Large dyke intrusion and small eruption: The December 24, 2018 Mt. Etna eruption imaged by Sentinel‐1 data

On December 24th, Mt. Etna volcano underwent a seismic crisis beneath the summit and upper southern flank of the volcano, accompanied by significant ash emission. Eruptive fissures opened at the base of summit craters, propagating SE‐wards. This lateral eruption lasted until December 27th. Despite the small eruption, seismic swarm and ground deformation were very strong. Sentinel‐1 interferograms show a wide and intense ground deformation with some additional features related to volcano‐tectonic structures. We inverted DInSAR data to characterise the magma intrusion. The resulting model indicates that a large dyke intruded but aborted its upraise at about the sea level; however, this big intrusion stretched the edifice, promoting the opening of the eruptive fissures fed by a shallower small dyke, and activating also several faults. This model highlights that a big intrusion beneath a structurally complex volcano represents a main issue even if the eruption is aborted.     

Seismological constraints on the 2018 Mt. Etna (Italy) flank eruption and implications for the flank dynamics of the volcano

3D earthquake locations, focal mechanisms and stress tensor distribution in a 16‐month interval covering the 2018 Mt. Etna flank eruption, enabled us to investigate the relationship between magma intrusion and structural response of the volcano and shed light on the dynamic processes affecting the instability of Mt. Etna. The magma intrusion likely caused tension in the flanks of the volcano, leading to significant ground deformation and redistribution of stress on the neighbouring faults at the edge of Mt. Etna's unstable sector, encouraging the ESE sliding of the eastern flank of the volcano. Accordingly, FPSs of the post‐eruptive events show strike slip faulting mechanisms, under a stress regime characterized by a maximum compressive σ₁, NE‐SW oriented. In this perspective, any flank eruption could temporarily enhance the sliding process of both the southern and eastern flanks of the volcano.     

High rate GPS data on active volcanoes: an application to the 2005–2006 Mt. Augustine (Alaska,USA) eruption

Volcanic eruptions are usually preceded by measurable signals of growing unrest, the most evident of which are the increase in seismicity and ground deformation. It is also important to identify precursors of a possible renewal of the volcanic activity and to distinguish between an eruptive activity characterized by an intrusion (with the related destructive power) and a migration of magma stored in the main conduits. The 2005–2006 eruption at Mt. Augustine (Alaska, USA) is a good example of a massive migration of magmatic fluids from depth (about 1 km b.s.l.) under the effect of gas overpressure. The movements, recorded by High Rate GPS (HRGPS) data (15 s of sampling and processing rate) from the stations deployed on the volcano, define the dimensions and the characteristics of the shallow plumbing system. In this study, we propose a model of the different stages preceding the effusive phase (the ‘precursory phase’), where gas overpressure in the body of the volcano opens the terminal conduit.     

Mechanical response of the south flank of kilauea volcano, hawaii, to intrusive events along the rift systems

Increased earthquake activity and compression of the south flank of Kilauea volcano, Hawaii, have been recognized by previous investigators to accompany rift intrusions. We further detail the temporal and spatial changes in earthquake rates and ground strain along the south flank induced by six major rift intrusions which occurred between December 1971 and January 1981. The seismic response of the south flank to individual rift intrusions is immediate; the increased rate of earthquake activity lasts from 1 to 4 weeks. Horizontal strain measurements indicate that compression of the south flank usually accompanies rift intrusions and eruptions. Emplacement of an intrusion at a depth greater than about 4 km, such as the June 1982 southwest rift intrusion, however, results in a slight extension of the subaerial portion of the south flank.Horizontal strain measurements along the south flank are used to locate the January 1983 east-rift intrusion, which resulted in eruptive activity. The intrusion is modeled as a vertical rectangular sheet with constant displacement perpendicular to the plane of the sheet. This model suggests that the intrusive body that compressed the south flank in January 1983 extended from the surface to about 2.4 km depth, and was aligned along a strike of N66°E. The intrusion is approximately 11 km in length, extended beyond the January 1983 eruptive fissures, which are 8 km in length and is contained within the 14-km-long region of shallow rift earthquakes.     

Evidence of a shallow magma intrusion beneath the NE Rift system of Mt. Etna during 2013

Continuous GPS (CGPS) data, collected at Mt. Etna between April 2012 and October 2013, clearly define inflation/deflation processes typically observed before/after an eruption onset. During the inflationary process from May to October 2013, a particular deformation pattern localised in the upper North Eastern sector of the volcano suggests that a magma intrusion had occurred a few km away from the axis of the summit craters, beneath the NE Rift system. This is the first time that this pattern has been recorded by CGPS data at Mt. Etna. We believe that this inflation process might have taken place periodically at Mt. Etna and might be associated with the intrusion of batches of magma that are separate from the main feeding system. We provide a model to explain this unusual behaviour and the eruptive regime of this rift zone, which is characterised by long periods of quiescence followed by often dangerous eruptions in which vents can open at low elevation and thus threaten the villages in this sector of the volcano.     

Extensional tectonics and volcano lateral collapses: insights from Ollagüe volcano (Chile‐Bolivia) and analogue modelling

Understanding the process of volcanic lateral collapse, which may be governed by numerous possible factors, can be significantly improved by identifying the role of each factor. Here we test the perturbation induced in a volcano by tectonic normal faulting in the basement, magma inflation and multiple flank deformation, based on fieldwork and analogue experiments. Ollagüe Volcano (Chile‐Bolivia) provides a good example of a sector collapse with exposed substrate extensional tectonics, and our experiments have been done with conditions consistent with field data. Results show that none of the possible tectonic conditions led to complete lateral failure; in agreement also with the field data, sector collapse of the model cone occurred only when a shallow magmatic intrusion within the volcano was reproduced. We also found out that volcano flank deformation is enhanced if a previous flank destabilization occurred, interleaved by new cone growth. Terra Nova, 18, 282–289, 2006     

盆地火山地层时空属性和岩石地层单位

火山地层具有如下显著特征:建造短暂和剥蚀长久的时间属性,受喷发方式和古地形控制的空间属性,地层产状变化规律与喷出口相关。尝试以地层界面反映时间属性、岩石组合和几何外形反映空间属性,结合产状变化规律对火山地层单位进行了厘定,从常用的地层单位中选用术语,从小到大依次是层、堆积单元、火山机构、段、组和群。本文详细介绍前三类单位的分类和识别标志:层是根据颜色、化学成分和岩石组构的差异划分;堆积单元依据喷发方式和就位环境划分为熔岩流/火山碎屑流/再搬运火山碎屑流3类,单元内地层产状变化连续,单元之间常以喷发不整合/整合界面分隔;火山机构是堆积单元有序叠置的产物,火山地层沿喷发口向四周倾斜、向边缘过渡时地层倾角逐渐变缓,火山机构间常以喷发间断不整合界面分隔。指出盆地火山地层格架的建立需要突出地层的空间属性、火山地层埋藏史应该基于火山机构的中心和远源两个区域来分析,基于重新厘定的火山地层单位建立的地层格架更有利于对储层分布规律的认识。     

Susceptibility of intrusion-related landslides at volcanic islands: the Stromboli case study

Susceptibility of intrusion-related landslides in an active volcano was evaluated coupling the landslide susceptibility estimation by random forest (RF), and the probabilistic volcanic vent opening distribution, as proxy for magma injection, using the QVAST tool. In order to develop and test the method proposed here, the RF/QVAST approach was adopted for Stromboli volcano (Southern Italy) since it experienced moderate to huge instability events, it is geomorphologically prone to instability events, and it is affected by active intense volcanic activity that can produce slope instability. The main destabilizing factors of the volcanic flanks are the slope, the aspect, the terrain roughness, the land cover and the litho-technical features of the outcropping rocks. Estimation of volcanic susceptibility shows that the areas with high probability of new vent opening are located in the north-western unstable volcano flank (Sciara del Fuoco), in the volcano summit and the north-eastern volcano flank coherent with the possible re-activation of the eruptive fissures related to the regional tectonic setting. The areas with higher probability of intrusion-related landslides are located in the upper part of the Sciara del Fuoco, while the rest of the island show moderate to low probability of intrusion-related landslide occurrence.     

吉林省龙岗火山群南龙湾第四纪火山碎屑颗粒特征研究

爆炸性火山喷发形成的碎屑颗粒的粒度、分选性、表面结构和内部结构等特征与火山喷发的机制、岩浆与水作用的程度、搬运过程等有着重要的联系。本文以此为线索,研究了龙岗火山群南龙湾火山的一个剖面,以探讨其喷发类型和特征。在该剖面上采集了不同层位火山碎屑颗粒样品,然后进行显微形貌观测、粒度分析和扫描电镜形貌观测。显微镜下观测表明,射汽爆发、射汽岩浆爆发和岩浆爆发的碎屑颗粒具有不同的成分和形貌特征。粒度分析结果显示,粒度与喷发类型之间存在很好的对应关系,不同的爆发类型具有不同的分维值D范围。SEM分析可以提供有关火山喷发特征对火山碎屑颗粒的影响。本文的研究结果表明,南龙湾火山喷发为爆炸式喷发,包括早期的射汽岩浆爆发,到岩浆爆发至晚期以射汽爆发为主的射汽岩浆爆发的不同阶段,该区火山喷发的不同时期,水参与喷发的程度不同。     

Volcanic and Scientific Activity at Kick ’em Jenny Submarine Volcano 2001–2002: Implications for Volcanic Hazard in the Southern Grenadines,Lesser Antilles

Kick em Jenny submarine volcano, ~8 km north of Grenada, has erupted at least 12 times since it was first discovered in 1939, making it the most frequently active volcano in the Lesser Antilles arc. The volcano lies in shallow water close to significant population centres and directly beneath a major shipping route, and as a consequence an understanding of the eruptive behaviour and potential hazards at the volcano is critical. The most recent eruption at Kick em Jenny occurred on December 4 2001, and differed significantly from past eruptions in that it was preceded by an intensive volcanic earthquake swarm. In March 2002 a multi-beam bathymetric survey of the volcano and its surroundings was carried out by the NOAA ship Ronald H Brown. This survey provided detailed three-dimensional images of the volcano, revealing the detailed morphology of the summit area. The volcano is capped by a summit crater which is breached to the northeast and which varies in diameter from 300 to 370 m. The depth to the summit (highest point on the crater rim) is 185 m and the depth to the lowest point inside the crater is 264 m. No dome is present within the crater. The crater and summit region of Kick em Jenny are located at the top of an asymmetrical cone which is about 1300 m from top to bottom on its western side. It lies within what appear to be the remnants of a much larger arcuate collapse structure. An evaluation of the morphology, bathymetry and eruptive history of the volcano indicates that the threat of eruption-generated tsunamis is considerably lower than previously thought, mainly because the volcano is no longer thought to be growing towards the surface. Of more major and immediate concern are the direct hazards associated with the volcano, such as ballistic ejecta, water disturbances and lowered water density due to degassing.     

SO2 degassing from Turrialba Volcano linked to seismic signatures during the period 2008–2012

In 1996, after 150 years of relative calm, Turrialba Volcano was reawakening. A visible plume and serious damage to surrounding vegetation due to acid rain are the most obvious signals. As part of the Network for Observation of Volcanic and Atmospheric Change project, four gas-monitoring stations were initially installed on the west flank of the volcano with the purpose of measuring sulphur dioxide emissions during this period of increased activity using the scanning-differential optical absorption spectroscopy technique. We present here the results of semicontinuous gas flux measurements over a period of 5 years (from 2008 to 2012), providing a novel data set that documents a relatively rapid increase in SO₂ fluxes from around 350 t day^?1 to around 4,000 t day^?1 leading up to an eruptive period, followed by a gradual return to the former baseline values. Gas flux data were also compared with seismic data for selected periods of interest, providing insights into the link between degassing and seismicity. The most important result from this comparison is the identification of an inflexion point in the gas emissions followed by a clearly increasing trend in seismic activity, distinguishable 6 months prior to a phreatic eruptive event that occurred on 5 January 2010. This signal can be interpreted as a possible indicator of future eruptive events. Monitoring of SO₂ thus complements seismic monitoring as a forecasting tool for eruptive events. Such monitoring is critical considering the proximity of Turrialba to the Central Valley, an area inhabited by more than 50 % of Costa Rica’s population.     

Interaction between seismic and volcanic deformation: a possible interpretation of ground deformation observed at Vulcano Island (1976–84)

Levelling measurements carried by Osservatorio Vesuviano over Vulcano Island (North Sicily) since June 1976 show a complex history of small but significant vertical movements which took place after the ‘Patti earthquake’ of 15/4/1978. Three phases can be identified in the time history of ground deformation: (I) co-seismic subsidence of the northern part of the Island with respect to the southern part, followed by (II) transient inflation of the central region surrounding ‘La Fossa’ volcano, and finally (III) deflation and subsidence to stationary values greater than phase I. Large variations in temperature and gas content of magmatic origin were also detected in fumaroles along the crater rim of ‘La Fossa’. The coincidence in time of the earthquake with the start of the deformation history, the proximity of the event to Vulcano Island and the favourable mechanism (right lateral) and orientation (NNW) of the fault strike, suggest that the earthquake triggered the observed deformation. Among the plausible models, one seems particularly able to reproduce the amplitude and time evolution of the geodetic data, in a manner consistent with the geochemical observations. According to this model the earthquake, while generating a compressive stress field in the quadrant of Vulcano Island, induced at first a relative coseismic subsidence of the northern part of the island, accompanied by a large increase of the mean stress within a magma chamber at ～ 6.5 km depth. Volatile fluids were then released from the top of the magma chamber and migrated towards the surface following the enhanced pressure gradient. As a result fluid pressure diffusion around the magma chamber induced a local transient uplift of ground that vanished after exhaustion of the overpressure at the source, and finally left a permanent dislocation deformation, possibly amplified by the post-seismic relaxation of the earthquake deviatoric stress. This interpretation is qualitatively consistent with the one suggested by Ferri et al. (1988).     

Forecasting volcanic events: some contemporary issues

As the regions around active volcanoes succumb to large increases in population, particularly in the developing world where most of the high-risk volcanoes are located, the threat posed by eruptions becomes increasingly serious. Improvements in eruption forecasting are critical to combat this situation, for reducing injury and loss of life, and for minimizing the detrimental effects to local economies and to the fabric of society. Better-constrained forecasts are strongly dependent on geophysical and other data gathered during a program of volcano surveillance, and we reveal how, if interpreted in terms of static rock fracturing, analysis of changes in volcanic seismicity and ground deformation may be used to forecast more accurately the onset of eruptive activity. As illustrated by recent events at several volcanoes, studies of previous activity, increased levels of monitoring, and improved training of scientists are also all crucial to improving forecasts of impending eruptions.     

Geomorphology and tectonics of the Dorrigo Plateau,N.S.W.

The Dorrigo Plateau is covered by basalt, which is a remnant of the 18 Ma old Ebor Volcano. The centre of this volcano is an intrusion in the Bellinger Valley. The volcano was erupted on a palaeoplain of moderate relief. Subsequent uplift and tilting led to erosion of the Nambucca Beds, together with much of the volcano, and creation of a major escarpment, part of the Great Escarpment of eastern Australia. In this area the Great Escarpment is younger than 18 Ma.     

长白山天池地区全新世以来火山活动及其特征

长白山火山全新世规模最大的喷发活动发生在公元1199-1200年,即800年前的大爆发,被确定为普林尼或布里尼(Plinian)式喷发。这次大爆发形成体积巨大的、分布广泛的以空中降落堆积物为主的火山喷发碎屑堆积物,在长白山火山周围,远至日本都留下了地质记录。文章辨认并划分了这次大爆发火山碎屑物的成因类型:火山喷发空中降落堆积物(airfalltephra)、火山碎屑流(pyroclasticflow)状堆积物和火山泥流(lahar)堆积物,并且点、面结合,近、远和国内、国外兼顾,分析了这些火山碎屑物的主要特征、分布和相互关系,进而确定这些火山碎屑物分别属于两次普林尼式爆发。第1次(早期)普林尼式爆发称赤峰期,火山喷发模式为:普林尼式喷发柱(赤峰空落浮岩层)-火山碎屑流(长白山火山碎屑流层),随即主要由火山碎屑流诱发火山泥流(二道白河火山泥流层);第2次(晚期)普林尼式爆发称园池期,喷发模式为:普林尼式喷发柱(园池空落浮岩火山灰层)-火山碎屑流(冰场火山碎屑流层)。在层序上将气象站期碱流岩置于800年前大爆发火山碎屑物之下是正确的,其时代为晚更新世-全新世早期。     

Models of Ground Deformation and Eruption Magnitude from a Deep Source at Popocatepetl Volcano,Central Mexico

Popocatepetl volcano in Central Mexico entered its latest stage of activity in late 1994. Due to the nature of its eruptive history and its location in a heavily populated area, it constitutes the highest risk in the cuntry. For this reason the volcano is currently under continuous surveillance; yet the interpretation of the information is carried out mostly on empirical basis and an integrating working model is lacking, at the present. In this paper, models of elastic deformation and mass erupted are developed to estimate the mass erupted according to the observed deformation patterns. We present results obtained from input based upon a gravimetric model of the volcano's internal structure and reasonable physical parameters of the volcanic system. These results are helpful in the planning of deformation and gravimetric observations aimed to forecast a major eruption.     

酸性,中酸性岩区火山构造洼地岩相—构造—成矿（找矿）模式

酸性、中酸性岩区火山构造洼地中火山－侵入岩浆活动广泛、强烈，因而在纵向上形成了一套巨厚的以酸性火山岩为主体，夹有火山喷沉积夹层的多旋回、多岩相组合的高钾钙碱性火山－侵入杂岩系，从定位的性质与深度可分为两个基本相带：以火山喷发为主的岩相划为地表管近地表相带；以次火山－浅成侵入为主的岩相划为近地表和火山根部相带。     

Volcanic hazard from San Martin Tuxtla Volcano,Tuxtla Volcanic Field,Veracruz, México: probability maps of ashfall deposition from possible future eruption

San Martin Tuxtla Volcano, the largest and highest edifice in the Tuxtla Volcanic Field, had explosive eruptions in 1664 and 1793. This volcano poses the highest hazard for the growing population centers surrounding it. The impacts and deposits of the 1793 eruption have been studied recently, and some of its characteristics, such as eruptive mass, grain-size distribution of the products and plume height, have been estimated. These data, together with daily data on wind velocities taken in the nearby city of Veracruz, have been used to conduct numerical modeling of ash distribution from an eruptive column comparable to that estimated during the 1793 event. Using wind velocities of randomly chosen days, we constructed probability maps of areas likely to receive, at least 1, 5, or 10 cm of ash. Our results indicate that an area about 1.3 × 10⁴ km² has a 12% probability of being covered by an ash fall more than 1 cm thick, if a mass of 10¹⁴ g was erupted and deposited from a 10-km-high eruptive plume. The results presented in this paper serve as a scientific basis to estimate volcano risk in the area from a possible eruption, consisting of one or several large explosive events, at San Martin Tuxtla volcano.     

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。     

Generation of Porphyritic and Equigranular Mafic Enclaves During Magma Recharge Events at Unzen Volcano, Japan

Mafic to intermediate enclaves are evenly distributed throughoutthe dacitic 1991–1995 lava sequence of Unzen volcano,Japan, representing hundreds of mafic recharge events over thelife of the volcano. This study documents the morphological,textural, chemical, and petrological characteristics of theenclaves and coexisting silicic host lavas. The eruptive productsdescribed in this study appear to be general products of magmamingling, as the same textural types are seen at many othervolcanoes. Two types of magmatic enclaves, referred to as Porphyriticand Equigranular, are easily distinguished texturally. Porphyriticenclaves display a wide range in composition from basalt toandesite, are glass-rich, spherical and porphyritic, and containlarge, resorbed, plagioclase phenocrysts in a matrix of acicularcrystals and glass. Equigranular enclaves are andesitic, non-porphyritic,and consist of tabular, medium-grained microphenocrysts in amatrix glass that is in equilibrium with the host dacite magma.Porphyritic enclaves are produced when intruding basaltic magmaengulfs melt and phenocrysts of resident silicic magma at theirmutual interface. Equigranular enclaves are a product of a moreprolonged mixing and gradual crystallization at a slower coolingrate within the interior of the mafic intrusion. KEY WORDS: mafic enclaves; quenched mafic inclusions; magma mingling; Unzen volcano; Unzen Scientific Drilling Project; resorbed plagioclase