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1.
Concentrations of Th and U in fresh ash ejected by active volcanoes in Kamchatka are generally considerably below their Clarke values in their respective types of rock. The bulk concentrations of Th and U in andesitic and basaltic ashes do not show any obvious differences. The concentrations of their mobile forms decrease with increasing basicity of the ash. We revealed overall positive linear trends in the series of bulk concentrations for Th and U and a negative trend of Th/U in ashes that have been arranged over eruption year. Considerable quantities of mobile forms of radioactive elements fall during ashfalls in dissolved form or are sorbed by falling snow directly from the dispersive medium of volcanic aerosols. The original fractions of all of the mobile forms are 0.68–1.93% for Th and 1.16–3.21% for U. The bulk of these come to the Earth’s surface during eruptions when no snow cover was available. The quantities of mobile forms of Th and U were considerably decreased when ejected by winter-time eruptions during the time they resided in the snow.  相似文献   

2.
Ash and lapilli derived from Holocene and Late Pleistocene volcanic cruptions cover approximately half of the North Island of New Zealand. Deposits from 16 separate series of showers are recognised in the surface soils and areas with 3 inches and more of each ash bed have been mapped out during soil surveys. These and other shower deposits are also recognised and described in fossil soils. The effects of the volcanic ashes on soil properties are related to the thickness and frequency of deposition, to mineral composition, and to the period of exposure to soil formation. Soils formed from shower deposits of Holocene age are extensive and have characteristic properties of friability, fine granular structure, deep humic topsoils and slippery non-sticky clays. The clays are chiefly amorphous and responsible for the notable practical properties of free drainage, high moisture retention, low bulk density, and critical limits of stability under pressure. In New Zealand the development of these characteristies increases with time up to about 15,000 years and then decreases with the crystallisation of the clays to halloysite. Soils formed from Late Pleistocene volcanic ashes are high in halloysite clay and with increasing age resemble soils formed from marine sedimentary rocks. Differing degrees of development of the characteristics are shown in the soil classification. The soils from volcanic ash are widely used for crop, pasture or forestry production. More intensive permanent usage depends on more detailed knowledge of the materials which will be obtained through combined volcanological and pedological research.  相似文献   

3.
Cu concentrations in surface (river and lake) and subsurface waters are determined. The geographic pattern of Cu distribution in natural water is identified. This pattern is controlled by the difference between its concentrations in drained rocks and soils and the geochemical redox conditions of its migration. Territories with low, medium, and elevated Cu concentrations in natural waters are identified. The concentrations of Cu in natural waters of the region are found to be generally lower than the Clarke values.  相似文献   

4.
The distribution of “ash” (the non-combustible fraction of marine suspended matter) and concentrations of particulate Al, Ca, Fe, Cr, Ni, Cu, Sr and234Th in surface waters and of210Pb,230Th and234Th in two vertical profiles (385–4400 m) of the Indian Ocean are reported.The ash concentrations in surface waters follow the primary productivity pattern, with higher abundances in samples south of 40°S and lower concentrations in the equatorial and subtropical regions. Opaline silica and CaCO3 are the dominant components of the ash in samples from >40°S and from 7°N to 39°S, respectively. Aluminosilicates are only a minor constituent of the surface particulate matter. The metal/Al ratios in the surface particles are significantly higher compared to their corresponding crustal ratios for all the metals analyzed in this work. Comparison of enrichment factors between marine aerosols, plankton and surface oceanic particles, seem to indicate that this high metal/Al ratio in surface particles most likely arises from their involvement in marine biogeochemical cycles. Particulate234Th activity in surface waters parallels the ash abundance implying that its scavenging efficiency from surface waters depends on the particulate concentration.The particulate230Th and210Pb concentration profiles increase monotonously with depth. It is difficult to ascribe this increase to a process other than the in-situ vertical scavenging of230Th and210Pb from the water column by settling particles. The mean settling velocities of particles calculated from the particulate230Th data using a one-dimensional settling model is about 2 × 10?3 cm/s. The settling velocity computed from the particulate230Th profiles does not appear to be compatible with the particulate210Pb depth profiles; one possible explanation to account for the disparity would be that230Th and210Pb are scavenged by different size populations of particles.On the whole, the geographic distribution of particulate matter, their composition and settling velocities in the Atlantic, Pacific and Indian Oceans are similar indicating that they are controlled by quite similar processes in the marine hydrosphere.  相似文献   

5.
Particulates amounting to 0.1–2.0 g efficiently collected from large volumes of Atlantic and Pacific surface waters have been analyzed for carbonate, opal, quartz and several natural and man-made radioisotopes.The concentrations of particles range between 10 and 600 μg/kg. In the equatorial regions particle concentrations are low and similar in both the oceans. At higher latitudes (>30°N or S), the Atlantic waters, however, have higher concentrations of particles compared to those in the Pacific. The latitudinal distribution exhibits a north-south symmetry with higher concentrations in the 30°–60° belt. Based on the particulate abundance for CaCO3 and opal and their sedimentation, we have estimated their production and in-situ integrated dissolution rates for a few regions.Radioisotopes having different source functions, namely14C and239Pu injected due to nuclear weapon tests,234Th,230Th and228Th produced in-situ in seawater,232Th which derives primarily from land,210Pb introduced via wet precipitations and226Ra introduced through diffusion from deep-sea sediments have been measured in the particulates. The relative enrichment factors for these nuclides in particles vary as Th ? Pu > Pb > Ra. The atmospheric bomb fallout pattern is discernible in the surface particulates; the239Pu concentration increases with latitude in both the hemispheres; however, the values are about a factor of two lower in the southern hemisphere.The distribution pattern of radioisotopes is found to be complex, even for234Th whose source function in the oceans is uniform. In view of the differences in the source functions it becomes possible to delineate the principal geochemical/geophysical processes which determine the concentrations of these nuclides in surface waters.  相似文献   

6.
Absract The manganese content of the surface (river, lake) and subsurface waters of Transbaikalia is determined. The geographical peculiarities of manganese distribution in natural waters are found to be due to different Mn concentrations in drained rocks and soils, as well as to the geochemical redox conditions of migration. The areas with low, medium, and high concentrations of Mn in natural waters and the sources of water in which Mn concentrations exceed MAC are revealed. __________ Translated from Vodnye Resursy, Vol. 32, No. 5, 2005, pp. 597–600. Original Russian Text Copyright ? 2005 by Kashin, Ivanov.  相似文献   

7.
The whole-deposit grain-size populations have been determined for two phreatoplinian ashes of the rhyolitic Taupo volcano (New Zealand). One is much finer than plinian pumice deposits studied from the same volcano, and the other differs in having a lower content of coarse pumice. The poor sorting of the two ashes is attributed mainly to water-scavenging of the ash cloud. The very limited fractionation with distance from source, combined with the very regular exponential thickness decrease, indicates that the scavenging water was an integral part of the ash cloud and was derived from Lake Taupo. At times when the proportion of erupted water to magma became particularly high, erosion of the underlying deposits took place, and to this is attributed the striking gullying of the surface which separates the two ashes.  相似文献   

8.
The article gives the results of studying the concentration and composition of aliphatic and polycyclic aromatic hydrocarbons in suspension in surface waters at sections from the English Channel and Skagerak Strait to various regions of the Baltic Sea (2010–2015) and in water and bottom sediments of the southeastern part of the sea in the water area of the Kravtsovskoe field (2008–2015). In recent years, the surface waters of open areas of the Baltic Sea showed a decrease in hydrocarbon concentrations down to background levels (12–33 μg/L). The maximal concentration of hydrocarbons (in excess of the MAC) was recorded in different seasons in navigation areas, including the English Channel and Pregola R. mouth. In the zone of the Kravtsovskoe field, the concentration and composition of hydrocarbons in water depends on their inflow from the bank, and the same characteristics in bottom sediments, on the rate of their leakage from sediment stratum. A decline in these processes have led to a decrease in hydrocarbon concentrations in the sediments of a local area near D-6 platform to background levels (5–7 μg/g) and to the predominance of terrigenous, rather than petroleum, alkanes in hydrocarbon compositions.  相似文献   

9.
Variations in the key indices of the chemical composition of surface waters are studied in a region where these waters are polluted by mining plant wastes. The forms of metals migration and their distribution in the bottom deposits of watercourses are examined. The possible steps for reducing the pollution of water in a watercourse are discussed.  相似文献   

10.
Most of the ash produced all over the world is primarily disposed off by wet disposal method onto the ash ponds, which are occupying huge valuable lands. This disposal problem can be minimized by utilizing ash in large geotechnical earthworks. However, its use in earthquake prone areas requires thorough understanding of its liquefaction resistance and nature of development of excess pore pressures under dynamic loading conditions. Investigations have been carried out in this paper on the liquefaction behaviour of pond ash by conducting cyclic triaxial tests on inflow and outflow ash samples collected from two different ash ponds. Distinctly different liquefaction phenomenon was observed for the ash samples from inflow and outflow points of the same ash pond. Inflow samples exhibited higher cyclic resistance than outflow samples and their strengths were comparable with the natural sands. Further studies revealed that the influence of various factors on liquefaction susceptibility of both the types of ashes is similar to that of natural sands.  相似文献   

11.
Fugen-dake, the main peak of Unzen Volcano, began a new eruption sequence on November 17, 1990. On May 20, 1991, a new lava dome appeared near the eastern edge of the Fugen-dake summit. Small-scale, 104–106 m3 in volume, Merapi-type block and ash flows were frequently generated from the growing lava dome during May–June, 1991. These pyroclastic flows were accompanied by co-ignimbrite ash plumes that deposited ash-fall deposits downwind of the volcano. Three examples of co-ignimbrite ash-fall deposits from Unzen pyroclastic flows are described. The volume of fall deposits was estimated to be about 30% by volume of the collapsed portions of the dome that formed pyroclastic flows. This proportion is smaller than that described for other larger co-ignimbrite ash-fall deposits from other volcanoes. Grain size distributions of the Unzen co-ignimbrite ash-fall deposits are bi-modal or tri-modal. Most ashes are finer than 4 phi and two modes were observed at around 4–7 phi and 9 phi. They are composed mainly of groundmass fragments. Fractions of another mode at around 2 phi are rich in crystals derived from dome lava. Some of the fine ash component fell as accretionary lapilli from the co-ignimbrite ash cloud indicating either moisture or electrostatic aggregation. We believe that the co-ignimbrite ash of Unzen block and ash flows were formed by the mechanical fracturing of the cooling lava blocks as they collapsed and moved down the slope. These ashes were entrained into the convective plumes generated off the tops of the moving flows.  相似文献   

12.
The use of magnetic susceptibility as a proxy for the relative degree of industrial pollution of soils and sediments is only qualitative and complications arise when unmixing the contributions from different sources. Detailed characterization of anthropogenic magnetic phases is needed in order to discriminate the input from different sources. The present study investigates magnetic fractions from fly ashes from different thermoelectric power plants and lagooned ash from metal works in Bulgaria, to further our knowledge of potential sources. Thermomagnetic analysis of saturation magnetization (Ms) and magnetic susceptibility (K) revealed a low-substituted magnetite-like phase in power-plant fly ashes and magnetite/maghemite phases in lagooned ash. Magnetic hysteresis measurements on single spherules from the wastes are combined with subsequent SEM/EDX examination of the same grains, allowing for the grain size dependence of the hysteresis parameters to be directly obtained for the studied anthropogenic phases. The results suggest that the structure-sensitive magnetic parameters for the lagooned ash show stronger size dependence compared to the published data for synthetic crushed magnetites, which is due to the complex internal structure and stress level in the anthropogenic phases formed under fast cooling conditions. Moreover, the Day plot for the studied single grains shows the presence of different correlation lines for fly ashes and the lagooned ash, i.e. it discriminates between the sources.  相似文献   

13.
Data of two field studies were used to analyze the concentrations of Na, K, Ca, Mg, Fe, Mn, Zn, Cu, Al, Cr, Ni, Cd, and Pb in the water, bottom deposits, zoobenthos, fish, and macrophytes of the Pond Bugach and in the soils near the pond. It was established that the majority of metals in the soils and bottom deposits correlate and their concentrations are governed by the universal geochemical factors of the region. The heavy metals were recognized that originate from anthropogenic sources and their concentrations were found to exceed the maximum admissible values for different components of the ecosystem. Five types of heavy metals migration were recognized in the soil–bottom deposits–zoobenthos–fish chain and in macrophytes. Statistically significant difference was found to exist between the concentrations of some heavy metals in the muscles of fish species with different food types (crucian carp and perch) as well as between the correlations of metals. The recorded concentrations were compared with the concentrations of metals measured in the last decade in other limnetic ecosystems in Siberia, Europe, North America, and China.  相似文献   

14.
The results of studying the elemental composition of surface continental waters in the European Russia from tundra to arid zone are discussed. The relative concentrations of elements in the solid residue of waters from various natural-climatic zones are evaluated, and the enrichment or dispersion of continental waters by these elements are analyzed as compared with their clarkes in the rocks that occur in the catchment areas. The coefficients of migration in water are evaluated, and the major elements with respect to which surface waters enrich under anthropogenic load are identified. The territorial distribution of higher concentrations of the most hazardous elements in waters of lakes is characterized.  相似文献   

15.
Anthropogenic mercury pollution was studied in Kastela Bay (Croatia), 10 years after chloralkaline plant (PVC) stopped production. The concentration of total mercury determined in sediments which are composed mainly of calcite and quartz, are in the range 14,280-30,400 ng/g. The values are higher than reported in the literature for Elbe and Seine estuaries and also above 25,000 ng/g used for criterion in remediation project in Minamata Bay. The concentration of methylmercury 6.05-36.74 ng/g are typical for slightly to highly contaminated estuarine sediments. The low ratio of methylmercury to total mercury found in sediments of Kastela Bay is in the range 0.04-0.18%. It can be explained that in this region predominate conditions which do not promote in-situ methylation. Sediments were found to be highly anoxic. Concentrations of total mercury in unfiltered surface waters are in the range 69-145 ng/l and in unfiltered bottom waters in the range 230-1,418 ngl(-1). High concentrations found in bottom waters suggest that either resuspension or partial dissolution of sediments takes place. An experiment performed on filtered and unfiltered waters showed that about 85% of total mercury in surface water and almost 100% in bottom water was retained on 45 microm filters. To demonstrate contrasts, two pristine estuaries from norths and south Europe were studied. Silicious sediments of Ore estuary (Sweden) and calcareous sediments of Krka estuary (Croatia) have total mercury concentrations close to accepted background level. The ratio of methylmercury to total mercury is < or = 1% in all samples with one exception. The highest observed ratio (2.70%) was in the surface sediment from E2 station in Krka estuary measured in March 2000. This location is suitable for studying methylmercury formation in pristine environment.  相似文献   

16.
The distribution of some microelements in the surface and stratified layers of bottom sediments in Lake Seliger is studied. Data on the bottom deposit pollution by heavy metals is used to determine the anthropogenic load on the lake ecosystem. Cd, Zn, and Pb are shown to rapidly accumulate in thick (>1 m) bottom deposits that have formed during the period of lake existence. The concentrations of Cd and Zn are shown to correlate with the organic matter in thick bottom deposits.  相似文献   

17.
The geochronology of cave deposits in the Cradle of Humankind UNESCO World Heritage Site in South Africa provides a timeframe essential for the interpretation of its fossils. The uranium-lead (U–Pb) and uranium-thorium disequilibrium (U/Th) dating of speleothems, mostly flowstones that underlie and blanket the fossil-bearing sediments, have been effective in this sense, but U–Pb is limited by the requirement of ∼1 ppm U concentrations and low common Pb contents, and U/Th has a c. 500 ka limit of applicability. Here we report age results for calcite-aragonite speleothems obtained using a new combined uranium-thorium-helium ((U,Th)–He) and U/Th dating routine. We reproduced within analytical uncertainty, the published U–Pb or U/Th ages for (a) flowstone in three drill core samples in the range 2000–3000 ka, (b) a flowstone hand sample taken at surface with an age of 1800 ka, and (c) five underground flowstone samples in the range 100–800 ka. Calcite retentivity for He under cave conditions is thus demonstrated. In the few cases where helium loss was observed in speleothems, only some of the subsamples were affected, and to varying degrees, suggesting loss by lattice damage not related to diagenetic processes, rather than volume diffusion. In the 100 to 800 ka range, the combined U/Th disequilibrium and (U,Th)–He method also yielded reliable values for initial (230Th/238U) and (234U/238U) activity ratios. Importantly, most subsamples had high initial (230Th/238U) values, ranging from 1.0 to 19.7, although having low Th/U ratios. This is probably due to incorporation of Fe–Mn oxides-hydroxides dust, on which 230Th was previously adsorbed. Such samples are mostly not dateable by U/Th without the additional input from the He analysis. If not detected and corrected for, such high initial (230Th/238U) values can lead to inaccurate U/Th and U–Pb ages. Our study shows that the incorporation of He analysis in U/Th dating has broad potential application, with four methods for calculating the ages, in carbonates from different environments where U-Pb or U/Th dating would not work.  相似文献   

18.
Surface transects and vertical profiles of total and leachable particulate Fe, Mn, Al and P, along with dissolved and soluble Fe were obtained during August 2003 in the southeastern Bering Sea. High concentrations of leachable particulate Fe were observed in the bottom waters over the Bering Sea shelf with an unusually high percentage of the suspended particulate Fe being leachable. Leachable particulate Fe averaged 81% of total particulate Fe, and existed at elevated concentrations that averaged 23 times greater than dissolved Fe in the isolated cool pool waters over the mid shelf where substantial influence of sedimentary denitrification was apparent. The elevated leachable particulate Fe is suggested to be a result of sedimentary Fe reduction in surficial sediments, diffusion of Fe(II) from the sediments to the bottom waters, and subsequent oxidation and precipitation of reduced Fe in the overlying bottom waters. Eddies and meanders of the Bering Slope Current can mix this Fe-rich water into the Green Belt at the outer shelf-break front. Elevated levels of leachable particulate Fe were observed in surface waters near the Pribilof Islands where enhanced vertical mixing exists. Storm events and/or cooling during fall/winter with the resultant destruction of the thermally stratified two-layer system can also mix the subsurface water into surface waters where the elevated leachable particulate Fe is a substantial source of biologically available Fe.  相似文献   

19.
By the example of an area near the active Karymskii Volcano (on the eastern coast of Kamchatka) it is shown that under conditions of regular supply of pyroclastic material on the diurnal surface, organic soil matter transforms very slowly and mobile trace elements of newly fallen volcanic ashes are the major plant nutrition source. Geochemical specialization of the studied area is characterized by lower concentrations of most trace elements relative to their clarkes for soils and by an excess of trace element contents over the clarkes for living matter in plants. Newly fallen ashes are enriched in mobile trace elements, which in dissolved form pass into adjacent media due to hypergene geochemical processes.  相似文献   

20.
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