Tyatya Volcano, southwestern Kuril arc: Recent eruptive activity inferred from widespread tephra

Abstract Tyatya Volcano, situated in Kunashir Island at the southwestern end of Kuril Islands, is a large composite stratovolcano and one of the most active volcanoes in the Kuril arc. The volcanic edifice can be divided into the old and the young ones, which are composed of rocks of distinct magma types, low‐ and medium‐K series, respectively. The young volcano has a summit caldera with a central cone. Recent eruptions have occurred at the central cone and at the flank vents of the young volcano. We found several distal ash layers at the volcano and identified their ages and sources, that is, tephras of ad 1856, ad 1739, ad 1694 and ca 1 Ka derived from three volcanoes of Hokkaido, Japan, and caad 969 from Baitoushan Volcano of China/North Korea. These could provide good time markers to reveal the eruptive history of the central cone, which had continued intermittently with Strombolian eruptions and lava flow effusions since before 1 Ka. Relatively explosive eruptions have occurred three times at the cone during the past 1000 years. We revealed that, topographically, the youngest lava flows from the cone are covered not by the tephra of ad 1739 but by that of ad 1856. This evidence, together with a report of dense smoke rising from the summit in ad 1812, suggests that the latest major eruption with lava effusion from the central cone occurred in this year. In 1973, after a long period of dormancy, short‐lived phreatomagmatic eruptions began to occur from fissure vents at the northern flank of the young volcano. This was followed by large eruptions of Strombolian to sub‐Plinian types occurring from several craters at the southern flank. The 1973 activity is evaluated as Volcanic Explosivity Index = 4 (approximately 0.2 km³), the largest eruption during the 20th century in the southwestern Kuril arc. The rocks of the central cone are strongly porphyritic basalt and basaltic andesite, whereas the 1973 scoria is aphyric basalt, suggesting that magma feeding systems are definitely different between the summit and flank eruptions.     

Probabilistic hazard analysis of Citlaltépetl (Pico de Orizaba) Volcano, eastern Mexican Volcanic Belt

Citlaltépetl or Pico de Orizaba is the highest active volcano in the North American continent. Although Citlaltépetl is at present in repose, its eruptive history reveals repetitive explosive eruptions in the past. Its relatively low eruption rate has favored significant population growth in areas that may be affected by a potential eruptive activity. The need of some criteria for hazards assessment and land-use planning has motivated the use of statistical methods to estimate the time and space distribution of volcanic hazards around this volcano. The analysis of past activity, from late Pleistocene to historic times, and the extent of some well-identified deposits are used to calculate the recurrence probabilities of eruptions of various size during time periods useful for land-use planning.     

岩浆补给作用对硅质火山岩浆系统演化的制约

硅质火山喷发作为大陆地壳岩浆活动的重要表现，在研究大陆地壳形成与演化、探讨岩浆过程与动力学机制等方面具有重要的价值，其通常所表现的强烈爆炸式喷发，甚至可以导致全球性的环境和气候变迁。硅质岩浆系统在开放体系中不同来源岩浆的贡献和相互作用是目前研究的热点问题。持续的岩浆补给可以延长岩浆存储的时间，促进岩浆房的对流、岩浆的分异演化以及晶体 熔体的分离和晶粥的再活化，同时也是触发火山喷发的重要机制之一。此外，岩浆补给以及硅质岩浆的晶体 熔体演化过程也是火山喷发产物多样性的原因，导致同一火山在其活动过程中喷发产物规律性的变化，如富晶体火山岩、贫晶体火山岩、火山岩成分分层、以及复活岩穹和中央侵入体等。因此，岩浆补给作用是制约硅质火山岩浆系统演化和火山岩成分多样性的重要因素，也是活动火山监测和灾害评估的重要依据。岩石学、岩石地球化学、矿物(长石、石英、石榴子石、锆石等)同位素及成分变化，以及模拟实验、地震层析成像等研究为揭示硅质岩浆系统中的岩浆补给作用和复杂岩浆过程提供了多种视角。     

Magma eruption rates of Merapi volcano,Central Java,Indonesia during one century (1890–1992)

The magma eruption rates of Merapi volcano form 1890 to 1992 are re-examined chronologically. For this volcano, movements of extruded lavas and domes as well as their extrusions are important because they control the modes of the subsequent activities and cause nuées ardentes and lahars. The monthly eruption rates varied widely, but the cumulative volume of lavas has increased linearly and is expressed as 0.1x10⁶ m³/month. The magma production rate of this volcano may have been constant for these 100 years. Recurrent excessive effusion of lavas is tentatively interpreted by assuming a magma reservoir. The averaged eruption rate is small in comparison with other volcanoes such as Nyramuragia, Kilauea and Vesuvio. However, it is remarkable that the activity has been continuous for these 100 years and the total amount of lava discharged during this period reached more than 10⁸ m³. A simple model for the formation of the 1992 lava dome is presented. The viscosity of the lavas is probably between 10⁶ and 10⁷ P and the length of the magma conduit is probably less than 10 km.     

石棉田湾地区的石英角斑岩及其地质意义

出露于石棉田湾乡杜河坝-菩萨岗一带的石英角斑岩，以前被认为是侵入的花岗岩，其所在地层组为苏雄组，经研究，该岩石与围岩为沉积接触关系而非侵入接触关系，具变余斑状结构和变余流纹构造，该石英角斑岩成因的确定，为所赋存的地层组更名为观音崖组提供了重要依据。     

洋壳、海水、大气间的相互作用——关于厄尼诺成因的探讨

本文通过海底火山和海底水热活动对海温影响实例,指出海水温度不仅受大气状态的影响,而且还受海洋地壳热力状态的影响。在对海温变化的研究中,除考虑海气间的相互作用外,洋壳对海温的影响也是不可忽视的。对全球气候有重大影响的厄尼诺事件可能是洋壳、海水、大气相互作用的结果。     

火山喷发对气候影响信号的检测

该文从时序叠加和序列分析两个方面系统地评述了近年来火山活动影响气候的研究进展和代表性工作。给出了火山活动特征，如火山喷发强度、喷发位置和季节等对气候影响的时空分布规律。讨论了与之有关的几个重要问题，如火山指标，火山活动影响气候的途径及其和ENSO的联系等。最后指出了今后研究的几个方向。     

火山活动对气候影响的数值模拟研究

文章系统地总结了火山活动对气候影响的数值模拟研究，主要结论如下:近百年至千年的气候变化和火山活动关系密切，强火山喷发可造成平流层4℃以上的增温和地表年、月平均温度约0.4℃、1℃的下降。地表温度下降的时空分布受许多因素的影响，如火山喷发特征（包括喷发位置、季节、强度等）；海陆分布；火山气溶胶的光学特性；及其由直接辐射强迫引起的经向潜热输送的变化等等。同时还回顾了1991年皮纳图博喷发的有关研究及其对全球气候的可能影响的数值模拟工作。     

GROUND-BASED REMOTE SENSING OF THE SIZE DISTRIBUTION OF PINATOBU''''S VOLCANIC CLOUD

In this paper,data of solar direct spectral radiance observation in summer and autumn of 1990 and 1991 were usedto derive the average atmospheric extinction spectra for very clear days each year.The difference of these two extinctionspectra is obvious and considered as the contribution of volcanic cloud resulting from Pinatobu's volcanic eruption inmiddle June of 1991.This average size distribution of volcanic cloud was retrieved from the difference spectra and givenin this paper which will be useful for estimation and modeling of the effects of volcanic eruption.