Non-volcanic Origin Research Articles

Mercury isotope evidence for a non-volcanic origin of Hg spikes at the Ordovician-Silurian boundary, South China

Ordovician-Silurian transition (OST) sections of South China contain extremely high mercury (Hg) concentrations (>1000 ppb) of uncertain provenance. The main hypotheses concerning their origin are: (1) contemporaneous elevated seawater Hg concentrations (e.g., due to volcanogenic inputs) combined with normal Hg-uptake processes by marine sediments, and (2) normal seawater Hg concentrations combined with enhanced Hg uptake by marine sediments (e.g., due to strong adsorption by sulfides). Here, we investigate Hg isotopes, which are a promising tool to track the sources of Hg in sediments, in OST strata of the Jiaoye drillcore from the Yangtze Platform of South China. Black shales and pyritic beds exhibit mass-independent fractionations of odd Hg isotopes (odd-MIF, i.e., Δ199Hg) of +0.13±0.05‰ and +0.13±0.03‰, respectively. These values are similar to those of modern and ancient marine sediments, supporting a seawater source of Hg in the study units and providing evidence against a volcanic source. We infer that the extreme Hg enrichment of the OST beds was due to elevated rates of Hg uptake from seawater through adsorption to pyrite. Local environmental conditions (e.g., intense euxinia and microbial sulfate reduction) played a dominant role in Hg enrichment of OST strata in South China.

Toward Real-Time Volcano Seismic Events’ Classification: A New Approach Using Mathematical Morphology and Similarity Criteria

This work proposes a new approach based on a suit combination of mathematical morphology and similarity criteria techniques to classify long-period and volcano-tectonic seismic events of the Cotopaxi volcano. The proposed method explores the seismic signal domain to compute a new feature space based on the edges map of the seismic events pattern represented in the gray-level spectrogram images, which is used to feed a set of similarity-based classifiers. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$L_{2}$ </tex-math></inline-formula> -norm was selected as the best metric to be implemented by the proposed method. In terms of classification performance, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$L_{2}$ </tex-math></inline-formula> -norm was statistically superior in the D1 data set (seismic events with overlapped signals of nonvolcanic origin) and similar in the D2 data set (events without overlapped signals) with respect to the other metrics, reaching accuracy mean scores of 93.34% and 96.88%, respectively. These results demonstrated that the computed edges map feature space is a better environment for separating both seismic events compared with the original gray-level space. Regarding the execution time, total time (TT) and time per-sample (TS) did not exceed 0.388 and 0.002 s during the training stage, respectively. During the testing stage, a TS of no more than 0.012 s was achieved. Finally, its execution time is faster, and the algorithm complexity is lower compared with the state-of-the-art methods, which makes it a practical and beneficial scheme to implement for real-time seismic events’ classification.

Land-sea correlations in the Eastern Mediterranean region over the past c. 800 kyr based on macro- and cryptotephras from ODP Site 964 (Ionian Basin)

Direct correlations between terrestrial and marine climate-proxy records are essential in order to determine potential lead/lag relationships in the response of the terrestrial and marine realms to climate forcing. In the Eastern Mediterranean region, such land-sea correlations have not yet been established beyond c. 200 ka. To explore the potential of tephra layers for Late and Middle Pleistocene land-sea correlations in the Eastern Mediterranean region, we have revisited yet unconfirmed tephra layers previously reported from Ocean Drilling Program (ODP) Site 964 (Ionian Basin) for the past c. 800 kyr in order to identify their origin and examine potential terrestrial counterparts. Using major- and trace-element glass analyses, we confirmed the presence of seven visible tephra layers with ages from 623 to 38 ka. These tephra layers represent known tephra isochrons from Italian volcanic centers (Y-5, Y-7, X-6, and V-0) and three yet unknown eruptions from Etna (623 ka), the Campanian Volcanic Zone (CVZ; 238 ka), and Pantelleria (238 ka). Because the majority of the previously reported tephra layers from ODP Site 964 were identified as clastic layers of non-volcanic origin, cryptotephra analyses were carried out for cores spanning Marine Isotope Stages (MIS) 13 to 9 (500–320 ka). This effort yielded 19 cryptotephra layers originating from Santorini volcano, the CVZ, possibly Roccamonfina volcano, and an undefined source in either the Aeolian Islands or the South Aegean Volcanic Arc. Two tephra layers are correlated with potential equivalents from terrestrial archives on the Italian and Balkan Peninsulas, including tephra isochrons SC5/A7/OH-DP-1966 (c. 493 ka; Mercure basin, Acerno basin, and Lake Ohrid) and TP09–65.95 (c. 359 ka; Tenaghi Philippon) that represent an unknown eruption of Roccamonfina and the Cape Therma 1 eruption of Santorini, respectively. Direct linking of the marine record from ODP Site 964 with the terrestrial records from Tenaghi Philippon, Lake Ohrid, and the Acerno basin via tephra tie points allowed us to circumvent shortcomings of the individual age models, and to obtain a comprehensive picture of climate variability in the greater Eastern Mediterranean region for the MIS 13–9 interval.

Exploring the unsupervised classification of seismic events of Cotopaxi volcano

This paper explores the use of six different clustering-based methods to classify long-period and volcano-tectonic seismic events and to find possible overlapping signals of non-volcanic origin that could occur at the same time or immediately after the occurrence of volcano-seismic events. According to the explored classifiers space, the BIRCH method with k = 2 was chosen as the best model in the classification of both pure seismic events, reaching a weighted balanced accuracy and accuracy scores of 0.81 and 0.88, respectively. The accuracy result represents a satisfactory and competitive classification performance when compared to the state of the art methods. Besides, the spectral-clustering method with k = 3 was able to classify seismic events with and without overlapped signals of non-volcanic origin, attaining a weighted balanced accuracy score of 0.51. This result was at least 0.18 units higher than the other classifiers. Additionally, the obtained true positive rates of 0.94 corroborated the excellent performance of this classifier to detect seismic events with overlapping. According to the obtained results, it is possible to state that the proposed clustering-based exploration was effective in providing competitive models for both the classification of uncontaminated seismic events as well as for the detection of seismic events with overlapped signals.

Mineralogy and Origin of Aerosol From an Arc Basaltic Eruption: Case Study of Tolbachik Volcano, Kamchatka

AbstractIntense emission of volcanic aerosol accompanied the 2012–2013 basaltic effusive eruption of Tolbachik volcano, Kamchatka. The aerosols sampled contain sulfuric acid droplets, glassy particles, and 70 mineral phases. All aerosol particles may be classified by their origin. The fragmentation aerosol includes magma fragments: silicate glass clasts, silicate microspheres, and small phenocrysts (olivine, pyroxene, and magnetite). The alteration aerosol comprises particles of quenched silicate melt covered with secondary minerals (fluorides, sulfates, and oxides/hydroxides of rock‐forming elements) and fragments of altered rocks composed solely of secondary minerals. The condensation aerosol dominated the mass during the later stages of the eruption when the explosive activity had ceased, and was characterized by the greatest variety of particle compositions. Na‐K sulfate and Fe (III) oxide comprised more than 95% of the solid fraction of the condensation aerosol. The remaining 5% was represented by native elements (Au, Ag‐Pt alloy, and Pt); sulfides of Fe, Cu, Ag, and Re; oxides and hydroxides of Al, Fe, Cu, Zn, Mo, W, Ta, and Zr; halides of Al, Mg, Na, K, Ca, Cd, Pb, Ag, and Tl; and sulfates of Na, K, Pb, Ca, and Ba; the only silicate was As‐bearing orthoclase. Droplets of H2SO4 formed the liquid phase of the condensation aerosol. Some of the aerosol components, such as magnetite spherules or phosphate‐carbonate‐fluorite association, likely had a nonvolcanic origin (country rocks and wood fly ash). The volcanic aerosols and their contained minerals, discharged at Tolbachik and elsewhere, result in a physical and chemical effect on the environment in the region of such volcanoes.

Role of weathering of pillow basalt, pyroclastic input and geomorphic processes on the genesis of the Monte Cerviero upland soils (Calabria, Italy)

In this paper we present new data on weathering and soil formation processes affecting alkaline pillow basalts on the summit of Mt. Cerviero (Calabria, southern Italy). We investigated two representative soil profiles using an integrated approach, including pedological, petrographic, mineralogical and geochemical investigations. We distinguished the main features inherited from the hydrothermal alteration of the pillow basalts in a submarine environment from the chemical weathering processes under meteoric conditions. Irregular geochemical patterns and chemical index of alteration values across the soil profiles indicate a lithological discontinuity between the bedrock and the upper soil horizons, as a response to soil rejuvenation, in turn controlled by erosive processes and an allochthonous pyroclastic input. The soil profiles display poor horizonation and an incipient to intermediate degree of weathering, in line with the clay mineralogy (chlorite or hydroxy-interlayered vermiculite, illite, kaolinite and varying mixed-layers). The degeneration microtextures of clay and iron-manganese coatings in one soil profile suggest their relict genesis, with an emplacement under warm-humid conditions during the last interglacial. A Late Pleistocene to Holocene age of soil development is supported by the trachytic composition of volcanic micropumices, correlated to explosive eruptions from the Campania Province or the Aeolian Islands, in both soil profiles. Geochemical indices obtained from selective extractions of pedogenetic Al, Fe and Si pools point to poor andic properties with humus-Al-complexes prevailing over short-range order minerals. Nonetheless, the latter are consistent with the presence of volcanic glass, an optically isotropic pedogenic matrix and the Andosol-like field features of the soil profiles, even if they developed in a non-volcanic area. This should lead to a partial reassessment of the volcanic versus non-volcanic origin of certain Andosols worldwide and claims a good field work as a basis for choosing the best-suited laboratory methods to fill the gap between ordinary lab and field results.

Geochemical characterisation of Taal volcano-hydrothermal system and temporal evolution during continued phases of unrest (1991–2017)

Taal volcano (Luzon Island, Philippines) has last erupted in 1977 but has known some periods of increased activity, characterised by seismic swarms, ground deformation, increased carbon dioxide flux and in some cases temperature anomalies and the opening of fissures. We studied major, trace element and sulphur and strontium isotopic composition of Taal lake waters and hot springs over a period of 25 years to investigate the geochemical evolution of Taal volcano's hydrothermal system and its response to volcanic unrest.Long-term evolution of Main Crater Lake (MCL) composition shows a slow but consistent decrease of acidity, SO4, Mg, Fe and Al concentrations and a trend from light to heavy sulphate, consistent with a general decrease of volcanic gases dissolving in the hydrothermal system. Na, K and Cl concentrations remain constant indicating a non-volcanic origin for these elements. Sulphate and strontium isotopic data suggest this neutral chloride-rich component represents input of geothermal water into Taal hydrothermal system. A significant deviation from the long-term baseline can be seen in two samples from 1995. That year, pH dropped from 2.6 to 2.2, F, Si and Fe concentrations increased and Na, K and Cl concentrations decreased. Sulphate was depleted in 34S and temperature was 4 °C above baseline level at the time of sampling. We attribute these changes to the shallow intrusion of a degassing magma body during the unrest in 1991–1994.More recent unrest periods have not caused significant changes in the geochemistry of Taal hydrothermal waters and are therefore unlikely to have been triggered by shallow magma intrusion. A more likely cause for these events is thus pressurisation of the hydrothermal reservoir by increasing degassing from a stagnant magma reservoir. Our study indicates that new magmatic intrusions that might lead to the next eruption of Taal volcano are expected to change the geochemistry of MCL in the same way as in 1994–1995, with the most notable effects being changes in temperature, pH, F and Si concentrations.

Atoll Reef Geomorphology of Sagori Island, SE Sulawesi: A Reconnaissance Study

DOI: 10.17014/ijog.4.3.181-191The Sagori Atoll of the Kabaena Island, SE Sulawesi is one of Indonesia’s remote tropical reefs and such has received little attention from reef researchers. Non of early scientific expeditions reported either geomorphology or ecology of the Sagori Atoll in detail. This study is the first investigation of the reef geomorphology and associated habitats of Sagori Atoll within a biodiversity of “Coral reef Triangle Initiative - CTI” region, using data from satellite imagery and on ground observation. The Sagori Atoll environment consists of reef-island, atoll rim, and lagoon in which six habitats are associated, including: sand cay, coralgal pavement, sand sheet (intertidal and subtidal), sand-hardground striation, and outer atoll rim and lagoon (shallow and deep). The reef-island is built from sediments that are entirely calcareous, resting on a platform of lithified coral conglomerate. The atoll rim is dominated by coralgal pavement consisting mainly of both encrusting and living coralline algae. The lagoon which is a semi-enclosed pool and opens to the eastern side, consists of sand and scattered corals. The atoll formation is considered to be of nonvolcanic origin, but is rising from the depth of due to anticlinal island subsidence.

Geochemistry and geothermometry of non-volcanic hot springs in West Malaysia

Although more than sixty hot springs have been reported in West Malaysia, their geochemistry, geothermometry and utilization as a potential energy source have not been considered yet. This study reports the geochemistry, geothermometry and mineral saturation indices of a number of hot springs in West Malaysia. The potential of these hot springs as a source of geothermal energy as well as their origin and possible mixing with surface cold waters have been discussed.Surface temperatures of the studied hot springs range from 41 to 99°C and pH values vary between 5.5 and 9. Geochemical data showed that among cations, Si, Na, Ca and K occur in relatively high contents, while Mg and Fe show very low concentrations. On the other hand, HCO3 is present in relatively high concentration compared to other anions (SO4, Cl and F). Data also illustrated that most of the studied hot springs are K–Na–bicarbonate rich waters although they represent different geological provenances in West Malaysia reflecting homogeneity in the geological formations and/or hydrochemical processes governing the characteristics of these waters. This homogeneity also indicates the insignificant effect of local geology on the chemistry of the studied hot springs. Saturation indices calculations of the studied thermal waters indicate that most of the secondary mineral phases such as goethite and hematite are apparently supersaturated while quartz and chalcedony are saturated. Conversely, amorphous silica is slightly under-saturated. These results suggest similar rock–water interactions for both geothermal and non-geothermal waters.The geological settings of the studied hot springs either in or close to granitic masses or along the major fault or shear zones as well as the Na-bicarbonate nature of the waters and low sulfate concentrations suggest their non-volcanic origin. They are also similar in their geological setting and water chemistry to other non-volcanic hot springs in other parts of the world. However, the possible mixing of the original hot waters with near surface cold water is evident from the clear disagreement between the silica and cation geothermometers as well as the disequilibrium with their associated host rocks as indicated from the plot of studied hot springs in the Na–K–Mg ternary diagram and saturation indices calculations.Quartz geothermometers gave equilibrium temperatures ranging from 93°C in the Ayer Hangat hot spring to 154°C in the Lojing hot spring. This requires 398 to 649kJ/kg energy to heat the water suggesting an intermediate enthalpy. These results also pointed out that some of the studied hot springs have potential to generate adequate heat, which could be harnessed for energy generation upon further work to prove their viability.

Characteristics of South Korea's Geothermal Water in Relation to Its Geological and Geochemical Feature

The volcanic type of geothermal water is linked intimately to active or potentially active volcanoes and takes place near the plate boundaries. In contrast to the volcanic type, the geothermal water in Korea has a non-volcanic origin. Korea’s geothermal water is classified into the residual magma (RM) type and deep groundwater (DG) type according to the criterion of 35 o C. This study reviewed the relationship between the physical and chemical features of the 281 geothermal water sources in South Korea in terms of the specific capacity, water temperature, and chemical compositions of two different basements (igneous rock and metamorphic rock) as well as the geological structures. According to the spatial relationship between the geothermal holes and geological faults, the length of the major fault is considered a key parameter determining the movement to a deeper place and the temperature of geothermal water. A negligible relationship between the specific capacity (Q/s) and temperature was found for both the RM type and DG type with the greater specific capacities of the RM- and DG-igneous types than the RM- and DG-metamorphic types. No relationship was observed between Q/s and the chemical constituents (K + , Na + , Ca 2+ , Mg 2+ , Zn 2+ , Cl � , SO4 2� , HCO3 � , and SiO2) in the DG-igneous and DG-metamorphic types. Furthermore, weak relationship between temperature and chemical constituents was found for both the RM type and DG type.

Morphologic characteristics of volcanic and sedimentary sequences on Mars

This paper presents morphometric parameters of Martian layered sequences of different origin that outcrop in the scarps and crater walls, which form natural geologic profiles. The objective of this study was to develop quantitative criteria that would allow distinguishing layers of volcanic and, presumably, sedimentary origin. As a result of measurements of large numbers of layers on images with the highest resolution (HiRISE camera, spatial resolution ∼0.25 m/px) it was established that the combination of total sinuosity and the slope of the spectrum of high-frequency sinuosity generally allow us to differentiate between layered sequences of different origin. For the majority of measured volcanic layers, the total sinuosity values exceed 1.3, and the slope of the power function approximating the sinuosity spectrum exceeds 0.015. The corresponding values are lower for layers of nonvolcanic origin. However, in some cases, the stratified rocks demonstrate such significant variations in these parameters (e.g., layered deposits on the bottom of the Galle crater), that it makes the genetic identification of these layers impossible using the formal criteria. A more robust validation of the genesis of layered sequences requires an integrated approach that includes both the morphometric parameters, and the qualitative criteria and the description and characteristics of the geological situation in a given exposure.

Atmospheric aerosol episodes over Lithuania after the May 2011 volcano eruption at Grimsvötn, Iceland

During the eruption of the volcano at Grimsvötn in Iceland (21 May 2011), an inflow of volcanic pollutants to the atmospheric surface layer of Vilnius, Lithuania from 0700 UTC 24 May until the end of 29 May 2011 was observed. A cloud of volcanic plume rose up from Grimsvötn and reached an altitude of 19km. The analysis of possible volcanic origin PM1 aerosol sources was supplemented with forward and backward air mass trajectories, concentration and composition measurements and size distribution calculations of aerosol particles. According to the forward air mass trajectories from the volcano at Grimsvötn, the plume from the layer of 3000–4500m was advected southeastward from Iceland towards the British Isles and the Baltic Sea. The plume reached Vilnius and descended from the troposphere to the surface after about 86h. After data analysis, four episodes selected in the time series of the atmospheric submicron aerosol particle (PM1) concentration of chemical components (sulfate, ammonium, nitrate and organics) were analyzed with the Aerodyne Quadrupole Aerosol Mass Spectrometer, and calculations of the size-resolved distribution spectra were made. Two clear episodes were detected when the main source of aerosols was the volcano, with well-defined size distribution spectra of PM1 chemical components in the accumulation mode. The ammonium to sulfate molar ratio (ASR) during Episodes 1 and 2 is 0.81, suggesting that sulfate particles were partially neutralized by ammonium and determined by volcanic eruptions. However, during Episodes 3 and 4 the ASR was higher (1.0) and determined by both volcanic and non-volcanic origin components. This study shows that the sulfate emissions from the volcano at Grimsvötn in Iceland reached distances farther than 3000km, and they can have an influence on the local concentration and size distribution spectra of PM1 chemical components. Over the period of the volcanic eruption (Episode 1) the sulfate concentrations increased by a factor of 3 and reached 90% of PM1, while the nitrate and organic levels remained low and unchanged. The volcanic sulfate contribution made up about 250% of the average concentration of anthropogenic sulfate in Vilnius.

Crustal Seismic Velocities of the Rwenzori Region, East African Rift, from Local Travel-Time Tomography: Evidence for Low-Velocity Anomalies beneath the Mountain Range

We investigate the upper crustal velocity structure beneath the Rwenzori Mountains in western Uganda. This mountain range of nonvolcanic origin is situated within the western branch of the East African rift and reaches altitudes of more than 5000 m. The cause for the extreme uplift within a rifting environment is currently being debated. The local tomographic inversion described here is based on 2053 earth­ quakes recorded by a network of up to 35 stations covering an area of 140 x 90 km2• The deployment was limited by the international border between Uganda and the Democratic Republic of the Congo, such that a number of recorded events lie outside the station perimeter. We perform synthetic tests to assess the effect of location uncertainty on the results. The tests show that the resolution is good between 3 and 15 km depth within a restricted area covered by the array. However, smearing can be significant in some parts. The inversion for P-and S-wave velocity anomalies is performed independently and agrees well. The interpretation of the results is based on a synthetic model that reproduces the same pattern of anomalies as that obtained after inversion of the real data. Our models exhibit a significant negative velocity anomaly (up to -8%) beneath the central Rwenzori Mountains. This could be an indication for active magmatic intrusions beneath the mountains in relation to the rifting. The pre­ sence of low velocities in the northwest of the range, within the rift, may be related to magmatic processes beneath the Buranga hot springs. Higher velocities are found elsewhere beneath the eastern rift shoulder and are thought to be related to old cratonic crust.

Conceptual model and numerical simulation of the hydrothermal system in Hammam Faraun hot spring, Sinai Peninsula, Egypt

The tectonic position of Egypt in the northeastern corner of the African continent suggests that it may possess significant geothermal resources, especially along its eastern margin. The most of the thermal springs in Egypt are located along the shores of Gulf of Suez and Red Sea. These springs are probably tectonic or nonvolcanic origin associated with the opening of the Red Sea—Gulf of Suez rifts, where the eastern shore of the Gulf of Suez is characterized by superficial thermal manifestations including a cluster of hot springs with varied temperatures. Hammam Faraun area consists of the hottest spring in Egypt where the water temperature is 70°C. Conceptual as well as numerical models were made on the Hammam Faraun hot spring based on geological, geochemical, and geophysical data. The models show that the heat source of the hot spring is probably derived from high heat flow and deep water circulation controlled by faults associated with the opening of the Red Sea and Gulf of Suez rifts.

Seismic structure, gravity anomalies, and flexure of the Amazon continental margin, NE Brazil

Seismic and gravity data have been used to determine the structure of the sediments, crust, and upper mantle that underlie the Amazon continental margin, offshore NE Brazil. Seismic reflection profile data reveal a major unconformity at ∼7 s two‐way travel time (TWTT) which we interpret as marking the onset of the transcontinental Amazon River and the formation of the Amazon deep‐sea fan system in the late Miocene. Seismic refraction data show mean sediment velocities that decrease by &gt;1.5 km s−1 in a seaward direction. We attribute this decrease to facies changes associated with sediment progradation and the development of topset, foreset, and bottomset beds. Seismic refraction data show that the sediments are underlain by oceanic crust that has a similar velocity structure compared to elsewhere in the Atlantic Ocean but is unusually thin (∼4.2 km). We attribute the thin crust to either slow seafloor spreading or a limited magma supply during the initial rifting of South America and Africa in the Early Cretaceous. The seismic data have been used to construct a new sediment thickness grid that together with gravity anomaly data, suggests the Amazon fan loaded lithosphere with an unusually high flexural strength. While a high‐strength lithosphere explains the overall depth of the seismic Moho, there are discrepancies (of up to 2 km) beneath the upper fan, where the modeled flexed Moho is shallower than the seismic Moho, and beneath the middle fan, where it is deeper. Gravity and seismic modeling suggest these discrepancies are caused by lateral changes in subcrustal density such that the mantle underlying the upper fan is denser than it is beneath the middle fan. We attribute these lateral density differences to proximity to the Ceara Rise, which is believed to have formed during the Late Cretaceous in a mid‐ocean ridge setting. Fan loading of a relatively strong, dense, and, hence, cold lithosphere predicts stress orientations that are consistent with borehole breakout data and the location and height of the Gurupé Arch onshore. Despite its proximity to “leaky” transform faults, the margin that underlies the Amazon fan appears to be of nonvolcanic origin. The main differences with other nonvolcanic margins, such as West Iberia and Newfoundland, are a greater sediment accumulation, a narrower zone of transitional crust, and a lack of any evidence for extreme extension and mantle serpentinization.

Atmospheric sulfur dioxide measurements during the 2005 and 2007 eruptions of the Piton de La Fournaise volcano: Implications for human health and environmental changes

Piton de La Fournaise is an active volcano located in the south-eastern part of Réunion Island, a tiny island found in the south-western Indian Ocean (21°S; 55,5°E). This volcano erupts regularly, at least once a year, with notable amount of degassing. Concerning the volcanic eruptions, the regulation of the French Ministry of Environment on the air quality is mainly focussed on the standards applicable for the sulfur dioxide (SO 2), in terms of public health and environmental changes. Air samples have been collected continuously every 10 days on passive diffusion tubes of SO 2, an atmospheric tracer of volcanic plumes, by ORA (Observatoire Réunionnais de l'Air), at 10 sites which have been located around the volcano since September 2005. The mean SO 2 concentrations measured over a 10-day period, in the absence of any volcanic eruption, range between very low values (1–15 μg/m 3) for all 10 sites. However, during the December 2005 eruption, notable SO 2 concentrations (factor ~ 5–25) have been measured at the locations situated on the north-west flanks of the volcano. The SO 2 degassing reached concentrations of 65–379 μg/m 3, which is mainly caused by the volcanic activity when coupled with the local-to-regional atmospheric circulations (land/sea breezes, easterlies, etc.). A wide range of atmospheric measurements was performed in the vicinity of Piton de La Fournaise in order to characterize the gaseous and particle emissions, during the April–May 2007 eruption. SO 2 concentrations were also measured continuously by SF-2000 analyser, at several coastal locations in the vicinity of the volcano, during and off eruption activities. In the absence of any volcanic eruption, the SO 2 concentrations showed day-to-day variations, with hourly-mean concentrations varying between 1 and 20 μg/m 3. These values correspond to the background concentrations for this coastal rural location and might as well come in part from non-volcanic origin. The SO 2 concentrations however were increased by a factor ~ 10–30 (with a maximum hourly-mean concentration of 2486 μg/m 3), during the April–May 2007 eruption. Hereby, several statutory thresholds were exceeded particularly at the Tremblet location. Indeed, the information and recommendation threshold (350 μg/m 3/h) as well as the alert threshold (500 μg/m 3 on 3 h consecutively) were exceeded 32 and 5 times respectively at this site. These measurements point out that during the times of eruptions with significant amounts of degassing, the threshold values for protecting the ecosystems and the air quality for human health were exceeded at several inhabited locations, with implications for human health and environmental changes, on local-to-regional scale.

New procedures to decompose geomagnetic field variations and application to volcanic activitiy

SUMMARY We report the development of numerical procedures for extracting long-term geomagnetic field variations caused by volcanic activity from an observed geomagnetic field by using statistical methods. The newly developed procedures are to estimate the trend from the observed data, as well as variations of non-volcanic origin such as periodic components, components related to external geomagnetic variations and observational noise. We also aim at referring to data obtained at a remote standard geomagnetic observatory rather than using a temporarily installed reference site for reasons of data quality. Two different approaches—a Bayesian statistical method and a Kalman filter method—are applied to decompose the geomagnetic field data into four components for comparison. The number of filter coefficients and the degree of condition realizations are optimized on the basis of minimization of the information criteria. The two procedures were evaluated by using a synthetic data set. Generally, the results of both methods are equally sufficient. Subtle differences are seen at the first, several data points due to arbitrarily selected initial values in the case of the Kalman filter method and at the smaller residual for the Bayesian statistical method. The largest differences are in computation time and memory size. The Kalman filter method runs a thousand times faster on a testing workstation and requires less memory than the Bayesian method. The Kalman filter method was applied to the total intensity data at Kuchi-erabu-jima volcano. The result suggests that the procedure works reasonably well.

An evaluation of nutritional constraints on sweet potato (Ipomoea batatas) production in the central highlands of Papua New Guinea

Sweet potato (Ipomoea batatas) is the staple food crop in the highlands of Papua New Guinea (PNG). Declining crop productivity, however, appears to be threatening the sustainability of sweet potato-based farming systems within the region, a probable cause being the exhaustion of soil nutrient reserves in continuously cultivated sweet potato gardens. To assess the extent of the problem, a survey of sweet potato gardens was conducted across four of the highlands provinces and information on soil and crop variables was obtained for old gardens (cultivated over many seasons) and new gardens (newly brought into cultivation) on soils of volcanic and non-volcanic origin. Crop leaf nutrient data collected in the survey were interpreted using the Diagnosis and Recommendation Integrated System (DRIS), to try to identify the main nutritional constraints on tuber production in different garden types on soils of volcanic or non-volcanic origin. The results suggested that K deficiency was the primary cause of poor crop production in almost a third of sweet potato gardens, but was more of a problem in old gardens than in new. Phosphorus deficiency was also a problem on volcanic soils, and S deficiency on non-volcanic soils. These latter deficiencies, however, were at least as prevalent in new gardens as in old. Important factors contributing to K and S depletion from garden systems were the removal of K and S-rich vines from cultivation areas, the shortening of fallow periods and the burning of weed and crop residues, the latter releasing S (SO2) to the atmosphere. Correction of K and S deficiencies may require the recycling of old vines back to sweet potato cultivation areas and the adoption of a zero-burn policy for fallow management. Correction of P deficiency may necessitate the use of P-accumulating fallow species, e.g. wild Mexican sunflower (Tithonia diversifolia), to extract the P fixed by sesquioxide and allophanic minerals

On strontium and barium anomalies in the sediments of Charkadio Cave (Tilos Island, Dodekanese, Greece)

The sediments of Charkadio Cave (Island of Tilos) have been object of chemical and mineralogical investigation. Sampling the speleothems of Charkadio Cave, it is possible to look back into the island’s younger geological history. Tilos is of non-volcanic origin but neighbored to several volcanoes of the Aegean (Kos, Nisyros, and Giali). We observed a certain coincidence of increased Ba and Sr values in such samples and volcanic activity. Some of the layers of these fine-grained sediments contain volcanic particles (ash grains and lapilli). Interestingly, these strata have the highest content of Ba and Sr, as determined by neutron activation analysis. Additionally to this discovery, Sr-rich barite crystals were found in some of these layers. Thus, Ba and Sr must either exist on the surface of tephra particles in volatile and water-soluble compounds and/or were released by weathering from Ba and Sr containing feldspars (originating from pumice) in the cave sediment environment. Since other cave sediments from Tilos, which were not exposed to volcanic products, contain very much lesser quantities of Ba and Sr, we conclude that mobile Ba and Sr compounds are contributed to the sediment by volcanic fallout.

未固結〜半固結堆積物中の変形構造形成の解釈

It has long been recognized that unconsolidated or partially consolidated sediments can be intensely deformed during burial, either from gravity-driven subhorizontal extension, or from tectonic shortening. Such deformation can be evaluated in the context of experimental and empirical results from engineering geology literature. We try to summarize this knowledge using several submarine and on-land examples that illustrate the concepts of pore-fluid pressure, shaking, permeability, and consolidation, and are applicable to the interpretation of geologic structures that develop in unconsolidated or partially consolidated sediments. We first review dish, web, and vein structures, scaly clay and liquefaction features, which are typical of unconsolidated or partially consolidated sediments along convergent plate margins. Then, some experimental aspects of permeability test results are applied to fluid flow phenomena in and around accretionary prisms to characterize the role and the importance of fluid flow parallel to the σ2 direction. The results are further applied to explain the concentration of hot springs of a non-volcanic origin along active, strike-slip faults, as well as how seepage along convergent margins occurs in an en echelon pattern on conjugate sets of strike slip faults. Additional experimental work is suggested to develop a better understanding of these geologic structures.