Magma storage beneath Axial volcano on the Juan de Fuca mid-ocean ridge.

Axial volcano, which is located near the intersection of the Juan de Fuca ridge and the Cobb-Eickelberg seamount chain beneath the northeast Pacific Ocean, is a locus of volcanic activity thought to be associated with the Cobb hotspot. The volcano rises 700 metres above the ridge, has substantial rift zones extending about 50 kilometres to the north and south, and has erupted as recently as 1998 (ref. 2). Here we present seismological data that constrain the three-dimensional velocity structure beneath the volcano. We image a large low-velocity zone in the crust, consisting of a shallow magma chamber and a more diffuse reservoir in the lower crust, and estimate the total magma volume in the system to be between 5 and 21 km3. This volume is two orders of magnitude larger than the amount of melt emplaced during the most recent eruption (0.1-0.2 km3). We therefore infer that such volcanic events remove only a small portion of the reservoir that they tap, which must accordingly be long-lived compared to the eruption cycle. On the basis of magma flux estimates, we estimate the crustal residence time of melt in the volcanic system to be a few hundred to a few thousand years.     

Long-term eruptive activity at a submarine arc volcano

Three-quarters of the Earth's volcanic activity is submarine, located mostly along the mid-ocean ridges, with the remainder along intraoceanic arcs and hotspots at depths varying from greater than 4,000 m to near the sea surface. Most observations and sampling of submarine eruptions have been indirect, made from surface vessels or made after the fact. We describe here direct observations and sampling of an eruption at a submarine arc volcano named NW Rota-1, located 60 km northwest of the island of Rota (Commonwealth of the Northern Mariana Islands). We observed a pulsating plume permeated with droplets of molten sulphur disgorging volcanic ash and lapilli from a 15-m diameter pit in March 2004 and again in October 2005 near the summit of the volcano at a water depth of 555 m (depth in 2004). A turbid layer found on the flanks of the volcano (in 2004) at depths from 700 m to more than 1,400 m was probably formed by mass-wasting events related to the eruption. Long-term eruptive activity has produced an unusual chemical environment and a very unstable benthic habitat exploited by only a few mobile decapod species. Such conditions are perhaps distinctive of active arc and hotspot volcanoes.     

徐家围子断陷火山机构类型及其地质指示意义

庆深气田的勘探开发实践表明,火山岩气藏呈现出以孤立火山机构控藏的特征.火山机构的横向分布规律及其预测成为火山岩勘探开发的难点.在徐家围子断陷营城组开展了精细的火山岩地层结构对比研究,发现火山喷发受深大断裂控制,具有横向迁移和纵向多旋回叠置的特征.根据火山机构的地球物理响应特征及其地质指示意义,将火山机构分为层状火山、平状火山、歪斜火山、熔岩穹窿、破火山五大类.层状火山和歪斜火山指示了火山沿构造断裂带大规模的爆发与喷溢,形成了大面积广泛发育的火山熔岩和火山碎屑岩互层的地层,构成营城组火山岩地层的主体.火山机构错叠连片,火山岩储层发育.平状火山指示了火山强烈的风化剥蚀作用,风化壳储层发育,可形成高产的火山岩气藏.破火山口和熔岩穹窿指示了火山活动的局部性,破火山是局部火山能量瞬间快速的释放,形成大量的火山碎屑堆积,以致密储层发育为特征;熔岩穹窿是火山作用后期的产物,储层发育,但规模较小.     

2022年汤加火山喷发与海啸观测

2022年1月15日世界标准时间4∶14，位于南太平洋汤加俯冲带火山链区域的Hunga Tonga-Hunga Ha’apai(HTHH,175.39°W,20.55°S)火山爆发并激发全球性海啸。聚焦火山喷发和海啸波的观测方法，介绍了海底传感器、大气波变化卫星图、电离层扰动对火山喷发和海啸的最新监测结果。结合该区域的地质构造与火山喷发历史资料，综述了2022年汤加HTHH火山喷发引起的海啸特征、最新观测手段，提出了对俯冲带火山海啸等进行详细的海洋地球物理调查、基于观测综合量化研究海底火山大规模喷发对全球气候的潜在影响等建议。     

Uplift, thermal unrest and magma intrusion at Yellowstone caldera

The Yellowstone caldera, in the western United States, formed approximately 640,000 years ago when an explosive eruption ejected approximately 1,000 km3 of material. It is the youngest of a series of large calderas that formed during sequential cataclysmic eruptions that began approximately 16 million years ago in eastern Oregon and northern Nevada. The Yellowstone caldera was largely buried by rhyolite lava flows during eruptions that occurred from approximately 150,000 to approximately 70,000 years ago. Since the last eruption, Yellowstone has remained restless, with high seismicity, continuing uplift/subsidence episodes with movements of approximately 70 cm historically to several metres since the Pleistocene epoch, and intense hydrothermal activity. Here we present observations of a new mode of surface deformation in Yellowstone, based on radar interferometry observations from the European Space Agency ERS-2 satellite. We infer that the observed pattern of uplift and subsidence results from variations in the movement of molten basalt into and out of the Yellowstone volcanic system.     

Spectroscopic evidence for a lava fountain driven by previously accumulated magmatic gas

Lava fountains are spectacular continuous gas jets, propelling lava fragments to heights of several hundred metres, which occasionally occur during eruptions of low-viscosity magmas. Whether they are generated by the effervescent disruption of fast-rising bubbly melt or by the separate ascent of a bubble foam layer accumulated at depth still remains a matter of debate. No field measurement has yet allowed firm discrimination between these two models. A key insight into the origin of lava fountains may be gained by measuring the chemical composition of the driving gas phase. This composition should differ markedly depending on whether the magma degassing occurs before or during eruption. Here we report the analysis of magmatic gas during a powerful (250-600 m high) lava fountain, measured with Fourier transform infrared spectroscopy on Mount Etna, Sicily. The abundances of volcanic gas species, determined from absorption spectra of lava radiation, reveal a fountain gas having higher CO2/S and S/Cl ratios than other etnean emissions, and which cannot derive from syn-eruptive bulk degassing of Etna basalt. Instead, its composition suggests violent emptying of a gas bubble layer previously accumulated at about 1.5 km depth below the erupting crater.     

Widespread uplift and 'trapdoor' faulting on Galápagos volcanoes observed with radar interferometry

Volcanic uplift, caused by the accumulation of magma in subsurface reservoirs, is a common precursor to eruptions. But, for some volcanoes, uplift of metres or more has not yet led to an eruption. Here we present displacement maps of volcanoes in the Galápagos Islands, constructed using satellite radar interferometry, that might help explain this dichotomy. We show that all but one of the seven volcanoes on the islands of Isabela and Fernandina deformed during 1992-99. Cerro Azul and Fernandina erupted during the observation period and show evidence of inflation, co-eruptive deflation and shallow dyke intrusion. In contrast, the largest volcano, Sierra Negra, has not erupted, yet exhibits spatially and temporally variable deformation, with a maximum uplift of 2.7 m between 1992 and 1999, which can be modelled by a shallow inflating sill. Inflation during 1997-98, however, was accompanied by 'trapdoor' faulting on a steeply dipping fracture system within the caldera. Repeated trapdoor faulting over geological time has formed an arcuate intra-caldera ridge within Sierra Negra and may have acted to relax stresses above the magma chamber, inhibiting summit eruptions. Similar processes may help explain large uplift unaccompanied by eruptive activity at other volcanoes.     

汤加火山的地震学研究

俯冲带的地震监测仍然是一个挑战，特别是对于人口稠密地区。2022年1月汤加的洪阿汤加—洪阿哈阿帕伊火山的喷发以及引发的地震凸显了这一需求的急迫性。综合汤加地震学观测，推测汤加部分火山近期仍有小规模喷发风险。选取2009—2010年覆盖汤加的海底地震仪台阵数据，应用机器学习算法进行数据处理，得到汤加火山岛链附近高分辨率的地震目录。     

长白山天池火山泥石流分布特征及其形成模式研究

长白山天池火山是我国最具灾害性喷发危险的活动火山,火山泥石流是最致命的火山灾害之一,根据距离火山口远近不同堆积物所展现的不同特征,将长白山天池火山泥石流分为;碎屑流相、过渡相和超富集流相.基于野外剖面对长白山天池火山1 000年大喷发形成的泥石流进行了详细的描述,探讨了火山泥石流的成因和灾害.     

三江地区阿中陆缘弧火山沉积作用与古环境恢复

岛弧从水下生长到水上其沉积环境也发生了演变 ,西藏东部三江地区中段的情况就是如此 ,厚度大于 1 2 1 0 m的上三叠统哇曲组 (T3w)由弧火山岩夹碳酸盐岩与碎屑岩组成 ,沉积相自下而上由海底扇发展到河流相。与此相对应的火山熔岩流形态也发生了变化 ,从下而上由块状向块体或枕状体的变化说明这是渐进的浅水环境。综合火山 -沉积物特征的研究 ,表明陆缘弧曾经历了水下浸没的深水环境而后上升到陆上环境的过程     

Evidence of recent volcanic activity on the ultraslow-spreading Gakkel ridge

Seafloor spreading is accommodated by volcanic and tectonic processes along the global mid-ocean ridge system. As spreading rate decreases the influence of volcanism also decreases, and it is unknown whether significant volcanism occurs at all at ultraslow spreading rates (<1.5 cm yr(-1)). Here we present three-dimensional sonar maps of the Gakkel ridge, Earth's slowest-spreading mid-ocean ridge, located in the Arctic basin under the Arctic Ocean ice canopy. We acquired this data using hull-mounted sonars attached to a nuclear-powered submarine, the USS Hawkbill. Sidescan data for the ultraslow-spreading (approximately 1.0 cm yr(-1)) eastern Gakkel ridge depict two young volcanoes covering approximately 720 km2 of an otherwise heavily sedimented axial valley. The western volcano coincides with the average location of epicentres for more than 250 teleseismic events detected in 1999, suggesting that an axial eruption was imaged shortly after its occurrence. These findings demonstrate that eruptions along the ultraslow-spreading Gakkel ridge are focused at discrete locations and appear to be more voluminous and occur more frequently than was previously thought.     

The role of dyking and fault control in the rapid onset of eruption at Chaitén volcano, Chile

Rhyolite is the most viscous of liquid magmas, so it was surprising that on 2?May 2008 at Chaitén Volcano, located in Chile's southern Andean volcanic zone, rhyolitic magma migrated from more than 5?km depth in less than 4?hours (ref.?1) and erupted explosively with only two days of detected precursory seismic activity. The last major rhyolite eruption before that at Chaitén was the largest volcanic eruption in the twentieth century, at Novarupta volcano, Alaska, in 1912. Because of the historically rare and explosive nature of rhyolite eruptions and because of the surprisingly short warning before the eruption of the Chaitén volcano, any information about the workings of the magmatic system at Chaitén, and rhyolitic systems in general, is important from both the scientific and hazard perspectives. Here we present surface deformation data related to the Chaitén eruption based on radar interferometry observations from the Japan Aerospace Exploration Agency (JAXA) DAICHI (ALOS) satellite. The data on this explosive rhyolite eruption indicate that the rapid ascent of rhyolite occurred through dyking and that melt segregation and magma storage were controlled by existing faults.     

用简易的熔体流动速率测试评价不同牌号HDPE的流变性

本文采用全负荷熔体流动速率测试仪测定六种牌号高密度聚乙烯（ＨＤＰＥ）的熔融指数，并参照高分子流变学的研究方法，初步尝试由所加载荷及熔融指数经过数据换算和处理，得到表征熔体流变性的三个重要参数：剪切应力、剪切速率和表观粘度．绘制不同参数的关系曲线从而得到六种牌号ＨＤＰＥ的流动曲线．结果证明：采用这一普通工厂具备的仪器以及本文的研究方法，可获得与设备昂贵和操作较复杂的毛细管流交仪相似的结果，对工厂选择原材料、确定加工工艺条件提供可靠的依据．     

Magmatic events can produce rapid changes in hydrothermal vent chemistry

The Endeavour segment of the Juan de Fuca ridge is host to one of the most vigorous hydrothermal areas found on the global mid-ocean-ridge system, with five separate vent fields located within 15 km along the top of the ridge segment. Over the past decade, the largest of these vent fields, the 'Main Endeavour Field', has exhibited a constant spatial gradient in temperature and chloride concentration in its vent fluids, apparently driven by differences in the nature and extent of subsurface phase separation. This stable situation was disturbed on 8 June 1999 by an earthquake swarm. Owing to the nature of the seismic signals and the lack of new lava flows observed in the area during subsequent dives of the Alvin and Jason submersibles (August-September 1999), the event was interpreted to be tectonic in nature. Here we show that chemical data from hydrothermal fluid samples collected in September 1999 and June 2000 strongly suggest that the event was instead volcanic in origin. Volatile data from this event and an earlier one at 9 degrees N on the East Pacific Rise show that such magmatic events can have profound and rapid effects on fluid-mineral equilibria, phase separation, 3He/heat ratios and fluxes of volatiles from submarine hydrothermal systems.     

Intrusion triggering of the 2010 Eyjafjallajökull explosive eruption

Gradual inflation of magma chambers often precedes eruptions at highly active volcanoes. During such eruptions, rapid deflation occurs as magma flows out and pressure is reduced. Less is known about the deformation style at moderately active volcanoes, such as Eyjafjallaj?kull, Iceland, where an explosive summit eruption of trachyandesite beginning on 14 April 2010 caused exceptional disruption to air traffic, closing airspace over much of Europe for days. This eruption was preceded by an effusive flank eruption of basalt from 20 March to 12 April 2010. The 2010 eruptions are the culmination of 18?years of intermittent volcanic unrest. Here we show that deformation associated with the eruptions was unusual because it did not relate to pressure changes within a single magma chamber. Deformation was rapid before the first eruption (>5?mm per day after 4 March), but negligible during it. Lack of distinct co-eruptive deflation indicates that the net volume of magma drained from shallow depth during this eruption was small; rather, magma flowed from considerable depth. Before the eruption, a ～0.05?km(3) magmatic intrusion grew over a period of three months, in a temporally and spatially complex manner, as revealed by GPS (Global Positioning System) geodetic measurements and interferometric analysis of satellite radar images. The second eruption occurred within the ice-capped caldera of the volcano, with explosivity amplified by magma-ice interaction. Gradual contraction of a source, distinct from the pre-eruptive inflation sources, is evident from geodetic data. Eyjafjallaj?kull's behaviour can be attributed to its off-rift setting with a 'cold' subsurface structure and limited magma at shallow depth, as may be typical for moderately active volcanoes. Clear signs of volcanic unrest signals over years to weeks may indicate reawakening of such volcanoes, whereas immediate short-term eruption precursors may be subtle and difficult to detect.     

Decadal to monthly timescales of magma transfer and reservoir growth at a caldera volcano

Caldera-forming volcanic eruptions are low-frequency, high-impact events capable of discharging tens to thousands of cubic kilometres of magma explosively on timescales of hours to days, with devastating effects on local and global scales. Because no such eruption has been monitored during its long build-up phase, the precursor phenomena are not well understood. Geophysical signals obtained during recent episodes of unrest at calderas such as Yellowstone, USA, and Campi Flegrei, Italy, are difficult to interpret, and the conditions necessary for large eruptions are poorly constrained. Here we present a study of pre-eruptive magmatic processes and their timescales using chemically zoned crystals from the 'Minoan' caldera-forming eruption of Santorini volcano, Greece, which occurred in the late 1600s BC. The results provide insights into how rapidly large silicic systems may pass from a quiescent state to one on the edge of eruption. Despite the large volume of erupted magma (40-60 cubic kilometres), and the 18,000-year gestation period between the Minoan eruption and the previous major eruption, most crystals in the Minoan magma record processes that occurred less than about 100 years before the eruption. Recharge of the magma reservoir by large volumes of silicic magma (and some mafic magma) occurred during the century before eruption, and mixing between different silicic magma batches was still taking place during the final months. Final assembly of large silicic magma reservoirs may occur on timescales that are geologically very short by comparison with the preceding repose period, with major growth phases immediately before eruption. These observations have implications for the monitoring of long-dormant, but potentially active, caldera systems.     

Mechanism of stratospheric decadal abrupt cooling in the Early 1990s as influenced by the Pinatubo eruption

Studies have suggested that one volcanic eruption can influence seasonal to inter-annual climate variations.This study indicates that the Pinatubo eruption in 1991 may have actually induced the stratospheric decadal cooling recorded in the early 1990s.Using the NCEP/NCAR reanalysis and TOMS/SBUV satellite data,a decadal abrupt cooling of stratospheric tropical air temperature was found to have occurred in the early 1990s during a long-term descending trend.We generated the spatio-temporal structures of the decadal abrupt changes(DACs) for the stratosphere,and explored the relationship between the Pinatubo volcano eruption in 1991 and stratospheric DACs in the early 1990s.Our results suggest that the eruption of Pinatubo prompted a decadal decrease of ozone by the activation of nitrate and sulfate volcanic aerosols on ClO free radicals.The stratospheric heat absorbed by ozone decreased over a decadal time scale.As a result,decadal abrupt cooling of stratospheric tropical air temperatures occurred in the early 1990s,and may be attributed to the Pinatubo eruption.The results therefore indicate that one strong volcanic eruption can induce stratospheric decadal climate variation.     

基于威布尔分布的核电厂仪表校验周期延长论证分析

威布尔分布常用在寿命数据分析中,以核电厂的主给水流量控制系统液位测量仪表数据和反应堆冷却剂系统温度测量仪表历史大修数据为例,建立威布尔分布可靠性模型,计算仪表的预计失效时间。结果表明:在仪表95%可靠度下,仪表的失效时间大于延长后的1.5 a的验证实验周期,这两组仪表具有良好的可靠性,周期延长可行。     

Earthquake-induced changes in a hydrothermal system on the Juan de Fuca mid-ocean ridge

Hydrothermal vents on mid-ocean ridges of the northeast Pacific Ocean are known to respond to seismic disturbances, with observed changes in vent temperature. But these disturbances resulted from submarine volcanic activity; until now, there have been no observations of the response of a vent system to non-magmatic, tectonic events. Here we report measurements of hydrothermal vent temperature from several vents on the Juan de Fuca ridge in June 1999, before, during and after an earthquake swarm of apparent tectonic origin. Vent fluid temperatures began to rise 4-11 days after the first earthquake. Following this initial increase, the vent temperatures oscillated for about a month before settling down to higher values. We also observed a tenfold increase in fluid output from the hydrothermal system over a period of at least 80 days, extending along the entire ridge segment. Such a large, segment-wide thermal response to relatively modest tectonic activity is surprising, and raises questions about the sources of excess heat and fluid, and the possible effect on vent biological communities.     

Detection of bromine monoxide in a volcanic plume

The emission of volcanic gases usually precedes eruptive activity, providing both a warning signal and an indication of the nature of the lava soon to be erupted. Additionally, volcanic emissions are a significant source of gases and particles to the atmosphere, influencing tropospheric and stratospheric trace-gas budgets. Despite some halogen species having been measured in volcanic plumes (mainly HCl and HF), little is known about bromine compounds and, in particular, gas-phase reactive bromine species. Such species are especially important in the stratosphere, as reactive bromine-despite being two orders of magnitude less abundant than chlorine-accounts for about one-third of halogen-catalysed ozone depletion. In the troposphere, bromine-catalysed complete ozone destruction has been observed to occur regularly during spring in the polar boundary layers as well as in the troposphere above the Dead Sea basin. Here we report observations of BrO and SO2 abundances in the plume of the Soufrière Hills volcano (Montserrat) in May 2002 by ground-based multi-axis differential optical absorption spectroscopy. Our estimate of BrO emission leads us to conclude that local ozone depletion and small ozone 'holes' may occur in the vicinity of active volcanoes, and that the amount of bromine emitted from volcanoes might be sufficiently large to play a role not only in the stratosphere, but also in tropospheric chemistry.