板内构造环境背景下出现岛弧或活动大陆边缘火山岩地球化学特征的现象。马鞍山、打鹰山和黑空山火山高钾钙碱性岩浆经历了岩浆房阶段辉石、钛铁矿的结晶分离作用和岩浆上升过程中斜长石的结晶分离作用,导致岩浆成分从中基性向中酸性演化,火山岩从玄武质粗安岩→粗安岩→粗面质英安岩演化。     

Sources of volatiles for a subduction zone volcano: Mutnovsky volcano,Kamchatka

Mass balance calculations of volatiles were performed for Mutnovsky volcano, Kamchatka, by comparing the chemical and isotopic compositions of gas emissions with the compositions of the main geochemical reservoirs in the subduction zone using a simple mixing model. The predominant deep component (up to 73% in the highest temperature fumaroles) is composed of slab fluid released during dehydration of the Pacific Plate. The mantle component does not exceed 2.1%. The fraction of gases from the continental crust varies from 0.5 to 5% depending on the composition of the crustal endmember that was used in the calculations. In terms of the gas composition, Mutnovsky volcano is a typical subduction volcano, but its fluid system has a complex structure. The observed compositional pattern in the volcanic fumaroles can be explained by degassing of two independent magma bodies.     

西昆仑阿什库勒大黑山火山岩浆作用过程研究

西昆仑阿什库勒火山群位于青藏高原西北缘,由于环境恶劣,研究程度低。大黑山火山为该区内熔岩分布面积最广、喷发规模最大的一座火山。本次对大黑山火山岩的显微结构、斑晶类型和化学成分进行了详细的测试分析,讨论其反映的岩浆过程。大黑山火山成分具有一个较大的范围,包括玄武粗安岩、粗安岩和粗面岩,主要氧化物与Si O2含量之间呈线性关系,说明三种类型岩浆存在岩浆演化关系。熔岩主要斑晶为辉石和斜长石,大量斑晶显示熔蚀、反环带和反应边结构,指示岩浆混合特征。温压计计算得到玄武粗安岩和粗安岩平衡温度在1124~1176℃之间,平衡压力在0.55~0.81GPa之间,对应的深度约16.5~24.3km,粗面岩的平衡温度1059~1071℃,平衡压力0.39~0.59GPa,对应深度11.8~17.7km。研究显示,大黑山火山下的主岩浆经历了玄武粗安岩、粗安岩和粗面岩的演化,三种岩浆可能以分层的形式同时存在于岩浆房中,三种岩浆存在着混合作用,并与周围偏酸性岩浆发生了混合作用。     

Naturally acid waters from Copahue volcano,Argentina

Volcanic acid sulfate–chloride brines form through absorption of volcanic vapors in shallow reservoirs of meteoric water. Reaction with surrounding volcanic rocks leads to partial neutralization of the fluids and precipitation of secondary minerals. Chemical data of such acid waters from Copahue volcano, Argentina, covering 8 years of observations, show evidence for changes in composition related to water rock interaction at depth prior to emergence of the fluids at the surface. The chemical composition changed dramatically during the 2000 eruption of Copahue, with enhanced concentrations and fluxes of Mg, Na, Fe and Al, followed in 2001 by rapidly declining concentrations and element fluxes. The subsequent 5 years saw more variable element ratios and strong depletions in K and Al. Most incompatible elements are released from the rock matrix stochiometrically, whereas some elements are enriched through vapor input from the magma (As, Pb, Zn). Most fluids have LREE enrichments relative to the rock matrix, but during periods of new magma intrusion the LREE enrichment decreases as does the magnitude of the negative Eu anomaly in the fluids. These observations are interpreted assuming early dissolution of plagioclase, olivine and volcanic glass that occurs during intrusion of new magma into the hydrothermal system. The high field strength elements are virtually immobile even in these hot acid fluids, with Nb and Ta more so than Hf and Zr. The mobility of U and Th in these fluids is comparable, at variance with Th behavior in neutral fluids. The local rivers and lakes of Copahue are fertilized by volcanic dissolved P, and most surface waters with pH < 3 have high levels of As. The acid fluids from Copahue may be surficial analogs for deep subduction fluids that evolve below zones of arc magma generation as well as for early Mars environments that are thought to have had large acid lakes.     

Evolution of Irruputuncu volcano,Central Andes,northern Chile

The Irruputuncu is an active volcano located in northern Chile within the Central Andean Volcanic Zone (CAVZ) and that has produced andesitic to trachy-andesitic magmas over the last ∼258 ± 49 ka. We report petrographical and geochemical data, new geochronological ages and for the first time a detailed geological map representing the eruptive products generated by the Irruputuncu volcano. The detailed study on the volcanic products allows us to establish a temporal evolution of the edifice. We propose that the Irruputuncu volcanic history can be divided in two stages, both dominated by effusive activity: Irruputuncu I and II. The oldest identified products that mark the beginning of Irruputuncu I are small-volume pyroclastic flow deposits generated during an explosive phase that may have been triggered by magma injection as suggested by mingling features in the clasts. This event was followed by generation of large lava flows and the edifice grew until destabilization of its SW flank through the generation of a debris avalanche, which ended Irruputuncu I. New effusive activity generated lavas flows to the NW at the beginning of Irruputuncu II. In the meantime, lava domes that grew in the summit were destabilized, as shown by two well-preserved block-and-ash flow deposits. The first phase of dome collapse, in particular, generated highly mobile pyroclastic flows that propagated up to ∼8 km from their source on gentle slopes as low as 11° in distal areas. The actual activity is characterized by deposition of sulfur and permanent gas emissions, producing a gas plume that reaches 200 m above the crater. The maximum volume of this volcanic system is of ∼4 km³, being one of the smallest active volcano of Central Andes.     

Activity of the carbonatite volcano Oldoinyo Lengai, 1966

From 1960 to August, 1966, the activity of Oldoinyo Lengai took the form of quiet extrusion of carbonatite lava. In August, 1966, the style of activity changed abruptly and violent ash eruptions took place. The activity varied from minor emissions of ash to major Plinian and Vulcanian type eruptions. A new ash-cone built up within the crater and ash was widely distributed on the slopes of the volcano and over the surrounding countryside.The ash consists of sodium carbonate mixed with crystals of nepheline, pyroxene, wollastonite, apatite, melanite and pyrite. Also blocks of ijolite and melteigite were ejected during the activity.

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Zusammenfassung Von 1960 bis zum August 1966 bestand die Tätigkeit des Vulkans Oldoinyo Lengai/Ostafrika in ruhigen Lava-Extrusionen. Im August 1966 änderte sich plötzlich die Art seiner Tätigkeit, und heftige Aschenbrüche fanden statt. Diese Tätigkeit variierte von kleineren Ascheneruptionen bis zu größeren Ausbrüchen plinianischen und vulkanischen Typs. Ein neuer Aschenkegel entstand in dem aktiven Krater, und Asche wurde weithin über die Abhänge des Vulkans und über die Umgebung verteilt.Die Asche besteht aus Natrium-Karbonatit mit einer Beimischung von Kristallen von Nephelin, Pyroxen, Wollastonit, Apatit, Melanit und Pyrit. Während des Ausbruchs wurden auch Ijolith- und Melteigitblöcke ausgeworfen.

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Résumé De 1960 jusqu'en août, 1966, l'activité du volcan Oldoinyo Lengai consistait en coulées tranquilles de lave carbonatitique. En août, 1966, le genre d'activité changea abruptement et de violentes éruptions de cendres se produisirent. L'activité consistait tantôt en de petites émissions de cendres, tantôt en éruptions majeures du genre Plinien et Vulcanien. Un cône neuf de cendres s'amoncelait dans le cratère actif, et les cendres se dispersaient sur le pays environnant.Les cendres se composaient de carbonatite alcaline avec des cristaux de nephéline, pyroxène, wollastonite, melanite et de pyrite. D'ailleurs des blocs d'ijolite et de melteigite furent projetés hors du cratère pendant l'activité.

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Dedicated to Professor Dr. A.Rittmann on the occasion of his 75. birthday     

长白山天池火山监测工作进展

长白山天池火山是我国最具有潜在喷发危险的活火山。本文介绍了天池火山监测系统建设的基本情况，报道了近些年在火山地震监测、大地形变监测以及地球化学监测等方面的工作进展。     

Temporal magmatic variation at Boqueron volcano,El Salvador

The relative ages of 21 lavas from Boqueron volcano in El Salvador were determined by superposition. The lavas are grey to black, porphyritic basalts, basaltic andesites and andesites with phenocrysts of plagioclase, augite, olivine, and magnetite. The andesitic lavas appear to have evolved from basaltic magma by fractionation of the observed phenocryst phases.The temporal variation in the chemical composition of the lavas at Boqueron is composed of three components. First, there is a crudely cyclical alternation of basalts and andesites. Second, these cycles are progressively shifted toward higher SiO₂ contents. Third, approximately in the middle of the stratigraphic section sampled, there is an abrupt change in chemical variation trends from an Al-rich and Fe-poor trend to an Fe-rich and Al-poor trend. This change is interpreted to have been caused by an increased proportion of plagioclase fractionation and a decreased porportion of augite fractionation. The crudely cyclical change in SiO₂ content with time is interpreted as a combination of crystal fractionation that increases SiO₂ content, followed by influxes of basaltic magma that mix with residual magma to decrease SiO₂ content. Successive cycles are shifted toward higher SiO₂ content because there is a significant volume of fractionated magma remaining in the chamber before each influx of basalt.     

Plinian eruptions of Nevado de Toluca volcano,Mexico

Zusammenfassung Die Unteren und die Oberen Bimssteine des Toluca sind dacitische air fall-Ablagerungen, die vor etwa 24 500 bzw. 11 600 Jahren gefördert wurden. Der Lower Toluca Pumice bedeckt ungefähr 400 km2 und hat ein Volumen von rund 0,33 km³ (porenfrei gerechnet von 0,16 km³). Nach der 10-cm-Mächtigkeitskurve zeigt er einen nordostgerichteten Verbreitungsfächer. Der Upper Toluca Pumice bedeckt mehr als 2000 km²; sein Volumen beträgt rund 2,3 km³, wenn man die 40-cm-Mächtigkeitskurve zugrundelegt. Das Gesamtvolumen dürfte bei 3,5 km³ (porenfrei gerechnet bei 1,54 km³) liegen. Sein symmetrischer Verbreitungsfächer hat die Richtung N 65° E.Die INMAN-Parameter, Median (Md) und Sortierung (), zusammen mit dem Zerkleinerungs-Index von granulometrischen Analysen aus 23 Bimssteinprofilen zeigen, daß beide Ausbrüche dem plinianischen Typ zuzuordnen sind. Die Korngrößen-Verteilung, verglichen mit einem einfachen mathematischen Modell, gibt einen annähernden Hinweis auf den Ausbruchsverlauf während der Ablagerung der gröbsten Anteile des unteren Teils der Upper Toluca Pumice-Serie. Nach Berechnungen ergibt sich eine Anfangsgeschwindigkeit der Eruption von 500 m/sek aus einem annähernd runden Schlot mit einem Durchmesser von 260 m, sowie eine horizontale Durchschnittswindgeschwindigkeit von 16,2 m/sek und eine Höhe der Eruptionswolke von 40 km. Die freigewordene kinetische Energie betrug rund 6 X 10¹⁹ erg/sek. Die jüngere Eruption dagegen hatte zehnmal mehr kinetische Energie als die ältere.

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The Lower and Upper Toluca Pumice Formations are dacitic airfall deposits that were erupted about 24,500 yr BP and 11,600 yr BP respectively. The Lower Toluca Pumice covers about 400 km², with a volume of 0.33 km³ (dense rock equivalent 0.16 km³) within the 10 cm isopach, and has a northeast-trending dispersal fan. The Upper Toluca Pumice covers more than 2,000 km², has a volume of 2.3 km³ within the 40 cm isopach, and an estimated total volume of 3.5 km³ (dense rock equivalent 1.54 km³). Its symmetrical dispersal fan trends N 65° E. The Inman parameters, median diameter (Md) and deviation (), together with the fragmentation indices, derived from granulometric studies of samples from 23 pumice sections, show that both eruptions were of Pliniantype. The particle-size distribution, compared with a simple mathematical model of a Plinian eruption, provides an approximate indication of the eruptive conditions during the deposition of the coarsest part of the Lower Member of the Upper Toluca Pumice. Computations give a muzzle velocity of 500 m/sec from a circular vent 260 m in diameter, a mean horizontal windspeed of 16.2 m/sec and an eruptive cloud 40 km high, with a maximum rate of release of kinetic energy of 6 × 10¹⁹ erg/sec. The younger eruption released about ten times more kinetic energy than the older.

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Resumen Las formaciones »Lower y Upper Toluca Pumice« son depósitos de caida libre, originados hace approximadamente 24,500 y 11,600 años A.P., respectivamente. El depósito »Lower Toluca Pumice« cubre un area de aproximadamente 400 km², y tiene un volumen de 0.33 km³ (0.16 km³ de roca masiva) dentro de la isopaca de 10 cm, y su area de dispersión se prolonga en dirección N.E. El depósito »Upper Toluca Pumice« cubre más de 2,000 km², tiene un volumen de 2.3 km³ dentro de la isopaca de 40 cm, y un volumen total estimado en 3.5 km³ (1.54 km³ de roca masiva); su dirección principal de dispersion es N 65° E. Considerando los parámetres de Inman; es decir, diámetro medio (Md) y desviación estandard (), además de los índices de fragmentatión, derivados todos de estudios granulométricos de muestras tomadas en 23 secciones en el campo, ambos depósitos se deben a erupciones del tipo Pliniano. La distribución de tamaños, comparada con un modelo matemático simple de una erupción tipo Pliniano, muestra los parámetres aproximados de la erupción al momenta de depositarse la fracción más gruesa del miembro inferior del depósito »Upper Toluca Pumice«. Los cálculos dan una velocidad de escape de 500 m/seg de un cráter circular 260 m de diámetro, una velocidad media del viento de 16.2 m/seg y una columna eruptiva de 40 km de altura, con un gasto máximo de energía cinética de 6 × 10¹⁹ ergios/seg. La energía cinética liberada por la última erupción fue diez veces mayor que la primera.

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Résumé Les formations inférieures et supérieures de Ponce de Toluca sont des dépôts dacitiques d'origine aérienne, qui ont été émis il y a environ 24,500 ans AP et 11,600 ans AP respectivement. Le »Lower Toluca Pumice«, qui couvre environ 400 km², avec un volume de 0.33 km³ (équivalent à 0.16 km³ de roche compacte) dans I'isopaque de Pumice«, couvre plus de 2000 km², a un volume de 2.3 km³ dans l'isopaque de 40 cm, et un volume global estimé à 3.5 km³ (équivalent à 1.54 km³ de roche compacte). Son éventail symétrique de dispersion est dirigé vers N 65° E. Les paramètres Inman, le diamètre médian (Md) et la déviation (), comme aussi les indices de fragmentation tirés des études granulométriques d'échantillons de 23 profils de ponce, montrent que ces deux éruptions étaient du type plinien. La distribution granulométrique des particules comparée à un modèle mathématique simple d'une éruption plinienne, fournit une indication approximative des conditions d'éruption pendant le dépôt de la fraction la plus grossière du membre inférieur du »Upper Toluca Pumice«. Des calculs donnent une vitesse initiale de 500 m/sec à partir d'un évent circulaire de 260 m de diamètre, une vitesse horizontale de vent de 16.2 m/sec et une nuée éruptive de 40 km de hauteur, avec une degré maximum de libération d'énergie cinétique de 6 × 10¹⁹ erg/sec. L'éruption plus récente a libéré environ dix fois plus d'énergie cinétique que l'éruption plus ancienne.

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, 24500 11600 . «Lower Toluca Pumice» 400 ² 0,33 ³, , — 0,16 ³. 10 , - . «Upper Toluca Pumice» , 2000 ²; 2,3 ³, 40 . 3,5 ³, 1,54 ³. 65°. INMAN, (Md Ø) 23 , . «Upper Toluca Pumica». 500 /, 260 , 16,2 /. 40 . 6&#x0445;10¹⁹ /. 10 , .

     

The Pyroclastic deposits of Mount Etna volcano,Sicily

Throughout most of its geological evolution Etna has been characterized by the eruption of lava flows of a predominantly hawaiitic composition, but within the stratigraphical record there are four major sequences of pyroclastic materials: the Acireale tephra and lahars (˜100000 B.P.); the ‘lower tephra’ and Milo lahars (both ˜26000 B.P.); the Biancavilla ignimbrites (15–15500 B.P.) and the ‘upper tephra’ (˜5000–6000 B.P.). This paper reports investigations carried out on these deposits in order to determine their stratigraphy, petrology, sedimentology, and likely origins. Whereas the Biancavilla ignimbrites were generated when a more evolved, gas-charged magma (benmoreite) was being produced by the volcano, the other suites of pyroclastic deposits were erupted from hawaiitic magmas—similar to those that have characterized the volcano during historical times. These deposits resulted from two processes: violent strombolian activity producing lapilli-rich. coarse, but well-sorted sediments, and hydrovolcanism when the mixing of water and magma in the conduit, brought about more violently explosive activity, giving rise to highly fragmented, poorly sorted, airfall tephra and lahars. Conditions favouring hydrovolcanism occurred at times in the volcano's history when palaeoenvironment and palaeogeography were conducive to the retention of large amounts of surface and subsurface water. Although climates favouring the retention of water at high levels on the volcano have occurred on many occasions in the history of the volcano, at ˜26.000 and ˜5000-6000 B.P. these occurred in conjunction with a construct of sufficient height and suitable configuration to allow storage of water and give rise to hydrovolcanic activity. The nature of the mechanisms responsible for the emplacement of these hydrovolcanic deposits is considered and it is concluded that airfall is the most probable process. Finally, the implications of this research for the assessment of hazard are reviewed.     

Mount Woolnough: the submerged volcano,SE of Sydney,NSW

Part of a larger investigation of the sea bed off Sydney was a study of the extinct submarine volcano Mount Woolnough. It is located approximately 41 km east of Kurnell, NSW, and protrudes 175 m above the sediment cover at depths of approximately ?550 to ?375 m. Volcanic rock, approximately 2.2 km in diameter, is exposed above the sediment sea floor and is much smaller than its magnetic expression (approximately 13 km in diameter). Samples dredged from Mount Woolnough were conglomerates with phosphatic nodules and volcanic fragments set in a fine foraminiferal sediment matrix. Zircons within the mafic fragments yielded a minimum age of 261 Ma.     

Petrology of recrystallized ultramafic xenoliths from Merelava volcano,Vanuatu

Xenoliths in primitive olivine tholeiite lavas from Merelava Volcano, Vanuatu, include recrystallized wehrlites and harzburgites characterized by extremely fine grain size (0.02–2 mm) and equigranular textures. The harzburgites display mineral segregations, have highly variable ratios of ol: opx, minor clinopyroxene and accessory Cr-spinel, and are interpreted as the residues of high degrees of melting of upper mantle peridotite. Annealed Cr-spinel aggregates in harzburgite sample # 31564B enclose numerous small inclusions of sodic sanidine and minor plagioclase, attributed to infiltration of the harzburgite by a residual melt derived from an earlier period of island arc magmatism. The recrystallized wehrlites have high ol/cpx ratios and depleted REE patterns compatible with a cumulus origin. The refractory nature of the phases in both groups of recrystallized xenoliths compares closely with phases in Alpine-type peridotites and primitive arc lavas, and is incompatible with compositions of abyssal peridotites. The recrystallized wehrlites give equilibration temperatures of 1070–1130° C and are interpreted as cumulates derived from an earlier period of Vanuatu Arc magmatism. The range of composition displayed by phases in the harzburgites is greater than phase variation in the wehrlites, and reflects a more complex thermal history. Textural, mineralogical, and geothermometric considerations indicate the harzburgites underwent cooling to 800°/900° C before being re-heated to 1000–1100° C by the current magmatic regime. A shallow crustal origin for these xenoliths is indicated by gravity data and tectonic considerations which strongly imply the presence of an ophiolite body beneath Merelava, representing the northward extension of the Pentecost Ophiolite. These interpretations are compatible with a published model for generation of the host basalts by partial melting at the crust/mantle boundary (ca. 17 km). Sr isotopic data show that the harzburgites are incompatible with residues of ocean-floor magmatism, or with residues of Merelava and Central Chain magmatism, but suggest an affinity with Vitiaz Arc magmatism of Eocene-lower Miocene age. Both groups of xenoliths were apparently entrained from wall rocks during ascent of the host magmas.     

Petrogenesis of a voluminous Quaternary adakitic volcano: the case of Baru volcano

The origin of adakite magmas remains controversial because initially the term adakite had petrogenetic significance implying an origin by direct melting of the eclogitized subducting oceanic crust. Many models have been produced for their origin, and until now there has not been a straightforward method to discriminate between these models in a given adakite suite. Here, we use detailed chronological and geochemical studies of selected adakitic edifices that allows for the determination of the magmatic output rate parameter (Qe), which has been correlated with the rates of magma generation deep within subduction zones. By providing temporal and eruption rate estimates, we provide constraints on the possible petrogenetic processes involved in the generation of adakite-like signatures. Adakite magmas derived from the melting of the subducting slab should be volumetrically insignificant when compared to the adakite-like magmas produced by typical arc magma generation processes. In this study, we use this observation and the extraordinary stratigraphic exposure from Miocene to present in an adakitic volcano in Panama and to study the temporal and chemical variation in erupted magmas to estimate rates of magma generation. Detailed chemical and geochronological analyses of Baru volcano indicate that the volcanic edifice was constructed in its entirety during the Quaternary and magmas display adakite-like features such as steep rare earth elements patterns, pronounced depletions in the heavy rare earth elements, low Y, high Sr, and high Sr/Y. The magmatic output rates (Qe) that we have calculated show that compared to other typical adakitic volcanoes, most of the volcanic edifice of Baru volcano was constructed extremely rapidly (<~213 k.a.) and in time frames that are similar to typical arc volcanoes. The observed chemical and mineralogical variation, coupled with the high magma production rates, indicate that Baru volcano is more representative of a typical arc volcano than a small-volume melt of the subducting oceanic crust. The technique we outline may have broader application in determining the petrogenetic conditions of other adakite suites.     

Magmatic inclusions in phenocrystals from andesitic lavas,Krakatau volcano,Indonesia

There is a great number of magmatic inclusions in different types of phenocrystals in andesitic lavas from the Krakatau volcano, Indonesia. Sequence of crystallization (from early to late) has been established for the phenocrystals on the basis of homogenization temperatures and chemical compositions of the magmatic inclusions: the cantral phase of plagioclase phenocrystals (An 83.2–72.6), olivine→ the intermediate phase of plagioclase phenocrystals (An 61.3), clinopyroxene, titanomagnetite→ the peripheral phase of plagioclase phenocrystals (An 54.4–42.6). The crystallization of the central phase of plagioclase phenocrystals takes place in the depth of magma chamber at about 5 Kbar. High pressures and high titanium contents favor the silicate-liquid immiscibility in the magmatic inclusions of early plagioclase phenocrystals. This is typical of many andesitic lavas generated in subduction regions.     

长白山火山最新监测信息

长白山火山最新监测结果显示,自2010年5月份开始,聚龙温泉2个泉点水温同步上升了3℃;2010年长白山北坡垂直位移量打破了火山锥体每年升高4mm左右的规律:与2009年相比,火山锥体的位移在垂向上发生逆转,海拔最高的水准点在1年内突降12.72mm.本文针对上述2个最新的火山监测信息进行了报道,并对造成这种变化的可能原因进行了讨论.火山活动进入活跃时段的标志是大量火山地震、震群的发生,以及幔源岩浆气体He含量的大幅度上升.然而,现阶段长白山火山区并未出现这2种现象.因此,本文讨论的2个异常还不足以作为长白山火山已经进入新的活跃时段的证据,准确的预测应该密切关注火山地震和幔源气体含量的变化.最后通过N2-He-CO2三角图解初步研究了天池火山气体来源,结果显示:2002～2005年火山出现“初始扰动”,深部气体He含量升高,三角图解中气体向He角运移;2005年后火山转入平静状态,气体组份又开始向N2角运移.He浓度的变化特征反应了岩浆房内岩浆成分的变化过程.     

Glacier Peak,Washington: A potentially hazardous cascade volcano

Recent field studies of postglacial volcanic deposits at Glacier Peak indicate the volcano has erupted more often, more voluminously, and more recently than previously thought. These past eruptions produced pyroclastic flows, extensive lahars, and widely distributed tephra falls. Analysis of the magnitude of past eruptions and the distribution of volcanic sediments indicates that future eruptions at Glacier Peak as large as those of the last several thousand years would dramatically affect people and property downstream and downwind from the volcano. Pyroclastic flows and lateral blasts would primarily affect uninhabited valleys within a few tens of kilometers of the volcano. Lahars and floods constitute the major hazard to populated areas from future eruptions, and could affect areas at low elevation along valley floors and in the Puget lowland as far as 100 km downvalley west of the volcano. Air-fall tephra from future eruptions will probably be deposited primarily east of Glacier Peak because of prevailing westerly winds.     

Evidence for a seismic activity mainly constituted of hybrid events at Cayambe volcano,Ecuador. Interpretation in a iced-domes volcano context

The high activity level of Hybrid Events (HE) detected beneath the Cayambe volcano since 1989 has been more thoroughly investigated with data from a temporary array. The unusual HE spectral content allows separating a high-frequency signal riding on a low-frequency one, with a probable single source. HEs are interpreted as high frequency VT events, produced by the interaction between magmatic heat and an underground water system fed by thaw water from the summital glacier, which trigger simultaneous low-frequency fluid resonance in the highly fractured adjacent medium. Pure VTs are interpreted as ‘aborted’ HEs occurring probably in the oldest and coldest part of the volcano complex. To cite this article: B. Guillier, J.-L. Chatelain, C. R. Geoscience 338 (2006).