Arsenic in Ground Water of the Western United States   总被引：12，自引：0，他引：12  

Alan H. Welch  Michael S. Lico  Jennifer L. Hughes 《Ground water》1988,26(3):333-347

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On the general character of coastal flow     

Roger L. Hughes 《Pure and Applied Geophysics》1990,133(4):665-689

It is well-known that some coastal currents such as the Florida Current have a recirculating region on their coastal side, while other currents such as the East Australian Current have no such region. Under the hypothesis that the form drag on a coastal current by an irregular coastal topography reduces the momentum transport of the current to a minimum for the given flow within the current, the hydraulic theory of coastal currents is used to explain this behaviour.  相似文献   

The politics of urban entrepreneurialism in Glasgow     

Mark Boyle  George Hughes 《Geoforum》1994,25(4)

North American literature on the changing role of the local state these past two decades has been dominated by the view of a transition from urban managerialism to urban entrepreneurialism. Associated with the transition has been the emergence of a New Urban Politics (NUP). Within a political economy framework. the NUP has been rooted in the material redistributive effects of the transition. This paper explores the character of this NUP, as experienced by one British city, and highlights some fundamental differences with the established political economy reading. Our argument, based upon the city of Glasgow, draws attention to two distinctive features. First, the institutional structure of urban governance in Glasgow differs from that of cities in the United States. In Glasgow, it has been the Left controlled local Council which has orchestrated the transition to entrepreneurialism, rather than the North American model of a coalition between local capital and the local state. Secondly, the transition in Glasgow has been marked not by a significant transfer of local state revenue from service provision to local economic development, but by a symbolic reorientation of the local state as marked by the central importance of large place marketing hallmark events. These events represent the city in ways which differ from traditional ‘self’ identities. Consequently, the transition has evoked a political response which has focused upon the symbolic posturing of the local state rather than the material consequences of the shift. In focusing upon local identity, the politics of urban entrepreneurialism in Glasgow points to a dimension of conflict which has received inadequate treatment in accounts of the NUP to date.  相似文献   

Vanadium sublimates from the fumaroles of Izalco volcano, El Salvador     

John M. Hughes  Richard E. Stoiber 《Journal of Volcanology and Geothermal Research》1985,24(3-4)

Prior to the recent discovery of high-temperature vanadium sublimates at the fumaroles of Izalco volcano, El Salvador, the only vanadium minerals known were those formed at low-temperature surface conditions. Six new vanadium compounds have already been discovered at Izalco volcano, and five of these have been elevated to mineral status. Two of the minerals are among the most vanadium-rich compounds known in nature.Field studies and studies of the crystal chemistry of the sublimate phases have allowed delineation of the conditions of exsolution of vanadium-bearing gases from the magma and conditions of sublimation of the vanadium compounds. A vanadium halogen or oxyhalogen gas phase was exsolved from a basaltic magma when the magma was 550 m below the summit crater. As the gas rose to the fumaroles and mixed with the atmosphere, the oxygen fugacity rose from that of the magma to at least 10^−3,5 bar. At the fumaroles, the vanadium compounds sublimated at various temperatures, but a minimum temperature of 760° can be determined for one of the phases based on geothermometry determined from phase relations in the system CuO-V₂O₅. The studies have demonstrated that a vanadium-bearing gas can segregate from a magma with normal basaltic concentrations of vanadium.  相似文献   

Olivine-normative dolerite dikes from western South Carolina: Mineralogy,chemical composition and petrogenesis     

R. D. Warner  D. S. Snipes  S. S. Hughes  J. C. Steiner  M. W. Davis  P. R. Manoogian  R. A. Schmitt 《Contributions to Mineralogy and Petrology》1985,90(4):386-400

This investigation describes five Mesozoic dolerite dikes which intrude Paleozoic metamorphic and igneous rocks of the Inner Piedmont of western South Carolina. The dikes are vertical or nearly so and strike approximately N40° W. Three major northeast-trending faults also occur in the study area. Left lateral displacement of one dolerite is documented at a locality near Cleveland, South Carolina. Elsewhere, several of the dolerite dikes appear to terminate at or near the faults. — The dolerite dikes have subophitic to microporphyritic textures and consist principally of plagioclase (generally An_70–80), olivine (dominantly Fo_80–90) and augite with subordinate pigeonite, titanomagnetite, chromite and brown, partly glassy mesostasis. In one dike pyroxene compositions trend from augite to ferroaugite in contrast to an augitesubcalcic augitepigeonite trend characteristic of the other dolerites. The contrasting trends primarily result from differences in SiO₂ abundance in the dolerite magmas. — Major and trace element analyses indicate the presence of two different olivine-normative dolerite magma types. The two magma types are not related by near surface crystal fractionation. Models for genesis of the olivine-normative dolerite magmas by partial melting of a plagioclase peridotite upper mantle source region are presented. The models require that the source region be enriched in LREE and incompatible elements such as Rb, Ba, Hf and Th relative to Cl chondritic abundances. One magma type appears to represent a primary dolerite magma that ascended from the source region with little subsequent compositional change. The second magma type most likely experienced assimilation of clinopyroxene-garnet (eclogite) during ascent, thereby acquiring a REE pattern with a less steep negative slope for the LREE and a slight positive slope in the HREE.  相似文献   

K-Ar ages of basic rocks in the Patia Valley, southwest Colombia     

Hughes A.F. De Souza  Armando Espinosa  Michel Delaloye 《Tectonophysics》1984,107(1-2)

The Patia Valley situated between the Western and Central Cordilleras of the southwest Colombian Andes contains two areas in which Mesozoic basic and ultrabasic rocks crop out in abundance. Late Cretaceous Diabase Group pillow basalts which make up much of the Western Cordillera are at least 81 ± 5 Ma in the E1 Tambo-E1 Peñol area. 105-97 Ma hornblende and whole-rock dates from the ophiolitic Los Azules complex indicate an Albian age of formation, although many dates are lower (65-62 Ma) owing the low-grade ocean-floor metamorphism. The metamorphic age distribution here supports an end of Cretaceous emplacement for the complex rather than the Early-Mid Cretaceous emplacement suggested for North Colombian ophiolites similarly aligned along the Romeral fault system. Tertiary dacites intruding the Low Azules complex are 36-15 Ma.  相似文献   

Milankovitch theory of ice ages: Hypothesis of ice-sheet linkage between regional insolation and global climate     

George H. Denton  Terence J. Hughes 《Quaternary Research》1983,20(2):125-144

J. D. Hays, J. Imbrie, and N. J. Shackleton (1976, Science194, 1121–1132) showed that the astronomical theory explained many features of late Quaternary ice-age climates, but they did not specify the physical mechanisms involved. Here it is proposed that interlocked variations of ice-sheet heat sinks in both polar hemispheres amplified and transmitted Milankovitch summer half-year insolation changes (a version of the astronomical theory) between 45° and 75°N into the globally synchronous climate changes recorded in geologic records. It is suggested that late Quaternary ice sheets had terrestrial components (grounded above sea level, melting margins, fluctuations controlled by climate) and marine components (grounded below sea level, drained largely by ice streams, limited melting margins, fluctuations controlled primarily by sea level and secondarily by climate, interior surface elevations coupled to downdraw through ice streams). Northern Hemisphere ice sheets were largely marine (with minor melting margins) in the Arctic and terrestrial (with major melting margins) in the midlatitudes. West Antarctic and peripheral East Antarctic ice was marine-based and lacked melting margins. Because of their geographic array, these terrestrial and marine components formed an ice-sheet system whose variations were coupled on a global scale. Milankovitch summer isolation changes near midlatitude Northern Hemisphere melting margins controlled most variations of this system, because advance or retreat of melting margins initiated concurrent eustatic sea-level change. Such sea-level change afforded the critical interlocking mechanism between terrestrial and marine components because it forced simultaneous expansion or contraction of marine margins in both polar hemispheres. This initiated an amplifying feedback loop among all marine components and influenced interior downdraw through ice streams. Arctic summer insolation change was less important because northern melting margins were relatively minor. Its greatest influence was on surface ablation of ice streams that controlled interior downdraw. This affected eustatic sea level and activated global linkage of marine sectors. By analogy with present-day Antarctica, late Quaternary ice sheets were enormous planetary heat sinks due to their reflective and radiative surface characteristics. It is suggested that the effectiveness of these ice-sheet heat sinks varied with their areal extent and interior surface elevation. Thus, it is postulated that concurrent growth or decay of these interlocked ice-sheet heat sinks in both polar hemispheres served as the global amplifier of regional Milankovitch summer insolation.  相似文献   

Reconstructions of spring/summer precipitation for the Eastern Mediterranean from tree-ring widths and its connection to large-scale atmospheric circulation     

Ramzi Touchan  Elena Xoplaki  Gary Funkhouser  Jürg Luterbacher  Malcolm K. Hughes  Nesat Erkan  Ünal Akkemik  Jean Stephan 《Climate Dynamics》2005,25(1):75-98

This study represents the first large-scale systematic dendroclimatic sampling focused on developing chronologies from different species in the eastern Mediterranean region. Six reconstructions were developed from chronologies ranging in length from 115 years to 600 years. The first reconstruction (1885–2000) was derived from principal components (PCs) of 36 combined chronologies. The remaining five, 1800–2000, 1700–2000, 1600–2000, 1500–2000 and 1400–2000 were developed from PCs of 32, 18, 14, 9, and 7 chronologies, respectively. Calibration and verification statistics for the period 1931–2000 show good levels of skill for all reconstructions. The longest period of consecutive dry years, defined as those with less than 90% of the mean of the observed May–August precipitation, was 5 years (1591–1595) and occurred only once during the last 600 years. The longest reconstructed wet period was 5 years (1601–1605 and 1751–1755). No long term trends were found in May–August precipitation during the last few centuries. Regression maps are used to identify the influence of large-scale atmospheric circulation on regional precipitation. In general, tree-ring indices are influenced by May–August precipitation, which is driven by anomalous below (above) normal pressure at all atmospheric levels and by convection (subsidence) and small pressure gradients at sea level. These atmospheric conditions also control the anomaly surface air temperature distribution which indicates below (above) normal values in the southern regions and warmer (cooler) conditions north of around 40°N. A compositing technique is used to extract information on large-scale climate signals from extreme wet and dry summers for the second half of the twentieth century and an independent reconstruction over the last 237 years. Similar main modes of atmospheric patterns and surface air temperature distribution related to extreme dry and wet summers were identified both for the most recent 50 years and the last 237 years. Except for the last few decades, running correlation analyses between the major European-scale circulation patterns and eastern Mediteranean spring/summer precipitation over the last 237 years are non-stationary and insignificant, suggesting that local and/or sub-regional geographic factors and processes are important influences on tree-ring variability over the last few centuries.  相似文献   

Geological controls on Pleistocene glaciation and cirque form in Greece   总被引：2，自引：0，他引：2  

P.D. Hughes  P.L. Gibbard  J.C. Woodward 《Geomorphology》2007,88(3-4):242-253

Limestone and ophiolite rocks are common across the eastern Mediterranean and many of the highest mountains are formed in these rock types. In northwest Greece, Pleistocene glacial erosion was much more effective on limestone terrain where pronounced glacial incision and subglacial glacio-karst processes produced locally-complex topography. This enabled Pleistocene glaciers to form on a range of slope orientations in contrast to ophiolite terrains, where glaciers were strongly controlled by aspect. On limestone terrains, the largest ice masses formed on south-facing slopes, whereas in neighbouring higher mountains formed in ophiolite, glaciers were much more restricted and predominantly formed on north- and east-facing slopes.  相似文献   

Solar dynamo theory: a new look at the origin of small-scale magnetic fields     

Fausto Cattaneo  David W Hughes FRAS 《Astronomy& Geophysics》2001,42(3):3.18-3.22

Fausto Cattaneo and David W Hughes delve beneath the surface of the Sun with numerical models of turbulent convection.
Although magnetic dynamo action is traditionally associated with rotation, fast dynamo theory shows that chaotic flows, even without rotation, can act as efficient small-scale dynamos. Indeed, numerical simulations suggest that granular and supergranular convection may generate locally a substantial part of the field in the quiet photosphere.  相似文献