Cristobalite in a rhyolitic lava dome: evolution of ash hazard   总被引：1，自引：1，他引：0  

Claire J. Horwell  Jennifer S. Le Blond  Sabina A. K. Michnowicz  Gordon Cressey 《Bulletin of Volcanology》2010,72(2):249-253

Prolonged and heavy exposure to particles of respirable, crystalline silica-rich volcanic ash could potentially cause chronic, fibrotic disease, such as silicosis, in individuals living in areas of frequent ash fall. Here, we show that the rhyolitic ash erupted from Chaitén volcano, Chile, in its dome-forming phase, contains increased levels of the silica polymorph cristobalite, compared to its initial plinian eruption. Ash erupted during the initial, explosive phase (2–5 May 2008) contained approximately 2 wt.% cristobalite, whereas ash generated after dome growth began (from 21 May 2008) contains 13–19 wt.%. The work suggests that active obsidian domes crystallise substantial quantities of cristobalite on time-scales of days to months, probably through vapour-phase crystallisation on the walls of degassing pathways, rather than through spherulitic growth in glassy obsidian. The ash is fine-grained (9.7–17.7 vol.% <4 μm in diameter, the respirable range) and the particles are mostly angular. Sparse, fibre-like particles were confirmed to be feldspar or glass.  相似文献   

Palynological dating and correlation of surface and subsurface sediments from Wardha valley coalfield,Maharashtra     

Neerja Jha  Pauline Sabina  K. Rajni Tewari  N. C. Mehrotra 《Journal of the Geological Society of India》2011,77(2):137-148

42 genera of palynomorphs have been reported from the qualitative and quantitative analysis of the palynoflora from both open cast mine and bore holes viz., Ballarpur open cast mine, Durgapur open cast mine and Bore hole CMWNM-57 on barrier between Kawadi/Majri open cast and Hindustan Lalpeth Colliery from the Wardha valley coalfield of Wardha basin. Two palynoassemblages have been recorded i.e., an Upper Karharbari palynoassemblage comprising dominance of radial monosaccate genus Parasaccites and subdominance of nonstriate disaccate genus Scheuringipollenites and a Lower Barakar palynoassemblage consisting of dominance of Scheuringipollenites and subdominance of striate disaccates chiefly Faunipollenites, suggesting an Early Permian age (Late Sakmarian to Early Artinskian) to the sediments. It is further authenticated by the occurrence of palynotaxa viz., Crucisaccites, Caheniasaccites, Indotriradites and Tiwariasporis. Upper Karharbari Formation has been demarcated for the first time in lithologically designated Barakar Formations in Ballarpur, Durgapur, Majri and Hindustan Lalpeth Colliery while the sample 57/2 of bore hole CMWNM from Kawadi area may belong to the Kamthi Formation on the basis of pinkish yellowish coarse grained to medium grained sandstone. An attempt has been made to correlate these palynoassemblages with other Lower Gondwana basins of Early Permian affinity.  相似文献   

A study of the spatial structure of the atmospheric boundary layer with a Doppler-Sodar network     

I. G. Granberg  V. F. Kramar  R. D. Kuznetsov  O. G. Chkhetiani  M. A. Kallistratova  S. N. Kulichkov  M. S. Artamonova  D. D. Kuznetsov  V. G. Perepelkin  V. V. Perepelkin  F. A. Pogarskii 《Izvestiya Atmospheric and Oceanic Physics》2009,45(5):541-548

The studies conducted in 1991–2004 by scientists of the A.M. Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences, and the Karpov Institute of Physical Chemistry yielded data on the structures of the surface air layer (to a height of 20 m) and both subinversion and inversion layers (to heights of from 800 m to 1 km), where arid aerosol is transported. One of the main objectives of the 2007 experiment was to record the space-vortex structures within a layer of 30–700 m that directly provide the removal and long-range transport of fine-dispersed (<5 µm) desert aerosol. This paper describes the organization of the Khar-Gzyr 2007 experiment (Black Lands, 2007) to study the convective removal of arid aerosol from desertificated lands, and it presents some data obtained from the remote sensing of the atmospheric boundary layer with a sodar network in the course of this experiment. The sodar network, which was developed to study a spatial structure of coherent vortices, included three identical minisodars (with carrier frequencies of 3.8 kHz) located at the apices of a triangle, each side of which was about 3.5 km, and a sodar (with a carrier frequency of 1.7 kHz). The vertical profiles of the three wind-velocity components and the characteristics of air temperature fluctuations were determined. The procedure of identifying coherent vortex structures is described. The variations in the vertical and horizontal wind-velocity components and the scales characteristic of such structures are estimated.  相似文献   

Experience in measuring the wind-velocity profile in an urban environment with a Doppler sodar     

V. P. Yushkov  M. A. Kallistratova  R. D. Kouznetsov  G. A. Kurbatov  V. F. Kramar 《Izvestiya Atmospheric and Oceanic Physics》2007,43(2):168-180

The experience of long-term acoustic remote measurements of vertical wind-velocity profiles at two sites in Moscow is reported. Equipment performances and measurement conditions are described. Acoustic measurement features characteristic of a large city with high traffic noise and spurious reflections from buildings are discussed. Criteria and techniques of rejecting noisy and false signals are described as well as the methods of statistical data processing suitable in the case of a signal-to-noise ratio rapidly varying in time and a significant number of rejected signals. Preliminary results of measurements are given.  相似文献   

Contrasting surface active faults and deep seismogenic sources unveiled by the 2009 L’Aquila earthquake sequence (Italy)     

Sabina Bigi  Piero Casero  Claudio Chiarabba  Daniela Di Bucci 《地学学报》2013,25(1):21-29

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On the Tomographic Reconstruction of the 3D Electron Density for the Solar Corona from STEREO COR1 Data     

M. Kramar  S. Jones  J. Davila  B. Inhester  M. Mierla 《Solar physics》2009,259(1-2):109-121

We present for the first time a three-dimensional reconstruction of the electron density in the corona at distances from 1.5R _⊙ to 4R _⊙ using COR1 STEREO observations. The reconstruction is performed using a regularized tomography inversion method for two biweekly periods corresponding to Carrington Rotations 2058 and 2066. Images from the two STEREO spacecraft are used to compare the reconstructed density structures with coronal features located by triangulation. We find that the location of a bright tip of a helmet streamer obtained from the tomographic reconstruction is in good agreement with the location obtained by triangulation. The reconstructed density structure of the equatorial streamer belt is largely consistent with the variation of the current sheet derived from a potential magnetic field extrapolation for most of the equatorial region and for an MHD model of the corona. A zero-value density region in the reconstruction is identified with a low-density region seen in an EUVI image below the reconstruction domain.  相似文献   

An ice-core based history of Siberian forest fires since AD 1250     

Anja Eichler  Willy Tinner  Sabina Brütsch  Susanne Olivier  Tatyana Papina  Margit Schwikowski 《Quaternary Science Reviews》2011,30(9-10):1027-1034

Forest fires play a key role in the global carbon cycle and thus, can affect regional and global climate. Although fires in extended areas of Russian boreal forests have a considerable influence on atmospheric greenhouse gas and soot concentrations, estimates of their impact on climate are hampered by a lack of data on the history of forest fires. Especially regions with strong continental climate are of high importance due to an intensified development of wildfires. In this study we reconstruct the fire history of Southern Siberia during the past 750 years using ice-core based nitrate, potassium, and charcoal concentration records from Belukha glacier in the continental Siberian Altai. A period of exceptionally high forest-fire activity was observed between AD 1600 and 1680, following an extremely dry period AD 1540–1600. Ice-core pollen data suggest distinct forest diebacks and the expansion of steppe in response to dry climatic conditions. Coherence with a paleoenvironmental record from the 200 km distant Siberian lake Teletskoye shows that the vegetational shift AD 1540–1680, the increase in fire activity AD 1600–1680, and the subsequent recovery of forests AD 1700 were of regional significance. Dead biomass accumulation in response to drought and high temperatures around AD 1600 probably triggered maximum forest-fire activity AD 1600–1680. The extreme dry period in the 16th century was also observed at other sites in Central Asia and is possibly associated with a persistent positive mode of the Pacific Decadal Oscillation (PDO). No significant increase in biomass burning occurred in the Altai region during the last 300 years, despite strongly increasing temperatures and human activities. Our results imply that precipitation changes controlled fire-regime and vegetation shifts in the Altai region during the past 750 years. We conclude that high sensitivity of ecosystems to occasional decadal-scale drought events may trigger unprecedented environmental reorganizations under global-warming conditions.  相似文献   

Application of limited fuzzy clusters to anomaly recognition in complex geological environments     

U. Kramar 《Journal of Geochemical Exploration》1995,55(1-3)

In stream sediment and soil surveys, samples represent mixtures of components from different geological environments. Such mixed samples are misclassified when using conventional “hard” cluster methods. In fuzzy clustering, each sample is allowed to belong to several clusters. Similar to element concentrations, these cluster contributions can be displayed in contour maps (e.g. kriging maps). The amount of an element that is explained by the cluster contribution and element residuals can be calculated. The modified fuzzy clustering algorithm called “limited fuzzy clusters” used in this paper avoids negative residuals.Stream sediment data of Sierra de San Carlos, Tamaulipas, Mexico are used to demonstrate the possibilities of limited fuzzy clustering in geochemical exploration and mapping. From the different drainage systems, 681 stream sediment samples were taken and analyzed for 24 elements. A nineteen-element data set was used to calculate limited fuzzy clusters and element residuals. The contribution values for the clusters and element residuals are displayed in contour maps. All geological units were outlined by the cluster contributions. Extended anomalies are characterized by their own cluster. Small anomalies are clearly identified from the element residuals.  相似文献   

L’influence de certaines substances toxiques,contenues dans les eaux d’égouts municipaux,sur les bactériesEscherichia coli etPseudomonas fluorescens     

Sabina Spandowska  Barbara Ŀubieńska  Stanisŀaw Koŀaczkowski 《Aquatic Sciences - Research Across Boundaries》1973,35(2):278-285

The toxic influence of phenol, aniline, pyridine and chrome, substances often found in municipal wastewaters, on the bacteriaEscherichia coli andPseudomonas fluorescens was examined. The non-toxic, growth limiting, toxic and lethal doses were determined on the basis of observations made ofE. coli andP. fluorescens reproduction and respiration patterns. Comparative test series were set up with the various doses in different nutrient cultures to ascertain whether the bacterias’ multiplication process or carbohydrate decomposition was more sensitive to the chemicals.  相似文献   

The importance of second order activation in the determination of trace elements in geological samples by instrumental neutron activation analysis     

U. Kramar 《Geochimica et cosmochimica acta》1980,44(2):379-382

This paper deals with the disturbance of INAA trace element determinations in rocks by second order activation. The degree of error in the determination of Gd by Eu in rocks is checked by experiments and compared with results of computer evaluations. The consequence of the Dy-interference for the determination of Ho was also calculated. Hints to avoid these interferences are given.  相似文献