Volcanic hazards to airports

Volcanic activity has caused significant hazards to numerous airports worldwide, with local to far-ranging effects on travelers and commerce. Analysis of a new compilation of incidents of airports impacted by volcanic activity from 1944 through 2006 reveals that, at a minimum, 101 airports in 28 countries were affected on 171 occasions by eruptions at 46 volcanoes. Since 1980, five airports per year on average have been affected by volcanic activity, which indicates that volcanic hazards to airports are not rare on a worldwide basis. The main hazard to airports is ashfall, with accumulations of only a few millimeters sufficient to force temporary closures of some airports. A substantial portion of incidents has been caused by ash in airspace in the vicinity of airports, without accumulation of ash on the ground. On a few occasions, airports have been impacted by hazards other than ash (pyroclastic flow, lava flow, gas emission, and phreatic explosion). Several airports have been affected repeatedly by volcanic hazards. Four airports have been affected the most often and likely will continue to be among the most vulnerable owing to continued nearby volcanic activity: Fontanarossa International Airport in Catania, Italy; Ted Stevens Anchorage International Airport in Alaska, USA; Mariscal Sucre International Airport in Quito, Ecuador; and Tokua Airport in Kokopo, Papua New Guinea. The USA has the most airports affected by volcanic activity (17) on the most occasions (33) and hosts the second highest number of volcanoes that have caused the disruptions (5, after Indonesia with 7). One-fifth of the affected airports are within 30 km of the source volcanoes, approximately half are located within 150 km of the source volcanoes, and about three-quarters are within 300 km; nearly one-fifth are located more than 500 km away from the source volcanoes. The volcanoes that have caused the most impacts are Soufriere Hills on the island of Montserrat in the British West Indies, Tungurahua in Ecuador, Mt. Etna in Italy, Rabaul caldera in Papua New Guinea, Mt. Spurr and Mt. St. Helens in the USA, Ruapehu in New Zealand, Mt. Pinatubo in the Philippines, and Anatahan in the Commonwealth of the Northern Mariana Islands (part of the USA). Ten countries—USA, Indonesia, Ecuador, Papua New Guinea, Italy, New Zealand, Philippines, Mexico, Japan, and United Kingdom—have the highest volcanic hazard and/or vulnerability measures for airports. The adverse impacts of volcanic eruptions on airports can be mitigated by preparedness and forewarning. Methods that have been used to forewarn airports of volcanic activity include real-time detection of explosive volcanic activity, forecasts of ash dispersion and deposition, and detection of approaching ash clouds using ground-based Doppler radar. Given the demonstrated vulnerability of airports to disruption from volcanic activity, at-risk airports should develop operational plans for ashfall events, and volcano-monitoring agencies should provide timely forewarning of imminent volcanic-ash hazards directly to airport operators.     

The Impact of Volcanic Eruption on Decadal-Scale Climate Prediction Skill of Pacic Sea Surface Temperatures in the IAP Near-Term Climate Prediction System(IAP DecPreS)

Explosive volcanic eruptions are known to be a leading cause of natural climate change. There has been a growing recognition that there is a measurable climate system response even to moderate-sized volcanic eruptions. In this study, we investigated the hindcast skills of the Pacific Sea Surface Temperatures (SSTs) using the hindcast experiments based on the near-term climate prediction system DecPreS developed by the Institute of Atmospheric Physics (IAP)(hereafter DP-EnOI-IAU experiments). The DP-EnOI-IAU experiments were run for initial years from 1960 to 2005. These hindcasts took into account observed stratospheric aerosol concentrations that included the four large tropical volcanic eruptions during that period. The time evolution over the entire hindcast period for skill in predicting the patterns of the 3~7 year prediction averages for Pacific SSTs showed that there was statistically significant skill for most years except for a dramatic drop in skill during the 1980s and 1990s. Decadal hindcast skill is reduced if the post-eruption model response deviates the internal El Niño variability in the observations. The simulations showed a post-eruption SST of a La Niña-like pattern in the third northern winter after the 1982 El Chichon eruption and a El Niño-like pattern after the 1991 Pinatubo eruption, which were opposite in sign to what was in the observations. This lead to the loss of hindcast skill for years in the 1980s and 1990s affected by the eruptions. Agung (1963) happened to have post-eruption Pacific SSTs more similar to the observations and thus did not degrade prediction skill in the hindcasts.     

Engineering geological conditions of the Holocene sediments of Anzali area,South Caspian Coast,North Iran

A broad assessment of the geological, sedimentological, and geotechnical characteristics of the coastal Holocene sediments of Anzali Area (North Iran) was made to provide a useful guide for development, planning, and construction. Based on the sedimentological and geotechnical properties of the sediments, three engineering geological units as Upper Sandy Zone (USZ), Middle Clayey Zone (MCZ), and Lower Sandy Zone (LSZ) were identified and introduced in the form of an engineering geological model. Then the engineering geological characteristics of the units of the model were analyzed and the main engineering geological problems associated with the deposits of each unit were identified. The results showed that USZ has high liquefaction potential, low bearing capacity, settlement susceptibility, and excavation problem; MCZ has low-bearing capacity as well as high settlement susceptibility and excavation problem; and LSZ has good geotechnical properties, then it poses few problems.     

Glacier Peak,Washington: A potentially hazardous cascade volcano

Recent field studies of postglacial volcanic deposits at Glacier Peak indicate the volcano has erupted more often, more voluminously, and more recently than previously thought. These past eruptions produced pyroclastic flows, extensive lahars, and widely distributed tephra falls. Analysis of the magnitude of past eruptions and the distribution of volcanic sediments indicates that future eruptions at Glacier Peak as large as those of the last several thousand years would dramatically affect people and property downstream and downwind from the volcano. Pyroclastic flows and lateral blasts would primarily affect uninhabited valleys within a few tens of kilometers of the volcano. Lahars and floods constitute the major hazard to populated areas from future eruptions, and could affect areas at low elevation along valley floors and in the Puget lowland as far as 100 km downvalley west of the volcano. Air-fall tephra from future eruptions will probably be deposited primarily east of Glacier Peak because of prevailing westerly winds.     

Explosive volcanic eruptions triggered by cosmic rays: Volcano as a bubble chamber

Volcanoes with silica-rich and highly viscous magma tend to produce violent explosive eruptions that result in disasters in local communities and that strongly affect the global environment. We examined the timing of 11 eruptive events that produced silica-rich magma from four volcanoes in Japan (Mt. Fuji, Mt. Usu, Myojin-sho, and Satsuma-Iwo-jima) over the past 306 years (from AD 1700 to AD 2005). Nine of the 11 events occurred during inactive phases of solar magnetic activity (solar minimum), which is well indexed by the group sunspot number. This strong association between eruption timing and the solar minimum is statistically significant to a confidence level of 96.7%. This relationship is not observed for eruptions from volcanoes with relatively silica-poor magma, such as Izu-Ohshima. It is well known that the cosmic-ray flux is negatively correlated with solar magnetic activity, as the strong magnetic field in the solar wind repels charged particles such as galactic cosmic rays that originate from outside of the solar system. The strong negative correlation observed between the timing of silica-rich eruptions and solar activity can be explained by variations in cosmic-ray flux arising from solar modulation. Because silica-rich magma has relatively high surface tension (~ 0.1 Nm^?1), the homogeneous nucleation rate is so low that such magma exists in a highly supersaturated state without considerable exsolution, even when located relatively close to the surface, within the penetration range of cosmic-ray muons (1–10 GeV). These muons can contribute to nucleation in supersaturated magma, as documented by many authors studying a bubble chamber, via ionization loss. This radiation-induced nucleation can lead to the pre-eruptive exsolution of H₂O in the silica-rich magma. We note the possibility that the 1991 Mt. Pinatubo eruption was triggered by the same mechanism: an increase in cosmic-ray flux triggered by Typhoon Yunya, as a decrease in atmospheric pressure results in an increase in cosmic-ray flux. We also speculate that the snowball Earth event was triggered by successive large-scale volcanic eruptions triggered by increased cosmic-ray flux due to nearby supernova explosions.     

Contribution of mafic melt to porphyry copper mineralization: evidence from Mount Pinatubo, Philippines, and Bingham Canyon, Utah, USA

Mount Pinatubo in the Philippines, known for its cataclysmic eruption in 1991, hosts several porphyry copper deposits and active geothermal systems. An underlying mafic melt supplied much of the sulphur for the dacitic magma and its injection into the dacitic magma chamber triggered the eruption. The eruption caused purging of the sulphur-rich fluid from the dacite to the atmosphere and extensive fracturing. Similar events took place at Bingham Canyon, Utah, site of the largest copper and gold deposit in North America at 38 Ma. The Bingham Canyon mineralization took place beneath an active stratovolcano and pyroclastic flows contemporaneous with the mineralization show evidence for magma mingling. Ascent of mafic melt supplied sulphur and chalcophile elements to the felsic magma, which consolidated to form the Bingham stock and its underlying magma chamber. Injections of the mafic melt caused periodic eruptions of felsic magma to form the stratovolcano and deposition of sulphide minerals in highly fractured rocks in and around the stock.     

Vulnerability of farm water supply systems to volcanic ash fall

Agriculture is critically dependent on continuity of water quality and quantity. It is well-established that even small quantities of volcanic ash can disrupt municipal water supplies, with known impacts to quality including: acidification, increases in turbidity and ionic concentrations. In addition, delivery systems may be blocked or damaged by hard and abrasive suspended ash and related ash-cleanup operations place extra stress on water reserves. The aim of this study was to characterise the key areas of vulnerability of farm water supplies to volcanic ashfall, and to identify management recommendations to reduce these. From literature review and case studies of farms impacted by the 1991 Pinatubo (Philippines) and 1991 Hudson (Chile) eruptions, key issues were: sedimentation of irrigation ditches and drinking water ponds, turbidity induced abrasion of sprinkler nozzles and water pumps, and damage to electric pumps (by ash on air-intakes). Building on this, we characterised the water-use regimes and water supply system vulnerability of eight case-study farms from across the North Island, New Zealand. From this, we propose an index system to evaluate the vulnerability of farm water supply systems. The key contributors to the vulnerability index include: water source, storage capacity, reliance on electricity, independence/interconnectedness of system elements, volume of water use and other load factors. These allow identification of key strategies for mitigating water supply vulnerability during prevention, preparation, response and recovery phases of a volcanic eruption.     

The global impact of the Minoan eruption of Santorini, Greece

 The Minoan eruption of Santorini was a large-magnitude natural event. However, in terms of scale it ranks smaller in erupted volume and eruptive intensity than the historical eruption of Tambora in 1815 AD, and smaller in sulphur emission and, by inference, climatic effects than both the Tambora and Mt. Pinatubo, 1991, eruptions. Eruption statistics for the past 2000 years indicate that Minoan-size eruptions typically occur at a rate of several per thousand years. Eruptions resulting in a Minoan-scale injection of sulphur to the stratosphere occur far more frequently – at a rate of one or two per century. Inferences of massive sociological, religious and political impacts from such eruptions owe more to mythology than reality. Received: 28 November 1995 · Accepted: 9 January 1996     

History of scoria-cone eruptions on the eastern shoulder of the Kenya–Tanzania Rift revealed in the 250-ka sediment record of Lake Chala near Mount Kilimanjaro

Reconstructions of the timing and frequency of past eruptions are important to assess the propensity for future volcanic activity, yet in volcanic areas such as the East African Rift only piecemeal eruption histories exist. Understanding the volcanic history of scoria-cone fields, where eruptions are often infrequent and deposits strongly weathered, is particularly challenging. Here we reconstruct a history of volcanism from scoria cones situated along the eastern shoulders of the Kenya–Tanzania Rift, using a sequence of tephra (volcanic ash) layers preserved in the ~250-ka sediment record of Lake Chala near Mount Kilimanjaro. Seven visible and two non-visible (crypto-) tephra layers in the Lake Chala sequence are attributed to activity from the Mt Kilimanjaro (northern Tanzania) and the Chyulu Hills (southern Kenya) volcanic fields, on the basis of their glass chemistry, textural characteristics and known eruption chronology. The Lake Chala record of eruptions from scoria cones in the Chyulu Hills volcanic field confirms geological and historical evidence of its recent activity, and provides first-order age estimates for seven previously unknown eruptions. Long and well-resolved sedimentary records such as that of Lake Chala have significant potential for resolving regional eruption chronologies spanning hundreds of thousands of years.     

Trace element geochemistry of the 1991 Mt. Pinatubo silicic melts, Philippines: Implications for ore-forming potential of adakitic magmatism

The dacite pumice erupted from Mt. Pinatubo on June 15, 1991 (whole-rock, rhyolitic groundmass glasses and homogenized melt inclusions) has been analyzed using inductively coupled plasma-mass spectrometry (ICP-MS), nanosecond and femtosecond laser ablation ICP-MS and secondary ion mass spectrometry (SIMS) to evaluate its ore-forming potential. Data suggest that adakite magmas are metal-rich and concentrate ore metals during magmatic differentiation. Sulfides segregate in limited amounts under the hydrous, oxidizing conditions typical of adakitic magmas resulting in incompatible behavior for Au (6-22 ppb), Cu (26-77 ppm), and Pb, Mo, As, and Sb in melts of dacitic to rhyolitic compositions. Metal transfer from this adakite magma to the coexisting aqueous phase was favored by the peraluminous composition of the rhyolitic melt and high aqueous chloride concentrations. Mass balance calculations suggest that the pre-eruptive aqueous phase could have extracted a minimum of 100 t Au and 5 × 10⁵ t Cu from the Mt. Pinatubo magma. Our data suggest that intrusives having adakitic signatures are genetically associated with Au-Cu and Cu-Mo mineralization, auriferous porphyry copper deposits, and epithermal gold veins. High H₂O, Cl, Sr/Y, Pb/Ce, Mo/Ce, As/Ce and Sb/Ce in Mt. Pinatubo melts reflect the contribution of deep fluids derived from subducted sediments and altered MORBs in the dacite genesis. The slab-derived fluids carrying mobile elements are likely responsible for the enrichment of adakite magmas in gold, associated metals and H₂O, and may explain the exceptional ore-forming potential of adakite magmatism.     

Fluvial response to sudden input of pyroclastic sediments during the 2008–2009 eruption of the Chaitén Volcano (Chile): The role of logjams

The rhyolitic Plinian eruption of the Chilean Chaitén Volcano, initiated on May 2, 2008, suddenly introduced abundant pyroclastic sediments in the Blanco River catchment area, which experienced important modifications. Before May 2, the river was characterised by gravelly and moderate to low-sinuosity channels crossing a vegetated and locally urbanised (Chaitén City) floodplain. This river, limited by steep and densely forested highlands, was connected with the Pacific Ocean via a tidally-influenced delta plain. After heavy rains in May 11–20, the river discharge increased and triggered several responses including logjam formation and breakage, crevassing, avulsion (and channel abandonment), changes in the pattern and dimensions of channels, and construction of a new delta plain area. In this context, the goals of this contribution were: i) to document the sedimentological processes within a detailed geomorphic framework and ii) to understand the influence of logjams on fluvial dynamics. Upstream of the logjam zone, the deposits are mostly composed of ash and lapilli with abundant palaeovolcanic (epiclastic) sediments, which were produced by dilute currents and debris flows. Downstream of the logjam zone, deposits are composed by ash and lapilli, both pumice-rich and lacking important participation of older (epiclastic) sediments. The abandoned and filled palaeochannel, and the proximal part of crevasse splays experienced transient dilute flows with variable sediment concentration and, subordinately, hyperconcentrated flows. The distal sectors of crevasse splays mostly record settling from suspension. At the delta plain, tephra transported by the Blanco River was mixed with older sediments by tide and wave action (dilute flows). We conclude that immediately after eruption, both geomorphic and sedimentary processes of the river were mainly controlled by a combination of high availability of incoherent pyroclastic sediments on steep slopes, abundant rains, large logs that jammed the river and huge areas of devastated forest. Logjams played an important role in the river response to the volcanic eruption; they were responsible of the marked compositional change recorded upstream and downstream of the logjam zone and its breakage resulted in downstream flooding and avulsion. The likelihood of formation of logjams in rivers draining forested volcanic areas should be considered in the evaluation of volcanic hazards related to Plinian eruptions.     

The Lerokis and Kali Kuning submarine exhalative gold-silver-barite deposits, Wetar Island, Maluku, Indonesia

Wetar, an island in the southern part of the Banda Arc, is made up submarine volcanic rocks, with the oldest rocks exposed being subvolcanic intrusions and flows dated at 12 Ma. Basaltic andesite pillow lavas and intercalated volcaniclastic sedimentary rocks grade upward into more felsic volcanic lavas, tuffs and breccias, and sedimentary rocks and epiclastic mudflows cap the sequence.Gold-silver mineralization occurs at Lerokis and Kali Kuning, 3.5 km apart on the north coast of the island, in stratiform barite sand, clay or silt. The sediments are underlain by Cu-rich massive pyrite in volcanic breccias and overlain by a limestone dated at about 4 Ma. Foot wall volcanic breccias and lavas show intense clay-pyrite alteration indicating temperatures higher than 230°C.In situ geological resources, prior to the inception of mining in 1990, totalled 2.9 Mt at 3.5 g/t Au, 114 g/t Ag and 40% barite at Lerokis and 2.2 Mt at 5.5 g/t Au, 146 g/t Ag and 60% barite at Kali Kuning. Most of the Au occurs as electrum, associated with limonite, jarosite and goethite, and most of the Ag is in tetrahedrite and sulphosalts. High Pb contents, between 0.5% and 1.4% Pb on average, derive from plumbojarosite, sulphosalts and cerrussite, and there is, on average, between 200 ppm to 900 ppm Cu, 0.2% Sb, 0.1% As, 100 ppm to 200 ppm Zn, and 18 ppm Hg. Underlying massive sulphide mineralization is mainly pyrite-marcasite with zones of Cu enrichment. A significant part of the Cu is contained in enargite.Formation likely took place at less than 600 m water depth in a sea floor caldera setting similar to the Kuroko district in Japan. The ferruginous sediments hosting the Au-barite deposits may have originated through erosion like the ochres of Cyprus. These stratiform Au-barite deposits highlight a new style of sea floor mineralization not clearly recognized before. Modern-day analogues have been described from a variety of sea floor settings.     

Engineering-geological model of the Segura River flood plain (SE Spain): a case study for engineering planning

This article presents a sedimentological and geotechnical study of the surficial sediments in the Segura River valley (SE Spain). We formulate an engineering-geological model consisting of four zones, each characterized by its geotechnical properties and by various geotechnical problems (namely low bearing capacity, significant ground settlement and liquefaction of sandy sediments). The model quantifies the geotechnical properties and potential problems in each zone. It serves as a useful tool for preliminary geotechnical investigations. The model also enables a better design of field surveys as well as optimal selection of geotechnical investigation techniques for future civil engineering works.     

Patterns of transformations in the compositions and properties of Icelandic hyaloclastites during lithogenesis

In Iceland, hyaloclastites form thick masses generated as a result of subglacial eruptions during Pliocene-Pleistocene surface glaciations. The formation of hyaloclastites and features of their alterations during lithogenesis were investigated. Hyaloclastites are extremely heterogeneous in their physical and physical-mechanical properties. A sequence of hyaloclastites secondary transformations was established from virgin, only slightly palagonitized hyaloclastites with contact-type cement to thoroughly transformed rocks with secondary minerals forming porous cement and partially substituting volcanic glass. A general tendency towards an increase in elasticity, density, strength, and thermal characteristics and towards a decrease in porosity and permeability has been observed with progression of secondary alterations, with the growth of age, from newer to more ancient deposits, and the depth of hyaloclastite burial.     

西太暖池区生物组分对海底表层沉积物物理力学性质的影响

西太平洋暖池区是指位于热带西太平洋及印度洋东部海表温度常年在28 ℃以上的海域,是全球海表温度最高的深海区,构造环境与沉积环境复杂,沉积物中的生物组分含量差异较大,生物组分会对深海沉积物物理力学性质产生显著影响,但目前对沉积物中生物组分含量和沉积物物理力学性质之间的相关性关系尚不明确。本文对西太平洋暖池区核心部位的表层沉积物样品进行现场物理力学性质测试和室内涂片鉴定,研究深海表层沉积物的物理力学性质与生物组分之间的关系。结果表明:研究区表层沉积物含水率范围为61.1%~435.1%,天然密度范围为1.04~1.76 g/cm³,贯入阻力范围为0~100 kPa,十字板剪切强度范围为0~8.6 kPa,整体具有高含水率、低密度、低强度等典型的深海沉积物物理力学性质特点。西加洛林海脊、海山等CCD以浅的区域为钙质生物组分>50%的钙质沉积区;西加洛林海槽西南部及其周边的深水沟槽地区一般为硅质生物组分>50%的硅质沉积;西加洛林海盆内部则主要为黏土沉积区。随钙质生物组分减少和硅质生物组分增多,表层沉积物类型分别为钙质沉积物、黏土沉积物和硅质沉积物,天然含水率变高,天然密度、贯入阻力和十字板剪切强度降低,表明深海表层沉积物的物理力学性质与生物组分含量密切相关:贯入阻力、十字板剪切强度、天然密度与钙质生物组分含量呈正相关,与硅质生物组分含量呈负相关;而天然含水率正好相反,与钙质生物组分含量呈负相关,与硅质生物组分含量呈正相关。本文建立了深海沉积物中生物组分与物理力学性质之间的相关关系,提出了沉积物生物组分含量与物理力学性质之间的拟合公式,可以为深海沉积物工程性质的评价提供参考。     

The Risk of Large Volcanic Eruptions and the Impact of this Risk on Future Ozone Depletion

Ozone depletion at mid-latitudes is caused by reactivehalogens from man-made halocarbons. The stratosphericsulphate aerosol which follows large volcaniceruptions enhances (multiplies) this ozone depletion(it has no effect on ozone without halocarbons). Mid-latitude depletion almost doubled for the twoyears after Mt. Pinatubo. Although the MontrealProtocol is expected to reduce atmospheric amounts ofhalocarbons in the 21st century, stratospheric ozonewill be at risk of depletion enhancement by largeeruptions for the next 50 years. Mechanisms ofvolcanoes suggest that large eruptions are random andthat their global rate is constant for severalcenturies. Measurements of large eruptions during thelast 1000 years in ice cores have a remarkable fit toa Poisson distribution, reinforcing the conclusionthat the global incidence is random and at a constantrate for this period. From this rate, the probabilityof one or more eruptions with at least the ozone-lossenhancement of Pinatubo is 58 % in 50 years. Thisprobability is large enough to be of serious concernfor future mid-latitude ozone loss.     

Groundwater use for snow melting on the road

Japan is very rich in active volcanoes, so that the surveillance and prediction of volcanic activities are indespensable in order to protect human life and properties from catastrophic volcanic eruptions. The author intends here to review the volcanic activities in Japan and the history and status quo of the volcanological observation and research by the Japan Meteorological Agency (JMA), universities, etc. for that purpose. Needless to say, in Japan, volcanoes are studied from various view points such as geophysical, geochemical, geological and geographical. However, the observations for the purpose of detecting of reliable premonitory symptoms of volcanic eruptions are mainly based on geophysical and geochemical methods. In this country, there are permanent observatories at 18 active volcanoes, and there are also several mobile teams of volcanologists. It must be noticed that almost all the volcanic activities including very slight volcanic extraordinary phenomena are nowadays detected in Japan, and unexpected eruptions are very scarce, because the information on the actual state of activities of Japanese volcanoes are made public frequently.     

The surveillance and prediction of volcanic activities in Japan

Japan is very rich in active volcanoes, so that the surveillance and prediction of volcanic activities are indespensable in order to protect human life and properties from catastrophic volcanic eruptions. The author intends here to review the volcanic activities in Japan and the history and status quo of the volcanological observation and research by the Japan Meteorological Agency (JMA), universities, etc. for that purpose. Needless to say, in Japan, volcanoes are studied from various view points such as geophysical, geochemical, geological and geographical. However, the observations for the purpose of detecting of reliable premonitory symptoms of volcanic eruptions are mainly based on geophysical and geochemical methods. In this country, there are permanent observatories at 18 active volcanoes, and there are also several mobile teams of volcanologists. It must be noticed that almost all the volcanic activities including very slight volcanic extraordinary phenomena are nowadays detected in Japan, and unexpected eruptions are very scarce, because the information on the actual state of activities of Japanese volcanoes are made public frequently.     

波浪导致黄河口海床沉积物超孔压响应现场试验研究

黄河口海床特殊的工程地质性质与复杂的工程动力稳定性问题,均与海床沉积物在波浪荷载作用下的孔压动力响应密切相关。在现代黄河水下三角洲潮间带岸滩选择4个典型研究点,现场模拟波浪作用对原状海床沉积物实施循环加载,利用孔隙水压力观测、沉积物强度测试、样品采集与实验室土工测试等方法手段,测定黄河口原状海床沉积物在循环荷载作用不同阶段的孔压响应与强度变化。研究发现,黄河口原状海床沉积物在经历循环加载过程中,典型的超孔压响应可分为逐渐累积、部分消散、快速累积、累积液化和完全消散5个阶段,分别对应沉积物强度的衰减、增大、衰减、丧失和恢复过程,沉积物的粒度组成与结构性强弱决定了超孔压的具体响应模式。波浪导致原状海床液化深度受沉积物的干密度、孔隙比、饱和度等初始物理性质影响显著,细颗粒组分的相对含量高低也在很大程度上控制着沉积物的液化特性。     

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.