THE VOLCANIC ACTIVITIES AND HAZARD PREDICTION OF WUDALIANCHI VOLCANIC BELT

More than 40 late Cenozoic monogenetic volcanoes formed a volcanic belt striking NNW from Keluo, through Wudalianchi to Erkeshan in NE China. These volcanoes belong to a unified volcano system, namely Wudalianchi volcanic belt(WVB for short). Based on the volcanic evolution history and the nature of monogenetic volcanic system, we estimate that the volcanic system of WVB is still active and has the potential to erupt again. Hence, this paper studied the temporal-spatial distribution and volcanic eruption types to evaluate the possible eruption hazard types and areas of influence in the future. Volcanic field characteristics and K-Ar radiometric data suggest two episodes of volcanism in the WVB, the Pliocene to early Pleistocene volcanism(4.59~1.00MaBP)and the middle Pleistocene to Holocene volcanism(0.79Ma to now). The early episode volcanoes are distributed only in the north of WVB(mainly in Keluo volcanic field), featured by effusive eruption, and mainly formed monogenetic shield, whose base diameter is large and slope is gentle. However, the late episode eruptions occurred over the entire WVB. The explosive eruption in this stage formed numerous relatively intact scoria cones of explosive origin. Meanwhile the effusive eruption formed widely distributed lava flows. Both effusive eruption and explosive eruption are common in WVB. The effusive eruption formed monogenetic shields and lava flows. The resulting pahoehoe lava, aa lava and block lava appeared in WVB. There are three end-member types of explosive eruption driven by magmatic volatile. Violent Strombolian eruption has the highest degree of fragmentation and mass flux, characterized by eruption column. Strombolian eruption has the high degree of fragmentation, but low mass flux, featured by pulse eruption. Hawaiian eruption has low degree of fragmentation, but high in mass flux, generating large scoria cones. In addition, this paper for the first time found phreatomagmatic eruption in WVB, which formed tuff cone. Transitional eruptions are also common in WVB, which have certain characteristics among the end-member eruption types. Besides, certain volcanoes displayed multiple explosive eruption types during the whole eruption span. According to the volcanic temporal-spatial distribution and eruption characteristics in WVB, the potential volcanic hazards in future are constrained. It appears that the violent Strombolian and Strombolian eruption will not have significant impact on aviation safety in the vertical direction. In the radial direction, the ejected volcanic bomb can reach as far as 1km from the vents and the fallout tephra may disperse downwind over a distance ranging from 1~10km. The major hazard of Hawaiian eruption and effusive eruption comes from lava flow, and its migration distance may reach 3.0~13.5km for pahoehoe lava and 2.9~14.9km for aa lava. The base surge in phreatomagmatic eruption can reach a velocity of 200~400m/s, and the migration distance is around 10km. This is a big threat that people should pay more attention to and take precautions in advance. Besides, it is necessary to strengthen the real-time observation of the volcanoes in the WVB, especially those formed in the late episode as well as near the active fault.     

图们江流域新生代火山岩Sr、Nd同位素初步研究

中国地震局地质研究所; 中国地震局地质研究所 北京     

The occurrence of Mt Barca flank eruption in the evolution of the NW periphery of Etna volcano (Italy)

Geological surveys, tephrostratigraphic study, and ⁴⁰Ar/³⁹Ar age determinations have allowed us to chronologically constrain the geological evolution of the lower NW flank of Etna volcano and to reconstruct the eruptive style of the Mt Barca flank eruption. This peripheral sector of the Mt Etna edifice, corresponding to the upper Simeto valley, was invaded by the Ellittico volcano lava flows between 41 and 29 ka ago when the Mt Barca eruption occurred. The vent of this flank eruption is located at about 15 km away from the summit craters, close to the town of Bronte. The Mt Barca eruption was characterized by a vigorous explosive activity that produced pyroclastic deposits dispersed eastward and minor effusive activity with the emission of a 1.1-km-long lava flow. Explosive activity was characterized by a phreatomagmatic phase followed by a magmatic one. The geological setting of this peripheral sector of the volcano favors the interaction between the rising magma and the shallow groundwater hosted in the volcanic pile resting on the impermeable sedimentary basement. This process produced phreatomagmatic activity in the first phase of the eruption, forming a pyroclastic fall deposit made of high-density, poorly vesicular scoria lapilli and lithic clasts. Conversely, during the second phase, a typical strombolian fall deposit formed. In terms of hazard assessment, the possible occurrence of this type of highly explosive flank eruption, at lower elevation in the densely inhabited areas, increases the volcanic risk in the Etnean region and widens the already known hazard scenario.     

松辽盆地营城组火山机构相带地震-地质解译

将火山机构按距火山口1远近划分为火山口-近火山口、近源和远源三个相带.营城组火山机构相带有6种地震相类型,分别是丘状、透镜状、穹状、池塘状、楔状和席状地震相.丘状、透镜状和穹状均见于火山机构中心相带,但所代表的优势岩相不同,分别与爆发相、喷溢相和侵出相对应.池塘状和楔状均为近源相带,但前者以喷溢相辫状熔岩流为主,而后者...     

petrological and geochemical characteristics of quarternary volcanic rocks in haixing area,eastern north china

Field investigation and lab analysis on samples were carried out for Quaternary volcanoes, including Xiaoshan volcano, Dashan volcano and Bianzhuang hidden volcano, in Haixing area, east of North China. Results show that Xiaoshan volcano with the eruptive material of volcanic scoria, crystal fragments and volcanic ash is a maar volcano, the eruptive pattern is pheatomagmatic eruption, and the influence scope is near the crater. Dashan volcano exploded in the early stage, and then the magma intruded, forming the volcanic neck. The eruption strength and scale are limited, and the eruptive materials are scoria, volcanic agglomerate and dense lava neck. The volcanic rocks in Bianzhuang are porosity and dense volcanic rocks and volcanic breccia, reflecting the pattern of weak explosive eruption and lava flow, and the K-Ar age dating on volcanic rocks indicates that the eruption happened in early Pleistocene. Xiaoshan volcanic scoria and Bianzhuang hidden volcanic rocks are mainly basaltic, Dashan volcanic rocks with lower SiO₂ content are nephelinite in composition. Their oxide contents have no linear relationship, indicating that there is no magma evolution relationship between these magmas from the three places. Three volcanic rocks all have enrichment of light rare earth. The Bianzhuang volcanic rocks are rich in large ion lithophile elements, and have no high field strength elements Zr and Hf, Ti losses. The volcanic materials from Xiaoshan and Dashan are intensively rich in Th, U, Nb and Ta, and significantly poor in K and Ti. Although the magmas from these three places in Haixing area may all come from asthenosphere, the volcanic materials have different petrological and geochemical features, and relatively independent volcanic structures, therefore, they experienced different magma processes.     

EARTHQUAKE-CAUSED SEISMIC VOLCANIC ROCKS AND THIXOTROPIC DEFORMATION OF SOFT SEDIMENTS IN THE UPPER CRETACEOUS SHIJIATUN MEMBER,JIAOZHOU CITY

A lot of seismic volcanic rocks and strong earthquake-induced thixotropic deformation structures in soft mud-sandy sediments(seismites)were identified from the Upper Cretaceous Shijiatun Member of the Hongtuya Formation for the first time in Jiaozhou City of the Zhucheng Sag, eastern China. Seismic volcanic rocks are volcanic rocks with co-seismic deformation structures which were produced by major earthquakes destroying volcano ejecta. Seismites are sediment layers with soft-sediment deformation structures formed by strong earthquake triggering saturated or semi-consolidated soft sediments to produce liquefaction, thixotropy, faults, cracks and filling and so forth. The Shijiatun Member of the Hongtuya Formation mainly consists of basaltic volcano rocks interbedded with mud-sandy(muddy sand and sandy mud)deposition layers of the river-lake facies. In the Shijiatun Member, main types of seismic volcanic rocks are shattered basalts with co-seismic fissures and seismic basaltic breccias. The thixotropic deformations of soft mud-sandy sediments mainly include thixotropic mud-sandy veins and thixotropic mud-sandy layers with tortuous boundaries. Under the strong earthquake action, saturated mud-sandy sediments could not be liquefied, instead resulting in thixotropy, i.e. their texture can be damaged and their flow-ability or rheology becomes strong. Because basaltic volcano rocks were damaged(shattered, seismic broken), a major earthquake can lead to thixotropic mud-sandy sediments flowing along seismic fissures in basalts, resulting in the formation of deformation structure of thixotropic veins, and boundaries between volcano rock and mud-sand layer became quite winding. Under the koinonia of gravity and vibration force, seismic breccia blocks sunk into thixotropic mud-sandy layers, resulting in the formation of inclusions of thixotropic mud-sandy sediments. Seismic intensity reflected by these strong earthquake records during the end stage of the Late Cretaceous was about Ⅶ to more than X degrees. The Shijiatun Member is mainly distributed in the south of the Baichihe fault in the northern Zhucheng Sag, and the fault has generated many strong tectonic and earthquake activities at the end of the late Cretaceous, also provided the channel for intrusion and eruption of basaltic magma then. At the end of the late Cretaceous, intermittent intrusion and eruption of basaltic magma took place along the Baichihe fault, meanwhile the volcano earthquakes took place or tectonic earthquakes were generated by the Baichihe fault which caused the deformation of the volcano lava and underlying strata of red saturated muddy-sand, resulting in the formation of various seismo-genesis deformations of volcanic rocks interbedded with mud-sandy sediment layers. Therefore, strong seismic events recorded by them should be responses to strong tectonic taphrogenesis of the Zhucheng Sag and intense activity of the Baichihe fault in the end of Late Cretaceous. In addition, these seismogenic deformation structures of rock-soil layers provide new data for the analysis of the failure effect produced by seismic force in similar rock-soil foundations.     

Products and processes in Pliocene–Recent, subaqueous to emergent volcanism in the Antarctic Peninsula: examples of englacial Surtseyan volcano construction

 Pliocene–Recent volcanic outcrops at Seal Nunataks and Beethoven Peninsula (Antarctic Peninsula) are remnants of several monogenetic volcanoes formed by eruption of vesiculating basaltic magma into shallow water, in an englacial environment. The diversity of sedimentary and volcanic lithofacies present in the Antarctic Peninsula outcrops provides a clear illustration of the wide range of eruptive, transportational and depositional processes which are associated with englacial Surtseyan volcanism. Early-formed pillow lava and glassy breccia, representing a pillow volcano stage of construction, are draped by tephra erupted explosively during a tuff cone stage. The tephra was resedimented around the volcano flanks, mainly by coarse-grained sediment gravity flows. Fine-grained lithofacies are rare, and fine material probably bypassed the main volcanic edifice, accumulating in the surrounding englacial basin. The pattern of sedimentation records variations in eruption dynamics. Products of continuous-uprush eruptions are thought to be represented by stacks of poorly bedded gravelly sandstone, whereas better bedded, lithologically more diverse sequences accumulated during periods of quiescence or effusive activity. Evidence for volcano flank failure is common. In Seal Nunataks, subaerial lithofacies (mainly lavas and cinder cone deposits) are volumetrically minor and occur at a similar stratigraphical position to pillow lava, suggesting that glacial lake drainage may have occurred prior to or during deposition of the subaerial lithofacies. By contrast, voluminous subaerial effusion in Beethoven Peninsula led to the development of laterally extensive stratified glassy breccias representing progradation of hyaloclastite deltas. Received: 5 February 1996 / Accepted: 17 January 1997     

Seismic activity accompanying the 1974 eruption of Mt. Etna

On January 30, 1974, an explosive eruption began on the western side of Etna. The activity evolved into two eruptive periods (January 30–February 17 and March 11–29). Two spatter cones (Mount De Fiore I and Mount De Fiore II) were formed at a height of about 1650 m a.s.l. and a distance of 6 km from the summit area. The effusive activity was very irregular with viscous lava flows of modest length.A seismic network of four stations was established around the upper part of the volcano on February 3. Moreover additional mobile stations were set up at several different sites in order to obtain more detailed informations on epicenter locations and spectral content of volcanic tremor.The volcanic activity is discussed in relation to the distribution of epicenters and the time-space distribution of the spectral characteristics of volcanic earthquakes and tremor. The characteristics of the seismic activity suggest that the flank eruption of Mount Etna was probably feed by a lateral branch of the main conduit yielding the activity at the Central Crater.     

Eruption processes and deposit characteristics at the monogenetic Mt. Gambier Volcanic Complex, SE Australia: implications for alternating magmatic and phreatomagmatic activity

The ～5 ka Mt. Gambier Volcanic Complex in the Newer Volcanics Province, Australia is an extremely complex monogenetic, volcanic system that preserves at least 14 eruption points aligned along a fissure system. The complex stratigraphy can be subdivided into six main facies that record alternations between magmatic and phreatomagmatic eruption styles in a random manner. The facies are (1) coherent to vesicular fragmental alkali basalt (effusive/Hawaiian spatter and lava flows); (2) massive scoriaceous fine lapilli with coarse ash (Strombolian fallout); (3) bedded scoriaceous fine lapilli tuff (violent Strombolian fallout); (4) thin–medium bedded, undulating very fine lapilli in coarse ash (dry phreatomagmatic surge-modified fallout); (5) palagonite-altered, cross-bedded, medium lapilli to fine ash (wet phreatomagmatic base surges); and (6) massive, palagonite-altered, very poorly sorted tuff breccia and lapilli tuff (phreato-Vulcanian pyroclastic flows). Since most deposits are lithified, to quantify the grain size distributions (GSDs), image analysis was performed. The facies are distinct based on their GSDs and the fine ash to coarse+fine ash ratios. These provide insights into the fragmentation intensities and water–magma interaction efficiencies for each facies. The eruption chronology indicates a random spatial and temporal sequence of occurrence of eruption styles, except for a “magmatic horizon” of effusive activity occurring at both ends of the volcanic complex simultaneously. The eruption foci are located along NW–SE trending lineaments, indicating that the complex was fed by multiple dykes following the subsurface structures related to the Tartwaup Fault System. Possible factors causing vent migration along these dykes and changes in eruption styles include differences in magma ascent rates, viscosity, crystallinity, degassing and magma discharge rate, as well as hydrological parameters.     

Evolution of Aoba caldera volcano,New Hebrides

Aoba is a basalt volcano situated in the northern part of a chain containing all the active volcanoes in the New Hebrides. The chain extends the length of the New Hebrides. Growing from a depth of 2,400 meters on the sea floor, the volcano probably emerged above sea level in the late Pliocene or early Pleistocene. The age of the oldest exposed rocks is unknown. Relatively fluid lavas with autobrecciated surfaces probably issued from tissures, initiating a shield-building stage as the volcano emerged. Airfall pyroclastics increase towards the top of these lavas and are overlain by agglomerates marking a more explosive episode. Activity continued with the effusion of picrite basalt, accompanied by spasms of ash emission that formed crystal tuff. Subsequently a more explosive episode produced agglomerate and tuff with occasional tongues of lava. The two oval summit calderas are apparently related to deep-seated subsidence. Lack of pumice deposits, and the basic nature of the magma suggest that the foundering of the calderas was a quiet event, possibly due to massive outpourings of lava at a lower level, although a substantial volume also erupted from the summit volcanoes at this time. A broad pyroclastic cone, which was still growing 360 years ago, occupies the centre of the inner caldera. It is surmounted by a wide crater, or possibly small caldera, containing a lake in which palagonite tuff cones have formed. The western end of the inner caldera is occupied by an explosion crater, and the eastern end by a semicircular lake. A thermal area containing a solfatara on the southeast shore of the eastern lake, and staining in the crater lake suggestive of fumarole activity, are the only evidence of vulcanicity at the present time. It is difficult to correlate events at the centre of the volcano with those at the lateral fissures. Later episodes at the centre are probably broadly contemporaneous with activity along the fissures, the inner ends of which are mantled by younger deposits of the central volcano. Accumulation of material about this axial fiissure system, marked by no less than 64 cruptive foci, mainly spatter cones, and phreatic explosion craters where they intersect the coast, has extended the island to the northeast and southwest, producing the present oval shape. Numerous flows spilled from these fissures, the last reaching the sea at N’dui N’dui only 300 years ago according to local legend. Abundant ash was emitted from both the summit calderas and flank fissures at a late stage, forming a tuff mantle with layers of accretionary lapilli. The last volcanic event was the formation of a lahar which destoyed a village on the northeast slope of the volcano about 100 years ago. No consistent variation with time is evident in the composition of the magma, although plagiophyric and aphyric lava erupted during the later stages. All the rocks are basaltic, and differ only in the presence or absence of phenocryst-forming minerals, and the proportions in which they occur. Picrite basalt and ankaramite erupted from the central volcano and flank fissures, respectively.     

Polygenic eruptions on Alba Patera,Mars

A combination of photogeologic mapping, analysis of Viking Orbiter thermal inertia data, and numerical modelling of eruption conditions has permitted us to construct a new model for the evolution of the martian volcano Alba Patera. Numerous digitate channel networks on the flanks of the volcano are interpreted to be carved by sapping due to the release of non-juvenile water from unconsolidated flank deposits. Using the thermal inertia measurements, we estimate the particle size of these deposits to be 3–10 µm, which, together with theoretical modelling of the disperison of explosively derived volcanic materials, leads us to conclude that the flank deposits on Alba Patera are low-relief pyroclastic flows. The recognition of numerous late-stage summit and sub-terminal lava flows thus makes Alba Patera a unique martian volcano that is transitional between the older pyroclastic-dominated highland paterae and the more recent effusive central-vent volcanoes such as the Tharsis Montes.     

大兴安岭焰山、高山火山——一种新的火山喷发型式

在野外地质资料基础上,利用火山形态学方法,探讨了大兴安岭焰山、高山火山的喷发型式。结果表明,大兴安岭哈拉哈河-绰尔河火山群中的焰山和高山火山不同于斯通博利式喷发形成的火山,其早期爆破喷发的火山碎屑形成火山渣锥、空降火山碎屑席和小型火山碎屑流,晚期溢出大量熔岩。两火山具有较高大的锥体(标高200～300m以上),在结构上,松散火山砾、火山弹等构成下部的降落锥,熔结集块岩构成上部的溅落锥。由火山砾和火山灰组成的空降火山碎屑席分布在火山锥体周围。两火山溢出的熔岩经历了从结壳熔岩→翻花石→渣状熔岩的演变。根据喷发产物可推断焰山和高山火山具有以下喷发特征:爆破喷发形成持续的喷发柱→斯通博利式喷发→熔岩喷泉喷溢,其中以持续时间较长的喷发柱区别于典型的斯通博利式喷发。类似焰山、高山火山的喷发特征,在龙岗第四纪火山群、镜泊湖全新世火山群中也都有个例,这是中国大陆火山作用中一种新的喷发型式。     

香港安山-英安质古火山颈群

香港中侏罗世屯门组火山岩主要由安山质熔岩、凝灰岩和凝灰角砾岩夹少量凝灰质砂岩组成。其中凝灰角砾岩初期曾误认为是沉积砾岩。1990年香港地质调查组重新研究后,确认是火山成因的凝灰角砾岩。按岩相分析,屯门组火山岩可分为火山通道相安山-英安质熔岩和爆发角砾岩,还有爆发空落相凝灰角砾岩。火山通道相又可分为火山颈相和岩墙相,分布在屯门组东西两侧。在青山东麓,出露一列NNW向呈断续、线状分布的火山颈群。近年来新出版的《香港地质考察指引》和《香港工程地质实践》等地质著作仍将该区爆发角砾岩误认为是沉积成因的砾岩,在地质勘探和工程设计上造成混乱,导致不应有的经济和时间上的损失。本文综合最新研究成果并与世界各地同类火山岩的特征进行对比,确证火山通道相爆发角砾岩的存在,并发现呈线状分布的古火山颈群。     

Volcanic Tremor at Mt. Etna,Italy, Preceding and Accompanying the Eruption of July – August, 2001

The July 17 – August 9, 2001 flank eruption of Mt. Etna was preceded and accompanied by remarkable changes in volcanic tremor. Based on the records of stations belonging to the permanent seismic network deployed on the volcano, we analyze amplitude and frequency content of the seismic signal. We find considerable changes in the volcanic tremor which mark the transition to different styles of eruptive activity, e.g., lava fountains, phreatomagmatic activity, Strombolian explosions. In particular, the frequency content of the signal decreases from 5 Hz to 3 Hz at our reference station ETF during episodes of lava fountains, and further decreases at about 2 Hz throughout phases of intense lava emission. The frequency content and the ratios of the signal amplitude allow us to distinguish three seismic sources, i.e., the peripheral dike which fed the eruption, the reservoir which fed the lava fountains, and the central conduit. Based on the analysis of the amplitude decay of the signal, we highlight the migration of the dike from a depth of ca. 5 km to about 1 km between July 10 and 12. After the onset of the effusive phase, the distribution of the amplitude decay at our stations can be interpreted as the overall result of sources located within the first half kilometer from the surface. Although on a qualitative basis, our findings shed some light on the complex feeding system of Mt. Etna, and integrate other volcanological and geophysical studies which tackle the problem of magma replenishment for the July–August, 2001 flank eruption. We conclude that volcanic tremor is fundamental in monitoring Mt. Etna, not only as a marker of the different sources which act within the volcano edifice, but also of the diverse styles of eruptive activity. An erratum to this article is available at .     

Dissolution/crystallization kinetics recorded in the 2002–2003 lavas of Stromboli (Italy)

On 28 December 2002, new vents opened on the flanks of Stromboli, just below the summit craters, interrupting the persistent activity of the volcano with a 7-month-long effusive eruption. We here report on the plagioclase size distribution (PlgSD) in lava samples collected following the chronology of the 2002–2003 eruption. Data reveal a linear PlgSD similar to that found in samples of normal Stromboli activity, indicating that the switch from Strombolian explosive to effusive activity is not associated with changes in texture. Nevertheless, the crystal size distribution slopes and intercepts exhibit slight sinusoidal temporal variations that are here ascribed to a magma supply mechanism able to induce “resonance” in the crystal size distribution, with an amplitude that depends on the supply rate.     

THE HISTORICAL RECORDS OF VOLCANIC ERUPTION IN THE KOREAN PENINSULA

The historical document record is of vital significance to determine the volcanic eruption history age in the volcanology research and it cannot be replaced by ¹⁴C dating and other methods. The volcanoes are widely distributed in the northeast area of China, but there is lack of relevant historical records. However, there are the records of the volcanic eruption in the historical documents of Goryeo Dynasty(AD918-1392)and Joseon Dynasty(AD1391-1910)in the Korean Peninsula which is separated by a river with China only. Some of the records have been widely used as important information to the research of Changbaishan Tianchi volcano eruption history by researchers both at home and abroad, but they have different opinions. On the basis of the historical documents in the Korean Peninsula, that is, the History of Goryeo Dynasty and the Annals of the Joseon Dynasty so on, the phenomena of volcanic eruptions, including the intuitive eruptive events and the doubtful volcanic eruption phenomenon such as "the ash fall", "the white hair fall", "the sky fire", "the dust fall" are investigated and put in order systematically in this paper. The results are as follows:1)The intuitive eruptive events are the 1002AD eruption of Mt. Halla volcano on Jeju Island, Korea Peninsula, and the 1007AD volcanic eruption offshore to the west of Jeju Island, Korea Peninsula, as well as the 1597AD eruption of Mt. Wangtian'e volcano in Changbai County, Jilin Province, China; 2)"The ash fall" is airborne volcanic ash, and those "ash falls" happening in 1265, 1401-1405, 1668, 1673 and 1702AD are possibly the tephra of Changbaishan Tianchi volcano; 3)"The white hair fall" is Pele's hair and it is speculated that the "white hair fall "happening in 1737AD is related to Changbaishan Tianchi volcanic eruption; 4)If regarding "the sky fire" as the volcanic eruption phenomenon, "the sky fire" happening in 1533AD is possibly the Changbaishan volcanic eruption event, and "the sky fire" in 1601-1609AD may be the eruptive event of the Longgang volcano in Jilin Province, China or Changbaishan Tianchi volcano; 5)"The dust fall" is recorded in many historical documents. However, "the dust fall" is not the volcanic ash fall but the phenomenon of loess fall. So, it is improper to determine the eruptive events of Changbaishan Tianchi volcano on the basis of "the dust fall".     

Shallow magma transport for the 2002–3 Mt. Etna eruption inferred from thermal infrared surveys

The 26 October 2002–28 January 2003 eruption of Mt. Etna volcano was characterised by lava effusion and by an uncommon explosivity along a 1 km-long-eruptive fissure on the southern, upper flank of the volcano. The intense activity promoted rapid growth of cinder cones and several effusive vents. Analysis of thermal images, recorded throughout the eruption, allowed investigation of the distribution of vents along the eruptive fissure, and of the nature of explosive activity. The spatial and temporal distribution of active vents revealed phases of dike intrusion, expansion, geometric stabilization and drainage. These phases were characterised by different styles of explosive activity, with a gradual transition from fire fountaining through transitional phases to mild strombolian activity, and ending with non-explosive lava effusion. Here we interpret the mechanisms of the dike emplacement and the eruptive dynamics, according to changes in the eruptive style, vent morphology and apparent temperature variations at vents, detected through thermal imaging. This is the first time that dike emplacement and eruptive activity have been tracked using a handheld thermal camera and we believe that its use was crucial to gain a detailed understanding of the eruptive event.     

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.     

Automatic Recognition of Landslides Based on Neural Network Analysis of Seismic Signals: An Application to the Monitoring of Stromboli Volcano (Southern Italy)

In the last 9 years, the amount and the quality of geophysical and volcanological observations of Stromboli's' activity have undergone a marked increase. This new information highlighted that the landslides on the Sciara del Fuoco flank are tightly linked to the volcanic activity. Actually, at the beginning of the December 28, 2002, effusive eruption, the seismic monitoring network was less dense than now, and therefore it is not known if there was an increase in the landslide rate before the eruption. Despite this, it is known that a big landslide occurred 2 days after the beginning of the eruption which caused a tsunami (December 30, 2002). More recently, the effusive eruption in February 2007 was preceded by an increase in landslides on the Sciara del Fuoco flank, which were recorded by the seismological monitoring system that had been improved after the 2002–2003 crisis. These episodes led us to believe that monitoring the Sciara del Fuoco flank instability is an important topic, and that landslides might be significant short-term precursors of effusive eruptions at the Stromboli volcano. To automatically detect landslide signals, we have developed a specialized neural algorithm. This can distinguish between landslides and the other types of seismic signals usually recorded at the Stromboli volcano (i.e., explosion quakes and volcanic tremor). The discrimination results show an average performance of 98.67 %. According to the experience of the crisis of 2007, to identify changes that can be considered as precursors of effusive eruptions, we set up an automatic decision-making method based on the neural network responses. This method can operate on a continuous data stream. It calculates a landslide percentage index (LPI) that depends on the number of records that are classified by the net as landslides over a given time interval. We tested the method on February 27, 2007, including the beginning of the effusive phase. The index showed an increase as early as at 09:00 UTC on that day and reached its maximum value (100 %) at 12:00, about 40 min before the onset of the eruption. After the beginning of the effusive phase, the index remains high due to the blocks that roll down along the slope from the front of the lava flow. On the basis of these tests, we propose a decision-making method that is able to recognize a trend in the LPI similar to that of 2007 eruption, allowing the identification of precursors of effusive phases at the Stromboli volcano.     

海口地区火山活动初步研究

海口地区的马鞍岭-雷虎岭火山群是中国为数不多的几个休眠火山群之一。通过对区域火山活动期次划分、深部岩浆囊探测以及对火山类型、规模、物质组成和溶岩覆盖面积的分析,总结了海口地区火山活动的时、空、强特征。结合对火山区地震、地磁、体应变和地热等观测资料的分析,对火山区深部岩浆活动的状态进行了初步评估。研究认为海口全新世火山区最后一次火山喷发距今约4 000a左右,其现今火山活动已趋于平静,未来的火山活动可能向1605年琼州7.5级大地震震中区迁移