中国历史文献中的异常大气光象记载与世界火山活动

中国历史文献记载的某些异常曙暮光、日月和天空颜色异常现象,可能是在适宜条件下由重大的火山喷发产生的火山尘幕所致.将15世纪以后的这类异常大气光象记载与世界重大火山活动的记录详细对比,发现1525年、1638年、1640年、1853年、1883年、1911年等年份多处地点观测到的异常大气光象与世界重大火山活动有很好的对应关系.以1883年和1640年为例,从火山的喷发时间、地理位置和大气环流条件等方面,推证这些异常的大气光象是火山尘幕的影响所致.认为这类历史记载可以作为火山活动的间接证据,从而为搜寻早期重大火山活动信息提示了新途径.     

关于2003年10～11月日地关系重大事件研究综述

发生于2003年10～11月许许多多日地关系重大事件,西方称为万圣节日地事件或风暴(Halloween Events 或Halloween Storms),并予以特别关注.本文综述对这次日地重大事件的国际集会讨论和公开出版的文献,在太阳爆发方面包括：（1）太阳活动区与耀斑;（2）日冕物质抛射CMEs;（3）日冕激波;（4）太阳高能粒子SFPs;（5）活动区能量与面积、耀斑大小和CME速率.在日球层与地球物理效应方面,包括：（1）日球层响应;（2）大磁暴与宇宙线磁层效应;（3）热层与电离层效应;（4）白天极光、臭氧亏损;（5）中国学者工作.期望我国在此基础上积极开展工作和取得创新.     

辽河盆地欧利坨子富钾质火山岩特征与成因探讨

欧利坨子位于辽河盆地东部凹陷中段,是新生代古近纪火山活动非常强烈的地区,主要岩性为玄武岩、粗面岩和火山碎屑岩。对该区富钾质火山岩(粗面岩)的喷发特征、喷发年代、地球化学和成因进行了研究。火山口位于该区的中部,属于裂隙式喷发,弧形裂隙的两端喷发强度大,并在晚期形成了破火山口。粗面岩的KAr年代学和地球化学表明,它们形成于沙三时期(38.0～43.0Ma),具有富碱(K2O Na2O=10.22%～12.47%)、富钾(K2O/Na2O=0.69～1.88)、高铝(Al2O3=17.82%～19.44%)、低钛(TiO2=0.19%～0.67%)的特点,属于典型的钾玄岩系。粗面岩的分布受火山裂隙控制,同时也受区域的断裂活动影响。在该区富钾质岩浆喷发前后,华北东部中、新生代构造体制存在由EW向挤压构造向NNE向以伸展为主的构造格局、由板缘向板内构造环境的重大转折,郯庐断裂由左旋走滑变为右旋走滑,辽河盆地在沙三期进入大幅度张裂期。欧利坨子富钾质火山岩的形成是裂谷期岩石圈伸展作用的产物,是玄武质岩浆经过大比例分离结晶作用的产物,可能与晚中生代太平洋板块俯冲残片的部分熔融有密切关系。     

广西涠洲岛南湾火山喷发特征

涠洲岛是北部湾内的一座火山岛, 火山熔岩构筑了该岛的基底, 岛南端的南湾火山喷发物形成了涠洲岛现代火山地貌.南湾火山喷发以岩浆喷发和射气岩浆喷发交替进行为特征, 火山碎屑岩和基浪堆积物向岛北延伸, 覆盖了大半个涠洲岛.选取了鳄鱼嘴和猪仔岛2个典型剖面, 对南湾火山喷发活动进行详细的观察和描述, 发现了诸如爬升层理、大型低角度交错层理和板状层理等射气岩浆喷发成因的基浪堆积物中特有的构造, 并且观察到射气岩浆作用的指相物质——增生火山砾.所有这些现象都反映了南湾火山是射气与岩浆交替喷发成因的复合火山, 其中射气岩浆喷发占据重要地位, 而喷发中心位于南湾海中.      

火山喷发和太阳活动对我国温度影响的研究

利用特征向量分析、时序叠加分析和谱分析相结合的方法,给出了近５０年来我国地面气温场中较为清晰的火山喷发和太阳活动信号。强烈的火山喷发导致全国大部分地区降温,降温最明显的时段是喷发１年多以后,并能持续约半年。除这个主信号以外,青藏高原、东南沿海和东北地区都可能出现较为复杂的温度变化。温度变化与太阳活动之间的联系更多地反映在二者的振荡关系上。     

火山灾害及减灾措施

火山能产生多种灾害,火山喷发能够产生破坏性的岩浆流、火山碎屑和气体的高速崩塌流;大量的火山灰云可漂浮至几百千米远,严重影响喷气式飞机的飞行,危害人体健康并造成财产损失。     

Flow localization in fissure eruptions

 During a basaltic fissure eruption heat transfer from the hot magma to the surrounding rock causes a dramatic increase in the magmatic viscosity and solidification at the margins. Both viscosity contrast and solidification can amplify initial variations in the flow rate and lead to localization of the flow along the strike of the fissure. However, for typical parameters, amplification driven by solidification is slower and significantly weaker than amplification driven by viscosity variations. In fact, for the parameters examined, the amplification due to solidification is so weak that its effect is almost insignificant, whereas viscosity variation provides a strong active mechanism for flow localization. Laboratory experiments illustrate viscous localization and suggest that this mechanism is robust. The dependence of viscosity on temperature can cause a small change in the pressure of the magma chamber to lead to a large jump in the flow rate of magma through the fissure. Received: 13 March 1998 / Accepted: 27 September 1998     

Complex effusive events at Kīlauea as documented by the GOES satellite and remote video cameras

 GOES provides thermal data for all of the Hawaiian volcanoes once every 15 min. We show how volcanic radiance time series produced from this data stream can be used as a simple measure of effusive activity. Two types of radiance trends in these time series can be used to monitor effusive activity: (a) Gradual variations in radiance reveal steady flow-field extension and tube development. (b) Discrete spikes correlate with short bursts of activity, such as lava fountaining or lava-lake overflows. We are confident that any effusive event covering more than 10,000 m² of ground in less than 60 min will be unambiguously detectable using this approach. We demonstrate this capability using GOES, video camera and ground-based observational data for the current eruption of Kīlauea volcano (Hawai'i). A GOES radiance time series was constructed from 3987 images between 19 June and 12 August 1997. This time series displayed 24 radiance spikes elevated more than two standard deviations above the mean; 19 of these are correlated with video-recorded short-burst effusive events. Less ambiguous events are interpreted, assessed and related to specific volcanic events by simultaneous use of permanently recording video camera data and ground-observer reports. The GOES radiance time series are automatically processed on data reception and made available in near-real-time, so such time series can contribute to three main monitoring functions: (a) automatically alerting major effusive events; (b) event confirmation and assessment; and (c) establishing effusive event chronology. Received: 12 January 1999 / Accepted: 13 July 1999     

Overview of the 1990–1995 eruption at Unzen Volcano

Following 198 years of dormancy, a small phreatic eruption started at the summit of Unzen Volcano (Mt. Fugen) in November 1990. A swarm of volcano-tectonic (VT) earthquakes had begun below the western flank of the volcano a year before this eruption, and isolated tremor occurred below the summit shortly before it. The focus of VT events had migrated eastward to the summit and became shallower. Following a period of phreatic activity, phreatomagmatic eruptions began in February 1991, became larger with time, and developed into a dacite dome eruption in May 1991 that lasted approximately 4 years. The emergence of the dome followed inflation, demagnetization and a swarm of high-frequency (HF) earthquakes in the crater area. After the dome appeared, activity of the VT earthquakes and the summit HF events was replaced largely by low-frequency (LF) earthquakes. Magma was discharged nearly continuously through the period of dome growth, and the rate decreased roughly with time. The lava dome grew in an unstable form on the shoulder of Mt. Fugen, with repeating partial collapses. The growth was exogenous when the lava effusion rate was high, and endogenous when low. A total of 13 lobes grew as a result of exogenous growth. Vigorous swarms of LF earthquakes occurred just prior to each lobe extrusion. Endogenous growth was accompanied by strong deformation of the crater floor and HF and LF earthquakes. By repeated exogenous and endogenous growth, a large dome was formed over the crater. Pyroclastic flows frequently descended to the northeast, east, and southeast, and their deposits extensively covered the eastern slope and flank of Mt. Fugen. Major pyroclastic flows took place when the lava effusion rate was high. Small vulcanian explosions were limited in the initial stage of dome growth. One of them occurred following collapse of the dome. The total volume of magma erupted was 2.1×10⁸ m³ (dense-rock-equivalent); about a half of this volume remained as a lava dome at the summit (1.2 km long, 0.8 km wide and 230–540 m high). The eruption finished with extrusion of a spine at the endogenous dome top. Several monitoring results convinced us that the eruption had come to an end: the minimal levels of both seismicity and rockfalls, no discharge of magma, the minimal SO₂ flux, and cessation of subsidence of the western flank of the volcano. The dome started slow deformation and cooling after the halt of magma effusion in February 1995.     

Ground temperature change observed at Unzen Volcano associated with the 1990–1995 eruption

Ground temperature associated with eruptive activity of Unzen Volcano, southwestern Japan, was observed in a cave about 680 m west of the central vent. Based on the data during 1991–1996, eliminating the effects of seasonal change, the temperature rose to the highest level probably around the first half of 1992. Hereafter the temperature decreased gradually year by year at least up to the autumn of 1996, beyond the level recovered at the beginning of the lava extrusion in May 1991. Although it is not necessarily conclusive, the present observation suggests a possible rise in ground temperature prior to the commencement of the first phreatic eruption in November 1990. If so, a careful observation may help to predict future eruptions by detecting a precursory rise of the ground temperature in this volcano.