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   

邯邢中基性侵入杂岩体的岩石学与地球化学特征及成因探讨   总被引：6，自引：0，他引：6  

黄福生  薛绥洲 《岩石矿物学杂志》1990,9(3):203-212

杂岩体呈由西向东展布的北北东向的三个岩带,并显示有规律的演化趋势。SiO2含量52.26—62.95,钙碱性C.A=57.6。AFM图上显示Fe.Mg降低而碱质增高的演化趋势。∑REE从126.2到185.1(ppm)呈依次渐增趋势。稀土元素配分型式呈右倾斜的轻稀土富集型,(La/Yb)N=11.27,δEu=1.07—1.15。δ18O在8.2—8.8之间数据迭置。岩浆中水的δD为-45和-68,δ18O为7.7和9.2,具原始岩浆水的特征。岩石具低铷高锶特征,初始锶比值为0.7053和0.7064。岩体中含有众多的岩石包体,除浅源和结晶基底的围岩捕虏体外,还显示保留有幔源的难熔残余超镁铁岩包体。杂岩体的岩石学与地球化学特征反映了岩浆物质的同源性以及揭示了可能起源于莫霍面附近的深源信息。  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   

浙江新昌早白垩世复合岩流中的岩浆混合作用   总被引：35，自引：7，他引：35  

周金城  俞云文 《岩石学报》1994,10(3):236-247

浙江新昌拔茅地区早白垩世复合岩流中各种火山岩（Ｒｂ－Ｓｒ等时线年龄为９６．３Ｍａ）属高钾钙碱性岩系，在其中发现了中生代火山活动中岩浆混合作用的确凿证据，岩相学及地球化学研究表明，这种复合岩流中的安山质岩浆是由同时代橄榄拉斑玄武岩浆和流纹岩浆相互混合而形成的。  相似文献   

大庆徐家围子火山岩热释光特征与火山活动期次及岩性判别     

谭文化李胜荣  申俊峰吴敏 《岩石矿物学杂志》2007,26(3):247-252

热释光的用途很广,但在判断火山活动旋回(期次)以及火山岩类型鉴定方面,尚未涉及。本文通过对大庆徐家围子升深7和杨参1井岩石样品以及其他井部分火山岩样品的热释光特征的研究,发现:①升深7井中,顶部峰型和总积分强度近似,可指示为同期喷发产物;中下部热释光特征表现为“顶底韵律效应”,可能是较晚阶段的火山喷发物对前一阶段顶部有热改造而消耗了部分辐射积累。②杨参1井中根据热释光特征可划分2个旋回和4个期次。下部旋回发育双峰,主峰积分强度差别较大,可能指示底部为多源喷出产物(如多机构产物)混堆,小旋回产物之间叠加;主峰积分强度从下到上依次减小,反映了火山岩喷发强度的降低。上部旋回发育单峰,热释光积分强度相差不大,可能为一套同源产物。③升深7井中未发生明显蚀变作用的安山岩热释光特征相似而杨参1井中岩相均一、未蚀变的凝灰质岩热释光特征也很相似,这表明热释光特征技术应用于火山空落相岩石和火山熔岩岩性判别是有可能的。最后总结了火山岩热释光研究应注意的问题。  相似文献   

Peperite formed by lava flows over sediments: An example from the central Paraná Continental Flood Basalts,Brazil     

Breno L. Waichel  Evandro F. de Lima  Carlos A. Sommer  Romulo Lubachesky 《Journal of Volcanology and Geothermal Research》2007

Pahoehoe flows interbedded with sediments have been identified in the superior portion of Paraná Continental Flood Basalts (PCFB), west portion of Paraná State, southern Brazil. In the study area peperites are generated by the interaction between lava flows and wet lacustrine sediments (silt and clay). Evidence that the sediments were unconsolidated or poorly consolidated and wet when the lava flowed over them includes vesiculated sediment, sediment in vesicles and fractures in lava flow and in juvenile clasts in the peperite and soft sediment deformation. Hydrodynamic mingling of lava and wet sediments (coarse mingling) is predominant and volcanic rocks and textures related to explosive phase of Molten Fuel Coolant Interaction (MFCI) are not observed in study area. Locally centimeter-sized areas display direct contact between ash-sized juvenile clasts and sediments formed by the collapse of a vapor film. The textures of fluidal peperites in the central PCFB indicate that the relevant factors that led to a coarse mingling between lava/sediment are (1) lava properties (low viscosity); (2) fine grained, unconsolidated or poorly consolidated wet sediment; and (3) a single episode of interaction between lava flows and sediment.  相似文献   

五大连池世界地质公园中“火山弹”与“喷气锥”景点定名商榷   总被引：1，自引：0，他引：1  

吕洪波 《地质论评》2007,53(3):383-388,I0004

位于中国东北黑龙江省的五大连池世界地质公园是世界上著名的自然景点,其引人之处就是新生代玄武岩火山地貌。然而,景点中有些火山构造的命名却存在着明显的错误,如：熔岩丘和增生熔岩球分别被错误地命名为“喷气锥”和“火山弹”。笔者根据著名专业网站（如：美国地质调查局网站）和经典教材中的相应定义讨论了这些火山构造。通过分析这些构造的形态、大小和成因,笔者将它们分别重新命名为熔岩丘和增生熔岩球。笔者建议：地质公园中所有景点的定名都应该经专家核实和评价,从而给出科学的、符合地质实际的名称。  相似文献