The role of the Pernicana Fault System in the spreading of Mt. Etna (Italy) during the 2002–2003 eruption

Flank instability and collapse are observed at many volcanoes. Among these, Mt. Etna is characterized by the spreading of its eastern and southern flanks. The eastern spreading area is bordered to the north by the E–W-trending Pernicana Fault System (PFS). During the 2002–2003 Etna eruption, ground fracturing along the PFS migrated eastward from the NE Rift, to as far as the 18 km distant coastline. The deformation consisted of dextral en-echelon segments, with sinistral and normal kinematics. Both of these components of displacement were one order of magnitude larger (~1 m) in the western, previously known, portion of the PFS with respect to the newly surveyed (~9 km long) eastern section (~0.1 m). This eastern section is located along a pre-existing, but previously unknown, fault, where displaced man-made structures give overall slip rates (1–1.9 cm/year), only slightly lower than those calculated for the western portion (1.4–2.3 cm/year). After an initial rapid motion during the first days of the 2002–2003 eruption, movement of the western portion of the PFS decreased dramatically, while parts of the eastern portion continued to move. These data suggest a model of spreading of the eastern flank of Etna along the PFS, characterized by eruptions along the NE Rift, instantaneous, short-lived, meter-scale displacements along the western PFS and more long-lived centimeter-scale displacements along the eastern PFS. The surface deformation then migrated southwards, reactivating, one after the other, the NNW–SSE-trending Timpe and Trecastagni faults, with displacements of ~0.1 and ~0.04 m, respectively. These structures, along with the PFS, mark the boundaries of two adjacent blocks, moving at different times and rates. The new extent of the PFS and previous activity over its full length indicate that the sliding eastern flank extends well below the Ionian Sea. The clustering of seismic activity above 4 km b.s.l. during the eruption suggests a deep décollement for the moving mass. The collected data thus suggests a significant movement (volume >1,100 km³) of the eastern flank of Etna, both on-shore and off-shore.Editorial responsibility: R. Cioni     

Quenched mafic inclusions in ≤2200 years B.P. deposits at Augustine Volcano,Alaska

Origins and positions of gold fields and ores, particularly of placers, in the Yana-Kolyma area and elsewhere in the Northeast, as indicated by the morphostructural analysis and the behavior of gold in endogenic and exogenic processes. – V.P. Sokoloff.     

新疆于田阿什库勒火山群若干新的野外地质证据

位于青藏高原北缘的新疆于田阿什库勒火山群地区是中国大陆现代火山和地震活动最活跃的构造区之一,是研究青藏高原演化的重要窗口,但由于地处高海拔(4700~5600m.a.s.l.)无人区,研究程度还很低,甚至还不曾开展过系统详细的野外地质调查。本文报道最近在这一地区的一次野外考察结果,在前人鲜为涉足的阿什库勒盆地北部发现了苏贝稀1号、苏贝稀2号和托甫热三个火山口,并且在前人有争议的盆地南部高台山地区找到确凿的证据,重新认定高台山火山的存在。我们还在高台山和椅子山火山之间考察了前人未曾报道的小黑沟火山。由小黑沟流向乌鲁克库勒湖的火山熔岩流动和冷却过程中形成的熔岩冢等火山地质景观在严酷的荒漠环境中迄今仍然保存完好,表明小黑山火山很可能是一座全新世的火山,是本次考察到的最年轻的火山。     

腾冲新生代火山作用流体组成及其来源——火山岩流体化学组成和碳同位素制约

腾冲新生代火山区是青藏高原唯一幔源挥发份大量排放的火山-地热区,大规模火山作用的流体组成的系统研究具有多方面的科学意义。对腾冲马鞍山、老龟坡和打鹰山等地新生代火山岩进行流体化学组成和碳同位素分析,结果表明腾冲新生代火山岩的流体组成中H2O占有极高的比例,CO2、N2和O2的含量较高,而且不同火山区的流体组成有所差异。CO2的δ13C值为-27.1‰~-7.5‰,位于地壳和地幔范围之间;CH4、C2H6、C3H8和C4H10等甲烷同系物的碳同位素组成随碳数增高具有整体正序、C2H6与C3H8局部反序的分布特征,显示海洋环境I型有机质热裂解成因烃类气体的特征。腾冲火山作用中存在地幔来源的CO2,岩浆存在轻微的CO2去气作用。含碳流体挥发份主要表现为俯冲大洋板片脱出流体挥发份的加入,特别是俯冲洋壳沉积有机质热裂解产物,大量的H2O可能来源于岩浆上升过程中围岩流体或再循环流体的加入,不同火山区岩浆上升演化的差异造成了流体组成的不同。     

基于GIS的建筑物地震保险损失评估研究

本文讨论了与我国大陆火山地区相关的主要火山灾害类型,即火山空降物、火山碎屑流、火山泥石流、火山熔岩穹与熔岩流的成灾机制和灾害效应,并回顾了国际上火山灾害区划的研究现状,在此基础上,提出了适合我国具体情况的具有概率含义的火山灾害区划图的编图思路。     

Viscosity of andesitic melts—new experimental data and a revised calculation model

The viscosity of a synthetic andesite-like melt was measured in the low viscosity range (10¹-10⁶ Pa s) using the falling sphere(s) method and in the high viscosity range (10⁸-10¹³ Pa s) using parallel-plate viscometry. Falling sphere experiments with melts containing 2.3 and 5.6 wt.% H₂O were carried out in an internally heated gas pressure vessel (IHPV) at 500 MPa confining pressure. The sinking velocity of Pt and Pd spheres and in one case of a corundum sphere was used to measure the melt viscosity. In addition, a creep experiment was performed at ambient pressure using a glass containing 2.73 wt.% H₂O . A more water-rich glass (5.6 wt.% H₂O ) was investigated with a high pressure parallel-plate viscometer at 400 MPa confining pressure in an IPHV. By combining our new data with previous results for a similar melt composition we derived the following expression to describe the viscosity η (in Pa s) as a function of temperature T (in K) and water content w (in wt.%)

     

A Potential Flood Hazard Caused by Tianchi Volcano Eruption in Changbai Mountain, Northeast China

Geohazards appear to be increasing in frequency globally. It is of necessity to actively manage these natural hazards to minimize loss of life and property. From an early warning perspective, this paper stresses the potential fatal flood hazard represented by the huge volume of water in Tianchi Lake, the unique geography of Changbai Mountain, and the limited flood control ability in the upstream of the Songhua River. Northeast Asian countries should keep a watchful eye on the Changbai volcano cooperatively,...     

Elementary analysis of data from Tianchi Volcano

Tianchi Volcano is the largest potential erupticve volcano in China. Analyzing these data on seismic monitoring, deformation observation and water chemistry investigation gained from the Tianchi Volcano Observatory (TVO), the authors consider that the Tianchi Volcano is in going into a new flourishing time.     

The 1984 to 1996 cyclic activity of Lascar Volcano, northern Chile: cycles of dome growth, dome subsidence, degassing and explosive eruptions

 Lascar Volcano (5592 m; 23°22'S, 67°44'W) entered a new period of vigorous activity in 1984, culminating in a major explosive eruption in April 1993. Activity since 1984 has been characterised by cyclic behaviour with recognition of four cycles up to the end of 1993. In each cycle a lava dome is extruded in the active crater, accompanied by vigorous degassing through high-temperature, high-velocity fumaroles distributed on and around the dome. The fumaroles are the source of a sustained steam plume above the volcano. The dome then subsides back into the conduit. During the subsidence phase the velocity and gas output of the fumaroles decrease, and the cycle is completed by violent explosive activity. Subsidence of both the dome and the crater floor is accommodated by movement on concentric, cylindrical or inward-dipping conical fractures. The observations are consistent with a model in which gas loss from the dome is progressively inhibited during a cycle and gas pressure increases within and below the lava dome, triggering a large explosive eruption. Factors that can lead to a decrease in gas loss include a decrease in magma permeability by foam collapse, reduction in permeability due to precipitation of hydrothermal minerals in the pores and fractures within the dome and in country rock surrounding the conduit, and closure of open fractures during subsidence of the dome and crater floor. Dome subsidence may be a consequence of reduction in magma porosity (foam collapse) as degassing occurs and pressurisation develops as the permeability of the dome and conduit system decreases. Superimposed upon this activity are small explosive events of shallow origin. These we interpret as subsidence events on the concentric fractures leading to short-term pressure increases just below the crater floor. Received: 12 December 1996 / Accepted: 6 May 1997