Stage Of Eruption Research Articles

Transient numerical model of magma ascent dynamics: application to the explosive eruptions at the Soufrière Hills Volcano

Volcanic activity exhibits a wide range of eruption styles, from relatively slow effusive eruptions that produce lava flows and lava domes, to explosive eruptions that can inject large volumes of fragmented magma and volcanic gases high into the atmosphere. Although controls on eruption style and scale are not fully understood, previous research suggests that the dynamics of magma ascent in the shallow subsurface (< 10 km depth) may in part control the transition from effusive to explosive eruption and variations in eruption style and scale. Here we investigate the initial stages of explosive eruptions using a 1D transient model for magma ascent through a conduit based on the theory of the thermodynamically compatible systems. The model is novel in that it implements finite rates of volatile exsolution and velocity and pressure relaxation between the phases. We validate the model against a simple two-phase Riemann problem, the Air-Water Shock Tube problem, which contains strong shock and rarefaction waves. We then use the model to explore the role of the aforementioned finite rates in controlling eruption style and duration, within the context of two types of eruptions at the Soufrière Hills Volcano, Montserrat: Vulcanian and sub-Plinian eruptions. Exsolution, pressure, and velocity relaxation rates all appear to exert important controls on eruption duration. More significantly, however, a single finite exsolution rate characteristic of the Soufrière Hills magma composition is able to produce both end-member eruption durations observed in nature. The duration therefore appears to be largely controlled by the timescales available for exsolution, which depend on dynamic processes such as ascent rate and fragmentation wave speed.

P31 九重火山の飯田火砕流堆積物と九重第 1 軽石の層序 : 飯田火砕流のステージの噴火史

P31 九重火山の飯田火砕流堆積物と九重第 1 軽石の層序 : 飯田火砕流のステージの噴火史

Eruption of magmatic foams on the Moon: Formation in the waning stages of dike emplacement events as an explanation of “irregular mare patches”

Volcanic eruptions on the Moon take place in conditions of low gravity and negligible atmospheric pressure, very different from those on Earth. These differences lead to characteristic lunar versions of hawaiian and strombolian explosive activity, and to the production of unusual eruption products neither predicted nor observed on Earth in the terminal stages of eruptions. These include the unusual mounds and rough (hummocky, blocky) floors of some small-shield summit pit crater floors, elongate depressions and mare flows (similar to those named “irregular mare patches”, IMPs, by Braden et al., 2014). We examine the ascent and eruption of magma in the waning stages of the eruptive process in small-shield summit pit crater floors and show that many IMP characteristics can be plausibly explained by basaltic magma behavior as the rise rate of the ascending magma slows to zero, volatiles exsolve in the dike and lava lake to form a very vesicular foam, and the dike begins to close. Stresses in the very vesicular and porous lava lake crust produce fractures through which the foam extrudes at a rate determined by its non-Newtonian rheology. Waning-stage extrusion of viscous magmatic foams to the surface produces convex mounds whose physical properties inhibit typical impact crater formation and regolith development, creating an artificially young crater retention age. This mechanism for the production and extrusion of very vesicular magmatic foams is also applicable to waning-stage dike closure associated with pit craters atop dikes, and fissure eruptions in the lunar maria, providing an explanation for many irregular mare patches. This mechanism implies that IMPs and associated mare structures (small shields, pit craters and fissure flows) formed synchronously billions of years ago, in contrast to very young ages (less than ~100millionyears) proposed for IMPs by some workers.

Distinguishing styles of explosive eruptions at Erebus, Redoubt and Taupo volcanoes using multivariate analysis of ash morphometrics

The style and dynamics of volcanic eruptions control the level and type of hazards posed for local populations and can have a temporary long-range impact on climate if eruptions are extremely energetic. The purpose of this study is to provide a statistical approach to ash morphometrics in order to provide a means by which to evaluate diverse eruption styles and mechanisms of fragmentation. The methodology presented can be applied to tephra deposits worldwide and may aid volcanic hazard mitigation by better defining a volcano's history of explosive behavior.Ash-sized grains were collected from tephra deposits on Mount Erebus, Antarctica (<10ka, phonolitic unit SC4), Mount Redoubt, Alaska (2009, andesitic events 2–4 & 9–18), and the Taupo volcano, New Zealand (1.8ka, rhyolitic unit 3D). Coarse ash from each deposit was carefully hand-sieved to ~1mm diameter and display diverse morphologies that vary from grains that are moderately vesicular and more rectangular (blocky) to highly vesiculated (spongy) grains that vary from angular to sub-rounded. A total of 264 grains were imaged by scanning electron microscopy. Morphometric properties were determined using image processing software and then evaluated by several statistical methods.Discriminant analysis of all parameters was found to be the best at differentiating the tephra deposits and allowing for interpretation of eruptive styles in conjunction with field observations. A linear array of data forming a positive slope in factor space, which explains >99% of the total data variance, is interpreted to represent a continuum between fragmentations involving water-magma interaction (“wet”) to grains that were formed predominately by magmatic (“dry”) fragmentation mechanisms. The Taupo Hatepe ash, which was deposited from a phreatoplinian eruption column, has the highest factor values in the array, which signifies, in part, more rectangular/blocky morphologies with smooth grain edges. Factor values for the 2009 Redoubt eruption (events 2–4) are nearly as high as Hatepe ash and based on this we suggest that it was produced, in part, by phreatomagmatic fragmentation. This is supported by field observations that document melting and eruption through glacial ice during the early phases of the 2009 activity. Redoubt ash grains from later stages of the same eruption (events 9–18) show a significant shift to lower values in factor space (more irregular/vesiculated grains) and are interpreted to be a consequence of ‘dryer’ conditions. Coarse ash data from Mount Erebus are completely separated from Taupo and Redoubt grains in factor space due primarily to the difference in mean gray value, which is a proxy for vesicle density and size. The vesicle characteristics (larger and deeper) are consistent with documented strombolian-style activity and the scatter in grain shape data support fragmentation by a mixture of wet and dry processes as has previously been proposed based on deposit characteristics and resemblance to tephra produced by current activity.

Petrographic Characterization of the Different Types of Basalts of Harrat Al Fatih, Ablah Area, West Central Arabian Shield, Saudi Arabia

Harrat Al Fatih is located southwest of Ablah area, Assir terrain, southwestern Arabian Shield. It is present as black laterally extended horizontal basaltic sheet just overlying folded strata of the volcano-sedimentary succession of Ablah Formation (green mudstones, dolostones and green and red volcaniclastic red beds). These basalts are rift-related and represent part of the Oligo-Miocene basic volcanics of the western part of Saudi Arabia. The detailed field and microscopic description of these basalts enable the author to classify it into two main types: 1) Grey tuffaceous glassy basalts that present overlying the Ablah Formation. This basalt type is generally soft, bedded and intercalated with grey, green and red tuffaceous mudstones. Microscopically it composed of minute lath-like plagioclase and pyroxene crystals embedded in glassy groundmass. 2) Black olivine-rich basalts which are present in the topmost part of harrat Al Fatih are generally black, hard and contain remarkable reddish brown oxidized olivine spots and some calcite and amorphous quartz domains. Under the microscope, this basalt type is microcrystalline and composed mainly of lamellar twined Ca-plagioclase and colored olivines and pyroxenes. The olivines show different stages of oxidation and formation of amorphous blood red iron-oxyhydroxides and black hematite. The present study revealed the formation of the grey basalts at the initial stages of the volcanic eruption in ephemeral lakes and the second type of basalt was during the consolidation of proper basic magmas at the final stages of the volcanic eruption.

Age estimation by stages of eruption of third molar in male population of Rajasthan

The present study was conducted on 200 healthy males among the age group of 17–25 years from Rajasthan state to observe the stage wise pattern of eruption of third molar for purpose of age estimation. Only those subjects were included in the study that did not show any diseased teeth or chronic illness in the form of endocrinal disorder or nutritional disorder or muscle skeletal disorder. The examination was done in good light with the help of torch and the teeth were considered erupted, in four stages with stage 0: No eruption with occlusal plane covered with alveolar bone; stage 1: When tip of crown of tooth penetrated the gum margin; stage 2: Partial eruption but not full occlusion; stage 3: Full eruption or full occlusion. All the data collected was entered into the excel sheet and the statistical analysis was done. The results were as follows: the mean age of eruption of left maxillary third molar was 21.0 ± 2.2 years, the mean age of eruption of right maxillary third molar was 21.0 ± 2.2 years, the mean age of eruption of left mandibular third molar was 21.0 ± 2.2 years, the mean age of eruption of right mandibular third molar was 21.0 ± 2.2 years.

Sealing Occlusal Dentin Caries in Permanent Molars: 7-Year Results of a Randomized Controlled Trial.

The purpose of this study was to investigate the possibility of postponing restorative intervention of manifest occlusal caries in young, permanent dentition by non-invasive sealing. This RCT-designed study included 521 occlusal lesions in 521 patients aged 6 to 17 y. Based on clinical and radiographic assessments, all lesions required restorative treatment. After randomization (ratio 2:1), 368 resin sealings and 153 composite-resin restorations were performed by 68 dentists in 9 municipalities. The primary aims were to 1) analyze survival of sealings until replacement by restoration, 2) compare longevity of sealings and restorations until retreatments, and 3) compare effectiveness of sealings and restorations to halt caries progression in sealed lesions and beneath restorations. Furthermore, we aimed to identify factors influencing longevity and the effectiveness of sealings and restorations. Treatments were annually controlled, clinically and radiographically. After 7 y, the drop out rate was 8%, and 54% of the treatments were completed due to age. Of the sealings, 48% were retreated, including 31% replaced by restorations; 12% were still functioning. Of the restorations, 7% were repaired/renewed and 20% were still functioning. No endodontics was performed. Kaplan-Meier and Cox regression survival analyses were performed on 341 sealings and 152 restorations in first and second molar teeth. The 7-y survival was 37% (CI, 29% to 45%) for sealings and 91% (CI, 85% to 96%) for restorations (P < 0.001). The median survival time for sealings not replaced by restorations was 7.3 y (CI, 6.4 y to NA). Survival of sealings was increased in patients with low caries risk and/or excellent oral hygiene, second molars compared with first molars, and lesions not extending the middle one-third of the dentin. Survival of sealings was not influenced by municipality, sex, eruption stage or clinical surface cavitation. The results underline that it is possible to postpone or avoid restorative intervention of occlusal dentin caries lesions in young permanent teeth by non-invasive sealing. Knowledge Transfer Statement: The first restoration can ultimately be fatal for a young permanent tooth. A restoration may not be the final treatment but the start of an ongoing treatment with still more loss of tooth substance. The present study shows the possibility of treating occlusal dentin caries lesions with non-invasive resin sealings instead of conventional resin composite restorations in children and adolescents. Improved oral health can be expected.

Forensic age estimation in anti-piracy trials in Seychelles: Experiences and challenges faced

Forensic age estimation (FAE) was conducted using a multifactorial method on thirteen Somali detainees claiming juvenile status during the anti-piracy trials of the Seychelles Supreme Court in 2014/2015. A multidisciplinary team, comprising of four of the authors covering specialties in forensic medicine, forensic odontology and radiology, conducted the FAE using a five-stage protocol. Each detainee was interviewed with an interpreter and examined for disorders affecting dental/skeletal development and for assessment of genital development through Tanner staging. Dental maturity was assessed clinically and radiologically. Eruption stage was assessed using Olze et al. and mandibular third-molar maturity was assessed using Demirjian’s classification. Skeletal maturity was assessed from hand-wrist X-rays according to Greulich & Pyle and from CT-clavicle according to Kellinghaus et al. and Schultz et al. Interpretation of findings was done using reference population data from similar ethnic and social backgrounds wherever possible. Final age-ranges were calculated by combining dental and clavicle maturity stages using the regression formula developed by Bassed et al. followed by a 10% correction factor. The team later testified on their findings under cross-examination.The protocol adopted by the authors increased the scientific validity of the findings and was useful in addressing cross-examination queries on exclusion of developmental disorders, ethnic/socioeconomic variability and maintaining chain of custody. Unforeseen jurisdictional and practical limitations were experienced but did not affect the outcome. Combining dental and clavicle developmental data provided the court with a much clearer picture on the likelihood of the detainees’ juvenile status which emphasizes the importance of conducting more population studies using combinations of different developmental sites. The authors note that available reference data is mostly from affluent populations whereas FAE is mostly required in individuals from less-developed regions. Regional networks that collate and share population-specific data need to be established to overcome these limitations.

Hypodontia, Microdontia and Tooth rotation: A rare clinical triad

Hypodontia, microdontia and rotations are developmental dental anomalies resulting from genetic and epigenetic disturbances during tooth initiation, morphogenesis and eruption stages; with variable effects on function and dentofacial esthetics depending upon their severity. Hypodontia and microdontia may occur in syndromic or isolated non-syndromic forms based on presence or absence of congenital defects. This article briefly reviews hypodontia, microdontia and tooth rotation; and discusses a rare case presenting combination of these anomalies along with a possible treatment proposal.

Hydrothermal fluid venting in the offshore sector of Campi Flegrei caldera: A geochemical, geophysical, and volcanological study

AbstractThe ongoing unrest at the Campi Flegrei caldera (CFc) in southern Italy is prompting exploration of its poorly studied offshore sector. We report on a multidisciplinary investigation of the Secca delle Fumose (SdF), a submarine relief known since antiquity as the largest degassing structure of the offshore sector of CFc. We combined high‐resolution morphobathymetric and seismostratigraphic data with onshore geological information to propose that the present‐day SdF morphology and structure developed during the initial stages of the last CFc eruption at Monte Nuovo in AD 1538. We suggest that the SdF relief stands on the eastern uplifted border of a N‐S‐trending graben‐like structure formed during the shallow emplacement of the Monte Nuovo feeding dike. We also infer that the high‐angle bordering faults that generated the SdF relief now preferentially allow the ascent of hot brines (with an equilibrium temperature of 179°C), thereby sustaining hydrothermal degassing on the seafloor. Systematic vertical seawater profiling shows that hydrothermal seafloor venting generates a sizeable CO2, pH, and temperature anomaly in the overlying seawater column. Data for the seawater vertical profile can be used to estimate the CO2 and energy (heat) outputs from the SdF area at ∼50 tons/d (∼0.53 kg/s) and ∼80 MW, respectively. In view of the cause‐effect relationship with the Monte Nuovo eruption, and the substantial gas and energy outputs, we consider that the SdF hydrothermal system needs to be included in monitoring programs of the ongoing CFc unrest.

Volcanism and sedimentation along the western margin of the Rio Grande rift between caldera-forming eruptions of the Jemez Mountains volcanic field, north-central New Mexico, USA

The Cerro Toledo Formation (CTF), a series of intracaldera rhyolitic dome complexes and their associated extracaldera tephras and epiclastic sedimentary deposits, records the dynamic interplay between volcanic, tectonic, and geomorphic processes that were occurring along the western margin of the Rio Grande rift between major caldera-forming eruptions of the Bandelier Tuff 1.65–1.26Ma. The Alamo Canyon and Pueblo Canyon Members differ significantly despite deposition within a few kilometers of each other on the Pajarito Plateau. These differences highlight spatial distinctions in vent sources, eruptive styles, and depositional environments along the eastern side of the Jemez Mountains volcanic field during this ca. 400,000year interval. Intercalated pyroclastic fall deposits and sandstones of the Pueblo Canyon Member reflect deposition with a basin. Thick Alamo Canyon Member deposits of block-and-ash-flow tuff and pyroclastic fall deposits fill a paleovalley carved into coarse grained sedimentary units reflecting deposition along the mountain front. Chemistry and ages of glass from fall deposits together with clast lithologies of sedimentary units, allow correlation of outcrops, subsurface units, and sources. Dates on pyroclastic fall deposits from Alamo Canyon record deep incision into the underlying Otowi Member in the southern part of the Pajarito Plateau within 100k.y. of the Toledo caldera-forming eruption. Reconstruction of the CTF surface shows that this period of rapid incision was followed by aggradation where sediments largely filled pre-existing paleocanyons. Complex sequences within the upper portion of the Otowi Member in outcrop and in the subsurface record changes in the style of eruptive activity during the waning stages of the Toledo caldera-forming eruption.

Timing of clinical eruption of third molars in a Jordanian population

ObjectivesThis study aimed at providing the first standards on the timing of third molar eruption in Jordanians. MethodsA total of 571 healthy Jordanian adolescents and young adults aged 15-27 years (275 males and 296 females distributed into one-year age groups) were clinically examined for third molar eruption. Presence of four clinical eruption stages from crown emergence to full eruption were counted and expressed each as a frequency relative to the total of participants within a given age group. Using probit regression, median ages at each of the eruption stages were calculated for the whole sample and for both genders. ResultsIn the whole sample, maxillary and mandibular third molars were found to emerge at 20 and 20.6 years and to reach full eruption at 22.7 and 23.5 years respectively. At all of the four clinical eruption stages, third molars of males and lower jaw slightly preceded those of females and upper jaw respectively. However, none of the differences were statistically significant. ConclusionsThe first data on the timing of clinical eruption of third molars in a Jordanian population have been provided to be utilized in various clinical and research fields of orthodontics, dental pathology, oral surgery, paleodontology, forensic dentistry and police sciences. As the clinical duration of third molar eruption ranges from 20 to 24 years, the responsibility for providing care of third molar eruption problems is shifted from secondary schools to tertiary education, governmental and private work bodies.

Transitions between explosive and effusive phases during the cataclysmic 2010 eruption of Merapi volcano, Java, Indonesia.

Transitions between explosive and effusive activity are commonly observed during dome-forming eruptions and may be linked to factors such as magma influx, ascent rate and degassing. However, the interplay between these factors is complex and the resulting eruptive behaviour often unpredictable. This paper focuses on the driving forces behind the explosive and effusive activity during the well-documented 2010 eruption of Merapi, the volcano’s largest eruption since 1872. Time-controlled samples were collected from the 2010 deposits, linked to eruption stage and style of activity. These include scoria and pumice from the initial explosions, dense and scoriaceous dome samples formed via effusive activity, as well as scoria and pumice samples deposited during subplinian column collapse. Quantitative textural analysis of groundmass feldspar microlites, including measurements of areal number density, mean microlite size, crystal aspect ratio, groundmass crystallinity and crystal size distribution analysis, reveal that shallow pre- and syn-eruptive magmatic processes acted to govern the changing behaviour during the eruption. High-An (up to ∼80 mol% An) microlites from early erupted samples reveal that the eruption was likely preceded by an influx of hotter or more mafic magma. Transitions between explosive and effusive activity in 2010 were driven primarily by the dynamics of magma ascent in the conduit, with degassing and crystallisation acting via feedback mechanisms, resulting in cycles of effusive and explosive activity. Explosivity during the 2010 eruption was enhanced by the presence of a ‘plug’ of cooled magma within the shallow magma plumbing system, which acted to hinder degassing, leading to overpressure prior to initial explosive activity.Electronic supplementary materialThe online version of this article (doi:10.1007/s00445-016-1046-z) contains supplementary material, which is available to authorized users.

Impact of the intermediary layer on sealant retention: a randomized 24-month clinical trial

The aims of this study were to assess long-term impact of tooth eruption stages (ES) on sealant retention on occlusal surfaces previously coated with intermediary bonding layer and to determine caries prevention. Sixty-five school children were selected (aged 6-10years), with four non-carious permanent first molar in different ES (OP (operculum present), ME (marginal edge), CE (completely erupted)). Split-mouth and single-blind study design was used. The teeth (260) were randomly selected according to treatment (sealant/technique): F (Fluroshield), H (Helioseal Clear Chroma), SF (Single Bond+F), EH (Excite+H). Sealant retention, marginal integrity, discoloration, and caries prevention were assessed after 6, 12, 18, and 24months by calibrated examiner (Spearman=0.91) using visual inspection. Data were submitted to the Cox proportional hazard model (survival analysis) and Likelihood ratio χ 2 test (correlation), p≤0.05. At baseline, ES was 20% in OP, 54% in ME, and 26% in CE. There was no significant difference on sealant retention between the treatments (p=0.2774). However, significant differences were found regarding the ES on sealant retention (p=0.0041). The CE stage showed the highest retention survival rate during the 24months. The overall sealant prevention average was found to be about 99.4% and showed no difference between the groups. Eruption stages affect sealant retention irregardless of the intermediate layer and type of sealant. However, there was caries prevention on tooth occlusal surfaces after 24months, regardless of treatment. Sealing is recommended to prevent occlusal caries of newly erupted teeth in high-caries-risk patients. However, its application is critical on moisture limited control surfaces independently of sealer material and technique.

Constructing cranial ontogenetic trajectories: A comparison of growth, development, and chronological age proxies using a known-age sample of Macaca mulatta.

Recent morphometric research has generated opposing conclusions regarding the ontogenetic trajectories of catarrhine crania, possibly due to the ontogenetic proxies used to calculate them. Therefore, we used three surrogates: size, molar eruption, and chronological age to generate trajectories in a known-age sample to produce ontogenetic trajectories and determine the similarities and differences between them. Forty-three landmarks from an ontogenetic series of 160 Macaca mulatta crania, with associated ages at death, were used to produce ontogenetic trajectories of cranial shape change. These were computed by sex through multivariate regression of Procrustes aligned coordinates against three surrogates for ontogeny: natural log of centroid size (growth), molar eruption stage (development), and chronological age. These trajectories were compared by calculating the angles between them. Each trajectory was also used to produce simulated adults from juveniles, which were then compared with each other and actual adults. The different trajectories are nearly parallel as each of the surrogates track similar aspects of ontogenetic cranial shape change, but chronological age was the most divergent. Simulated adults produced using the developmental stage trajectories were most similar to actual adults. When simulated adults were produced from opposite sex trajectories, they resembled the sex from which the trajectory was produced, not the sex of the juvenile specimen. We discuss properties of the trajectories produced from each of the surrogates, the possible reasons for previously opposing conclusions, how these properties can inform future investigations, and how our investigation bears on analyses of heterochrony.

Explosive eruptive activity and temporal magmatic changes at Yotei Volcano during the last 50,000 years, southwest Hokkaido, Japan

To understand the eruptive history, structure, and magmatic evolution of Yotei Volcano, southwest Hokkaido, Japan, we investigated the geology and petrology of tephras located around the base of the volcano. We identified 43 tephra units interbedded with soils (in descending stratigraphic order, tephras Y1–Y43), and four widespread regional tephras. Ten radiocarbon ages were obtained from soils beneath the Yotei tephras. On the basis of petrologic differences and, the stratigraphic positions of thick layers of volcanic ash soil, indicative of volcanic stratigraphic gaps, the Yotei tephras are divided into four groups (in ascending stratigraphic order): Yotei tephra groups I, II-1, II-2, and II-3. We calculated the age of each eruptive deposit based on the soil accumulation rate, and estimated the volume of each eruption using isopach maps or the correlation between eruption volume and the maximum thickness at ~10km from the summit crater. The results regarding eruptive activity and the rate of explosive eruptions indicate four eruptive stages at Yotei Volcano over the last 50,000years. Stage I eruptions produced Yotei tephra group I between ca. 54cal.kaBP and up to at least ca. 46cal.kaBP, at relatively high average eruption rates of 0.07km3 dense-rock equivalent (DRE)/ky. After a pause in activity of ca. 8000years, Stage II-1 to II-2 eruptions produced Yotei tephra groups II-1 and II-2 from ca. 38 to ca. 21cal.kaBP at high average eruption rates (0.10km3DRE/ky), after a pause in activity of 2000–3000years. Finally, after another pause in activity of 4000–5000years, Stage II-3 eruptions produced Yotei tephra group II-3 from ca. 16.5cal.kaBP until the present day, at low average eruption rates (0.009km3DRE/ky). Whole-rock geochemical compositions vary within each tephra group over the entire eruption history. For example, group I and II-3 tephras contain the lowest and highest abundances, respectively, of K2O, P2O5, and Zr. Group II-1 has the highest abundances of Zr and Y. These trends indicate that the explosive activity was controlled by an evolving magma system. An understanding of these temporal changes in the chemical composition of the magma will enable future correlations of tephras with volcanic edifices, thereby revealing the full eruptive history and structure of Yotei Volcano, and constraining the timing of geological events in the region.

A STATISTICAL STUDY OF THE AVERAGE IRON CHARGE STATE DISTRIBUTIONS INSIDE MAGNETIC CLOUDS FOR SOLAR CYCLE 23

ABSTRACT Magnetic clouds (MCs) are the interplanetary counterparts of coronal magnetic flux ropes. They can provide valuable information regarding flux rope characteristics at their eruption stage in the corona, which is unable to be explored in situ at present. In this paper, we make a comprehensive survey of the average iron charge-state ( ) distributions inside 96 MCs for solar cycle 23 using Advanced Composition Explorer (ACE) data. Since the in the solar wind are typically around 9+ to 11+, the Fe charge state is defined as being high when the is larger than 12+, which implies the existence of a considerable amount of Fe ions with high charge states (e.g., ≥16+). The statistical results show that the distributions of 92 (∼96%) MCs can be classified into four groups with different characteristics. In group A (11 MCs), the shows a bi-modal distribution with both peaks being higher than 12+. Group B (4 MCs) presents a unimodal distribution of , with its peak being higher than 12+. In groups C (29 MCs) and D (48 MCs), the remains higher and lower than 12+ throughout ACE’s passage through the MC, respectively. Possible explanations of these distributions are discussed.

SO2 flux and the thermal power of volcanic eruptions

A description of the dynamics, chemistry and energetics governing a volcanic system can be greatly simplified if the expansion of magmatic gas can be assumed to be adiabatic as it rises towards the surface. The conditions under which this assumption is valid are clarified by analysis of the transfer of thermal energy into the low conductivity wallrocks traversed by fractures and vents from a gas phase expanding over a range of mass flux rates. Adiabatic behavior is predicted to be approached typically within a month after perturbations in the release of source gas have stabilized, this timescale being dependent upon only the characteristic length scale on which the host rock is fractured and the thermal diffusivity of the rock. This analysis then enables the thermal energy transport due to gas release from volcanoes to be evaluated using observations of SO2 flux with reference values for the H2O:SO2 ratio of volcanic gas mixtures discharging through high temperature fumaroles in arc and mantle-related volcanic systems. Thermal power estimates for gas discharge are 101.8 to 104.1MWH during quiescent, continuous degassing of arc volcanoes and 103.7 to 107.3MWH for their eruptive stages, the higher value being the Plinean Pinatubo eruption in 1991. Fewer data are available for quiescent stage mantle-related volcanoes (Kilauea 102.1MWH) but for eruptive events power estimates range from 102.8MWH to 105.5MWH. These estimates of thermal power and mass of gas discharges are commensurate with power estimates based on the total mass of gas ejected during eruptions. The sustained discharge of volcanic gas during quiescent and short-lived eruptive stages can be related to the hydrodynamic structure of volcanic systems with large scale gaseous mass transfer from deep in the crust coupled with episodes of high level intrusive activity and gas release.

Evolution of the 120 ka caldera-forming eruption of Kutcharo volcano, eastern Hokkaido, Japan: Geologic and petrologic evidence for multiple vent systems and rapid generation of pyroclastic flow

We investigated the eruptive sequence and temporal evolution of juvenile materials during the 120ka Kutcharo pumice flow IV (Kp IV) eruption, which was the most voluminous (175km3: bulk volume) caldera-forming eruption of Kutcharo volcano. The eruptive deposits are divided into four units in ascending order. Unit 1 is widely dispersed and consists of silt-sized, cohesive ash. Unit 2 is a thin, moderately sorted pumice fall deposit with a restricted distribution and small volume (<0.2km3). Unit 3, consisting of widely distributed ignimbrite, is the most voluminous. Unit 4 is also composed of pyroclastic flow deposits, but its distribution is limited to the northwest side of the caldera. Juvenile materials consist mainly of rhyolite pumice (74%–78% SiO2) associated with a minor amount of scoria (52%–73% SiO2) that are found only northwest of the caldera in Unit 3 and Unit 4. These scoriae can be classified on the basis of the P2O5 contents of their matrix glass into low-P, medium-P, and high-P types, which are almost entirely restricted to the lower part of Unit 3, Unit 4, and the upper part of Unit 3, respectively. These three types display distinct mixing trends with the rhyolitic compositions in SiO2–P2O5 variation diagrams. This evidence indicates that three distinct mafic magmas were independently and intermittently injected into the main body of silicic magma to erupt from the northwestern part of the magma system. Mafic injections did not occur in the southern part of the magma system. This petrologic evidence implies that the northwestern and southeastern flows of Unit 3 are heterotopic, contemporaneous products derived from multiple vent systems. Although Unit 2 was derived from an eruptive column, its volume is very small compared to Plinian fall deposits of typical caldera-forming eruptions. In our interpretation, the activity of the Kp IV eruption reached its climax rapidly, depositing Unit 3, without first producing a stable Plinian column. The presence of multiple vent systems could have allowed the system to bypass an initial eruptive stage with a stable Plinian column and begin its climactic stage, represented by Unit 3, rapidly. Multiple vents could have been the result of sequential injections of mafic magma in the early stages of the Kp IV eruption.

Lightning and electrical activity during the Shiveluch volcano eruption on 16 November 2014

Abstract. According to World Wide Lightning Location Network (WWLLN) data, a sequence of lightning discharges was detected which occurred in the area of the explosive eruption of Shiveluch volcano on 16 November 2014 in Kamchatka. Information on the ash cloud motion was confirmed by the measurements of atmospheric electricity, satellite observations and meteorological and seismic data. It was concluded that WWLLN resolution is enough to detect the earlier stage of volcanic explosive eruption when electrification processes develop the most intensively. The lightning method has the undeniable advantage for the fast remote sensing of volcanic electric activity anywhere in the world. There is a good opportunity for the development of WWLLN technology to observe explosive volcanic eruptions.