Statistical analysis of intermittent volcanic tremor associated with the September 1989 summit explosive eruptions at Mount Etna, Sicily     

E. Privitera  T. Sgroi  S. Gresta   《Journal of Volcanology and Geothermal Research》2003,120(3-4):235-247

The pattern of volcanic tremor accompanying the 1989 September eruption at the south-east summit crater of Mount Etna is studied. In specific, sixteen episodes of lava fountaining, which occurred in the first phase of the eruption, are analysed. Their periodic behaviour, also evidenced by autocorrelation, allows us to define the related tremor amplitude increases as intermittent volcanic tremor episodes. Focusing on the regular intermittent behaviour found for both lava fountains and intermittent volcanic tremors, we tried an a posteriori forecast using simple statistical methods based on linear regression and the Student’ t-test. We performed the retrospective statistical forecast, and found that several eruptions would have been successfully forecast. In order to focus on the source mechanism of tremor linked to lava fountains, we investigated the relationship between volcanic and seismic parameters. A mechanism based on a shallow magma batch ‘regularly’ refilled from depth is suggested.  相似文献   

Asymptotic waveform inversion for unbiased velocity and attenuation measurements: numerical tests and application for Vesuvius lava sample analysis     

A. Ribodetti  S. Gaffet  S. Operto  J. Virieux  G. Saracco 《Geophysical Journal International》2004,158(1):353-371

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Geology and geochemistry of Karasugasen lava dome, Daisen–Hiruzen Volcano Group, southwest Japan     

Jun-Ichi  Kimura  Mamiko  Tateno  Isaku  Osaka 《Island Arc》2005,14(2):115-136

Abstract   The geology and geochemistry of pyroclastic flows and fallout tephras formed during the Karasugasen dome eruption in the Daisen–Hiruzen Volcano Group in southwest Japan have been examined in detail. The Karasugasen lava dome erupted at about 26 ka. The eruption began with a vulcanian ash fall, and this was followed by at least eight block and ash flows and a pumice flow. The block and ash flows were produced by the successive collapses of a growing lava dome. This main eruption phase was followed by an eruption of vulcanian ash falls, and finally ended with a sub-Plinian pumice fall. This eruption sequence is typical of the Daisen Volcano during the last three eruption events, which occurred at 58, 26 and 17 ka. The magma produced during the Karasugasen eruption was a typical adakite, with extremely high Sr/Y ratios and low HREE/LREE ratios compared to normal arc lavas. The chemistry of the Karasugasen lavas is almost identical to other Daisen–Hiruzen lavas that were produced from eruptions over an interval of a million years. The continuous supply of a huge amount of adakitic magma (>100 km³) for such a long period suggests a massive homogeneous source material, such as molten Philippine Sea Plate slab. Slab melting is a plausible mechanism for the production of the adakitic lavas at Karasugasen, and hence the Daisen–Hiruzen Volcano Group.  相似文献   

新疆巴里坤县三塘湖北卡拉岗组火山岩特征   总被引：6，自引：0，他引：6  

马雪  冯成贵  虞卫东 《新疆地质》2005,23(3):234-238

新疆东准噶尔巴里坤县三塘湖盆地以北老爷庙额仁山一带，广泛分布一套红色、红褐、黄色酸性火山岩，前人（1：20万）将其归为下石炭统黑山头组（C1h）和中一上石炭统哈尔加乌组（C2～P1h），1999-2001年在这一带开展1：5万区调时发现，这一套火山岩不整合于下伏地层之上，从而将火山岩从老爷庙组（D3l），黑山头组和哈尔加乌组中解体出来，划归为卡拉岗组（P1k），为一套陆相酸性火山岩．以喷溢相流纹岩、霏细岩为主，是造山后弛张期大陆板内火山岩，时代为早二叠世．  相似文献   

The internal structure of lava flows—insights from AMS measurements II: Hawaiian pahoehoe, toothpaste lava and 'a'     

Edgardo Can-Tapia  George P. L. Walker  Emilio Herrero-Bervera 《Journal of Volcanology and Geothermal Research》1997,76(1-2)

We studied the anisotropy of magnetic susceptibility (AMS) of 22 basaltic flow units, including S-type pahoehoe, P-type pahoehoe, toothpaste lava and 'a' emplaced over different slopes in two Hawaiian islands. Systematic differences occur in several aspects of AMS (mean susceptibility, degree of anisotropy, magnetic fabric and orientation of the principal susceptibilities) among the morphological types that can be related to different modes of lava emplacement. AMS also detects systematic changes in the rate of shear with position in a unit, allowing us to infer local flow direction and some other aspects of the velocity field of each unit. 'A' flows are subject to stronger deformation than pahoehoe, and also their internal parts behave more like a unit. According to AMS, the central part of pahoehoe commonly reveals a different deformation history than the upper and lower extremes, probably resulting from endogenous growth.  相似文献   

Kinematic Modeling of Pyroclastic Flows Produced by Gravitational Dome Collapse at Soufriere Hills Volcano, Montserrat     

Donald M. Hooper  Glen S. Mattioli 《Natural Hazards》2001,23(1):65-86

Volcanic activity commenced 18 July 1995 at SoufriereHills volcano and has led to the creation of a newlava dome, which has repeatedly collapsed between 1996and 1999 resulting in highly mobile pyroclastic flows. The majority of associated pyroclastic flow phenomenaare consistent with initiation by gravitationalcollapse as blocks fall from oversteepened flanks ofthe new dome. If gravity controls the energy transferof such collapses, then areas likely to be affectedcan be predicted on the basis of topography. We focuson `dense' flows initiated by non-explosive,gravitational collapse (`Merapi-type' pyroclasticflows) and employ a graphical computer model (Flow3D)written to simulate this type of volcanic flow. Theprogram constructs a digital terrain model based upona 3D network of (x, y, z) triplets, which serves as thebasis for the numerical computations. A synthetic domewas added to the topographic model to improve theaccuracy of the simulations. After estimating thesmall number of key adjustable parameters, simulatedflow pathways, runout distances, and velocitiesclosely approximated observed Merapi-type pyroclasticflows on Montserrat. These simulations demonstrate thevalidity of a simple kinematic method to model densepyroclastic flow phenomena. While the simulationspresented here do not elucidate additional physics ofpyroclastic flow phenomena, this type of modeling canbe completed easily and without extensivea priori knowledge of volcano-specific parameters otherthan topography. Accordingly, it may serve as a rapidand inexpensive first-order approach for initialhazard assessment.  相似文献   

Development of the 1990 Kalapana Flow Field,Kilauea Volcano,Hawaii     

Tari N. Mattox  Christina Heliker  Jim Kauahikaua  Ken Hon 《Bulletin of Volcanology》1993,55(6):407-413

The 1990 Kalapana flow field is a complex patchwork of tube-fed pahoehoe flows erupted from the Kupaianaha vent at a low effusion rate (approximately 3.5 m³/s). These flows accumulated over an 11-month period on the coastal plain of Kilauea Volcano, where the pre-eruption slope angle was less than 2°. the composite field thickened by the addition of new flows to its surface, as well as by inflation of these flows and flows emplaced earlier. Two major flow types were identified during the development of the flow field: large primary flows and smaller breakouts that extruded from inflated primary flows. Primary flows advanced more quickly and covered new land at a much higher rate than breakouts. The cumulative area covered by breakouts exceeded that of primary flows, although breakouts frequently covered areas already buried by recent flows. Lava tubes established within primary flows were longer-lived than those formed within breakouts and were often reoccupied by lava after a brief hiatus in supply; tubes within breakouts were never reoccupied once the supply was interrupted. During intervals of steady supply from the vent, the daily areal coverage by lava in Kalapana was constant, whereas the forward advance of the flows was sporadic. This implies that planimetric area, rather than flow length, provides the best indicator of effusion rate for pahoehoe flow fields that form on lowangle slopes.  相似文献   

柯克巴斯套古火山机构及其原始熔岩湖的漂浮产物     

张安  丁天府  李嵩龄 《岩石学报》1988,4(4)

柯克巴斯套古火山机构是新发现的一个中心式陆相古火山构造。形成时代为早二叠世末期。喷发产物主要为酸性熔岩,按岩性结构特征及产状的不同,由内向外可分中心火山颈相、熔岩湖相、爆发相、火山脉岩相等四个火山岩相。在原始熔岩湖相中发育大量各种原始熔岩湖漂浮产物,其结构形态独特,在空间上作有规律的展布,较充分地反映了古火山机构的喷发环境和原始熔岩湖存在的自然面貌。  相似文献   

Development of lava tubes in the light of observations at Mauna Ulu,Kilauea Volcano,Hawaii     

Donald W. Peterson  Robin T. Holcomb  Robert I. Tilling  Robert L. Christiansen 《Bulletin of Volcanology》1994,56(5):343-360

During the 1969–1974 Mauna Ulu eruption on Kilauea's upper east rift zone, lava tubes were observed to develop by four principal processes: (1) flat, rooted crusts grew across streams within confined channels; (2) overflows and spatter accreted to levees to build arched roofs across streams; (3) plates of solidified crust floating downstream coalesced to form a roof; and (4) pahoehoe lobes progressively extended, fed by networks of distributaries beneath a solidified crust. Still another tube-forming process operated when pahoehoe entered the ocean; large waves would abruptly chill a crust across the entire surface of a molten stream crossing through the surf zone. These littoral lava tubes formed abruptly, in contrast to subaerial tubes, which formed gradually. All tube-forming processes were favored by low to moderate volume-rates of flow for sustained periods of time. Tubes thereby became ubiquitous within the pahoehoe flows and distributed a very large proportionof the lava that was produced during this prolonged eruption. Tubes transport lava efficiently. Once formed, the roofs of tubes insulate the active streams within, allowing the lava to retain its fluidity for a longer time than if exposed directly to ambient air temperature. Thus the flows can travel greater distances and spread over wider areas. Even though supply rates during most of 1970–1974 were moderate, ranging from 1 to 5 m³/s, large tube systems conducted lava as far as the coast, 12–13 km distant, where they fed extensive pahoehoe fields on the coastal flats. Some flows entered the sea to build lava deltas and add new land to the island. The largest and most efficient tubes developed during periods of sustained extrusion, when new lava was being supplied at nearly constant rates. Tubes can play a major role in building volcanic edifices with gentle slopes because they can deliver a substantial fraction of lava erupted at low to moderate rates to sites far down the flank of a volcano. We conclude, therefore, that the tendency of active pahoehoe flows to form lava tubes is a significant factor in producing the common shield morphology of basaltic volcanoes.  相似文献   

Explosive volcanic eruptions—VIII. The role of magma recycling in controlling the behaviour of Hawaiian-style lava fountains     

L. Wilson  E. A. Parfitt  J. W. Head III 《Geophysical Journal International》1995,121(1):215-225

Explosive eruptions of mafic magmas produce lava fountains whose heights are a function of the exsolved volatile content of the magma, its erupted mass flux, and the geometry of the vent (which may be an elongate fissure or a localized, near-circular conduit). The geometry of the initial vent (and the eruptive behaviour) can be distinctly modified by lava drainback and accumulating ejecta. Hot pyroclasts landing near the vent may coalesce to form rootless flows, some of which may drain back into the vent to be recycled into the eruption products. Rootless flows may be at least partially confined by pre-existing topographic features, or by spatter or cinder ramparts being built up by the eruption itself, so that they accumulate into a lava pond over and around the vent. The erupting jet of magmatic gas and pyroclasts must force its way through such a pond and will entrain some of the pond lava as it does so. The energy expended in entraining and accelerating previously erupted materials will reduce the eruption velocity and the lava fountain height by an amount which can be calculated as a function of the eruption conditions and the lava pond depth (or lava drainback rate). The results of such calculations are presented, and are used to assess the influence of this process on attempts to infer magma volatile contents from field observations of lava fountain heights.  相似文献