Fluorine speciation in topsoils of three active volcanoes of Sicily (Italy)

Fluorine is one of the many environmental harmful elements released by volcanic activity. The content of total oxalate-extractable and water-extractable fluorine was determined in 96 topsoils of three active volcanic systems of southern Italy (Mt Etna, Stromboli and Vulcano). Total fluorine (F) content (F _TOT) ranges from 112 to 7,430 mg kg⁻¹, F extracted with oxalate (F _OX) ranges from 16 to 2,320 mg kg⁻¹ (2–93% of F _TOT) and F extracted with distilled water ( ) ranges from 1.7 to 159 mg kg⁻¹ (0.2–40 % of F _TOT). Fluorine in the sampled topsoils derives both from the weathering of volcanic rocks and ashes and from the enhanced deposition due to volcanic gas emissions either from open-conduit passive degassing (Mt Etna and Stromboli) or from a fumarolic field (Vulcano). Fluorine accumulation in the studied soils does not generally present particular environmental issues except for a few anomalous sites at Vulcano, where measured contents could be dangerous both for vegetation and for grazing animals.     

H2S fluxes from Mt. Etna, Stromboli, and Vulcano (Italy) and implications for the sulfur budget at volcanoes

We present here new measurements of sulfur dioxide and hydrogen sulfide emissions from Vulcano, Etna, and Stromboli (Italy), made by direct sampling at vents and by filter pack and ultraviolet spectroscopy in downwind plumes. Measurements at the F0 and FA fumaroles on Vulcano yielded SO₂/H₂S molar ratios of ≈0.38 and ≈1.4, respectively, from which we estimate an H₂S flux of 6 to 9 t · d⁻¹ for the summit crater. For Mt. Etna and Stromboli, we found SO₂/H₂S molar ratios of ≈20 and ≈15, respectively, which combined with SO₂ flux measurements, suggest H₂S emission rates of 50 to 113 t · d⁻¹ and 4 to 8 t · d⁻¹, respectively. We observe that “source” and plume SO₂/H₂S ratios at Vulcano are similar, suggesting that hydrogen sulfide is essentially inert on timescales of seconds to minutes. This finding has important implications for estimates of volcanic total sulfur budget at volcanoes since most existing measurements do not account for H₂S emission.     

Italian active volcanoes

The eruptive histories, styles of activity and general modes of operation of the main active Italian volcanoes,Etna, Vulcano, Stromboli, Vesuvio, Campi Flegrei and Ischia, are described in a short summary.     

Seismic assessment of phreatic-explosion hazard at ‘La Fossa’ Volcano (Island of Vulcano,Italy)

Active volcanic areas are sometimes affected by phreatic eruptions, which are explosions due to the outbreak of a confined pocket of steam and gas without the direct involvement of molten magma. Eruptive activity at La Fossa Volcano, Island of Vulcano (Italy), typically starts with a phreatic explosion, continues as phreatomagmatic and turns into a late magmatic stage, depending on the reduction in the efficiency of magma-water interaction. The present risk is mainly related to a village located at the very foot of the active volcanic cone, which in summer seasons is inhabited by more than 10,000 people. Because the last eruptive episode occurred in 1888–1890, when no local instrumental control was performed, the scientific community does not have any information about the seismic phenomena which could precede the initial phreatic blast. Inferences from similar monitored volcanoes, which awakened in the last few years after more or less long quiescence, are therefore made to tentatively depict possible pre-eruptive seismic scenarios and also to evaluate the most appropriate surveillance and alert criteria to adopt. Appreciable signs of volcanic unrest have been detected in recent years, mainly related to modifications in the physical and chemical features of fumarolic fluids discharged at the active crater. Following the classification of local seismic shocks, the recording oflong-period events (peak frequency 2 Hz) should be taken into account as a realistic seismic warning of volcanic hazard enhancement. A likely short-term seismic precursor may be finally given by the appearance of the so-calledbanded tremor, a seismic signal likely produced by intermittent hydrothermal boiling accompanying the hydraulic fracturing of rocks at the top of a pressurized aquifer. Real-time recognition of tremor can be therefore very useful to avoid, at least, injuries to volcanologists and visitors working or staying on the most dangerous sectors of the volcano.     

Geochemical similarities between the Vesuvius, Phlegraean Fields and Stromboli Volcanoes: petrogenetic, geodynamic and volcanological implications

Summary Vesuvius and Stromboli are two active and extensively studied volcanoes that traditionally have been considered as having different styles of eruption, rock composition and tectonic setting. Data reveal close compositional affinities between these two volcanoes. The abundant 13–15 Ka old Stromboli leucite-tephritic rocks have radiogenic isotope signatures, and abundances and ratios of incompatible elements with the exception of Rb and K, which are identical to those of Vesuvius. The Phlegraean Fields also show close affinities to these volcanoes. The similarity between Stromboli leucite-tephrites and Vesuvius rocks cannot be the result of low pressure processes, given the differences between the two volcanoes in terms of structural features, eruptive behaviour and type of basement rocks. Instead, the observed geochemical signatures are likely to represent a primary magma composition and reveal a common homogeneous source for the two suites. The higher K and Rb contents in the Vesuvius rocks suggest either selective enrichment during magma ascent or a role for phlogopite melting during mantle anatexis. The most primitive rocks from Vesuvius, Phlegraean Fields and Stromboli reveal intermediate compositions between arc and intraplate volcanics. It is suggested that the mantle sources beneath these volcanoes consist of a mixture of intraplate- and slab-derived components. Intraplate material was probably provided by inflow of asthenosheric mantle into the wedge above the subducting Ionian Sea plate, either from the Apulian plate and/or from the Tyrrhenian Sea region. Fluids or melts released from the sinking slab and associated sediments generated metasomatic modification of the intraplate material, whose melting gave rise to the Stromboli, Vesuvius and Phlegraean Fields magmas. The present study demonstrates how comparative investigations of various volcanic centres from southern Italy allow clarification of a number of problems involving magma genesis and evolution, composition of mantle sources and geodynamic significance, which have been long debated and are difficult to solve if individual volcanoes are considered in isolation. Received July 20, 2000; revised version accepted March 19, 2001     

Chemical composition of precipitation at Mt. Vesuvius and Vulcano Island,Italy: volcanological and environmental implications

Natural precipitation and water samples from passive devices were collected at Mt. Vesuvius and Vulcano Island, Italy, during the period 2004–2006, in order to investigate its possible interactions with fumarolic gases. Evidence of chemical reactions between fumarolic fluids and rain samples before and after its deposition into the sampling devices was found at Vulcano Island. Very low pH values (down to 2.5) and significant amounts of chlorine and sulfate (up to 22 mEq/l) were measured at sampling points located close to the fumarolic field. In contrast, anthropogenic contributions and/or dissolution of aerosols (both maritime and continental) influence the chemistry of rainwaters at Mt. Vesuvius, which show inter-annual variations that are highly consistent with those recorded at the coastal site at Vulcano Island. Chemistry of waters directly exposed to fumarolic fluids may then give useful information about its temporal evolution, holding the signal of the “maximum” chemical event occurred in the meanwhile. In addition, the observation of the health status of vegetation colonizing the immediate surroundings of the fumarolic fields, due to its strong dependence on the interactions with these fluids, may work as a possible biomarker of volcanic activity.     

Lichens as bioindicators in volcanic areas: Mt. Etna and Vulcano Island (Italy)

 The aim of this paper is to verify whether lichens have the capacity to accumulate atmospheric contaminators linked to volcanic activity. About 100 lichens were collected in 1994 and 1995 from two active volcanic areas in Italy: Mount Etna and Vulcano Island. Twenty-seven elements were analyzed for each individual lichen using Instrumental Neutronic Activation Analysis and Inductively Coupled Plasma-Mass Spectrometry. Lichen composition reflects the contribution of the volcanic particulate material, and the two areas investigated can be distinguished on the basis of the concentration of some lithophile elements. Moreover, the distribution in lichens of the elements (As, Sb, Br, Pb) – derived from gas emissions (plume, fumaroles) – also shows different geochemical trends on Mt. Etna and Vulcano. Received: 20 April 1998 · Accepted: 4 July 1998     

Geophysical and petrological modelling of the structure and composition of the crust and upper mantle in complex geodynamic settings: The Tyrrhenian Sea and surroundings

Information on the physical and chemical properties of the lithosphere–asthenosphere system (LAS) can be obtained by geophysical investigation and by studies of petrology–geochemistry of magmatic rocks and entrained xenoliths. Integration of petrological and geophysical studies is particularly useful in geodynamically complex areas characterised by abundant and compositionally variable young magmatism, such as in the Tyrrhenian Sea and surroundings.A thin crust, less than 10 km, overlying a soft mantle (where partial melting can reach about 10%) is observed for Magnaghi, Vavilov and Marsili, which belong to the Central Tyrrhenian Sea backarc volcanism where subalkaline rocks dominate. Similar characteristics are seen for the uppermost crust of Ischia. A crust about 20 km thick is observed for the majority of the continental volcanoes, including Amiata–Vulsini, Roccamonfina, Phlegraean Fields–Vesuvius, Vulture, Stromboli, Vulcano–Lipari, Etna and Ustica. A thicker crust is present at Albani – about 25 km – and at Cimino–Vico–Sabatini — about 30 km. The structure of the upper mantle, in contrast, shows striking differences among various volcanic provinces.Volcanoes of the Roman region (Vulsini–Sabatini–Alban Hills) sit over an upper mantle characterised by V_s mostly ranging from about 4.2 to 4.4 km/s. At the Alban Hills, however, slightly lower V_s values of about 4.1 km/s are detected between 60 and 120 km of depth. This parallels the similar and rather homogeneous compositional features of the Roman volcanoes, whereas the lower V_s values detected at the Alban Hills may reflect the occurrence of small amounts of melts within the mantle, in agreement with the younger age of this volcano.The axial zone of the Apennines, where ultrapotassic kamafugitic volcanoes are present, has a mantle structure with high-velocity lid (V_s ∼ 4.5 km/s) occurring at the base of a 40-km-thick crust. Beneath the Campanian volcanoes of Vesuvius and Phlegraean Fields, the mantle structure shows a rigid body dipping westward, a feature that continues southward, up to the eastern Aeolian arc. In contrast, at Ischia the upper mantle contains a shallow low-velocity layer (V_s = 3.5–4.0 km/s) just beneath a thin but complex crust. The western Aeolian arc and Ustica sit over an upper mantle with V_s ∼ 4.2–4.4 km/s, although a rigid layer (V_s = 4.55 km/s) from about 80 to 150 km occurs beneath the western Aeolian arc. In Sardinia, no significant differences in the LAS structure are detected from north to south.The petrological–geochemical signatures of Italian volcanoes show strong variations that allow us to distinguish several magmatic provinces. These often coincide with mantle sectors identified by V_s tomography. For instance, the Roman volcanoes show remarkable similar petrological and geochemical characteristics, mirroring similar structure of the LAS. The structure and geochemical-isotopic composition of the upper mantle change significantly when we move to the Stromboli–Campanian volcanoes. The geochemical signatures of Ischia and Procida volcanoes are similar to other Campanian centres, but Sr–Pb isotopic ratios are lower marking a transition to the backarc mantle of the Central Tyrrhenian Sea. The structural variations from Stromboli to the central (Vulcano and Lipari) and western Aeolian arc are accompanied by strong variations of geochemical signatures, such as a decrease of Sr-isotope ratios and an increase of Nd-, Pb-isotope and LILE/HFSE ratios. The dominance of mafic subalkaline magmatism in the Tyrrhenian Sea basin denotes large degrees of partial melting, well in agreement with the soft characteristics of the uppermost mantle in this area. In contrast, striking isotopic differences of Plio-Quaternary volcanic rocks from southern to northern Sardinia does not find a match in the LAS geophysical characteristics.The combination of petrological and geophysical constraints allows us to propose a 3D schematic geodynamic model of the Tyrrhenian basin and bordering volcanic areas, including the subduction of the Ionian–Adria lithosphere in the southern Tyrrhenian Sea, and to place constraints on the geodynamic evolution of the whole region.     

Arsenic in volcanic gases

 Total arsenic contents were determined in volcanic gases by analysis of fumarolic condensates collected in the period 1984–1992 from different volcanoes around the world. Arsenic concentrations range from <0.006 to 30 μg/g. The highest values (1.2–30 μg/g) were found at Vulcano, Aeolian Islands (southern Italy). The analytical data show that volcanic gases have a large variability of arsenic contents possibly related to both the different physicochemical features of magma source and rock properties within the volcanic system. Received: 2 October 1996 · Accepted: 29 January 1997     

内蒙中部辉腾锡勒第四纪火山群初步研究

辉腾锡勒火山群位于内蒙古中部卓资县、察哈尔右翼中旗和后旗交界处的高山草原区。处于中国东部大同-阿尔山-诺敏河第四纪火山喷发带南段。火山群坐落在太古宙变质岩系、二叠纪花岗岩和新近纪汉诺坝玄武岩之上。平面上呈低洼的菱形台地，四周为山地，总面积约260km²。因上覆在汉诺坝玄武岩台地之上，故以往将其误归为新近纪汉诺坝玄武岩。火山群内发育近百座火山，大多数火山形貌保存基本完整。火山产物主要为一套碱性橄榄玄武岩，次为不同成因的火山碎屑物（岩）。碱性玄武岩覆盖在晚更新世坡积物和黄土之上。火山活动的时代主体为晚更新世，可进一步分为早、中、晚三期。早期为裂隙-中心式喷发，火口已剥蚀殆尽；中期主要形成"地池式"和玛珥式火山，火山形貌较完整，火口呈特征的圆形或椭圆形，大部分积水成湖，当地习称"九十九眼泉"或"海子"。晚期以熔浆的溢流为主，形成结构完整的盾片状火山。火山活动经历了沿裂隙的喷溢到中心式弱爆发、溢流-射汽岩浆爆发-溢流再到溅落堆积的演化过程。辉腾锡勒火山群是在新近纪汉诺坝玄武岩台地上新解体确定的第四纪火山群，这为研究蒙古高原南部地壳深部结构及其活动性提供了又一天然窗口，对了解新构造活动、环境及灾害预警研究都具有重要的理论和实际意义。     

深圳大鹏半岛火山和香港火山活动特征对比研究北大核心CSCD

深圳大鹏半岛和香港地区古火山活动带,分布于广东省东部火山活动亚带莲花山火山喷发带上,属于浙闽粤港火山活动带,也是环太平洋火山活动带的一部分。为研究两地火山岩的成因机制、构造演化过程以及两地火山活动的异同点,本文采用实地考察、同位素测年等方法,从火山地层、构造和火山活动性等方面,对大鹏半岛与香港火山活动特征异同点进行对比研究。研究发现两地火山具有相似的沉积环境、相同区域地质构造背景,经历了相似的地质演化过程,火山活动时期也基本相同。二者的不同之处是地貌特征和地质景观不同,各具特色。香港的火山机构存在超级破火山口,六边形柱状节理普遍发育。大鹏半岛火山以火山穹丘为特征,典型火山地质现象是球粒、石泡、流纹、火山碎屑较为发育。根据同位素测年分析,大鹏半岛火山岩同位素年龄值为137~161 Ma,为侏罗纪晚期至白垩纪早期的产物。     

Geochronology and evolution of quaternary volcanism at the Keli Highland,Greater Caucasus

The paper reports newly obtained stratigraphic, petrographic, and isotope-geochronological data on modern moderately acid lavas from the Keli Highland at the Greater Caucasus and presents a geological map of the territory, in which 35 volcanoes active in Late Quaternary time were documented by the authors. The total duration of volcanic activity at the highland was estimated at 250 ka. The volcanic activity was discrete and occurred in three phases: Middle Neopleistocene (245−170 ka), Late Neopleistocene (135−70 ka), and Late Neopleistocene-Holocene (<30 ka). Newly obtained lines of evidence indicate that certain volcanoes erupted in the latest Neopleistocene-Holocene. The first phase of volcanic activity was connected mainly with lava volcanoes, and eruptions during the later phases of volcanic activity in this part of the Greater Caucasus produced mainly lavas. The most significant eruptions are demonstrated to occur in the territory during the second phase. The major evolutionary trends of volcanic processes during the final phase in the Keli Highland are determined. It was also determined that the overwhelming majority of volcanoes that were active less than 30 ka B.P. are spatially restricted to long-liven local magmatic zones, which were active during either all three or only the final two phases of activity. These parts of the territory are, perhaps, the most hazardous in terms of volcanic activity.     

大别山北麓晚侏罗世金刚台组火山岩地质及岩相构造特征

摘　 要　 金刚台组火山岩分布在大别山北缘金寨与商城之间, 为一套以爆发相为主体的中酸 性钙碱性火山岩系, 时代属晚侏罗世。 根据喷发韵律、 岩石组合、 角砾成分和蚀变矿化等特 征, 可分为早、 晚两个亚旋回。 通过火山岩相和火山构造研究表明, 火山活动以中心式喷发 为特征, 属复式火山机构类型, 就其形态特点来看属于锥状火山和破火山口。     

Sampling and analytical procedures for the determination of VOCs released into air from natural and anthropogenic sources: A comparison between SPME (Solid Phase Micro Extraction) and ST (Solid Trap) methods

In the present study, two sampling and analytical methods for VOC determination in fumarolic exhalations related to hydrothermal-magmatic reservoirs in volcanic and geothermal areas and biogas released from waste landfills were compared: (a) Solid Traps (STs), consisting of three phase (Carboxen B, Carboxen C and Carbosieve S111) absorbent stainless steel tubes and (b) Solid Phase Micro Extraction (SPME) fibers, composed of DiVinylBenzene (DVB), Carboxen and PolyDimethylSiloxane. These techniques were applied to pre-concentrate VOCs discharged from: (i) low-to-high temperature fumaroles collected at Vulcano Island, Phlegrean Fields (Italy), and Nisyros Island (Greece), (ii) recovery wells in a solid waste disposal site located near Florence (Italy). A glass condensing system cooled with water was used to collect the dry fraction of the fumarolic gases, in order to allow more efficient VOC absorption avoiding any interference by water vapor and acidic gases, such as SO₂, H₂S, HF and HCl, typically present at relatively high concentrations in these fluids. Up to 37 organic species, in the range of 40–400 m/z, were determined by coupling gas chromatography to mass spectrometry (GC–MS). This study shows that the VOC compositions of fumaroles and biogas determined via SPME and ST are largely consistent and can be applied to the analysis of VOCs in gases released from different natural and anthropogenic environments. The SPME method is rapid and simple and more appropriate for volcanic and geothermal emissions, where VOCs are present at relatively high concentrations and prolonged gas sampling may be hazardous for the operator. The ST method, allowing the collection of large quantities of sample, is to be preferred to analyze the VOC composition of fluids from diffuse emissions and air, where these compounds are present at relatively low concentrations.     

Volcanic hazards to airports

Volcanic activity has caused significant hazards to numerous airports worldwide, with local to far-ranging effects on travelers and commerce. Analysis of a new compilation of incidents of airports impacted by volcanic activity from 1944 through 2006 reveals that, at a minimum, 101 airports in 28 countries were affected on 171 occasions by eruptions at 46 volcanoes. Since 1980, five airports per year on average have been affected by volcanic activity, which indicates that volcanic hazards to airports are not rare on a worldwide basis. The main hazard to airports is ashfall, with accumulations of only a few millimeters sufficient to force temporary closures of some airports. A substantial portion of incidents has been caused by ash in airspace in the vicinity of airports, without accumulation of ash on the ground. On a few occasions, airports have been impacted by hazards other than ash (pyroclastic flow, lava flow, gas emission, and phreatic explosion). Several airports have been affected repeatedly by volcanic hazards. Four airports have been affected the most often and likely will continue to be among the most vulnerable owing to continued nearby volcanic activity: Fontanarossa International Airport in Catania, Italy; Ted Stevens Anchorage International Airport in Alaska, USA; Mariscal Sucre International Airport in Quito, Ecuador; and Tokua Airport in Kokopo, Papua New Guinea. The USA has the most airports affected by volcanic activity (17) on the most occasions (33) and hosts the second highest number of volcanoes that have caused the disruptions (5, after Indonesia with 7). One-fifth of the affected airports are within 30 km of the source volcanoes, approximately half are located within 150 km of the source volcanoes, and about three-quarters are within 300 km; nearly one-fifth are located more than 500 km away from the source volcanoes. The volcanoes that have caused the most impacts are Soufriere Hills on the island of Montserrat in the British West Indies, Tungurahua in Ecuador, Mt. Etna in Italy, Rabaul caldera in Papua New Guinea, Mt. Spurr and Mt. St. Helens in the USA, Ruapehu in New Zealand, Mt. Pinatubo in the Philippines, and Anatahan in the Commonwealth of the Northern Mariana Islands (part of the USA). Ten countries—USA, Indonesia, Ecuador, Papua New Guinea, Italy, New Zealand, Philippines, Mexico, Japan, and United Kingdom—have the highest volcanic hazard and/or vulnerability measures for airports. The adverse impacts of volcanic eruptions on airports can be mitigated by preparedness and forewarning. Methods that have been used to forewarn airports of volcanic activity include real-time detection of explosive volcanic activity, forecasts of ash dispersion and deposition, and detection of approaching ash clouds using ground-based Doppler radar. Given the demonstrated vulnerability of airports to disruption from volcanic activity, at-risk airports should develop operational plans for ashfall events, and volcano-monitoring agencies should provide timely forewarning of imminent volcanic-ash hazards directly to airport operators.     

From sink to volcanic source: Unravelling missing terrestrial eruption records by characterization and high‐resolution chronology of lacustrine volcanic density flow deposits,Lake Inawashiro‐ko,Fukushima, Japan

Eruption records in the terrestrial stratigraphy are often incomplete due to erosion after tephra deposition, limited exposure and lack of precise dating owing to discontinuity of strata. A lake system and sequence adjacent to active volcanoes can record various volcanic events such as explosive eruptions and subaqueous density flows being extensions of eruption triggered and secondary triggered lahars. A lacustrine environment can constrain precise ages of such events because of constant and continuous background sedimentation. A total of 71 subaqueous density flow deposits in a 28 m long core from Lake Inawashiro‐ko reveals missing terrestrial volcanic activity at Adatara and Bandai volcanoes during the past 50 kyr. Sedimentary facies, colour, grain size, petrography, clay mineralogy, micro X‐ray fluorescence analysis and chemistry of included glass shards characterize the flow event deposits and clarify their origin: (i) clay‐rich grey hyperpycnites, extended from subaerial cohesive lahars at Adatara volcano, with sulphide/sulphate minerals and high sulphur content which point to a source from hydrothermally altered material ejected by phreatic eruptions; and (ii) clay‐rich brown density flow deposits, induced by magmatic hydrothermal eruptions and associated edifice collapse at Bandai volcano, with the common presence of fresh juvenile glass shards and low‐grade hydrothermally altered minerals; whereas (iii) non‐volcanic turbidites are limited to the oldest large slope failure and the 2011 Tohoku‐oki earthquake events. The high‐resolution chronology of volcanic activity during the last 50 kyr expressed by lacustrine event deposits shows that phreatic eruption frequency at Adatara has roughly tripled and explosive eruptions at Bandai have increased by ca 50%. These results challenge hikers, ski‐fields and downstream communities to re‐evaluate the increased volcanic risks from more frequent eruptions and far‐reaching lahars, and demonstrate the utility of lahar and lacustrine volcanic density flow deposits to unravel missing terrestrial eruption records, otherwise the recurrence rate may be underestimated at many volcanoes.     

火山学述评

火山学研究有了长足的进步。笔者总结近些年全球火山学研究各个方面的成果,包括对火山基本概念的新的认识、火山机构、火山的各种分类、火山岩石学和地球化学、火山岩相学、评估火山爆发大小的火山爆发指数、岩石和地球化学分类、各种常量和微量元素区分图、活火山分布与板块构造理论的关系、活火山给人类带来的灾害与利益和活火山的监测、曾经的火山活动与生物毁灭、单成因火山研究等。火山—构造是未来火山学研究的一个方向,通过火山与构造关系的研究以揭示火山的分布和地球的演化。火山喷出的岩浆是其通过地下以岩墙或管道形式为通道运移到地表的结果。中朝边境上的长白山的位置是个特例,应当值得深入的研究。中国分布有许多新生代火山,它们是否为单成因火山、这些火山在成分上是否有演化规律、它们的分布与大地构造的关系等都有待深入和系统的研究。     

Numerical model of the Stromboli volcano (Italy) including the effect of magma pressure in the dyke system

Summary  The Stromboli island, in the Aeolian archipelago (Italy), is one of the most active volcanoes in Europe. In the last 13,000 years, its growth has been complicated by four sector collapses affecting the NW flank, the latest of which resulting in the formation of Sciara del Fuoco (SdF) horseshoe-shaped depression. Slope instability phenomena are represented not only by giant deep-seated gravitational slope deformations, but also by more frequent large landslides, such as occurred in December 2002–January 2003, and shallow landslides, involving loose or weakly cemented deposits, that constitute a natural hazard and affect residential and tourists safety. It is noteworthy that in volcanic environment the instability factors are manifold and much more complex than in other non-volcanic contexts. This paper deals with the Stromboli NW flank instability, and focuses on the effects of magma pressure in the feeding system. Two main objectives have been pursued: (1) to test a methodological approach, in order to evaluate a complex instability process; (2) to contribute to the understanding of volcano deformation and collapse mechanisms and associated hazard. A numerical model was developed by the Finite Difference Method and the FLAC 4.0 code, considering a cross-section of the entire volcano, orthogonal to the SdF and including both subaerial and submerged slopes. The stability of the volcano was analysed under gravity alone, and by introducing the magma pressure effect, both related to magmastatic and overpressure components. The results indicate that gravity alone is not sufficient to affect the stability of the volcano slopes, nor is the magmastatic pressure component. If an excess magma pressure component is introduced, instability is produced in accordance with field evidences and recent slope dynamics. Correspondence: Tiziana Apuani, Dipartimento di Scienze della Terra “A. Desio”, via Mangiagalli 34, 20133 Milano, Italy     

青海尕林格南地区火山岩地球化学特征及锆石U-Pb年龄

在东昆仑山脉西段祁漫塔格山中东部的尕林格南地区发育一套火山岩,调查显示火山活动爆发相→溢流相相间的韵律周期较明显,见由玄武质含火山角砾凝灰岩→玄武岩、玄武质凝灰岩→安山岩、安山质角砾凝灰岩→安山岩,以及安山质含火山角砾凝灰岩和安山岩质凝灰岩→玄武岩组成的4个韵律。根据研究区安山质火山角砾凝灰岩的LA-ICP-MS锆石U-Pb年龄222.2±2.1Ma,将该火山岩地层由前人划分的顶志留统—下泥盆统契盖苏组火山岩段重新厘定为上三叠统鄂拉山组。岩石地球化学研究结果表明,该套火山岩属于亚碱性钙碱性系列岩石,具有富钾、同源岩浆演化的特点,并具弧火山岩和碰撞火山岩的地球化学特征,为陆内造山作用下的产物,较好地记录了东昆仑祁漫塔格造山带在晚三叠世岩浆演化的地质信息。