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Cristobalite is a low-pressure high-temperature polymorph of SiO2 found in many volcanic rocks. Its volcanogenic formation has received attention because (1) pure particulate cristobalite can be toxic when inhaled, and its dispersal in volcanic ash is therefore a potential hazard; and (2) its nominal stability field is at temperatures higher than those of magmatic systems, making it an interesting example of metastable crystallization. We present analyses (by XRD, SEM, EPMA, Laser Raman, and synchrotron μ-cT) of representative rhyolitic pyroclasts and of samples from different facies of the compound lava flow from the 2011–2012 eruption of Cordón Caulle (Chile). Cristobalite was not detected in pyroclasts, negating any concern for respiratory hazards, but it makes up 0–23 wt% of lava samples, occurring as prismatic vapour-deposited crystals in vesicles and/or as a groundmass phase in microcrystalline samples. Textures of lava collected near the vent, which best represent those generated in the conduit, indicate that pore isolation promotes vapour deposition of cristobalite. Mass balance shows that the SiO2 deposited in isolated pore space can have originated from corrosion of the adjacent groundmass. Textures of lava collected down-flow were modified during transport in the insulated interior of the flow, where protracted cooling, additional vesiculation events, and shearing overprint original textures. In the most slowly cooled and intensely sheared samples from the core of the flow, nearly all original pore space is lost, and vapour-deposited cristobalite crystals are crushed and incorporated into the groundmass as the vesicles in which they formed collapse by strain and compaction of the surrounding matrix. Holocrystalline lava from the core of the flow achieves high mass concentrations of cristobalite as slow cooling allows extensive microlite crystallization and devitrification to form groundmass cristobalite. Vapour deposition and devitrification act concurrently but semi-independently. Both are promoted by slow cooling, and it is ultimately devitrification that most strongly contributes to total cristobalite content in a given flow facies. Our findings provide a new field context in which to address questions that have arisen from the study of cristobalite in dome eruptions, with insight afforded by the fundamentally different emplacement geometries of flows and domes. 相似文献
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Prof. Dr. Hans Ertel 《Pure and Applied Geophysics》1962,52(1):139-142
Resumen Presentamos un método numérico para la determinación del efecto regulador de un lago. Este método se basa en una transformación de la integral de la ecuación diferencial del efecto de embalse, utilizando una ley lineal del desagüe.
Zusammenfassung Es wird ein numerisches Verfahren zur Berechnung der Seeretention dargelegt, das aus einer Umformung des Integrals der Retentionsgleichung mit linearem Abflußgesetz entwickelt wird.相似文献
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《水文科学杂志》2013,58(3):406-417
Résumé Le soutien de la crue annuelle du Fleuve Sénégal par le Barrage multi-objectifs de Manantali nécessite de fin août à début octobre de fortes lâchures qui peuvent grever la production hydroélectrique de l'ouvrage. Pour faciliter la programmation de cet objectif par estimation du stock disponible dans le réservoir en fin de mousson, on cherche à prévoir en août le volume de crue naturel du fleuve de septembre—octobre à partir d'index d'anomalies pluviométriques calculés fin juillet pour ces deux mois par le modèle ARPEGE Climat. Après analyse en composantes principales de ces index produits sur un maillage de 300 × 300 km couvrant l'Afrique de l'Ouest, on détermine une zone de 1200 × 1200 km décalée à l'est du bassin où les vecteurs propres des index sont reliés au débit naturel de septembre—octobre par une régression linéaire à cinq paramètres (R 2 = 0.651). Cette relation statistique calée sur la période 1979–2000 est validée sur la période 2001–2005. 相似文献
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Volcanic history of El Chichón Volcano (Chiapas, Mexico) during the Holocene, and its impact on human activity 总被引：1，自引：0，他引：1
J. M. Espíndola J. L. Macías R. I. Tilling M. F. Sheridan 《Bulletin of Volcanology》2000,62(2):90-104
2 abundance and depletion in MgO, CaO, TiO2, as well as trace and rare earth elements. This suggests segregation of olivine and orthopyroxene from the melt. Since human
settlements in southeast Mexico and Central America can be traced as far back as approximately 2500 years BP, most of these
events probably affected human activity. In fact, there are reports of pottery shards and other artifacts in deposits from
the eruption of 1250 BP. Pottery fragments in deposits of an eruption that took place 2500 BP are also reported in this paper.
Thus, the impact of the volcano on human activities has been frequent, with most of the repose intervals lasting between 100
to 600 years. The impact of the eruptions was probably of greater than local extent, because airfall tephra could reach distant
sites and possibly even affect weather. The eruptive history of El Chichón also offers clues in the investigation of the Maya
civilization. Several researchers have considered the volcano as an important factor in the answer to some intriguing questions
such as the extensive use of volcanic ash in Late Classic Maya ceramics or, of greater importance, the causes of the collapse
of the Classic Maya civilization.
Received : 4 May 1998 / Accepted: 1 November 1999 相似文献
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Yuri Taran Tobias P. Fischer Boris Pokrovsky Yuji Sano Maria Aurora Armienta Jose Luis Macias 《Bulletin of Volcanology》1998,59(6):436-449
The 1982 eruption of El Chichón volcano ejected more than 1 km3 of anhydrite-bearing trachyandesite pyroclastic material to form a new 1-km-wide and 300-m-deep crater and uncovered the
upper 500 m of an active volcano-hydrothermal system. Instead of the weak boiling-point temperature fumaroles of the former
lava dome, a vigorously boiling crater spring now discharges / 20 kg/s of Cl-rich (∼15 000 mg/kg) and sulphur-poor ( / 200 mg/kg
of SO4), almost neutral (pH up to 6.7) water with an isotopic composition close to that of subduction-type magmatic water (δD=–15‰,
δ18O=+6.5‰). This spring, as well as numerous Cl-free boiling springs discharging a mixture of meteoric water with fumarolic
condensates, feed the crater lake, which, compared with values in 1983, is now much more diluted (∼3000 mg/kg of Cl vs 24 030 mg/kg),
less acidic (pH=2.6 vs 0.56) and contains much lower amounts of S ( / 200 mg/kg of SO4, vs 3550 mg/kg) with δ34S=0.5–4.2‰ (+17‰ in 1983). Agua Caliente thermal waters, on the southeast slope of the volcano, have an outflow rate of approximately
100 kg/s of 71 °C Na–Ca–Cl water and are five times more concentrated than before the eruption (B. R. Molina, unpublished
data). Relative N2, Ar and He gas concentrations suggest extensional tectonics for the El Chichón volcanic centre. The 3He/4He and 4He/20Ne ratios in gases from the crater fumaroles (7.3Ra, 2560) and Agua Caliente hot springs (5.3Ra, 44) indicate a strong magmatic contribution. However, relative concentrations of reactive species are typical of equilibrium
in a two-phase boiling aquifer. Sulphur and C isotopic data indicate highly reducing conditions within the system, probably
associated with the presence of buried vegetation resulting from the 1982 eruption. All Cl-rich waters at El Chichón have
a common source. This water has the appearence of a "partially matured" magmatic fluid: condensed magmatic vapour neutralized
by interaction with fresh volcaniclastic deposits and depleted in S due to anhydrite precipitation. Shallow ground waters
emerging around the volcano from the thick cover of fresh pumice deposits (Red waters) are Ca–SO4–rich and have a negative oxygen isotopic shift, probably due to ongoing formation of clay at low temperatures.
Received: 21 July 1997 / Accepted: 4 December 1997 相似文献
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Résumé De nombreux travaux de recherche pétrolière par sismique réflexion et sondages profonds ont été réalisés en Tunisie méridionale. La présente étude concerne la réinterprétation de ces données dans le secteur du Jérid en vue d'appréhender la géométrie et le fonctionnement de l'aquifère du Continental Intercalaire (CI), cible potentielle pour l'alimentation en eau. Pour ce faire, nous avons identifié sur les différentes sections sismiques le réflecteur correspondant à la dolomie aptienne qui marque le toit de l'aquifère. Elaborée en conséquence, la carte des isochrones de cet horizon montre l'influence de la tectonique sur la géométrie du CI dans le Jérid. Le plissement des séries du Crétacé inférieur, la réactivation des accidents NE–SO et E–O en failles inverses et le jeu normal des accidents NO–SE sont à l'origine d'un aquifère compartimenté en blocs soulevés et affaissés. Les coupes géosismiques révèlent que cette structuration a des implications sur la profondeur des réservoirs et la circulation des eaux souterraines. Les résultats obtenus permettent de rationaliser les travaux de recherche hydrogéologique qui seront ultérieurement menés dans le secteur du Jérid. Citation Guellala, R., Ben Marzoug, H., Inoubli, M. H. & Moumni, L. (2011) Apports de la sismique réflexion à l'étude de l'aquifère du Continental Intercalaire du Jérid (Tunisie). Hydrol. Sci. J. 56(6), 1040–1052. 相似文献
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Marie-No?lle Guilbaud Claus Siebe Paul Layer Sergio Salinas 《Bulletin of Volcanology》2012,74(5):1187-1211
The 690?km2 Tacámbaro-Puruarán area located at the arc-front part of the Michoácan-Guanajuato volcanic field in the Trans-Mexican Volcanic Belt (TMVB) records a protracted history of volcanism that culminated with intense monogenetic activity in the Holocene. Geologic mapping, 40Ar/39Ar and 14C radiometric dating, and whole-rock chemical analyses of volcanic products provide insights to that history. Eocene volcanics (55–40?Ma) exposed at uplifted blocks are related to a magmatic arc that preceded the TMVB. Early TMVB products are represented by poorly exposed Pliocene silicic domes (5–2?Ma). Quaternary (<2?Ma) volcanoes (114 mapped) are mainly scoria cones with lavas (49 vol.%), viscous lava flows (22 vol.%), and lava shields (22 vol.%). Erupted products are dominantly either basaltic andesites (37 vol. %), or andesites (17 vol.%), or span across both compositions (28 vol.%). Basalts (9 vol.%), dacites (4 vol.%), shoshonites (2 vol.%), and other alkali-rich rocks (<3 vol.%) occur subordinately. Early-Pleistocene volcanism was bimodal (dacites and basalts) and voluminous while since 1?Ma small-volume eruptions of intermediate magmas have dominated. Higher rates of lithospheric extension in the Quaternary may have allowed a larger number of small, poorly evolved dikes to reach the surface during this period. Eruptive centers as old as 1.7?Ma are aligned in a NE direction parallel to both, basement faults and the direction of regional compressive stress, implying structural control on volcanic activity. Data suggest that volcanism was strongly pulsatory and fed by localized low-degree partial melting of mantle sources. In the Holocene, at least 13 eruptions occurred (average recurrence interval of 800?years). These produced ~3.8?km3 of basaltic andesitic to andesitic magma and included four eruptions dated at ~1,000; 4,000; 8,000; and 11,000?years bc (calibrated 14C ages). To date, this is one of the highest monogenetic eruption frequencies detected within such a small area in a subduction-related arc-setting. These anomalous rates of monogenetic activity in an area with thick crust (>30?km) may be related to high rates of magma production at depth and a favorable tectonic setting. 相似文献
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An analysis is made of microseismic and seismic activity for a period of about 3 months prior to the 1958 eruption in the Virunga Volcanoes, Western Rift Valley of Central Africa. It is believed that it would have been possible to predict the eruption some 30 h before, on the basis of two series of small earthquakes preceeding the 2 outbrakes by some 50 h, and presenting an exponential decay of the total number of shocks. 相似文献
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《水文科学杂志》2013,58(3):526-537
Abstract The study of the Continental Intercalaire aquifer system of southern Tunisia, based on the interpretation of geochemical (major elements) and isotopic (18O, 2H, 13C and 14C) data, has aided the understanding of the hydrodynamics of this multi-layer aquifer system, which is greatly influenced by tectonics. The determination of the origin of groundwater salinization and the understanding of the hydrogeological and geochemical behaviour of this aquifer were achieved by studying the correlation between the major elements and total mineralization (TDS). By using isotopic tools, it was shown that the water of this aquifer has been recharged under cooler, palaeoclimatic conditions. The technique also made it possible to better understand the hydrodynamic functioning of the aquifer system: it showed that the relatively recent recharge of the aquifer has been by direct infiltration from carbonate and sandy outcrops of the Cretaceous and Miocene, respectively, located in the eastern and northeastern parts of the aquifer. The 18O content was used to calculate the altitude of recharge basins. The isotopic gradient defined in this study is ?0.5 δ18O ‰/100 m. 相似文献
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According to the data of the IMAGE network of magnetometers the latitudinal profile of the amplitude of the Pc5 geomagnetic
pulsations is constructed, which are excited in the Earth’s magnetosphere in the form of the resonance Alfvén magnetohydrodynamic
pulsations. The approaches to the solution of two problems are studied on a specific example. The first concerns the anharmonicity
of Alfvén’s resonances. The displacement of the peak of the resonance curve towards to the north with the reduction of the
amplitude of the pulsations is discovered. Based on the results of measurements, the nonlinear distortion coefficient of the
latitudinal profile is determined. The second problem is connected with the magnetotelluric sounding. Information about the
resonance structure of the Alfvén pulsations is useful for magnetotelluric sounding. This information gives the possibility
of evaluating the accuracy of the sounding with the application of the local impedance relationship and of introducing corrections
if necessary. 相似文献
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The volcano-tectonic evolution of Concepción,Nicaragua 总被引：1，自引：1，他引：0
We describe the evolution of Concepción volcano by integrating regional geology, eruptive activity, morphology, stratigraphy,
petrology, structure and active deformation data. This Nicaraguan volcano is set close to the back limb of the northwest-trending
Tertiary Rivas anticline, a regional structure that bounds the southwest side of Lake Nicaragua. Concepción rises 1,600 m
above a 1-km-thick sequence of Quaternary lacustrine mud-stones. There is no record of volcanism in the lake prior to Concepción.
In addition, the only nearby volcano, Maderas volcano, has not deposited material on Concepción because of the trade winds.
Thus, Concepción (and Made ras, too) can be considered as pristine volcanic environments, unaffected by other centres. A topographic
rise forms an annulus 20 km in diameter around the cone. The rise is created by thrust-related folds at the western base,
where the trade winds have accumulated a thick sequence of tephra, and by mud diapirs at the eastern base where only lake
mudstones are present. Four magmatic-eruptive episodes exist in the stratigraphic record. The first begins with primitive
low-alumina basalt and subsequently evolves to dacitic compositions. The following three episodes begin with high-alumina
basalts and evolve only to silicic andesites. The occurrence of the high-alumina basalt after the first episode is indicative
of crystal fractionation at lower crustal depths. The first episode may be associated with a compressive phase of volcano
evolution. In this phase, the edifice load compresses substrata, allowing a longer magma residence time and differentiation
in a shallow reservoir (possibly located at the density contrast between the lake sediments and the Tertiary flysch). During
the next three episodes the weak sediments below the volcano started to rupture and yield under its increasing load, beginning
a thrusting/diapiring phase of volcano evolution. Because of outward thrusting, vertical and horizontal stresses above the
chamber were reduced, allowing magma to erupt more easily and to reach a lesser degree of evolution. If we consider the future
evolution of Concepción, the differentiation in the shallow reservoir has probably generated a cumulitic complex, which eventually
will start to deform and spread, beginning another, this time plutonic, spreading phase. This phase, which may be beginning
now, could allow less evolved magmas to be erupted again. Four components influence the phases of volcano evolution: (1) the
regional geology that is the boundary condition of the environment, (2) the substrata rheology that controls deformation,
(3) the load of the volcanic edifice and (4) the magma, which provides the input of mass and energy. Our model of volcanic
evolution suggests that Concepción is a complex geologic environment. The volcanic activity, tectonics and hazards can only
be constrained through a complete knowledge of the many components of this environment.
Published online: 20 February 2003
Editorial responsibility: R. Cioni 相似文献
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Fabrizio Alfano Costanza Bonadonna Alain C. M. Volentik Charles B. Connor Sebastian F. L. Watt David M. Pyle Laura J. Connor 《Bulletin of Volcanology》2011,73(5):613-630
On May 1st 2008 Mount Chaitén (southern Chile) interrupted a long period of quiescence, generating a sequence of explosive
eruptions and causing the evacuation of Chaitén town located a few kilometers south of the volcano. The activity was characterized
by several explosive events each associated with plumes which reached up to about 19 km above sea level. The products were
dispersed across a wide area, with the finest ash reaching the Atlantic coast of Argentina. Our field observations in the
proximal-medial area (3–25 km from the vent) indicate that the May 2008 tephra deposit consists of numerous layers, most of
which can be correlated with individual eruptive events. These layers vary from extremely fine-grained ash to layers of lapilli
and blocks, composed of both juvenile and lithic material. Here we describe the stratigraphy and physical characteristics
of the May 2008 deposits, and propose a reconstruction of the timing of the May 2008 events. The deposits are mainly associated
with the three main explosive phases which occurred on 1st–2nd May, 3rd–5th May and 6th May, with an estimated bulk tephra
volume of 0.5–1.0 km3 (integration of both exponential and power-law fitting). For the 6th May event, represented by a layer composed mainly of
lithic lapilli and blocks (>2 mm), an isopleth map was compiled from which a 19 km plume height was determined, which is in
good agreement with satellite observations. 相似文献
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Souaad Bouzid-Lagha 《水文科学杂志》2013,58(1):186-201
Résumé Ce travail décrit l'étude du phénomène d'eutrophisation des eaux du Barrage de Hammam Boughrara, situé au Nord-Ouest de l'Algérie, dans la Wilaya de Tlemcen. L'exploitation d'une base de données, de neuf ans, relative à 19 variables physico-chimiques, chimiques et biotiques, a permis de déterminer: l'évolution dans le temps de chaque variable, les corrélations entre variables, le degré d'eutrophisation des eaux, les espèces phytoplanctoniques dominantes (e.g. chlorophycées, diatomophycées) ainsi que leur nutriment principal, le phosphore. L'étude statistique multidimensionnelle, par analyse en composantes principales (ACP), confirme les résultats ainsi obtenus, notamment l'importante pollution et l'hyper-eutrophie des eaux. La lutte contre le phénomène d'eutrophisation des eaux nécessite des moyens adéquats de gestion des éléments polluants. Ainsi, l'élaboration d'un modèle adapté à notre site, permettant de prédire les concentrations en phosphore à partir de sa charge et de gérer ainsi la prolifération d'algues en limitant les teneurs en nutriments, peut constituer une contribution notable à cette lutte. Editeur Z.W. Kundzewicz Citation Bouzid-Lagha, S. et Djelita, B., 2012. Etude du phénomène d'eutrophisation dans le Barrage de Hammam Boughrara (Wilaya de Tlemcen, Algérie). Hydrological Sciences Journal, 57 (1), 186–201. 相似文献