Dynamics of volcanic eruptions: Understanding electric signatures for activity monitoring

Aside common methods as seismology, ground deformation, and geochemistry, electromagnetic and especially electric ones can efficiently be applied for imaging and monitoring active volcanoes and hydrothermal systems that most often control the initial eruptive phase. Surveys and mappings image ground fluids flow, faults systems, and structural interfaces with anomalies up to several hundred of mV. Reiteration of surveys highlights time and spatial evolution. Continuous networks must extend surveys when the activity becomes stronger. Resolution in the data can reach a few microvolts as compared to the tens of millivolts for surveys. Observations made on several volcanoes definitively show that electric signals, up to some tens of millivolts, may appear some hours to a few weeks before ground deformation and seismicity, and are related to some extent to the location of the future activity. These transient signals may have a relationship with those recorded aboard satellites. Both of them appear during the transition period between the “fatigue” and the “dynamical” stages, which announces accelerating and irreversible processes.     

长白山火山喷发物的堆积类型及火山活动机理

本文对长白山火山地质发展过程中的两大喷发期和七个喷发阶段作了系统阐述,详细划分、描述了喷发物堆积类型及特征,论述了火山活动机理及演化历程。首次指出长白山火山基浪堆积,对新发现的侵入相和次火山岩相岩百与喷出相岩石做了对比,指出同源于一个碱性岩浆房。     

吉林长白山天池火山岩年代-40Ar-39Ar

本文综合分析了长白山天池火山岩的类型及年代学研究结果,在此基础上对白头山期两期粗面岩进行了Ar-Ar年代学研究,确定了这两期火山活动的时代分别为123±7和123±10千年.文章还讨论了全新世天池火山喷发的环境意义及对东亚气候变化的影响.     

Evolution of the seismic activity from the 1982 eruption of El Chichon Volcano, Chiapas, Mexico

 We analyzed more than 1700 earthquakes related to the 1982 eruption of El Chichon volcano in southern Mexico. The data were recorded at specific periods throughout the whole eruptive interval of March to April 1982, by three different networks. The seismic activity began several months before the first eruption on 28 March. During this period the seismicity consisted of hybrid and long-period shallow earthquakes most likely related to processes of faulting, fracturing, and fluid movement underneath the volcano. The foci of events occurring before the eruption circumscribe an aseismic zone from approximately 7 to 13 km below the volcano. After the eruption, the seismic activity consisted of tectonic-type earthquakes that peaked at 1200 events/h. This later activity occurred over a wide range of depths, mostly between 5 and 20 km, that includes the former aseismic zone and is roughly limited by the major tectonic faults in the area. Received: 19 May 1998 / Accepted: 13 June 1999     

Geochemistry of recent hydrothermal systems of Mendeleev Volcano （Kuril Islands） and surrounding waters

On the Kuril Islands there are 85 volcanoes, 39 of which are active. Hot springs and mud pots are wide spread in this area and have significant inputs on the chemical composition of the surrounding surface waters and environment. We present results of trace elements as well as data on H, O, S, and He isotope ratios for hydrothermal systems of the Mendeleev Volcano （Kunashir Island） and surrounding surface waters. Water and gas samples were taken from springs and holes as well as creeks and the Lesnaya River. Among the thermal water types, three main groups can be distinguished. The first group includes the waters, in which SO4^- ion predominant. The water temperature on the surface reaches 97℃, and TDS varies from a few g/L to 7 g/L. These waters are acid to superacid with pH values ranging 0.6 to 2.3. The second group is sodium-chloride waters. A maximum TDS is 14.2 g/L. The waters are neutral or alkaline; pH varies from 6.9 to 8.2. The third group is the sodium-chloride-sulfate-bicarbonate water. The Stolbovskie springs, located in the periphery of the Mendeleev Volcano are representative of this type. The pH of these waters is close to neutral. TDS is 1.9 g/L. They are rather the derivatives of sodium-chloride waters arisen from dilution of them by subsurface waters. The Kuslyi Creek and Lesnaya River are located near the Mendeleev Volcano. The most acid springs discharge into the Kislyi Creek as a result pH of this creek being 2.5, and contents of most elements rather high. For example, the contents of dissolved solids of Si, Fe, Al, Mn, Zn, in waters of the Kislaya Creek are 22.1, 8.1, 6.2, 1.29, and 0.28 mg/L, and correspondently. The water of the Lesnaya River, （Before the Kislyi Creek, pH is about 8 with TDS 102 mg/L, but after the Kuslyi Creek, pH decreases and the concentrations of chemical elements increase. Debit of the Kislayi Creek in summer season is about 370 L/sec. It means that every day only this small creek inputs in the Lesnay River about 706 kg of Si;     

参量阵浅地层剖面仪在海底羽状流探测中的应用——以ATLAS P70在马克兰海域调查为例

海底渗漏的羽状流是沉积层赋存天然气水合物的重要证据之一,基于非线性水声学原理的参量阵浅地层剖面仪作为海洋探测的重要设备,对于获得羽状流在水体中的物性特征和渗漏点的浅地层信息有着重大意义.本文根据ATLAS P70浅地层剖面仪在马克兰海域调查中得到的浅地层剖面数据,结合多道地震数据、多波束数据以及地质样品等资料,刻画了研究区内羽状流形态特征,分析了羽状流区海底地层流体运移的通道以及近海底微地形地貌特征.通过研究发现在羽状流区伴随泥火山喷发,自生碳酸盐岩发育,剥蚀海底松散沉积物形成大小不一的麻坑,滋生生物群落等特征.反映在浅剖初始高频(20 kHz)数据界面上羽状流表现为柱状浑浊反射异常,形态呈火焰状,高度由80 m到1500 m不等;对应在次级低频(4 kHz)信号界面可以清晰显示流体渗漏的浅地层结构特征,从中不仅可以识别出流体的运移通道,如泥火山和管状通道等,而且揭示了流体逸散的残留地貌,如麻坑构造和海底滑坡等.本文依托参量阵浅地层剖面数据,对巴基斯坦马克兰海域羽状流有了较全面的认识,为天然气水合物的研究垫定了基础.     

腾冲、长白山、五大连池新生代火山岩Sr、Nd、Pb同位素地球化学特征

概括了腾冲、长白山、五大连池新生代火山岩岩石学、岩石化学基本特征,探讨了Ｓｒ、Ｎｄ、Ｐｂ同位素地球化学特征和岩浆源区性质。腾冲火山岩为高钾钙碱性岩系,高８７Ｓｒ／８６Ｓｒ、高２０６Ｐｂ／２０４Ｐｂ、２０８Ｐｂ／２０４Ｐｂ、低１４３Ｎｄ／１４４Ｎｄ,岩浆源区为俯冲带再循环富集地幔。长白山火山岩为超钾钙碱性岩系,低Ｓｒ高８７Ｓｒ／８６Ｓｒ,εＮｄ为－２３—＋２９,Ｐｂ同位素组成变化不大,岩浆源区为俯冲带再循环地幔。五大连池火山岩为超钾碱性岩系,高８７Ｓｒ／８６Ｓｒ、低１４３Ｎｄ／１４４Ｎｄ和２０６Ｐｂ／２０４Ｐｂ、２０８Ｐｂ／２０４Ｐｂ,岩浆源区为地幔内部交代作用所产生的富集地幔。     

Large debris avalanches and associated eruptions in the Holocene eruptive history of Shiveluch Volcano, Kamchatka, Russia

 Shiveluch Volcano, located in the Central Kamchatka Depression, has experienced multiple flank failures during its lifetime, most recently in 1964. The overlapping deposits of at least 13 large Holocene debris avalanches cover an area of approximately 200 km² of the southern sector of the volcano. Deposits of two debris avalanches associated with flank extrusive domes are, in addition, located on its western slope. The maximum travel distance of individual Holocene avalanches exceeds 20 km, and their volumes reach ∼3 km³. The deposits of most avalanches typically have a hummocky surface, are poorly sorted and graded, and contain angular heterogeneous rock fragments of various sizes surrounded by coarse to fine matrix. The deposits differ in color, indicating different sources on the edifice. Tephrochronological and radiocarbon dating of the avalanches shows that the first large Holocene avalanches were emplaced approximately 4530–4350 BC. From ∼2490 BC at least 13 avalanches occurred after intervals of 30–900 years. Six large avalanches were emplaced between 120 and 970 AD, with recurrence intervals of 30–340 years. All the debris avalanches were followed by eruptions that produced various types of pyroclastic deposits. Features of some surge deposits suggest that they might have originated as a result of directed blasts triggered by rockslides. Most avalanche deposits are composed of fresh andesitic rocks of extrusive domes, so the avalanches might have resulted from the high magma supply rate and the repetitive formation of the domes. No trace of the 1854 summit failure mentioned in historical records has been found beyond 8 km from the crater; perhaps witnesses exaggerated or misinterpreted the events. Received: 18 August 1997 / Accepted: 19 December 1997     

Identifying volcanic regimes using Hidden Markov Models

We examine the application of Hidden Markov Models (HMMs) to volcanic occurrences. The parameters in HMMs can be estimated from data by means of the Expectation–Maximization (EM) algorithm. Various formulations permit modelling the activity level of a volcano through onset counts, the intensity of a Markov Modulated Poisson Process (MMPP), or through the intervals between onsets. More elaborate models allow investigation of the relationship between durations and reposes. After fitting the model, the Viterbi algorithm can be used to identify the underlying (hidden) activity level of the volcano most consistent with the observations. The HMM readily provides forecasts of the next event, and is easily simulated. Data of flank eruptions 1600–2006 from Mount Etna are used to illustrate the methodology. We find that the volcano has longish periods of Poissonian behaviour, interspersed with less random periods, and that changes in regime may be more frequent than have previously been identified statistically. The flank eruptions of Mount Etna appear to have a complex time-predictable character, which is compatible with transitions between an open and closed conduit system. The relationship between reposes and durations appears to characterize the cyclic nature of the volcanoes activity.     

Fluvial sediment transport and deposition following the 1991 eruption of Mount Pinatubo

The 1991 eruption of Mount Pinatubo generated extreme sediment yields from watersheds heavily impacted by pyroclastic flows. Bedload sampling in the Pasig–Potrero River, one of the most heavily impacted rivers, revealed negligible critical shear stress and very high transport rates that reflected an essentially unlimited sediment supply and the enhanced mobility of particles moving over a smooth, fine-grained bed. Dimensionless bedload transport rates in the Pasig–Potrero River differed substantially from those previously reported for rivers in temperate regions for the same dimensionless shear stress, but were similar to rates identified in rivers on other volcanoes and ephemeral streams in arid environments. The similarity between volcanically disturbed and arid rivers appears to arise from the lack of an armored bed surface due to very high relative sediment supply; in arid rivers, this is attributed to a flashy hydrograph, whereas volcanically disturbed rivers lack armoring due to sustained high rates of sediment delivery. This work suggests that the increases in sediment supply accompanying massive disturbance induce morphologic and hydrologic changes that temporarily enhance transport efficiency until the watershed recovers and sediment supply is reduced.