A fast GIS-based risk assessment for tephra fallout: the example of Cotopaxi volcano, Ecuador

We present a comprehensive probabilistic hazard assessment for tephra fallout of Cotopaxi volcano (Ecuador), a quiescent but active stratovolcano known for its highly explosive behaviour. First, we developed a set of possible eruptive scenarios based on thorough field investigations, literature studies and using the Global Volcanism Program (GVP) database. Five eruption scenarios were identified, including two based on large pre-historical sub-Plinian/Plinian eruptions with eruptive parameters constrained from field investigations (One Eruption Scenario; OES) and three Eruption Range Scenarios (ERS) based on the Volcanic Explosivity Index (VEI) classification, for which eruptive parameters (i.e. erupted volume, plume height and median grainsize) were stochastically sampled within boundaries defined by VEI 3, 4 and 5. Second, the modelling was performed using the advection-diffusion model TEPHRA2 in combination with wind profiles from the NOAA NCEP/NCAR Reanalysis 1 database. We performed 1,000 runs for each eruption scenario, stochastically sampling a wind profile (OES and ERS) and a set of eruptive parameters (ERS only) at each run. Using the conditional probabilities of occurrence of eruption of VEI 3, 4 and 5 calculated from the GVP catalogue, we assessed the probability of tephra accumulation in a given time window. Based on the GVP database, a simple Poisson model shows that an eruption of VEI???3 has a 36?% probability of occurrence in the next 10?years. Finally, the hazard assessment was compiled based on three different outputs, including (i) probability maps for a given tephra accumulation, (ii) isomass maps for a given probability value and (iii) hazard curves for a given location. We conclude that the area west of Cotopaxi is exposed to light to severe tephra fallout for the smallest eruption magnitude considered (i.e. VEI 3). This area comprises a main communication axis (Panamerican Highway) topographically constrained at the bottom of the Interandean Valley, as well as the capital Quito and the town of Latacunga. In a companion paper, Biass et?al. (this volume) propose a method for a rapid risk assessment for tephra fallout using global and easily accessible data and the hazard assessment described here.     

长白山火山灾害及其对大型工程建设的影响

长白山火山是世界著名的活火山,历史时期有过多次喷发,有再次爆发的危险.长白山火山最大的一次爆发发生在公元1199-1200年,这次大爆发的火山灰最远到达距其1 000km远的日本北部.依据这次大爆发由火山喷发空中降落堆积物、火山碎屑流和火山泥流造成的巨大火山灾害,预测了长白山火山未来爆发火山灾害的类型、强度和范围,并编制了长白山火山未来爆发火山喷发空中降落堆积物灾害预测图、火山碎屑流灾害预测图和火山泥流灾害预测图.该研究可预防和减轻火山灾害,指导核电站等大型工程选址.     

中国火山灾害区划研究历史回顾与未来展望

火山灾害区划是防御和减轻火山灾害的一种有效的方法.以中国境内规模最大、喷发危险性最高、潜在火山灾害最强的长白山天池火山为例,回顾我国火山灾害区划研究历史,讨论典型火山喷发活动引起的主要火山灾害类型、成灾机制和灾害效应,总结不同历史阶段各种不同类型火山灾害区划图的优缺点,并结合目前国际上火山灾害区划的研究现状和编图技术,对我国未来编制具有概率含义的火山灾害区划图的思路提出展望.     

Multi-hazard risk mapping and assessment on an active volcano: the GRINP project at Mount Cameroon

To help improve the safety of its population faced with natural disasters, the Cameroon Government, with the support of the French Government, initiated a programme of geological risk analysis and mapping on Mount Cameroon. This active volcano is subject to a variety of hazards: volcanic eruptions, slope instability and earthquakes. Approximately 450,000 people live or work around this volcano, in an area which includes one of Cameroon’s main economic resources. An original methodology was used for obtaining the information to reply to questions raised by the authorities. It involves several stages: identifying the different geological hazard components, defining each phenomenon’s threat matrix by crossing intensity and frequency indices, mapping the hazards, listing and mapping the exposed elements, analysing their respective values in economic, functional and strategic terms, establishing typologies for the different element-at-risk groups and assessing their vulnerability to the various physical pressures produced by the hazard phenomena, and establishing risk maps for each of the major element-at-risk groups (population, infrastructures, vegetation, atmosphere). At the end of the study we were able (a) to identify the main critical points within the area, and (b) provide quantified orders of magnitude concerning the dimensions of the risk by producing a plausible eruption scenario. The results allowed us to put forward a number of recommendations to the Cameroon Government concerning risk prevention and management. The adopted approach corresponds to a first level of response to the authorities. Later developments should make it possible to refine the quality of the methodology.     

Alert system to mitigate tephra fallout hazards at Mt. Etna Volcano,Italy

Volcanic eruptions may create a wide range of risks in inhabited areas and, as a consequence, major economic damage to the surrounding territory. An example of volcanic hazard was given between 1998 and 2001 by Mt. Etna volcano, in Italy, with its frequent paroxysmal explosive activity that caused more than a hundred fire-fountain episodes. In the period January–June 2000, in particular, 64 lava fountains took place at the Southeast Crater. During the most intense explosive phase of each episode, a sustained column often formed, reaching up to 6 km above the eruptive vent. Then, the column started to expand laterally causing more or less copious tephra fallout on the slopes of Etna; ash and lapilli, therefore, constituted a serious danger for vehicular and air traffic. A software and hardware warning system was developed to mitigate the volcanic hazard indicating the areas affected by potential ash and lapilli fallout. The alert system was mainly based on the good correspondence between the pattern of volcanic tremor amplitude and the evolution of explosive activity. When a fixed tremor threshold was exceeded, a semiautomatic process started to send faxes to Civil Defence and Municipalities directly affected by tephra fallout, together with information on wind directions from the Meteorological Office. The application of this methodology, during the last 14 eruptive episodes in 2000 and the 14 events occurred in 2001, demonstrated the good correspondence between the forecasts on the areas affected by tephra fallout and the effective tephra distribution on land. Despite the integrity of the performance provided by the alert system, small discrepancies occurred in the technical procedure of alerting, for which possible solutions have been discussed. The improvement of this type of system, could become basic for the Etnean region and be proposed for similar volcanic areas throughout the world.     

The first ascent to the volcano Cotopaxi in Ecuador by Wilhelm Reiss (1838–1908)

The volcano Cotopaxi in South America is 5,897 m high and is one of the highest active volcanoes of the world and the second highest volcano in the Andes after the Chimborazo (6,310 m). In Ecuador, there are more than 20 volcanoes contributing to the spectacular mountain range diving this country between the western and eastern lowlands. There have been more than 50 reports of volcanic activity at Cotopaxi since 1738, among which those from the years 1744, 1768, and 1877 are the largest. During the 1877 eruption, the whole summit glacier collapsed and a huge mudflow spread out for more than 100 km and flooded the city of Latacunga. Five years prior to this catastrophic event, the German geologist Wilhelm Reiss from the University of Heidelberg ascended Cotopaxi for the first time together with his supporter Angel M. Escobar from Columbia.     

The Holocene tephrostratigraphic record of Lake Shkodra (Albania and Montenegro)

Two cores were recovered in the southeastern part of Lake Shkodra (Montenegro and Albania) and sampled for identification of tephra layers. The first core (SK13, 7.8 m long) was recovered from a water depth of 7 m, while the second core (SK19, 5.8 m long) was recovered close to the present‐day shoreline (water depth of 2 m). Magnetic susceptibility investigations show generally low values with some peaks that in some cases are related to tephra layers. Naked‐eye inspection of the cores allowed the identification of four tephra layers in core SK13 and five tephra layers in core SK19. Major element analyses on glass shards and mineral phases allowed correlation of the tephra layers between the two cores, and their attribution to six different Holocene explosive eruptions of southern Italy volcanoes. Two tephra layers have under‐saturated composition of glass shards (foiditic and phonolitic) and were correlated to the AD 472 and the Avellino (ca. 3.9 cal. ka BP) eruptions of Somma‐Vesuvius. One tephra layer has benmoreitic composition and was correlated to the FL eruption of Mount Etna (ca. 3.4 cal. ka BP). The other three tephra layers have trachytic composition and were correlated to Astroni (ca. 4.2 cal. ka BP), Agnano Monte Spina (ca. 4.5 cal. ka BP) and Agnano Pomici Principali (ca. 12.3 cal. ka BP) eruptions of Campi Flegrei. The ages of tephra layers are in broad agreement with eight ¹⁴C accelerator mass spectrometric measurements carried out on plant remains and charcoal from the lake sediments at different depths along the two cores. The recognition of distal tephra layers from Italian volcanoes allowed the physical link of the Holocene archive of Lake Shkodra to other archives located in the central Mediterranean area and the Balkans (i.e. Lake Ohrid). Five of the recognised tephra layers were recognised for the first time in the Balkans area, and this has relevance for volcanic hazard assessment and for ash dispersal forecasting in case of renewed explosive activity from some of the southern Italy volcanoes. Copyright © 2009 John Wiley & Sons, Ltd.     

Economic risk assessment of Cotopaxi volcano,Ecuador, in case of a future lahar emplacement

Natural Hazards - The Cotopaxi volcano in north-central Ecuador is one of the most dangerous volcanoes of the world due to its ability to generate far-reaching lahars, which are able to destroy...     

The 2011 eruption of Nabro volcano,Eritrea: perspectives on magmatic processes from melt inclusions

The 2011 eruption of Nabro volcano, Eritrea, produced one of the largest volcanic sulphur inputs to the atmosphere since the 1991 eruption of Mt. Pinatubo, yet has received comparatively little scientific attention. Nabro forms part of an off-axis alignment, broadly perpendicular to the Afar Rift, and has a history of large-magnitude explosive silicic eruptions, as well as smaller more mafic ones. Here, we present and analyse extensive petrological data obtained from samples of trachybasaltic tephra erupted during the 2011 eruption to assess the pre-eruptive magma storage system and explain the large sulphur emission. We show that the eruption involved two texturally distinct batches of magma, one of which was more primitive and richer in sulphur than the other, which was higher in water (up to 2.5 wt%). Modelling of the degassing and crystallisation histories demonstrates that the more primitive magma rose rapidly from depth and experienced degassing crystallisation, while the other experienced isobaric cooling in the crust at around 5 km depth. Interaction between the two batches occurred shortly before the eruption. The eruption itself was likely triggered by recharge-induced destabilisation of vertically extensive mush zone under the volcano. This could potentially account for the large volume of sulphur released. Some of the melt inclusions are volatile undersaturated, and suggest that the original water content of the magma was around 1.3 wt%, which is relatively high for an intraplate setting, but consistent with seismic studies of the Afar plume. This eruption was smaller than some geological eruptions at Nabro, but provides important insights into the plumbing systems and dynamics of off-axis volcanoes in Afar.     

全球主要火山灾害及其分布特征

本文研究了火山灾害各种致灾因子的物理过程和灾害特点,根据文献中记载的全球火山灾害,在进行火山灾害分区研究的基础上,研究了全球火山灾害分布特征.全球主要的火山灾害分布在8个主要区域.有记载的火山灾害在热带占73%,远高于火山喷发分布于热带区的比例.全球两个最强烈的火山灾害分布区都是围绕着位于板块结合部表现为复杂构造结的班达海和加勒比海,而且每一个灾害区都有3条分支.热带区第3个灾害区为中非区,地幔上隆是这里主要的动力学背景.本文还研究了1700年以来火山灾害时间分布特征,以及1993年以来各种火山灾害发生频次.     

Tephra Discovered in High Resolution Peat Sediment and Its Indication to Climatic Event

Floating tephra was deposited together with ice core,snow layer,abyssal sediment,lake sediments,and other geological records.It is of great significance to interpret the impact on the climate change of volcanic eruptions from these geological records.It is the first time that volcanic glass was discovered from the peat of Jinchuan(金川)Maar,Jilin(吉林)Province,China.And it is in situ sediments from a near-source explosive eruption according to particle size analysis and identification results.The tephra were neither from Tianchi(天池)volcano eruptions,Changbai(长白)Mountain,nor from Jinlongdingzi(金龙顶子)volcano about 1 600 aBP eruption,but maybe from an unknown eruption of Longgang(龙岗)volcano group according to their geochemistry and distribution.Geochemical characters of the tephra are similar to those of Jingiongdingzi,which are poor in s.Jica,deficient in alkali,Na20 content is more than K20 content,and are similar to distribution patterns of REE and incompatible elements,which helps to speculate that they originated from the same mantle magma with rare condemnation,and from basaltic explosive eruption of Longgang volcano group.The tephra,from peat with age proved that the eruption possibly happened in 15 BC-26 AD,is one of Longgang volcano group eruption that was not recorded and is earlier than that of Jinglongdingzi about 1 600 aBP eruption.And the sedimentary time of tephra is during the period of low temperature alteration.which may be the influence of eruption toward the local climate according to the correlativity of eruption to local temperature curve of peat cellulose oxygen isotope.     

Potential Hazards of Eruptions around the Tianchi Caldera Lake, China

Since the eruption of the Tianchi volcano about 1000 years ago, there have been at least 3 to 5 eruptions of small to moderate size. In addition, hazardous avalanches, rock falls and debris flows have occurred during periods between eruptions. A future eruption of the Tianchi volcano is likely to involve explosive interaction between magma and the caldera lake. The volume of erupted magma is almost in a range of 0.1-0.5 km3. Tephra fallout may damage agriculture in a large area near the volcano. If only 1% of the lake water were ejected during an eruption and then precipitated over an area of 200 km2, the average rainfall would be 100 mm. Moreover, lahars are likely to occur as both tephra and water ejected from the caldera lake fall onto flanks of the volcano. Rocks avalanching into the caldera lake also would bring about grave hazards because seiches would be triggered and lake water with the volume equal to that of the landslide would spill out of the existing breach in the caldera and cause flooding     

GIS and Volcanic Risk Management

Volcanic catastrophes constitute a majorproblem in many developing and developed countries. Inrecent years population growth and the expansion ofsettlements and basic supply lines (e.g., water, gas,etc.) have greatly increased the impact of volcanicdisasters. Correct land-use planning is fundamental inminimising both loss of life and damage to property.In this contribution Geographical Information Systems(GIS), linked with remote sensing technology andtelecommunications/warning systems, have emerged asone of the most promising tools to support thedecision-making process. Some GIS are presented fortwo volcanic areas in Italy, Mt. Etna and Vesuvius.GIS role in risk management is then discussed, keepingin mind the different volcanic scenarios of effusiveand explosive phenomena. Mt. Etna system covers alarge area (more than 1,000 km²) potentiallyaffected by effusive phenomena (lava flows) whichcause damage to both houses and properties in general.No risk to life is expected. The time-scales of lavaflows allow, at least in principle, modification ofthe lava path by the building of artificial barriers.Vesuvius shows typically an explosive behaviour. Inthe case of a medium size explosive eruption, 600,000people would potentially have to be evacuated from anarea of about 200 km² around the Volcano, sincethey are exposed to ruinous, very fast phenomena likepyroclastic surges and flows, lahars, ash fallout,etc. Ash fallout and floods/lahars are also expectedin distal areas, between Vesuvius and Avellino,downwind of the volcano. GIS include digital elevationmodels, satellite images, volcanic hazard maps andvector data on natural and artificial features (energysupply lines, strategic buildings, roads, railways,etc.). The nature and the level of detail in the twodata bases are different, on the basis of thedifferent expected volcanic phenomena. The GIS havebeen planned: (a) for volcanic risk mitigation (hazard,value, vulnerability and risk map assessing), (b) toprovide suitable tools during an impending crisis, (c)to provide a basis for emergency plans.     

Tephrochronology of the Siple Dome ice core,West Antarctica: correlations and sources

A total of 24 tephra-bearing volcanic layers have been recognized between 550 and 987 m depth in the Siple Dome A (SDM-A) ice core, in addition to a number already recognized tephra in the upper 550 m (Dunbar et al., 2003, Kurbatov et al., 2006). The uniform composition and distinctive morphological of the particles composing these tephra layers suggest deposition as a result of explosive volcanic eruptions and that the layers therefore represent time-stratigraphic markers in the ice core. Despite the very fine grain size of these tephra (mostly less than 20 microns), robust geochemical compositions were determined by electron microprobe analysis. The source volcanoes for these tephra layers are largely found within the Antarctic plate. Statistical geochemical correlations tie nine of the tephra layers to known eruptions from Mt. Berlin, a West Antarctic volcano that has been very active for the past 100,000 years. Previous correlations were made to an eruption of Mt. Takahe, another West Antarctic volcano, and one to Mt. Hudson, located in South America (Kurbatov et al., 2006). The lowest tephra layer in the ice core, located at 986.21 m depth, is correlated to a source eruption with an age of 118.1 ± 1.3 ka, suggesting a chronological pinning point for the lower ice. An episode of anomalously high volcanic activity in the ice in the SDM-A core between 18 and 35 ka (Gow and Meese, 2007) appears to be related to eruptive activity of Mt. Berlin volcano. At least some of the tephra layers found in the SDM-A core appear to be the result of very explosive eruptions that spread ash across large parts of West Antarctica, off the West Antarctic coast, as well as also being recognized in East Antarctica (Basile et al., 2001, Narcisi et al., 2005, Narcisi et al., 2006). Some of these layers would be expected to should be found in other deep Antarctic ice cores, particularly ones drilled in West Antarctica, providing correlative markers between different cores. The analysis of the tephra layers in the Siple Dome core, along with other Antarctic cores, provides a timing framework for the relatively proximal Antarctic and South American volcanic eruptive events, allowing these to be distinguished from the tropical eruptions that may play a greater role in climate forcing.     

An assessment of the risk from future eruptions of the Soufriere volcano of St. Vincent,West Indies

The Soufriere volcano is a 1220 m high stratovolcano which occupies the northern part of the island of St. Vincent. It is one of the most active centres of volcanism in the Caribbean and has a record of activity dating back to the Pleistocene. Historic eruptions (since 1718) have caused over 1600 deaths and resulted in damage to property valued in excess of 4.8 million USD. In addition, current development plans for the area point towards increased risk of disastrous consequences from future activity at the volcano.All aspects of risk relevant to the volcano, are discussed, with particular emphasis on the manner in which these are perceived and on the question of acceptable risk. A method is presented for use in risk assessment of volcanic hazard and a number of risk zones are defined for the Soufriere volcano. Numerical estimates of the relative loss expected within each zone are obtained from a consideration of the value of property at risk, its vulnerability to the hazardous volcanic events and the expected spatial impact of volcanic events. Such estimates suggest that the northern-most third of the island is at least ten times more at risk than areas further south. The likelihood of death and destruction is extreme in such high risk areas, while the most feasible method of loss reduction is evacuation before an eruption occurs.Formerly at Department of Earth Sciences, University of Leeds, Leeds LS2 9JT, United Kingdom.     

中国东部全新世火山的镭-钍同位素年代学

活火山是指1万年来有过喷发历史的全新世火山。火山的高分辨年代学对火山灾害评估和火山分类具有重要意义。对于缺乏历史记载的全新世火山,直接对火山岩进行同位素定年很困难。本文利用具有高时间分辨率的镭-钍-铀非平衡确定中国东部年轻火山的年龄。根据镭-钍-铀同位素,海南岛的马鞍岭和雷虎岭是全新世火山(马鞍岭:4.3ka;雷虎岭:4.7ka);镜泊湖火山(4.9ka)也是全新世火山;龙岗火山存在晚更新世和全新世活动(7.0ka,15.0ka);大兴安岭阿尔山和诺敏河Ra/Th非平衡消失但~(230)Th/~(238)U非平衡显著,属于晚更新世喷发(阿尔山:63ka;诺敏河:71ka)。海南岛的马鞍岭火山、雷虎岭火山和东北地区的龙岗火山、镜泊湖火山,是4座活火山。至于东北地区的阿尔山和诺敏河火山是否是活火山,有待测试更多样品的Ra/Th同位素。五大连池老黑山和火烧山有历史喷发记录,这与它们都存在显著Ra/Th非平衡一致。五大连池老黑山和火烧山的岩浆滞留年龄分别小于4.2ka和3.2ka,岩浆上升速率 18～23m/y。     

~5.9 cal ka bp Towada-Chuseri tephra from Towada volcano: a mid-Holocene marker layer from Japan to northeast China

Far-travelled ash layers from explosive volcanic eruptions can provide invaluable marker horizons for dating and correlating regional to global sedimentary archives. Here, we present a new cryptotephra associated with the ~5.9 cal ka bp Towada-Chuseri eruption (To-Cu) in a peat sediment record from northeast China. This tephra exhibits a rhyolitic glass composition that can be distinguished from other widespread tephra layers around the region of Japan and northeast China. Our findings extend the known range of this ash significantly, making it now traceable about 1200 km from its source, Towada volcano, Japan. Notably, this tephra provides an important isochron for synchronising palaeoenvironmental studies during the mid-Holocene period from the western Pacific, central Japan, Japan Sea and northeast China.     

The 18.7 ka phreatomagmatic flank eruption on Etna (Italy): relationship between eruptive activity and sedimentary basement setting

This paper documents a phreatomagmatic flank eruption that occurred 18 700 ± 100 a BP , on the lower north-eastern slope of Etna during the Ellittico volcano activity, which produced fall and surge deposits. This type of eruption is connected to a sedimentary basement ridge at Etna. The interaction between the rising magma and the shallow groundwater hosted in the volcanic pile overlying the impermeable sediments resulted in phreatomagmatic instead of strombolian activity. Three eruptive phases are distinguished based on field and analytical data: (i) an explosive phreatomagmatic opening, (ii) a main phase producing coarse lithic-rich fallout and a strombolian deposit, and (iii) the final pulsating surge-forming phase. The discovery of this phreatomagmatic flank eruption, which occurred at lower altitude, raises important issues for previous hazard assessments at Etna.     

Probabilistic assessment of tephra fallout hazard at Changbaishan volcano,Northeast China

Natural Hazards - Tephra fallout is an important type of hazard caused by volcanic eruption, and is also one of the main hazards at Changbaishan volcano, Northeast China. Numerical simulation is an...     

Lahar hazard micro-zonation and risk assessment in Yogyakarta city, Indonesia

Yogyakarta urban area (500,000 inhab.) is located in Central Java on the fluvio-volcanic plain beside Merapi volcano, one of the most active of the world. Since the last eruption of Merapi in November 1994, the Code river, which goes across this city, is particularly threatened by lahars (volcanic debris flows). Until now, no accurate hazard map exists and no risk assessment has been done. Therefore, we drew a detailed hazard map (1/2,000 scale), based on morphometric surveys of the Code channel and on four scenarios of discharge. An additional risk assessment revealed that about 13,000 people live at risk along this river, and that the approximate value of likely loss is US $ 52 millions. However, the risk level varies between the urban suburbs. This revised version was published online in July 2006 with corrections to the Cover Date.