Development of an automatic volcanic ash sampling apparatus for active volcanoes

We develop an automatic system for the sampling of ash fall particles, to be used for continuous monitoring of magma ascent and eruptive dynamics at active volcanoes. The system consists of a sampling apparatus and cameras to monitor surface phenomena during eruptions. The Sampling Apparatus for Time Series Unmanned Monitoring of Ash (SATSUMA-I and SATSUMA-II) is less than 10 kg in weight and works automatically for more than a month with a 10-kg lead battery to obtain a total of 30 to 36 samples in one cycle of operation. The time range covered in one cycle varies from less than an hour to several months, depending on the aims of observation, allowing researchers to target minute-scale fluctuations in a single eruptive event, as well as daily to weekly trends in persistent volcanic activity. The latest version, SATSUMA-II, also enables control of sampling parameters remotely by e-mail commands. Durability of the apparatus is high: our prototypes worked for several months, in rainy and typhoon seasons, at windy and humid locations, and under strong sunlight. We have been successful in collecting ash samples emitted from Showa crater almost everyday for more than 4 years (2008–2012) at Sakurajima volcano in southwest Japan.     

A statistical method linking geological and historical eruption time series for volcanic hazard estimations: Applications to active polygenetic volcanoes

The probabilistic analysis of volcanic eruption time series is an essential step for the assessment of volcanic hazard and risk. Such series describe complex processes involving different types of eruptions over different time scales. A statistical method linking geological and historical eruption time series is proposed for calculating the probabilities of future eruptions. The first step of the analysis is to characterize the eruptions by their magnitudes. As is the case in most natural phenomena, lower magnitude events are more frequent, and the behavior of the eruption series may be biased by such events. On the other hand, eruptive series are commonly studied using conventional statistics and treated as homogeneous Poisson processes. However, time-dependent series, or sequences including rare or extreme events, represented by very few data of large eruptions require special methods of analysis, such as the extreme-value theory applied to non-homogeneous Poisson processes. Here we propose a general methodology for analyzing such processes attempting to obtain better estimates of the volcanic hazard. This is done in three steps: Firstly, the historical eruptive series is complemented with the available geological eruption data. The linking of these series is done assuming an inverse relationship between the eruption magnitudes and the occurrence rate of each magnitude class. Secondly, we perform a Weibull analysis of the distribution of repose time between successive eruptions. Thirdly, the linked eruption series are analyzed as a non-homogeneous Poisson process with a generalized Pareto distribution as intensity function. As an application, the method is tested on the eruption series of five active polygenetic Mexican volcanoes: Colima, Citlaltépetl, Nevado de Toluca, Popocatépetl and El Chichón, to obtain hazard estimates.     

Injection and arrest of dykes: implications for volcanic hazards

Dykes are the principal channels through which magma reaches the surface in volcanic eruptions. For this reason dykes observed in the field are commonly assumed to be feeders to lava flows. The actual proportion of dykes reaching the surface is, however, poorly known. In order to develop models for the purpose of estimating volcanic hazard, this proportion must be known. This follows because such models should not only consider the probability of dykes being injected from magma chambers during periods of unrest in the associated volcanoes, but also the probability of the injected dykes being arrested. This paper presents field data on several thousand dykes from Iceland and Tenerife (Canary Islands) indicating that many, and probably most, dykes become arrested at various crustal levels and never reach the surface to feed eruptions. Using the results of analytical and numerical models, it is shown that, for common loading conditions, the stress field in the vicinity of a magma chamber may favour the injection and propagation of dykes while the stress field at a certain distance from the chamber favours dyke arrest. This means that many dykes that are injected from the chamber propagate only for a very limited distance from the chamber to the point where they become arrested. The implication is that during periods of unrest in volcanoes, the probability of volcanic eruption is only a small fraction of the probability of dyke injection from the source magma chamber.     

The weathering and element fluxes from active volcanoes to the oceans: a Montserrat case study

The eruptions of the Soufrière Hills volcano on Montserrat (Lesser Antilles) from 1995 to present have draped parts of the island in fresh volcaniclastic deposits. Volcanic islands such as Montserrat are an important component of global weathering fluxes, due to high relief and runoff and high chemical and physical weathering rates of fresh volcaniclastic material. We examine the impact of the recent volcanism on the geochemistry of pre-existing hydrological systems and demonstrate that the initial chemical weathering yield of fresh volcanic material is higher than that from older deposits within the Lesser Antilles arc. The silicate weathering may have consumed 1.3% of the early CO₂ emissions from the Soufrière Hills volcano. In contrast, extinct volcanic edifices such as the Centre Hills in central Montserrat are a net sink for atmospheric CO₂ due to continued elevated weathering rates relative to continental silicate rock weathering. The role of an arc volcano as a source or sink for atmospheric CO₂ is therefore critically dependent on the stage it occupies in its life cycle, changing from a net source to a net sink as the eruptive activity wanes. While the onset of the eruption has had a profound effect on the groundwater around the Soufrière Hills center, the geochemistry of springs in the Centre Hills 5 km to the north appear unaffected by the recent volcanism. This has implications for the potential risk, or lack thereof, of contamination of potable water supplies for the island’s inhabitants.     

The respiratory health hazards of volcanic ash: a review for volcanic risk mitigation

Studies of the respiratory health effects of different types of volcanic ash have been undertaken only in the last 40 years, and mostly since the eruption of Mt. St. Helens in 1980. This review of all published clinical, epidemiological and toxicological studies, and other work known to the authors up to and including 2005, highlights the sparseness of studies on acute health effects after eruptions and the complexity of evaluating the long-term health risk (silicosis, non-specific pneumoconiosis and chronic obstructive pulmonary disease) in populations from prolonged exposure to ash due to persistent eruptive activity. The acute and chronic health effects of volcanic ash depend upon particle size (particularly the proportion of respirable-sized material), mineralogical composition (including the crystalline silica content) and the physico-chemical properties of the surfaces of the ash particles, all of which vary between volcanoes and even eruptions of the same volcano, but adequate information on these key characteristics is not reported for most eruptions. The incidence of acute respiratory symptoms (e.g. asthma, bronchitis) varies greatly after ashfalls, from very few, if any, reported cases to population outbreaks of asthma. The studies are inadequate for excluding increases in acute respiratory mortality after eruptions. Individuals with pre-existing lung disease, including asthma, can be at increased risk of their symptoms being exacerbated after falls of fine ash. A comprehensive risk assessment, including toxicological studies, to determine the long-term risk of silicosis from chronic exposure to volcanic ash, has been undertaken only in the eruptions of Mt. St. Helens (1980), USA, and Soufrière Hills, Montserrat (1995 onwards). In the Soufrière Hills eruption, a long-term silicosis hazard has been identified and sufficient exposure and toxicological information obtained to make a probabilistic risk assessment for the development of silicosis in outdoor workers and the general population. A more systematic approach to multi-disciplinary studies in future eruptions is recommended, including establishing an archive of ash samples and a website containing health advice for the public, together with scientific and medical study guidelines for volcanologists and health-care workers.     

Environmental hazards of fluoride in volcanic ash: a case study from Ruapehu volcano, New Zealand

The vent-hosted hydrothermal system of Ruapehu volcano is normally covered by a c. 10 million m³ acidic crater lake where volcanic gases accumulate. Through analysis of eruption observations, granulometry, mineralogy and chemistry of volcanic ash from the 1995–1996 Ruapehu eruptions we report on the varying influences on environmental hazards associated with the deposits. All measured parameters are more dependent on the eruptive style than on distance from the vent. Early phreatic and phreatomagmatic eruption phases from crater lakes similar to that on Ruapehu are likely to contain the greatest concentrations of environmentally significant elements, especially sulphur and fluoride. These elements are contained within altered xenolithic material extracted from the hydrothermal system by steam explosions, as well as in residue hydrothermal fluids adsorbed on to particle surfaces. In particular, total F in the ash may be enriched by a factor of 6 relative to original magmatic contents, although immediately soluble F does not show such dramatic increases. Highly soluble NaF and CaSiF₆ phases, demonstrated to be the carriers of ‘available’ F in purely magmatic eruptive systems, are probably not dominant in the products of phreatomagmatic eruptions through hydrothermal systems. Instead, slowly soluble compounds such as CaF₂, AlF₃ and Ca₅(PO₄)₃F dominate. Fluoride in these phases is released over longer periods, where only one third is leached in a single 24-h water extraction. This implies that estimation of soluble F in such ashes based on a single leach leads to underestimation of the F impact, especially of a potential longer-term environmental hazard. In addition, a large proportion of the total F in the ash is apparently soluble in the digestive system of grazing animals. In the Ruapehu case this led to several thousand sheep deaths from fluorosis.     

A simple method for the collection and analysis of volcanic gas samples

Investigations into the chemistry of volcanic gases depend on the availability of complete and accurate analyses of volcanic exhalations. The wide variety of sampling and analysis methods hitherto used, often supplying only partial analyses of low precision, made intercomparison, and thus a systematic study of volcanic gases, difficult. With the method proposed here, complete volcanic gas samples are obtained permitting the accurate determination of all major species by standard analytical methods without the need for highly specialised ancillary equipment. The samples are collected in evacuated 300 ml pyrex flasks through titanium tubes deeply inserted into the gas vent. Two types of flask are used, a single compartment flask allowing the easy determination of the major constituents and containing 50 ml 4 N NaOH, and a double compartment flask for the separate analysis of the sulfur species and containing 25 ml 0.1 N As₂O₃ in 1 N HClO₄ in the first, and 50 ml 4 N NaOH in the second compartment. Non-absorbed gases are determined by gas chromatography, the rest by standard analytical procedures. The determination of H₂O, CO₂, SO₂, SO₂, S₂, H₂S, HCl, HF, H₂, N₂, O₂, CH₄, CO and NH₂ is described.     

Social studies of volcanology: knowledge generation and expert advice on active volcanoes

This paper examines the philosophy and evolution of volcanological science in recent years, particularly in relation to the growth of volcanic hazard and risk science. It uses the lens of Science and Technology Studies to examine the ways in which knowledge generation is controlled and directed by social forces, particularly during eruptions, which constitute landmarks in the development of new technologies and models. It also presents data from a survey of volcanologists carried out during late 2008 and early 2009. These data concern the felt purpose of the science according to the volcanologists who participated and their impressions of the most important eruptions in historical time. It demonstrates that volcanologists are motivated both by the academic science environment and by a social concern for managing the impact of volcanic hazards on populations. Also discussed are the eruptions that have most influenced the discipline and the role of scientists in policymaking on active volcanoes. Expertise in volcanology can become the primary driver of public policy very suddenly when a volcano erupts, placing immense pressure on volcanologists. In response, the epistemological foundations of volcanology are on the move, with an increasing volume of research into risk assessment and management. This requires new, integrated methodologies for knowledge collection that transcend scientific disciplinary boundaries.     

Impact of volcanic fluoride and SO2 emissions from moderated activity volcanoes on the surrounding vegetation

Studies in the regions of the volcanoes Etna (Italy) and Masaya (Nicaragua) show that the continuous emissions of gaseous pollutants (HF and SO₂) from moderated activity volcanoes causes a chronic pollution in the surrounding vegetation with certain economical and ecological consequences.Reciprocally the measure of the pollutants in the plants growing in volcanic regions may be a simple and fast method to investigate some characteristics of the volcanic plume: for example, intensity of the emissions of gas, direction and extent of the plume.     

Silicic volcanism in Iceland: Composition and distribution within the active volcanic zones

Silicic volcanic rocks within the active volcanic zones of Iceland are mainly confined to central volcanoes. The volcanic zones of Iceland can be divided into rift zones and flank zones. Each of these zones contains several central volcanoes, most of which have produced minor amounts of silicic rocks. The silicic rocks occur as lavas and domes or as tephra layers, welded tuffs and ignimbrites, formed both in effusive and explosive eruptions. They tend to be glassy or very fine-grained, containing small amounts of phenocrysts. Plagioclase (andesine–oligoclase), anorthoclase or occasionally sanidine coexist with minerals such as augite, fayalite, pigeonite, orthopyroxene and magnetite. Quartz phenocrysts are exceedingly rare. Zoning of phenocrysts is limited and the pattern is variable. A set of 90 samples representing all active central volcanoes that have erupted silicic rocks was analysed for major- and trace-elements. The silicic rocks can be classified as dacites, trachytes, low-alkali rhyolites and alkalic rhyolites. Some of the trachytes and alkalic rhyolites are peralkaline (mostly comenditic). Trachytes and alkalic rhyolites are only found within the flank zones, while dacites and low-alkali rhyolites are mostly confined to the rift zones. The Icelandic rhyolites plot close to the thermal minimum in the “granite” system, while dacites and trachytes plot within the plagioclase field and towards the alkali feldspar temperature minimum. The silicic rocks are relatively Fe-rich and Ca-poor indicating low water pressure in the source. Trace element concentrations follow similar patterns in most central volcanoes. Exceptions are Torfajökull where silicic rocks display a negative correlation of Ba to Th and unusually high Th-contents, and the western flank zone where Ba-concentrations are highly variable. The ratios of different high field-strength elements are generally similar within each central volcano or region, which probably reflects different ratios in the source materials. Isotope systematics indicate that the silicic rocks are derived from older basaltic rocks similar to those from the same volcano, and that meteoric water has played a role in the genesis of the silicic rocks. Traditionally, the petrogenesis of silicic rocks in Iceland has been explained by various models of fractional crystallization or partial melting. The available data seems to be better explained by near-solidus differentiation than by near-liquidus differentiation. The silicic minimum melts can be extracted from the rigid framework of the near-solidus source by the process of solidification front instability or by deformation-assisted melt segregation. The source of the silicic rocks is within the intrusive complex beneath a central volcano rather than in a large, long-lived magma chamber.     

Ra or Ra/Ba dating of Holocene volcanic rocks: application to Mt. Etna and Merapi volcanoes

This paper shows how ²²⁶Ra–²³⁰Th disequilibria can be used to date Holocene volcanic rocks from some well selected volcanoes. A systematic study of these disequilibria on historical or well-dated volcanic samples is indeed first required to test the applicability of this method. Two examples are described here to illustrate its potential. In the case of Mt. Etna, the good correlation observed between (²²⁶Ra)₀ activities at the time of eruption and Th contents in lava flows from the last two millennia [M. Condomines, J.C. Tanguy, V. Michaud, Magma dynamics at Mt. Etna: constraints from U–Th–Ra–Pb radioactive disequilibria and Sr isotopes in historical lavas, Earth Planet. Sci. Lett. 132 (1995) 25–41] is used to infer the ages of several newly analysed lava flows. The calculated ages are in good agreement with those deduced from the archaeomagnetic curve describing the variation of the geomagnetic field direction in southern Italy [J.C. Tanguy, I. Bucur, J.F.C. Thompson, Geomagnetic secular variation in Sicily and revised ages of historic lavas from Mt. Etna, Nature 318 (1985) 453–455, J.C. Tanguy, M. Le Goff, V. Chillemi, A. Paiotti, C. Principe, S. La Delfa, G. Patane, Variation séculaire de la direction du champ géomagnétique enregistrée par les laves de l'Etna et du Vésuve pendant les deux derniers millénaires, C. R. Acad. Sci. Paris 329 (1999) 557–564, J.C. Tanguy, M. Le Goff, C. Principe, S. Arrighi, V. Chillemi, A. Paiotti, S. La Delfa, G. Patane, Archaeomagnetic dating of Mediterranean volcanics of the last 2100 years: validity and limits. Earth Planet. Sci. Lett. 211 (2003) 111–124]. We also present a whole set of new U-series data on historical, recent, and older samples from Merapi (Indonesia), and show that the (²²⁶Ra)/Ba ratio has probably maintained a quasi-steady state value during at least the past four millennia, and can be used to infer the (²²⁶Ra)₀/Ba ratio of old volcanics at the time of eruption, and thus their ages. Comparison with ¹⁴C ages available on three samples [R. Gertisser, J. Keller, Temporal variations in magma composition at Merapi volcano (Central Java, Indonesia): magmatic cycles during the past 2000 years of explosive activity, J. Volcanol. Geotherm. Res. 123 (2003) 1–23] shows an excellent agreement. These dating methods, based on the post-eruptive decrease of ²²⁶Ra excesses can be confidently used to date young rocks on both volcanoes, an important step to infer their recent eruptive history and magmatic evolution. It also opens the possibility to extend the geomagnetic field variation curve back into the past few millennia. The promising results obtained in this work should encourage new systematic U-series studies to test the applicability of such methods to other permanently active volcanoes showing ²²⁶Ra excesses.     

Evaluation methods of heat discharge and their applications to the major active volcanoes in Japan

The rates at which thermal energy is released by non-eruptive mechanisms associated with active volcanoes in Japan have been estimated from surface temperature distributions or from shapes of the fumarolic plume rise. Values of 5.3 x 10⁷ W and 1.2 x 10⁸ W have been calculated for non-eruptive release rates in 100-km segments of the Northeast and the Southwest Japan Arc, respectively. It appears that non-eruptive heat discharge is of the same order as that caused by eruptions.     

Chemistry and metal contents of magmatic gases: the new Tolbachik volcanoes case (Kamchatka)

The gaseous products of new Tolbachik volcanoes were studied during 1975 to 1977 throughout all eruptive stages and during the post eruptive activity. In investigations the northern break-out gases emitted during the eruption from the moving and consolidated lava flows there have been detected H₂O (the main component), H₂, HF, HCl, SO₂ and H₂S, CO₂, CO, NH₃, CH₄ and other hydrocarbons, NH₄Cl predominated in compositions of condensates and subtimates on lava flows and the most characteristic microcomponents were Zn, Cu, Pb, Sn, Ag and others. Sampling of gases and condensates at the southern break-out was conducted immediately from the flowing melt. In gases there have been detected H₂O (98 mol. %). HCl and H₂ (0.9 mol. % each) as well as HF, SO₂, H₂S, CO₂ and in small quantities O₂ and N₂, Gases reached the equilibrium state atT andP sampling and were characteristic of gas composition of the southern break-out magma. HCl, HF and H₂SO₄ were predominant during condensate and sublimate mineralization. The major raicrocomponents were represented by Pt, Sb, As, Zn, Cu, Pb, Ni, Co and others. Comparison of compositions of gases and of products of their reactions at the northern and at the southern break-outs allows us to assume the presence of the deeper magma source at the northern break-out and of shallow magma source at the southern break-out.     

A comparative analysis of magnetic properties in rocks: Five active submarine volcanoes in the western Pacific

We studied the petrophysical and magnetic properties of dredged rocks that compose the edifices of five active submarine volcanoes in the Pacific Ocean, viz., the Fukujin, Esmeralda, Kovachi, and Simbo at island arcs, and Ile des Cendres in a marginal sea. We measured the standard petrophysical and magnetic characteristics and performed three kinds of thermomagnetic analysis as well as an electron-probe analysis. Comparative analysis of magnetic properties in rocks showed that they are strongly differentiated by the value of natural remanent magnetization and of magnetic susceptibility. The greatest values are shown by the Esmeralda aphyric basaltic andesites, the lowest occur in the Ile des Cendres xenoliths. The principal carriers of magnetization in the rocks are grains of unaltered and/or oxidized titanomagnetite with varying domain structures. All the samples are magnetically isotropic.     

Abundances,distribution and sizes of volcanoes in the Pacific Ocean and implications for the origin of non-hotspot volcanoes

In this paper I present data on the abundances, sizes and crustal age for all volcanoes (volcanic islands and seamounts) which appear on published bathymetric charts of the Pacific Ocean. These new data shed light on the origin of non-hotspot volcanoes and are important, in combination with data on the chemical compositions of seamounts and volcanic islands, for estimates of the bulk composition of ocean crust. These data also provide firm constraints on off-ridge oceanic volcanism models. Results of this study show that the size-frequency distribution of Pacific volcanoes is Poisson-like and that the smallest volcanoes are much more abundant than large ones. This study shows clearly that the most abundant volcanoes on the Earth are the submerged oceanic volcanoes which comprise 5–25% of the oceanic volcanic layer. On Pacific crust of Eocene age and younger, the abundance of volcanoes (number of volcanoes per unit area) increases monotonically with increasing age. Assuming steady state, the production rate of new off-ridge volcanoes (number of volcanoes per unit area per unit time) is inversely proportional to the square root of the lithosphere age [1]. On crust older than Eocene, the number of volcanoes per unit area of crust decreases monotonically with increasing age, however the total volume of lava represented by these edifices increases with increasing age. Size frequency distributions of volcanoes on swaths of successively older crust indicate that these abundance patterns are partly due to the effect of sediment burial of small edifices on old Pacific crust as well as the effect of increased lithosphere thickness on seamount size. These general patterns are not appreciably changed by omitting from consideration known hotspot volcanoes [2] and volcanoes built at fossil constructional plate margins [3].     

Ages of calderas,large explosive craters and active volcanoes in the Kuril-Kamchatka region,Russia

The ages of most of calderas, large explosive craters and active volcanoes in the Kuril-Kamchatka region have been determined by extensive geological, geomorphological, tephrochronological and isotopic geochronological studies, including more than 600 ¹⁴C dates. Eight Krakatoa-type and three Hawaiian-type calderas and no less than three large explosive craters formed here during the Holocene. Most of the Late Pleistocene Krakatoa-type calderas were established around 30 000–40 000 years ago. The active volcanoes are geologically very young, with maximum ages of about 40 000–50 000 years. The overwhelming majority of recently active volcanic cones originated at the very end of the Late Pleistocene or in the Holocene. These studies show that all Holocene stratovolcanoes in Kamchatka were emplaced in the Holocene only in the Eastern volcanic belt. Periods of synchronous, intensified Holocene volcanic activity occurred within the time intervals of 7500–7800 and 1300–1800 ¹⁴C years BP.     

Hazard assessment at volcanic fields: the Campi Flegrei case history

Volcanological analysis of the 10 000 yr –1538 explosive activity at Campi Flegrei shows that the most common explosive eruptions are characterized by the emplacement of flow or surge deposits, originating from the interaction between magma and shallow and/or sea water. The minimum volumes of pyroclastic products range between 0.04 and 0.7 km³; the proximal areas covered by these products range from 3–4 to 40–50 km². The pyroclastic flow and surge deposits occurring inside the caldera have been strongly controlled by pre-existent morphology; because of this, the area of present Napoli city was blanketed by approximately 5 m of pyroclastic deposits, during the last 5000 yr.Previous analysis suggests that the presence of even very low topographic obstacles may influence pyroclastic density current run out such that future eruptive deposits would mainly be confined inside the caldera rim. We suggest that a future eruption at Campi Flegrei would not seriously involve the urbanized area of Napoli city located on the hills. On the contrary, the plains located on the eastern side of the caldera (Fuorigrotta, Bagnoli) would be the most damaged area.