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.     

LiDAR-based digital terrain analysis of an area exposed to the risk of lava flow invasion: the Zafferana Etnea territory, Mt. Etna (Italy)

The town of Zafferana Etnea, located on the southeastern slope of Mt. Etna volcano (Italy), has been repeatedly threatened by lava flows in recent centuries. The last serious threat occurred during the 1991–1993 eruption, when the lava front came to a halt only 1.7 km from the centre of town. Morphostructural data derived from light detection and ranging (LiDAR) surveys carried out on Etna in 2005 have enabled us to evaluate the risk of lava invasion in a section (16 km²) of the Zafferana Etnea territory. Qualitative and quantitative results are obtained combining the information derived from LiDAR analysis with geological, morphological and structural data using geographic information systems technology (GIS). The study quantifies in unprecedented detail the areal extent and volume of forested and urban areas and its degree of exposure to different levels of hazard from future lava invasion. Nearly 52% of the urban texture fall into areas of moderate to high risk from lava invasion. Future land use planning should take these findings into account and promote new development preferentially in areas of lower risk.     

Effusive Activity at Mount Etna Volcano (Italy) During the 20th Century: A Contribution to Volcanic Hazard Assessment

Mount Etna is an open conduit volcano, characterised by persistent activity, consisting of degassing and explosive phenomena at summit craters, frequent flank eruptions, and more rarely, eccentric eruptions. All eruption typologies can give rise to lava flows, which represent the greatest hazard by the volcano to the inhabited areas. Historical documents and scientific papers related to the 20th century effusive activity have been examined in detail, and volcanological parameters have been compiled in a database. The cumulative curve of emitted lava volume highlights the presence of two main eruptive periods: (a) the 1900–1971 interval, characterised by a moderate slope of the curve, amounting to 436 × 10⁶ m³ of lava with average effusion rate of 0.2 m³/s and (b) the 1971–1999 period, in which a significant increase in eruption frequency is associated with a large issued lava volume (767 × 10⁶ m³) and a higher effusion rate (0.8 m³/s). The collected data have been plotted to highlight different eruptive behaviour as a function of eruptive periods and summit vs. flank eruptions. The latter have been further subdivided into two categories: eruptions characterised by high effusion rates and short duration, and eruptions dominated by low effusion rate, long duration and larger volume of erupted lava. Circular zones around the summit area have been drawn for summit eruptions based on the maximum lava flow length; flank eruptions have been considered by taking into account the eruptive fracture elevation and combining them with lava flow lengths of 4 and 6 km. This work highlights that the greatest lava flow hazard at Etna is on the south and east sectors of the volcano. This should be properly considered in future land-use planning by local authorities.     

内蒙锡林浩特鸽子山火山地质研究

鸽子山火山位于内蒙古自治区锡林浩特市东南,处于大兴安岭-大同新生代火山喷发带中段,是锡林浩特-阿巴嘎火山群中保存最为完好的一座玄武质火山。火山喷发物的分布面积约55km²,主要为降落火山渣、溅落熔结火山碎屑岩和熔岩流,成分主要为碧玄岩,晚期有少量的橄榄拉斑玄武岩,碧玄岩中含有较多二辉橄榄岩包体和辉石及歪长石巨晶。火山由锥体、熔岩流和火山碎屑席组成,锥体由早期的降落锥和晚期溅落锥复合而成。火山口经历多次塌陷而成为破火口。锥体西侧及北东侧出露两个仍保留了原始形态的熔岩溢出口,熔岩流类型为结壳熔岩,由多个岩流单元组成,局部地区的熔岩流中发育较多保存完好的喷气锥、喷气碟或喷气塔。火山碎屑席主要分布在锥体的东侧,厚度由锥体向外逐渐减薄。火山活动可分为早、晚两个阶段,早期为爆破式喷发,形成火山渣锥和碎屑席,属亚布里尼型喷发,晚期主要为溢流式喷发,形成溅落锥和大规模熔岩流,其活动时代为晚更新世末-全新世。     

中国火山灾害区划研究历史回顾与未来展望

火山灾害区划是防御和减轻火山灾害的一种有效的方法.以中国境内规模最大、喷发危险性最高、潜在火山灾害最强的长白山天池火山为例,回顾我国火山灾害区划研究历史,讨论典型火山喷发活动引起的主要火山灾害类型、成灾机制和灾害效应,总结不同历史阶段各种不同类型火山灾害区划图的优缺点,并结合目前国际上火山灾害区划的研究现状和编图技术,对我国未来编制具有概率含义的火山灾害区划图的思路提出展望.     

A new map of the lava flow field of Nyamulagira (D.R. Congo) from satellite imagery

Nyamulagira (3058 m a.s.l.), a volcano of the Virunga volcanic province in the western branch of the East African Rift, is Africa’s most active volcano with one eruption every 2–4 years. It represents a hazard for the Virunga National Park and its vicinity. Despite such a frequent activity, Nyamulagira remains poorly studied. The only existing volcanological map was produced in the sixties by Thonnard et al. (1965). The occurrence of 19 eruptions since its publication makes it obsolete. In the present study we mapped the Nyamulagira lava flows from 1938 up to the last eruption to date in 2010 using optical (Landsat, ASTER) and radar (ENVISAT-ASAR, ERS, JERS) imagery. The results are integrated into a Geographical Information System (GIS) and coupled with additional data sources. GIS use makes the new database a flexible – and easy-to-update – tool for scientific purposes as well as for risk, environmental and humanitarian management. Here a new lava flow map was produced. Volumes of the successive lava flows and affected areas of the Virunga National Park were estimated.     

Exploring lava‐flow hazards at Pico Island,Azores Archipelago (Portugal)

Pico, the youngest island of the Azores Archipelago (Portugal), is characterized by a central volcano and a 30‐km‐long fissure zone. Its eruption rate is the highest of the Azores islands, with more than 35 eruptions in the last 2000 years. Here, we estimate the lava‐flow hazard for Pico Island by combining the vent opening probability derived from the spatial distribution of eruptive fissures, the classes of expected eruptions inferred from the physical and chemical characteristics of historical eruptions, and the lava‐flow paths simulated by the MAGFLOW model. The most likely area to host new eruptions is along a WNW–ESE trend centred on the central volcano, with the highest hazard affecting the two main residential zones of Lajes do Pico and Madalena. Our analysis is the first attempt to assess the lava‐flow hazard for Pico Island, and may have important implications for decision‐making in territorial management and future land‐use planning.     

The development of compound lava fields at Mount Etna

The formation of compound lava fields is a common feature of basaltic volcanic areas such as Mount Etna and Hawaii. It is generally promoted by a breakin-slope which results into a decrease of the mean flow velocity and the rapid adjustment to new rheological conditions. In fact, on a steep slope the flow is generally focused into long-lived lava tubes or channels. On the contrary, in correspondence of a flat ground the propagation of a lava field is guaranteed by the continuos opening of new ephemeral vents, and by the overlapping of lava lobes or tongues the length of which is order of 10⁻¹−10² m. At Mount Etna these flow units show a complex structure which reflects the existence of a central plug zone and lateral shear zones, and an internal structure characterized by a succession of lava layers separated by gas-rich layers which occur in correspondence of vesicle alignments. Such internal structure insulates the active moving core and preserves high lava temperatures, favoring the advancement of the flow units. The evolution of a compound lava field may be thus envisaged as a spatial and temporal succession of lava tubes. An example of this situation may be found in the 1983 and 1991–93 Etnean eruptions, where the propagation of long-lived compound lava fields through a great number of small subarterial flow units gave origin to a source of natural hazards for some of the communities living on the flanks of the volcano. The detailed study of the structure of the described lava flows helps understand their emplacement dynamics and evaluate the associated volcanic, hazard.     

长白山火山灾害及其对大型工程建设的影响

长白山火山是世界著名的活火山,历史时期有过多次喷发,有再次爆发的危险.长白山火山最大的一次爆发发生在公元1199-1200年,这次大爆发的火山灰最远到达距其1 000km远的日本北部.依据这次大爆发由火山喷发空中降落堆积物、火山碎屑流和火山泥流造成的巨大火山灾害,预测了长白山火山未来爆发火山灾害的类型、强度和范围,并编制了长白山火山未来爆发火山喷发空中降落堆积物灾害预测图、火山碎屑流灾害预测图和火山泥流灾害预测图.该研究可预防和减轻火山灾害,指导核电站等大型工程选址.     

全球主要火山灾害及其分布特征

本文研究了火山灾害各种致灾因子的物理过程和灾害特点,根据文献中记载的全球火山灾害,在进行火山灾害分区研究的基础上,研究了全球火山灾害分布特征.全球主要的火山灾害分布在8个主要区域.有记载的火山灾害在热带占73%,远高于火山喷发分布于热带区的比例.全球两个最强烈的火山灾害分布区都是围绕着位于板块结合部表现为复杂构造结的班达海和加勒比海,而且每一个灾害区都有3条分支.热带区第3个灾害区为中非区,地幔上隆是这里主要的动力学背景.本文还研究了1700年以来火山灾害时间分布特征,以及1993年以来各种火山灾害发生频次.     

Characteristics of the 2000 fissure eruption and lava flow fields at Mount Cameroon volcano,West Africa: a combined field mapping and remote sensing approach

This study focuses on the compound pahoehoe lava flow fields of the 2000 eruption on Mount Cameroon volcano, West Africa and it comprehensively documents their morphology. The 2000 eruption of Mount Cameroon took place at three different sites (sites 1, 2 and 3), on the southwest flank and near the summit that built three different lava flow fields. These lava flow fields were formed during a long‐duration (28th May–mid September) summit and flank eruption involving predominantly pahoehoe flows (sites 2 and 3) and aa flows (site 1). Field observations of flows from a total of four cross‐sections made at the proximal end, midway and at the flow front, have been supplemented with data from satellite imagery (SRTM DEM, Landsat TM and ETM+) and are used to offer some clues into their emplacement. Detailed mapping of these lava flows revealed that site 1 flows were typically channel‐fed simple aa flows that evolved as a single flow unit, while sites 2 and 3 lava flow fields were fed by master tubes within fissures producing principally tube‐fed compound pahoehoe flows. Sites 2 and 3 flows issued from ∼ 33 ephemeral vents along four NE–SW‐trending faults/fissures. Pahoehoe morphologies at sites 2 and 3 include smooth, folded and channelled lobes emplaced via a continuum of different mechanisms with the principal mechanism being inflation. The dominant structural features observed on these flow fields included: fissures/faults, vents, levees, channels, tubes and pressure ridges. Other structural features present were pahoehoe toes/lobes, breakouts and squeeze‐ups. Slabby pahoehoe resulting from slab‐crusted lava was the transitionary lava type from pahoehoe to aa observed at all the sites. Transition zones correspond to slopes of > 10°. Variations in flow morphology and textures across profiles and downstream were repetitive, suggesting a cyclical nature for the responsible processes. Copyright © 2010 John Wiley & Sons, Ltd.     

Hazard assessment at San Martín volcano based on geological record, numerical modeling, and spatial analysis

The San Martín shield volcano, located in the Los Tuxtlas Volcanic Field, has experienced effusive shield-building activity, as well as explosive eruptions, as evidenced by direct observations during the last eruption in 1793. The threat to the surrounding villages consists principally of lahars, especially because of the tropical climate in the region. Ash fallout and lava flows represent additional hazards. In addition, the surrounding Quaternary monogenetic field includes more than 300 scoria cones and about 40 explosion craters (mainly maars) that also represent a hazard source. In the present study we constructed hazard maps using field data, orthophotos, spatial analysis, and specialized software (LAHARZ and HAZMAP) to deliminate lahar inundation zones, areas that could potentially be affected by ash fallout (including the evaluation of houses prone to roof collapse due to ash load), and the most susceptible areas for hosting future monogenetic vent formation.     

Evolution of Irruputuncu volcano,Central Andes,northern Chile

The Irruputuncu is an active volcano located in northern Chile within the Central Andean Volcanic Zone (CAVZ) and that has produced andesitic to trachy-andesitic magmas over the last ∼258 ± 49 ka. We report petrographical and geochemical data, new geochronological ages and for the first time a detailed geological map representing the eruptive products generated by the Irruputuncu volcano. The detailed study on the volcanic products allows us to establish a temporal evolution of the edifice. We propose that the Irruputuncu volcanic history can be divided in two stages, both dominated by effusive activity: Irruputuncu I and II. The oldest identified products that mark the beginning of Irruputuncu I are small-volume pyroclastic flow deposits generated during an explosive phase that may have been triggered by magma injection as suggested by mingling features in the clasts. This event was followed by generation of large lava flows and the edifice grew until destabilization of its SW flank through the generation of a debris avalanche, which ended Irruputuncu I. New effusive activity generated lavas flows to the NW at the beginning of Irruputuncu II. In the meantime, lava domes that grew in the summit were destabilized, as shown by two well-preserved block-and-ash flow deposits. The first phase of dome collapse, in particular, generated highly mobile pyroclastic flows that propagated up to ∼8 km from their source on gentle slopes as low as 11° in distal areas. The actual activity is characterized by deposition of sulfur and permanent gas emissions, producing a gas plume that reaches 200 m above the crater. The maximum volume of this volcanic system is of ∼4 km³, being one of the smallest active volcano of Central Andes.     

Volcanic hazards in the surroundings of Pico de Orizaba,eastern Mexico

Volcanic hazards from Pico de Orizaba volcano are presented here tor the first time. Some 1.3 million people live within the hazard zone, which in the most severe case would encompass the Mexican Gulf coast, east of the volcano. Three major cities located in the eastern part of the hazard zone account for 800 000 of this population and about 200 000 people live within a 20 km radius of the volcano. Probability calculations are presented as an attempt to quantify the hazards in the surroundings of the volcano. Such quantification can be of use in planning for future land use within the hazard zones.A zone of about 10 km radius centred on the top crater is a high hazard zone for gravity-driven flows and fallout ejecta. For large volume eruptions, the radius could be extended to 120 km to the east and 60 km to the west. The asymmetrical distribution is related to the topography of the volcano. Hazards from Pyroclastic-fall deposits are principally to the west of the volcano, since easterly winds are dominant in the area lava-flow hazards are greatest within a 10 km radius from the summit crater. Pyroclastic flow hazards are high up to 20 km from the volcano summit.In the case of reactivation of the volcano, melting of a glacier covering the summit of Pico de Orizaba having a volume equivalent to some 45 × 10⁹ litres of water, would produce lahars which would descend the flanks of the volcano.     

Volcanic Risk Assessment and Mapping in the Vesuvian Area Using GIS

This paper assesses the risk to people and property from lava flow hazard in the Vesuvian area of Italy using a Geographical Information System (GIS). The intense urbanisation and dense population near Mt. Vesuvius make the area very hazardous. Due to the large amount of available data, GIS is an essential tool to facilitate risk evaluation and constant monitoring of the zone. This analysis is based mainly on a lava flow hazard map of Mt. Vesuvius, determined from volcanic activity between 1631 and 1944. A land-use zonation map of the area was created in order to show areal distribution of the resources, built-up centres and population. For each of the 17 municipalities in the area, demographic and urban data were entered into the GIS database and linked to each appropriate geographic unit in order to create a set of reference maps at the 1:50 000 scale. The lava flow hazard map was overlain on the land use map, and spatial and numerical information of risk were extracted from the resulting maps.     

Types and Characteristics of Volcanostratigraphic Boundaries and?Their Oil-Gas Reservoir?Significance

Just like in sedimentary stratigraphy, the volcanostratigraphic boundary is an important factor for constructing volcanostratigraphic framework. The fundamental factor of volcanostratigraphic boundaries is to classify the types and define their characteristics. Based on field investigation and cross-wells section analysis of Mesozoic volcanostratigraphy in NE China, 5 types of volcanostratigraphic boundaries have been recognized, namely eruptive conformity boundary(ECB), eruptive unconformity boundary(EUB), eruptive interval unconformity boundary(EIUB), tectonic unconformity boundary(TUB) and intrusive contacts boundary(ICB). Except ICB, the unconformity boundaries can be divided into angular unconformity and paraconformity. The time spans and signs of these boundaries are analyzed by using age data of some volcanic fields that have been published. The time spans of ECB and EUB are from several minutes to years. In lava flows, cooling crust is distributed above and below ECB and EUB; in pyroclastic flows, airfalls and lahars, a fine layer below these boundaries has no discernable erosion at every part of the boundary. EUB may be curved or cross curved and jagged. The scale of ECB/EUB is dependent on the scale of lava flow or pyroclastic flows. The time span of EIUB is from decades to thousands of years. There is also weathered crust under EIUB and sedimentary rock beds overlie EIUB. In most instances, weathered crust and thin sedimentary beds are associated with each other laterally. The boundary is a smooth curved plane. The scale of EIUB is dependent on the scale of the volcano or volcano groups. The characteristics of TUB are similar to EIUB’s. The time interval of TUB is from tens of thousands to millions of years. The scale of TUB depends on the scale of the basin or volcanic field. Both the lab data and logging data of wells in the Songliao Basin reveal that the porosity is greatly related to the boundaries in the lava flows. There is a high-porosity belt below ECB, EUB or EIUB, and the porosity decreases when it is apart from the boundary. The high-porosity belt below ECB and EUB is mainly contributed by primary porosity, such as vesicles. The high-porosity belt below EIUB is mainly contributed by primary and secondary porosity, such as association of vesicles and spongy pores, so the area near the boundary in lava flows is a very important target for reservoirs.     

Large-scale assessment of avalanche and debris flow hazards in the Sakhalin region,Russian Federation

We explore the challenges of avalanche and debris flow hazard assessment for urban areas exposed in the Sakhalin region. Avalanches are a threat to more than 60 settlements in the region and debris flows to more than 30. Data are provided for avalanche and debris flow events that occurred in the Sakhalin region between 1928 and 2015. In this paper, the method for the design of hazard maps for snow avalanches and debris flows is described, providing the starting point for any planning constraints in general settlement planning schemes. These maps further allow conducting an assessment of avalanche and debris flow risk within a short time period for a larger territory and at minimum cost.

     

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.     

长白山天池火山近代喷发中气象站组熔岩—碎屑岩流研究

中晚全新世以来,长白山天池火山的活动多为爆炸性喷发和形成火山碎屑流,熔岩流出较少,气象站组熔岩—碎屑岩流则是为数不多的熔岩溢流活动之一,它是天池火山一个寄生火山的喷发产物。气象站组熔岩—碎屑岩流的岩性为碱流岩质,岩浆粘度大,流动缓慢。据研究其喷发时间大约4 ka BP,应属天池火山的近代喷发产物。     

松辽盆地改造残留的古火山机构与现代火山机构的类比分析

现代火山机构形态有盾状、锥状和穹状,可按喷发样式进一步划分为7种类型。据此分类,在松辽盆地周缘剖面及其北部徐家围子断陷区可识别出4类火山机构：盾状火山机构,由喷溢相熔岩组成,可夹有薄层爆发相火山碎屑岩;层火山机构,由互层的熔岩与火山碎屑岩组成,喷溢相与爆发相交替的序列明显;火山碎屑锥,几乎全部由火山碎屑（熔）岩组成,爆发相为主;熔岩穹丘由高粘度的流纹质、英安质熔岩堵塞火山口后缓慢挤出形成,喷溢相和侵出相发育,兼有火山通道相。盆地内埋藏火山机构最小坡度为3°,最大坡度为25°,底部直径为2～14 km,分布面积为4～50 km²,火山岩厚度为100～600 m;总体上呈现出数目多、个体规模小、受区域大断裂控制、具裂隙式-多中心喷发、彼此相互叠置的特征。火山岩岩性和岩相是控制松辽盆地古火山机构类型及形态的主要因素。