月球火山碎屑堆积物光谱研究

月球的火山作用是月球的重要内生地质过程,反映了月球的内部演化。由爆发式火山作用形成的月球火山碎屑堆积物（LPD）代表了比月海玄武岩更深部的物质,是月球探测的优先目标之一。反射光谱是研究月球火山碎屑堆积物、在全球尺度上区分月球爆发式火山与溢流式火山的重要手段。文中选取29个已经确认的火山碎屑堆积物并结合模拟月球玻璃样品开展光谱学研究,建立了富玻璃的LPD光谱识别指标。根据模拟月球玻璃的铁钛含量与其1 μm处吸收特征的关系比较了富玻璃火山碎屑堆积的相对铁钛含量,为今后提高月球火山碎屑堆积物的铁钛反演精度提供思路。研究结果表明,在这29个火山碎屑堆积中,Sulpicius Gallus、Gauss、Walther A、Birt E和Aristarchus是较为富玻璃的火山碎屑堆积。Aristarchus、Sulpicius Gallus和Birt E的钛含量低于Walther A、Gauss,Birt E, 1 μm左吸收肩偏短波方向,1 μm吸收深度较浅,这可能因为Birt E具有异常低的Fe含量,或者其光学成熟度较高。鉴于火山碎屑堆积物重要意义,其是未来月球采样的较佳候选地区。     

当代火山喷发碎屑堆积物的研究进展及其主要类型

火山喷发碎屑堆积物主要分为：火山喷发空中降落堆积物、火山碎屑、流状堆积物、火山泥流堆积物和火山基浪堆积物。简述了这些火山碎屑堆积物的成因及主要特征。     

火山碎屑岩的百年研究

火山碎屑岩是爆破性火山喷发行为的直接产物,不同的碎屑成分、粒度及结构反映了不同岩相的堆积动力学过程,对火山碎屑岩岩石学和岩相组合的研究发展成了以物理火山学为代表的现代火山学研究体系。作为火山爆发碎屑物质的集合,其中不同成因类型的火山碎屑物往往可以直接对应不同阶段火山作用动力学参数特征。火山碎屑物3个最基本的堆积物成因类型是火山碎屑降落物、火山碎屑流和火山碎屑涌浪。火山喷发时碎屑化过程主要涉及挥发分的出溶和岩浆碎屑化过程以及不同火山流体内部的碎屑化过程。对于岩浆喷发、射汽岩浆喷发以及射汽喷发的直接产物,火山碎屑岩在组成上都包含了岩浆破碎的同源碎屑、火山通道裹进的异源碎屑以及火山流体在地表流动时捕获的表生碎屑。火山碎屑定义为爆破性火山喷发的直接行为产物,而包括坡移、滑坡体、火山泥石流等火山降解过程的表生碎屑与熔岩流在自生、淬碎碎屑化过程产生的碎屑则被定义为火山质碎屑。火山岩岩相的建立,为20世纪80年代后期向火山学研究阶段的转变奠定了基础。在地质研究的基础上探索火山活动过程和控制机制的经验模型、实验模拟和数值模拟研究,其中流体动力学的介入对理解火山喷发的基本过程具有里程碑式的推动意义。由此形成的火山学是研究火山与火山喷发的形成机理、喷发过程和产物特性的科学。     

火山碎屑岩的百年研究

火山碎屑岩是爆破性火山喷发行为的直接产物,不同的碎屑成分、粒度及结构反映了不同岩相的堆积动力学过程,对火山碎屑岩岩石学和岩相组合的研究发展成了以物理火山学为代表的现代火山学研究体系。作为火山爆发碎屑物质的集合,其中不同成因类型的火山碎屑物往往可以直接对应不同阶段火山作用动力学参数特征。火山碎屑物3个最基本的堆积物成因类型是火山碎屑降落物、火山碎屑流和火山碎屑涌浪。火山喷发时碎屑化过程主要涉及挥发分的出溶和岩浆碎屑化过程以及不同火山流体内部的碎屑化过程。对于岩浆喷发、射汽岩浆喷发以及射汽喷发的直接产物,火山碎屑岩在组成上都包含了岩浆破碎的同源碎屑、火山通道裹进的异源碎屑以及火山流体在地表流动时捕获的表生碎屑。火山碎屑定义为爆破性火山喷发的直接行为产物,而包括坡移、滑坡体、火山泥石流等火山降解过程的表生碎屑与熔岩流在自生、淬碎碎屑化过程产生的碎屑则被定义为火山质碎屑。火山岩岩相的建立,为20世纪80年代后期向火山学研究阶段的转变奠定了基础。在地质研究的基础上探索火山活动过程和控制机制的经验模型、实验模拟和数值模拟研究,其中流体动力学的介入对理解火山喷发的基本过程具有里程碑式的推动意义。由此形成的火山学是研究火山与火山喷发的形成机理、喷发过程和产物特性的科学。     

基于多源数据的月球大地构造纲要图编制: 以LQ-4地区为例

月球表面的地质构造要素主要包括环形构造、线性构造、地体构造及大型盆地构造等。月球大地构造纲要图从物质组成、构造要素、构造单元上对月表的构造状态进行全面的梳理、统计和分析。利用CE 1 CCD 2C像数据、LROC宽视角影像数据、CE 1 IIM 2C干涉成像光谱仪数据、Clementine紫外可见光影像数据、LOLA激光高度计数据识别月球表面各类矿物组分、线形构造、环形构造、火山构造和穹窿构造以及确定构造要素和构造单元的时代、古老撞击坑和大型盆地边界以及对月球表面撞击坑形态、大小、分布、密度及月球断裂和环形影像解译,充分认识月表基本情况,精细划分月表构造地貌单元,综合利用上述分析结果与国际上研究的进展,确定大地构造区划的基本原则,厘定月表重大构造事件与演化序列。依据岩石、月壤、构造地貌与构造形迹的综合分类,拟定大地构造区划的图例、图识规范,确定不同类型环形构造影像、线性构造影像、高地、盆地和月海等大地构造单元,进而编制大地构造区划图,并对重点区域构造形迹进行研究。虹湾区域(LQ 4)月球数字构造编图研究,充分借鉴国际行星地质编图的已有技术标准和规范,结合国内数字地质编图的技术标准和规范,建立了中国自己的月球与行星地质编图标准、规范和制图流程,也为最终完成月球大地构造区划提供地貌和构造方面的基础信息。     

长白山天池地区全新世以来火山活动及其特征

长白山火山全新世规模最大的喷发活动发生在公元1199-1200年,即800年前的大爆发,被确定为普林尼或布里尼(Plinian)式喷发。这次大爆发形成体积巨大的、分布广泛的以空中降落堆积物为主的火山喷发碎屑堆积物,在长白山火山周围,远至日本都留下了地质记录。文章辨认并划分了这次大爆发火山碎屑物的成因类型:火山喷发空中降落堆积物(airfalltephra)、火山碎屑流(pyroclasticflow)状堆积物和火山泥流(lahar)堆积物,并且点、面结合,近、远和国内、国外兼顾,分析了这些火山碎屑物的主要特征、分布和相互关系,进而确定这些火山碎屑物分别属于两次普林尼式爆发。第1次(早期)普林尼式爆发称赤峰期,火山喷发模式为:普林尼式喷发柱(赤峰空落浮岩层)-火山碎屑流(长白山火山碎屑流层),随即主要由火山碎屑流诱发火山泥流(二道白河火山泥流层);第2次(晚期)普林尼式爆发称园池期,喷发模式为:普林尼式喷发柱(园池空落浮岩火山灰层)-火山碎屑流(冰场火山碎屑流层)。在层序上将气象站期碱流岩置于800年前大爆发火山碎屑物之下是正确的,其时代为晚更新世-全新世早期。     

月表典型区撞击坑形态分类及分布特征

月球表面环形构造主要有撞击坑、火山口和月海穹窿3种,其中撞击坑分布最广泛,是研究月表环形构造的主要内容。由于月表撞击坑数量大、种类多及其形成伴随着整个月球地质的演化过程,因此这种月表地形地貌比较完整地记录了月球表面地貌随时间的改造过程以及改造类型。文中通过研究撞击坑遥感影像及形貌特征,总结归纳为简单型、碗型、平底型、中央隆起型、同心环型、复杂型及月海残留型7种撞击坑类型,用来描述月表典型区域撞击坑的形态特征。从结构和物质两方面进行了月表典型区域撞击坑的形态地貌参数提取,综合利用嫦娥一号CCD 影像数据、LROC数据,得到了该区域撞击坑形态数据(坑底、坑唇、坑壁、坑缘、溅射物覆盖层、中央峰)和形态测量数据(直径、深度、地理位置)。研究发现,LQ 4地区的撞击坑分布可分为月陆区和月海区,月陆区的撞击坑多以中小型撞击坑为主,其分布密度极高,形成年代较早,月海区撞击坑多为年轻的撞击坑,分化程度较低,分布密度也较低。     

大兴安岭哈拉哈河—淖尔河地区第四纪火山活动初步研究

大兴安岭中部哈拉哈河-淖尔河地区受基底断裂控制,发育28座第四纪火山,这些火山总体呈北东向带状分布。研究区第四纪火山岩分布面积约1000km^2,岩性主要为碱性玄武岩。根据喷发时代和火山地质特征,这里的火山大体可分为更新世和全新世两期。按照火山作用方式不同,区内火山可分为岩浆成因和射汽岩浆成因两类：前者活动产物主要包括火山碎屑锥、碎屑席、熔岩流,其中发育结壳熔岩、渣状熔岩、块状熔岩,以及喷气锥、熔岩冢等火山地质现象;后者产物主要是射汽岩浆喷发形成的基浪堆积物,其中发育大型平行层理及交错层理。不同的火山作用形成了火山口湖、低平火山口湖、火山堰塞湖和塌陷熔岩湖四种不同规模与形态特征的湖泊,这种水火相容的火山地质现象为阿尔山火山温泉国家地质公园增添了景观。     

吉林龙岗火山群火山碎屑基浪堆积特征与成因机理

吉林龙岗火山群火山碎屑基浪堆积是中国少数保存较好的、近代喷发的低平火山区之一。基于岩性、岩相与相序的识别与分析,火山碎屑基浪堆积序列由分选性和磨圆度较差的玄武质砂、砾和火山灰构成的毫米级-厘米级厚高频率韵律有序叠置而成,堆积物中发育大量的块状层理、似丘状层理、低角度板状交错层理、槽泊层理、平行层理、冲蚀槽等堆积构造。横向上低平火山由内至外其碎屑粒度、堆积构造、厚度存在着一定规律变化,与易混淆的火山岩区地面流水沉积和火山碎屑流堆积物存在明显的差别。岩浆射汽喷发晚期往往伴随斯通博利式喷发和夏威夷式熔岩流,三者构成一个完整火山活动旋回。     

老黑山火山碎屑降落堆积物研究

由中心式喷发形成的老黑山火山碎屑降落堆积物，主要是玄武质火山渣、火山弹、火山饼和少量岩屑。在火山爆发自身能量和北北西风的影响下，形成高耸的火山渣锥和向南南东展布的低缓的火山碎屑席地貌景观。区域上系统测量了火山碎屑席中火山碎屑的厚度、最大平均粒径、分选系数和中值粒径，均呈现规律性变化；剖面层序则反映老黑山火山经过两个大喷发阶段，多次脉动式喷发。经估算，老黑山火山碎屑席中火山碎屑量比火山渣锥中要少得多，老黑山火山碎屑属“建造火山锥”火山碎屑沉积。据投点，老黑山火山喷发属斯通博里型。老黑山、火烧山火山仍有再次爆发的可能。未来火山喷发的潜在危险主要来自火山喷发空落堆积物。老黑山、火烧山火山的南东、东和南，包括五大连池市在内有必要对未来火山爆发加以防范。     

Factors influencing the morphology of volcanic landforms: An earth-moon comparison

The products of volcanism on the Earth and Moon differ widely in terms of morphology, distribution, composition, and age. These differences result partly from the different thermal histories of the two bodies and partly through the different controls on volcanic eruption conditions. The controls of volcanism are here separated into three groups: (1) controls which remain constant on any one body but which differ from planet to planet: (2) parameters that are controlled by the rheology of the magma: and (3) controls which are intrinsic properties of individual eruptions and are themselves dependent upon the planetary and rheological variables. In terms of planetary variables it can be predicted that lunar volcanic morphologies are influenced by greater tephra range, hemispherical eruption clouds, lesser lithostatic pressures at corresponding depths, slower cooling, slower erosion, lesser horizontal stress differences, and no features typical of hydrosphere-magma interaction. In terms of rheology, the lunar eruptions had different rock and gas compositions, low yield strengths and viscosities, and high densities. Many lunar basalts appear to have been produced at high eruption rates, to have been derived from monogenetic volcanoes, and to have flowed in a turbulent manner.The weight of available data points to the vast majority of lunar craters being of impact origin though some dark halo craters, sinuous rille source craters, rimless pits, and craters atop domes and cones are undoubtedly of volcanic origin. Other impact craters appear to have been modified by volcanic events. Included within this latter group are the floor-fractured craters and the mare basins.Studies of volcanic morphologies on bodies other than the Earth may help isolate the effectiveness of those controls of volcanism which remain constant on any one body. Although volcanology has advanced substantially within the last few decades, much more detailed integrated scientific research is required before we are able to predict confidently the environmental hazards that result from volcanism and to understand the role of volcanism in planetary evolution.     

Note on the evolution of a Miocene composite volcano in an extensional setting, Zârand Basin (Apuseni Mts., Romania)

Bontâu is a major eroded composite volcano filling the Miocene Zârand extensional basin, near the junction between the Codru-Moma and Highi?-Drocea Mountains, at the tectonic boundary between the South and North Apuseni Mountains. It is a quasi-symmetric structure (16–18 km in diameter) centered on an eroded vent area (9×4 km), buttressed to the south against Mesozoic ophiolites and sedimentary deposits of the South Apuseni Mountains. The volcano was built up in two sub-aerial phases (14–12.5 Ma and 11–10 Ma) from successive eruptions of andesite lava and pyroclastic rocks with a time-increasing volatile budget. The initial phase was dominated by emplacement of pyroxene andesite and resulted in scattered individual volcanic lava domes associated marginally with lava flows and/or pyroclastic block-and-ash flows. The second phase is characterized by amphibole-pyroxene andesite as a succession of pyroclastic eruptions (varying from strombolian to subplinian type) and extrusion of volcanic domes that resulted in the formation of a central vent area. Numerous debris flow deposits accumulated at the periphery of primary pyroclastic deposits. Several intrusive andesitic-dioritic bodies and associated hydrothermal and mineralization processes are known in the volcano vent complex area. Distal epiclastic deposits initially as gravity mass flows and then as alluvial volcaniclastic and terrestrial detritic and coal filled the basin around the volcano in its western and eastern part. Chemical analyses show that lavas are calc-alkaline andesites with SiO₂ ranging from 56–61%. The petrographical differences between the two stages are an increase in amphibole content at the expense of two pyroxenes (augite and hypersthene) in the second stage of eruption; CaO and MgO contents decrease with increasing SiO₂. In spite of a ～4 Ma evolution, the compositions of calc-alkaline lavas suggest similar fractionation processes. The extensional setting favored two pulses of short-lived magma chamber processes.     

月球雨海北部陆地区域构造及其含义

月球雨海北部陆地是雨海多环盆地的第二层,平均高程约-1 km。DEM图像显示,大量来自虹湾与柏拉图月坑的掘积物使本地区高程变得非常不均一。统计了研究区内的月坑,并根据其深度与宽度之比(深宽比)将它们划分为4组。深宽比较小而扁率较大的月坑被认为是较古老的月坑。这些古老月坑分布于比较接近月海的位置。对研究区内线性构造的制图研究揭示了3个优选方位,分别是E—W、NEE—SWW和NW—SE向。这种分布样式与月球格子构造系统大致匹配,因而它们很可能形成于雨海事件之前。这些线性构造,包括断裂与月溪,在月海玄武岩泛滥时期为玄武质岩浆的侵入提供了大量通道。在研究区内一些地形较低的地点,玄武岩上侵并出露在月表,它们的FeO平均含量接近但是略低于月海玄武岩。总结了本地区的地质构造演化历史,并且推论月球上的确存在类月海的陆地。     

From seamount to oceanic island, Porto Santo, central East-Atlantic

The uplifted and deeply eroded volcanic succession of Porto Santo (central East-Atlantic) is the product of a wide spectrum of dynamic processes that are active in shoaling to emergent seamounts. Two superimposed lapilli cones marking the base of the exposed section are interpreted as having formed from numerous submarine to subaerial phreatomagmatic explosions, pyroclastic fragmentation being subordinate. The lower basaltic and the upper mugearitic to trachytic sections are dominated by redeposited tephra and are called 'lapilli cone aprons'. Vertical growth due to accumulation of tephra, voluminous intrusions, and minor pillowed lava flows produced ephemeral islands which were subsequently leveled by wave erosion, as shown by conglomerate beds. Periods of volcanic quiescence are represented by abundant biocalcarenite lenses at several stratigraphic levels. The loose tephra piles became stabilized by widespread syn-volcanic intrusions such as dikes and trachytic to rhyolitic domes welding the volcanic and volcaniclastic ensemble into a solid edifice. Shattering of a submarine extrusive trachytic dome by pyroclastic and phreatomagmatic explosions, accentuated by quench fragmentation, resulted in pumice- and crystal-rich deposits emplaced in a prominent submarine erosional channel. The dome must have produced an island as indicated by a collapse breccia comprising surf-rounded boulders of dome material. Subaerial explosive activity is represented by scoria cones and tuff cones. Basaltic lava flows built a resistant cap that protected the island from wave erosion. Some lava flows entered the sea and formed two distinct types of lava delta: 1. closely-packed pillow lava and massive tabular lava flows along the southwestern coast of Porto Santo, and 2. a steeply inclined pillow-hyaloclastite breccia prism composed of foreset-bedded hydroclastic breccia, variably-shaped pillows, and thin sheet flows capped by subhorizontal submarine to subaerial lava flows along the eastern coast of Porto Santo.The facies architectures indicate emplacement: 1. on a gently sloping platform in southwestern Porto Santo, and 2. on steep offshore slopes along high energy shorelines in eastern Porto Santo.Growth of the pillow-hyaloclastite breccia prism is dominated by the formation of foreset beds but various types of syn-volcanic intrusions contributed significantly. Submarine flank eruptions occurred in very shallow water on the flanks of the hyaloclastite prism in eastern Porto Santo. The island became consolidated by intrusion of numerous dikes and by emplacement of prominent intrusions that penetrate the entire volcanic succession. Volcanic sedimentation ended with the emplacement of a debris avalanche that postdates the last subaerial volcanic activity.     

Geoheritage values of one of the largest maar craters in the Arabian Peninsula: the Al Wahbah Crater and other volcanoes (Harrat Kishb, Saudi Arabia)

Al Wahbah Crater is one of the largest and deepest Quaternary maar craters in the Arabian Peninsula. It is NW-SE-elongated, ～2.3 km wide, ～250 m deep and surrounded by an irregular near-perpendicular crater wall cut deeply into the Proterozoic diorite basement. Very few scientific studies have been conducted on this unique site, especially in respect to understanding the associated volcanic eruption processes. Al Wahbah and adjacent large explosion craters are currently a research subject in an international project, Volcanic Risk in Saudi Arabia (VORiSA). The focus of VORiSA is to characterise the volcanic hazards and eruption mechanisms of the vast volcanic fields in Western Saudi Arabia, while also defining the unique volcanic features of this region for use in future geoconservation, geoeducation and geotourism projects. Al Wahbah is inferred to be a maar crater that formed due to an explosive interaction of magma and water. The crater is surrounded by a tephra ring that consists predominantly of base surge deposits accumulated over a pre-maar scoria cone and underlying multiple lava flow units. The tephra ring acted as an obstacle against younger lava flows that were diverted along the margin of the tephra ring creating unique lava flow surface textures that recorded inflation and deflation processes along the margin of the post-maar lava flow. Al Wahbah is a unique geological feature that is not only a dramatic landform but also a site that can promote our understanding of complex phreatomagmatic monogenetic volcanism. The complex geological features perfectly preserved at Al Wahbah makes this site as an excellent geotope and a potential centre of geoeducation programs that could lead to the establishment of a geopark in the broader area at the Kishb Volcanic Field.     

Physical character of archean felsic volcanism in the vicinity of the Helen iron Mine,Wawa, Ontario,Canada

Archean felsic volcanic rocks form a 2000 m thick succession stratigraphically below the Helen Iron Formation in the vicinity of the Helen Mine, Wawa, Ontario. Based on relict textures and structures, lateral and vertical facies changes, and fragment type, size and distribution, the felsic volcanic rocks have been subdivided into (a) lava flows and domes (b) hyalotuffs, (c) bedded pyroclastic flows, (d) massive pyroclastic flows, and (e) block and ash flows.Lava flows and domes are flow-banded, massive, and/or brecciated and occur throughout the stratigraphic succession. Dome/flow complexes are believed to mark the end of explosive eruptive cycles. Deposits interpreted as hyalotuffs are finely bedded and composed dominantly of ash-size material and accretionary lapilli. These deposits are interlayered with bedded pyroclastic flow deposits and probably formed from phreatomagmatic eruptions in a shallow subaqueous environment. Such eruptions led to the formation of tuff cones or rings. If these structures emerged they may have restricted the access of seawater to the eruptive vent(s), thus causing a change in eruptive style from short, explosive pulses to the establishment of an eruption column. Collapse of this column would lead to the accumulation of pyroclastic material within and on the flanks of the cone/ring structure, and to flows which move down the structure and into the sea. Bedded pyroclastic deposits in the Wawa area are thought to have formed in this manner, and are now composed of a thicker, more massive basal unit which is overlain by one or more finely bedded ash units. Based on bed thickness, fragment and crystal size, type and abundance, these deposits are further subdivided into central, proximal and distal facies.Central facies units consist of poorly graded, thick (30–80 m) basal beds composed of 23–60% lithic and 1–8% juvenile fragments. These are overlain by 1–4 thinner ash beds (2–25 cm). Proximal facies basal beds range from 2–35 m in thickness and are composed of 15–35% lithic and 4–16% juvenile fragments. Typically, lithic components are normally graded, whereas juvenile fragments are inversely graded. These basal beds are overlain by ash beds (2–14 in number) which range from 12 cm to 6 m in thickness. Distal basal beds, where present, are thin (1–2 m), and composed of 2–8% lithic and 6–21% juvenile fragments. Overlying ash beds range up to 40 in number.The climax of pyroclastic activity is represented by a thick (1000 m) sequence of massive, poorly sorted, pyroclastic flow deposits which are composed of 5–15% lithic fragments and abundant pumice. These deposits are similar to subaerial ash flows and appear to mark the rapid eruption of large volumes of material. They are overlain by felsic lavas and/or domes. Periodic collapse of the growing domes produced abundant coarse volcanic breccia. The overall volcanic environment is suggestive of caldera formation and late stage dome extrusion.     

Lunar deposits of possible pyroclastic origin

Glass droplets of possible pyroclastic origin are present in the lunar regolith at the Apollo 11, 15, and 17 sites. The droplets may be derived from deposits, interbedded with mare lava flows, which have been partly mixed into the regolith by impact processes. Orange glass droplets from the Apollo 17 site (spheres, ovoids, broken droplets) are both chemically and texturally homogeneous and have rare olivine phenocrysts. None of the droplets contain shock damaged crystals which are common in glass produced during meteorite impacts. The droplets are similar to those formed in terrestrial lava fountains and are here interpreted as tephra.The homogeneous glass droplets sampled at the Apollo 11, 15 and 17 sites are located on or close to mare basin rims. Vents for the youngest mare lava flows, located near basin rims, have been identified photogeologically. Dark mantle deposits, interpreted as pyroclastic blankets in some locations, and numerous rules are also present on the mare surface, near basin rims. The glass droplets, having ages nearly contemporaneous with the associated mare lavas, may be concentrated locally near such vent areas. This association is in accordance with the limited extent of ash deposits from terrestrial lava fountains (? km from the vent).     

Formation of Subaqueous Felsic Domes and Accompanying Pyroclastic Deposits on the Foça Peninsula (Izmir,Turkey)

In western Anatolia, a thick volcanic succession of andesitic to rhyolitic lavas and volcaniclastic rocks crops out extensively. On Foça Peninsula, the westernmost part of the region, a dominantly rhyolitic sequence is exposed where massive rhyolites occur as dome or domelike stubby lava flows. These rhyolite domes vertically and laterally pass into blanketing volcaniclastic sequences. The gradational boundary relations and the facies characteristics of the surrounding volcaniclastic sequences indicate that the silicic domes directly intruded a subaqueous environment and were shattered upon sudden contact with water to form hyaloclastic blankets.

In and around these rhyolite domes, we have defined six different volcanic and volcaniclastic facies, consisting of: (1) massive rhyolite; (2) massive perlite; (3) hyaloclastic breccias; (4) rhyolite pumice and lithic fragment-bearing volcaniclastic rocks; (5) subaqueous welded ignimbrites; and (6) brecciated perlite. The massive rhyolite facies have distinct structures from the centers to the peripheries of the domes and stubby lava flows. Massive lava facies gradually pass into hyaloclastic breccias and massive perlite facies, indicating water-magma interaction during the emplacement. Phreatomagmatic explosive activity and doming caused the subaqueous pyroclastic flows on the flanks of the volcanic center. Welding in the upper parts of these pyroclastic flow deposits indicates the high-temperature emplacement of the pyroclastic material and relatively slow cooling caused by the cushioning effect of the gas-vapor mixture and rapid deposition of younger pyroclastic units.     

Merapi (Java,Indonesia): anatomy of a killer volcano

Merapi is Indonesia's most dangerous volcano with a history of deadly eruptions. Over the past two centuries, the volcanic activity has been dominated by prolonged periods of lava dome growth and intermittent gravitational or explosive dome failures to produce pyroclastic flows every few years. Explosive eruptions, such as in 2010, have occurred occasionally during this period, but were more common in pre‐historical time, during which a collapse of the western sector of the volcano occurred at least once. Variations in magma supply from depth, magma ascent rates and the degassing behaviour during ascent are thought to be important factors that control whether Merapi erupts effusively or explosively. A combination of sub‐surface processes operating at relatively shallow depth inside the volcano, including complex conduit processes and the release of carbon dioxide into the magmatic system through assimilation of carbonate crustal rocks, may result in unpredictable explosive behaviour during periods of dome growth. Pyroclastic flows generated by gravitational or explosive lava dome collapses and subsequent lahars remain the most likely immediate hazards near the volcano, although the possibility of more violent eruptions that affect areas farther away from the volcano cannot be fully discounted. In order to improve hazard assessment during future volcanic crises at Merapi, we consider it crucial to improve our understanding of the processes operating in the volcano's plumbing system and their surface manifestations, to generate accurate hazard zonation maps that make use of numerical mass flow models on a realistic digital terrain model, and to utilize probabilistic information on eruption recurrence and inundation areas.