Deposits and physical properties of pyroclastic density currents during complex Subplinian eruptions: the AD 472 (Pollena) eruption of Somma-Vesuvius, Italy   总被引：2，自引：0，他引：2  

ROBERTO SULPIZIO  DANIELA MELE  PIERFRANCESCO DELLINO  LUIGI LA VOLPE 《Sedimentology》2007,54(3):607-635

Small-scale pyroclastic density currents (PDCs) associated with the AD 472 (Pollena) eruption of Somma-Vesuvius, Italy, were generated by both magmatic and phreatomagmatic explosive fragmentation. The resulting deposits were emplaced under flow boundary conditions dominated by varying combinations of grain interaction, fluid escape and traction processes. Stratigraphic and lithofacies analysis of these PDCs offers a new perspective on the en masse versus progressive aggradation debate for PDC deposition. In particular, the analyses indicate that PDCs were density stratified with a basal underflow dominated by grain interactions. The underflows comprised trains of self-organized granular pulses of variable thickness and magnitude, depending on the overall particle concentration and fluid turbulence. A change in gradient between the upper and lower slopes of the volcano promoted deposition and the different pulses aggraded sequentially (stepwise). In this model each pulse stops en masse and the whole deposit aggrades progressively. Particle concentration, density, mean velocity, and flow height were assessed for the studied PDCs using differaent methods for massive and stratified deposits. The calculated mobility of the flows was 0·2 to 0·3, in the expected range for small-scale PDCs.  相似文献   

Rapport (1966–1976) sun les Eléments en Traces Dans Trois Roches Standards Géochimiques Du CRPG . Basalte BR et Granites, GA et GH     

K. GOVINOARAJU  H. DE LA  ROCHE 《Geostandards and Geoanalytical Research》1977,1(1):67-100

Cinquième de la serie des rapports d'étude coopérative sur les standards géochimiques du CRPG, ce rapport est consacré exclusivement aux éeléments en traces dans trois éahantillons en circulation depuis 1963: les Granites GA et GH et le Basalte BR. La pré-sentation de plus de 2000 données analytiques réporties sur 50 éléments est accompagnée d'une évaluation statistique et critique, échantillon par éahmtillon et élément par élément. La discussion est menée dans le sens d'un dialogue direct avec I'utilisateur en nuançant et en hiérarchieant les valeurs que nous veoamnandons ou proposons. Quant à I'analyste practician, il trouvera une table des valeurs "utilisables" pour une trentaine d'éléments dans les trois échantillons de référence (Table 4). Rappelons que ces échantillons sont déjà bien caractérises en ce qui concerne leurs constituants majeurs et mineurs, grâce aux quatre rapports d'étude coopérative dont le dernier est paru en 1370.  相似文献   

Multi-wavelength spectroscopy of the stable shell star HD 193182     

L. Denizman  T. Koktay  M. Hack  T. Eker 《Astrophysics and Space Science》1993,208(1):135-151

HD 193182 is one of the most interesting stable shell stars and presents stable shell features which seems to be constant over decades. In this research we analyzed optical, ultraviolet and near-infrared spectra of this little-studied shell star. In the meantime we applied model calculations to the measured spectral parameters of HD 193182 in order to present a more complete view of its stellar and envelope characteristics.  相似文献   

1960-2012年河西内陆河上游山区降水量变化及其区域性差异分析     

蓝永超  刘金鹏  丁宏伟  鲁承阳  沈永平  胡兴林  喇承芳  宋洁  高黎明 《冰川冻土》2013,35(6):1474-1480

基于我国河西内陆河流域有关水文、气象台站的观测数据,对1960年代以来河西走廊的石羊河、黑河、疏勒河三大内陆河水系上游山区降水变化特征、趋势及区域时空变化差异进行了分析.结果表明：受全球变暖的影响,石羊河、黑河、疏勒河流域上游的降水量年代际、年际及季节性的变化总体上呈增加的态势,但不同区域降水增幅存在着一定的差异.其中,1960年代,位于祁连山东部的石羊河水系上游山区、中部的黑河水系上游山区及西部的疏勒河水系上游山区普遍少雨;1970年代,石羊河山区降水偏多并持续至今,黑河、疏勒河水系上游山区则降水偏少;1980年代,三大水系上游山区均多雨;1990年代的黑河、疏勒河山区和2000年代的三大水系上游山区均多雨;2010年以来,黑河山区降水偏少,石羊河与疏勒河山区降水均偏多.相对而言,位于祁连山西部山区的疏勒河水系上游年降水量与夏季降水量的增长较为显著.  相似文献   

盐生植物萌发期对盐胁迫的适应研究进展          下载免费PDF全文

胡娟  张洁  盛洲  周宸宇  张旭萍  拉本 《盐湖研究》2022,30(1):95-100

目前我国盐溃土地面积较大,尤其是青藏高原的盐溃地,常伴有干旱、半干旱的生境,导致植物不易生长,生态环境相对恶劣,这种生态现状亟待解决.盐生植物具有一定的耐盐性和耐旱性,是改善盐渍地的首选植物,种子的活力决定了种子萌发的情况,多数学者为改善严峻的生态环境开始了盐生植物引种的研究.测定种子活力有直接方法和间接方法,大多数学...  相似文献   

Toxicity assessment of New Zealand and Pacific dinoflagellates Ostreopsis and Gambierdiscus (Dinophyceae) extracts using bioassays     

PA Argyle  DT Harwood  LL Rhodes  O Champeau  LA Tremblay 《新西兰海洋与淡水研究杂志》2016,50(3):444-456

The dinoflagellate genus Ostreopsis produces palytoxin-like compounds (PLTXs) and the genus Gambierdiscus produces ciguatoxins (CTXs) and maitotoxin (MTX). Human illness has been recorded following the consumption of CTX-contaminated finfish. Their effects on the flora and fauna in the environment are largely unexplored. Toxin profiles of extracts of Ostreopsis and Gambierdiscus isolates from the Pacific region were characterised using liquid chromatography tandem mass spectrometry. Sea urchin (Evechinus chloriticus) fertilisation was unaffected by any algal extracts, but extracts containing maitotoxin-3 (MTX-3, but not MTX or CTXs), or with high concentrations of PLTXs, were toxic to urchin larval development. Gambierdiscus extracts containing CTXs elicited toxic responses in zebrafish (Danio rerio) embryo toxicity assays; extracts containing only MTX-3 elicited a limited response. Ostreopsis extracts containing PLTXs caused no response. The results demonstrate potential impacts of toxic dinoflagellates on larval organisms and the potential of embryonic assays as toxicity screening tools.  相似文献