Large debris avalanches and associated eruptions in the Holocene eruptive history of Shiveluch Volcano, Kamchatka, Russia     

Vera V. Ponomareva  Maria M. Pevzner  Ivan V. Melekestsev 《Bulletin of Volcanology》1998,59(7):490-505

 Shiveluch Volcano, located in the Central Kamchatka Depression, has experienced multiple flank failures during its lifetime, most recently in 1964. The overlapping deposits of at least 13 large Holocene debris avalanches cover an area of approximately 200 km² of the southern sector of the volcano. Deposits of two debris avalanches associated with flank extrusive domes are, in addition, located on its western slope. The maximum travel distance of individual Holocene avalanches exceeds 20 km, and their volumes reach ∼3 km³. The deposits of most avalanches typically have a hummocky surface, are poorly sorted and graded, and contain angular heterogeneous rock fragments of various sizes surrounded by coarse to fine matrix. The deposits differ in color, indicating different sources on the edifice. Tephrochronological and radiocarbon dating of the avalanches shows that the first large Holocene avalanches were emplaced approximately 4530–4350 BC. From ∼2490 BC at least 13 avalanches occurred after intervals of 30–900 years. Six large avalanches were emplaced between 120 and 970 AD, with recurrence intervals of 30–340 years. All the debris avalanches were followed by eruptions that produced various types of pyroclastic deposits. Features of some surge deposits suggest that they might have originated as a result of directed blasts triggered by rockslides. Most avalanche deposits are composed of fresh andesitic rocks of extrusive domes, so the avalanches might have resulted from the high magma supply rate and the repetitive formation of the domes. No trace of the 1854 summit failure mentioned in historical records has been found beyond 8 km from the crater; perhaps witnesses exaggerated or misinterpreted the events. Received: 18 August 1997 / Accepted: 19 December 1997  相似文献   

Modelling the dynamics and thermodynamics of volcanic degassing     

David S. Stevenson  Stephen Blake 《Bulletin of Volcanology》1998,60(4):307-317

 The rates of passive degassing from volcanoes are investigated by modelling the convective overturn of dense degassed and less dense gas-rich magmas in a vertical conduit linking a shallow degassing zone with a deep magma chamber. Laboratory experiments are used to constrain our theoretical model of the overturn rate and to elaborate on the model of this process presented by Kazahaya et al. (1994). We also introduce the effects of a CO₂–saturated deep chamber and adiabatic cooling of ascending magma. We find that overturn occurs by concentric flow of the magmas along the conduit, although the details of the flow depend on the magmas' viscosity ratio. Where convective overturn limits the supply of gas-rich magma, then the gas emission rate is proportional to the flow rate of the overturning magmas (proportional to the density difference driving convection, the conduit radius to the fourth power, and inversely proportional to the degassed magma viscosity) and the mass fraction of water that is degassed. Efficient degassing enhances the density difference but increases the magma viscosity, and this dampens convection. Two degassing volcanoes were modelled. At Stromboli, assuming a 2 km deep, 30% crystalline basaltic chamber, containing 0.5 wt.% dissolved water, the ∼700 kg s^–1 magmatic water flux can be modelled with a 4–10 m radius conduit, degassing 20–100% of the available water and all of the 1 to 4 vol.% CO₂ chamber gas. At Mount St. Helens in June 1980, assuming a 7 km deep, 39% crystalline dacitic chamber, containing 4.6 wt.% dissolved water, the ∼500 kg s^–1 magmatic water flux can be modelled with a 22–60 m radius conduit, degassing ∼2–90% of the available water and all of the 0.1 to 3 vol.% CO₂ chamber gas. The range of these results is consistent with previous models and observations. Convection driven by degassing provides a plausible mechanism for transferring volatiles from deep magma chambers to the atmosphere, and it can explain the gas fluxes measured at many persistently active volcanoes. Received: 26 September 1997 / Accepted: 11 July 1998  相似文献   

腾冲、长白山、五大连池新生代火山岩Sr、Nd、Pb同位素地球化学特征   总被引：5，自引：2，他引：3  

周真恒  姜朝松  李波 《地震研究》1998,21(4):379-387

概括了腾冲、长白山、五大连池新生代火山岩岩石学、岩石化学基本特征,探讨了Ｓｒ、Ｎｄ、Ｐｂ同位素地球化学特征和岩浆源区性质。腾冲火山岩为高钾钙碱性岩系,高８７Ｓｒ／８６Ｓｒ、高２０６Ｐｂ／２０４Ｐｂ、２０８Ｐｂ／２０４Ｐｂ、低１４３Ｎｄ／１４４Ｎｄ,岩浆源区为俯冲带再循环富集地幔。长白山火山岩为超钾钙碱性岩系,低Ｓｒ高８７Ｓｒ／８６Ｓｒ,εＮｄ为－２３—＋２９,Ｐｂ同位素组成变化不大,岩浆源区为俯冲带再循环地幔。五大连池火山岩为超钾碱性岩系,高８７Ｓｒ／８６Ｓｒ、低１４３Ｎｄ／１４４Ｎｄ和２０６Ｐｂ／２０４Ｐｂ、２０８Ｐｂ／２０４Ｐｂ,岩浆源区为地幔内部交代作用所产生的富集地幔。  相似文献   

Dynamics of volcanic eruptions: Understanding electric signatures for activity monitoring     

《Comptes Rendus Geoscience》2015,347(3):112-123

Aside common methods as seismology, ground deformation, and geochemistry, electromagnetic and especially electric ones can efficiently be applied for imaging and monitoring active volcanoes and hydrothermal systems that most often control the initial eruptive phase. Surveys and mappings image ground fluids flow, faults systems, and structural interfaces with anomalies up to several hundred of mV. Reiteration of surveys highlights time and spatial evolution. Continuous networks must extend surveys when the activity becomes stronger. Resolution in the data can reach a few microvolts as compared to the tens of millivolts for surveys. Observations made on several volcanoes definitively show that electric signals, up to some tens of millivolts, may appear some hours to a few weeks before ground deformation and seismicity, and are related to some extent to the location of the future activity. These transient signals may have a relationship with those recorded aboard satellites. Both of them appear during the transition period between the “fatigue” and the “dynamical” stages, which announces accelerating and irreversible processes.  相似文献   

Magma plumbing system of the 2000 eruption of Miyakejima Volcano, Japan   总被引：1，自引：0，他引：1  

Mizuho Amma-Miyasaka  Mitsuhiro Nakagawa  Setsuya Nakada 《Bulletin of Volcanology》2005,67(3):254-267

During the 2000 eruption at Miyakejima Volcano, two magmas with different compositions erupted successively from different craters. Magma erupted as spatter from the submarine craters on 27 June is aphyric basaltic andesite (<5 vol% phenocrysts, 51.4–52.2 wt% SiO₂), whereas magma issued as volcanic bombs from the summit caldera on 18 August is plagioclase-phyric basalt (20 vol% phenocrysts, 50.8–51.3 wt% SiO₂). The submarine spatter contains two types of crystal-clots, A-type and A-type (andesitic type). The phenocryst assemblages (plagioclase, pyroxenes and magnetite) and compositions of clinopyroxene in these clots are nearly the same, but only A-type clots contain Ca-poor plagioclase (An < 70). We consider that the A-type clots could have crystallized from a more differentiated andesitic magma than the A-type clots, because FeO*/MgO is not strongly influenced during shallow andesitic differentiation. The summit bombs contain only B-type (basaltic type) crystal-clots of Ca-rich plagioclase, olivine and clinopyroxene. The A-type and B-type clots have often coexisted in Miyakejima lavas of the period 1469–1983, suggesting that the magma storage system consists of independent batches of andesitic and basaltic magmas. According to the temporal variations of mineral compositions in crystal-clots, the andesitic magma became less evolved, and the basaltic magma more evolved, over the past 500 years. We conclude that gradually differentiating basaltic magma has been repeatedly injected into the shallower andesitic magma over this period, causing the andesitic magma to become less evolved with time. The mineral chemistries in crystal-clots of the submarine spatter and 18 August summit bombs of the 2000 eruption fall on the evolution trends of the A-type and B-type clots respectively, suggesting that the shallow andesitic and deeper basaltic magmas existing since 1469 had successively erupted from different craters. The 2000 summit collapse occurred due to drainage of the andesitic magma from the shallower chamber; as the collapse occurred, it may have caused disruption of crustal cumulates which then contaminated the ascending, deeper basalt. Thus, porphyritic basaltic magma could erupt alone without mixing with the andesitic magma from the summit caldera. The historical magma plumbing system of Miyakejima was probably destroyed during the 2000 eruption, and a new one may now form.Editorial responsibility: S Nakada, T Druitt  相似文献   

Apatite as a monitor of late-stage magmatic processes at Volcán Irazú, Costa Rica   总被引：1，自引：1，他引：0  

Jeremy W. Boyce  Richard L. Hervig 《Contributions to Mineralogy and Petrology》2009,157(2):135-145

Apatite phenocrysts from the 1963 and 1723 eruptions of Irazú volcano (Costa Rica) record a volatile evolution history that confirms previous melt inclusion studies, and provides additional information concerning the relative and absolute timing of subvolcanic magmatic events. Measurements of H, Cl, and F by secondary ion mass spectrometry reveal multiple populations of apatite in both 1723 and 1963 magmas. Assuming nominal apatite/melt partition coefficients allows us to compare the pattern of melt inclusions and apatites in ternary space, demonstrating the fidelity of the record preserved in apatite, and revealing a complex history of magma mixing with at least two components. The preservation of heterogeneous populations of apatite and of internally heterogeneous crystals requires short timescales (days to years) for these magmatic processes to occur.  相似文献   

内蒙古巴彦敖包地区安格尔音乌拉组地层锂土壤地球化学异常成因研究     

金松  梁秋生 《化工矿产地质》2019,(2):82-89

内蒙古巴彦敖包地区广泛出露上泥盆统安格尔音乌拉组地层,1∶5万土壤地球化学测量工作圈定的31处锂单元素异常与安格尔音乌拉组地层分布范围吻合良好。安格尔音乌拉组地层锂元素的富集与该套地层的原生沉积作用密切相关,未发生次生富集。通过对安格尔音乌拉组地层碎屑物源区及沉积作用的研究,认为其锂元素物质来源与镁铁质火山岩中锂元素的侵蚀溶出有关。溶出的锂元素被碎屑物中的粘土矿物吸附随后沉积成岩造成区内广泛分布的锂土壤地球化学异常。进而做出推断,研究区内晚泥盆世甚至更早存在大规模中基性火山活动,应该存在大规模古火山机构。提出一种新的沉积型锂矿成矿模式,即古火山机构周边的粘土矿物含量较高的碎屑岩层位在一定构造背景及沉积环境下可以具备锂元素富集成矿的条件。  相似文献   

Renewed uplift at the Yellowstone Caldera measured by leveling surveys and satellite radar interferometry     

Daniel Dzurisin  Charles Wicks Jr.  Wayne Thatcher 《Bulletin of Volcanology》1999,61(6):349-355

 A first-order leveling survey across the northeast part of the Yellowstone caldera in September 1998 showed that the central caldera floor near Le Hardy Rapids rose 24±5 mm relative to the caldera rim at Lake Butte since the previous survey in September 1995. Annual surveys along the same traverse from 1985 to 1995 tracked progressive subsidence near Le Hardy Rapids at an average rate of –19±1 mm/year. Earlier, less frequent surveys measured net uplift in the same area during 1923–1976 (14±1 mm/year) and 1976–1984 (22±1 mm/year). The resumption of uplift following a decade of subsidence was first detected by satellite synthetic aperture radar interferometry, which revealed approximately 15 mm of uplift in the vicinity of Le Hardy Rapids from July 1995 to June 1997. Radar interferograms show that the center of subsidence shifted from the Sour Creek resurgent dome in the northeast part of the caldera during August 1992 to June 1993 to the Mallard Lake resurgent dome in the southwest part during June 1993 to August 1995. Uplift began at the Sour Creek dome during August 1995 to September 1996 and spread to the Mallard Lake dome by June 1997. The rapidity of these changes and the spatial pattern of surface deformation suggest that ground movements are caused at least in part by accumulation and migration of fluids in two sill-like bodies at 5–10 km depth, near the interface between Yellowstone's magmatic and deep hydrothermal systems. Received: 30 November 1998 / Accepted: 16 April 1999  相似文献   

Kīlauea summit overflows: their ages and distribution in the Puna District, Hawai'i     

David A. Clague  Jonathan T. Hagstrum  Duane E. Champion  Melvin H. Beeson 《Bulletin of Volcanology》1999,61(6):363-381

 The tube-fed pāhoehoe lava flows covering much of the northeast flank of Kīlauea Volcano are named the 'Ailā'au flows. Their eruption age, based on published and six new radiocarbon dates, is approximately AD 1445. The flows have distinctive paleomagnetic directions with steep inclinations (40°–50°) and easterly declinations (0°–10°E). The lava was transported ∼40 km from the vent to the coast in long, large-diameter lava tubes; the longest tube (Kazumura Cave) reaches from near the summit to within several kilometers of the coast near Kaloli Point. The estimated volume of the 'Ailā'au flow field is 5.2±0.8 km³, and the eruption that formed it probably lasted for approximately 50 years. Summit overflows from Kīlauea may have been nearly continuous between approximately AD 1290 and 1470, during which time a series of shields formed at and around the summit. The 'Ailā'au shield was either the youngest or the next to youngest in this series of shields. Site-mean paleomagnetic directions for lava flows underlying the 'Ailā'au flows form only six groups. These older pāhoehoe flows range in age from 2750 to <18,000 BP, and the region was inundated by lava flows only three times in the past 5000 years. The known intervals between eruptive events average ∼1600 years and range from ∼1250 years to >2200 years. Lava flows from most of these summit eruptions also reached the coast, but none appears as extensive as the 'Ailā'au flow field. The chemistry of the melts erupted during each of these summit overflow events is remarkably similar, averaging approximately 6.3 wt.% MgO near the coast and 6.8 wt.% MgO near the summit. The present-day caldera probably formed more recently than the eruption that formed the 'Ailā'au flows (estimated termination ca. AD 1470). The earliest explosive eruptions that formed the Keanakāko'i Ash, which is stratigraphically above the 'Ailā'au flows, cannot be older than this age. Received: 10 October 1998 / Accepted: 12 May 1999  相似文献   

Evolution of the seismic activity from the 1982 eruption of El Chichon Volcano, Chiapas, Mexico     

Z. Jiménez  V. H. Espíndola  J. M. Espíndola 《Bulletin of Volcanology》1999,61(6):411-422

 We analyzed more than 1700 earthquakes related to the 1982 eruption of El Chichon volcano in southern Mexico. The data were recorded at specific periods throughout the whole eruptive interval of March to April 1982, by three different networks. The seismic activity began several months before the first eruption on 28 March. During this period the seismicity consisted of hybrid and long-period shallow earthquakes most likely related to processes of faulting, fracturing, and fluid movement underneath the volcano. The foci of events occurring before the eruption circumscribe an aseismic zone from approximately 7 to 13 km below the volcano. After the eruption, the seismic activity consisted of tectonic-type earthquakes that peaked at 1200 events/h. This later activity occurred over a wide range of depths, mostly between 5 and 20 km, that includes the former aseismic zone and is roughly limited by the major tectonic faults in the area. Received: 19 May 1998 / Accepted: 13 June 1999  相似文献