Location Analysis in Ground-Water Remediation Using Neural Networks   总被引：3，自引：0，他引：3  

Virginia M. Johnson  Leah L. Rogers 《Ground water》1995,33(5):749-758

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Large-scale volcanic cone collapse: The 1888 slope failure of Ritter volcano,and other examples from Papua New Guinea     

R. W. Johnson 《Bulletin of Volcanology》1987,49(5):669-679

A largely submarine avalanche amphitheatre that formed catastrophically in 1888 on Ritter volcano has been identified from a bathymetric survey. Collapse of the volcano in 1888 therefore is considered to have been caused by rapid, large-scale slope failure, rather than by cauldron subsidence, as previously supposed. Escarpments of pre-historic slope failures are common on other Papua New Guinea volcanoes. Directions of avalanching on some volcanoes in the Bismarck volcanic arc appear to be controlled by a regional stress pattern, and those for some volcanoes in the Fly-Highlands province on mainland Papua New Guinea point away from the regional centre of Pliocene uplift. Large amphitheatres such as at Doma Peaks in the Fly-High-lands province probably originated by multiple collapses.  相似文献   

Comments on P.K. Theobald's Presidential Address, Hannover, 1980     

S. M. Johnson 《Journal of Geochemical Exploration》1982,17(2)

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Solubility of rhodochrosite (MnCO₃) in water and seawater     

Kenneth S. Johnson 《Geochimica et cosmochimica acta》1982,46(10):1805-1809

The solubility product of rhodochrosite (MnCO₃) was measured in seawater, deionized water and dilute NaCl solutions. The solubility product extrapolated to infinite dilution at 25.0 C was (2.60 ± 0.07)× 10^?11. The stoichiometric solubility product measured in seawater of 34.27%. salinity was (3.24 ± 0.23) × 10^?9 at 25.0 C and (2.28 ± 0.24) × 10^?9 at 3.3 C. The stoichiometric solubility product is in good agreement with the value calculated from an ion association model. The enthalpy of the reaction is in fair agreement with the estimated value.  相似文献   

Folding of passive layers and forms of minor structures near terminations of blind thrust faults—application to the central Appalachian blind thrust     

Philip Berger  Arvid M. Johnson 《Journal of Structural Geology》1982,4(3):343-353

The existence of detachment surfaces or décollement zones beneath folded rocks of the Valley and Ridge and Plateau provinces of the Appalachians has been recognized as an important condition of folding. Large folds at the border between the two provinces resulted primarily from repetition of strata by thrusting of blocks over ramp faults that connect detachement surfaces at different horizons. Some investigators have suggested that folds in the Plateau province of Pennsylvania were produced by splay faults arising from detachment surfaces, but field observations and theoretical analyses by Sherwin and by Wiltschko & Chapple suggest that the folds are a result of buckling of multilayered rocks above a décollement. An exception may be the Burning Springs anticline in West Virginia, which appears to have formed at the termination of a detachment surface.Investigation of the translation of an homogenous, viscous material above a flat detachment surface that terminates laterally indicates that the termination produces a broad, low-amplitude anticline in passive layering as a result of thickening induced by a gradient of shear stresses in the vertical direction. This thickening above the termination of a detachment is a mechanism of folding. If the viscous fluid contained mechanical layering, the fold would become amplified by buckling. Computations of stresses in the material indicate that minor faults should be generated first near the termination of the flat detachment surface. The Burning Springs anticline probably was initiated by termination of a detachment surface and subsequently amplified by buckling.  相似文献   

Pleistocene volcanic rocks from the Fly-Highlands province of western Papua New Guinea: A note on new Sr and Nd isotopic data and their petrogenetic implications     

P.J. Hamilton  R.W. Johnson  D.E. Mackenzie  R.K. O'Nions 《Journal of Volcanology and Geothermal Research》1983,18(1-4)

RB-Sr and Sm-Nd isotopic and trace-element-abundance values have been determined for 15 mafic and intermediate rocks from six Pleistocene volcanic centres of the Fly-Highlands province. ⁸⁷Sr/⁸⁶Sr and _{N d} values range from 0.70362 to 0.70540, and +1.9 to +5.9, respectively. These new data can be accounted for by contamination of mantle-derived magmas by the continental crust through which the magmas have risen. They do not, however, preclude derivation of some of the Sr and Nd from subducted crust, nor are they inconsistent with Sr and Nd enrichments having taken place by means of mantle metasomatic events. Nevertheless, there is no Benioff zone beneath the Fly-Highlands province (although there is geological evidence for Cretaceous subduction). A preferred interpretation is that uncontaminated, mantle-derived magmas are related to the Pliocene crustal uplift that caused the development of the highlands and which formed in response to a mid-Tertiary continent/island-arc collision.  相似文献   

The interpretation of the isotopic ratio235U/238U in fission track dating: Comment     

V. E. McGee  N. M. Johnson 《Mathematical Geosciences》1983,15(3):497-498

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Coupling of oceanic and continental crust during Eocene eclogite-facies metamorphism: evidence from the Monte Rosa nappe,western Alps   总被引：1，自引：0，他引：1  

Thomas J. Lapen  Clark M. Johnson  Lukas P. Baumgartner  Giorgio V. Dal Piaz  Susanne Skora  Brian L. Beard 《Contributions to Mineralogy and Petrology》2007,153(2):139-157

High precision U–Pb geochronology of rutile from quartz–carbonate–white mica–rutile veins that are hosted within eclogite and schist of the Monte Rosa nappe, western Alps, Italy, indicate that the Monte Rosa nappe was at eclogite-facies metamorphic conditions at 42.6 ± 0.6 Ma. The sample area [Indren glacier, Furgg zone; Dal Piaz (2001) Geology of the Monte Rosa massif: historical review and personal comments. SMPM] consists of eclogite boudins that are exposed inside a south-plunging overturned synform within micaceous schist. Associated with the eclogite and schist are quartz–carbonate–white mica–rutile veins that formed in tension cracks in the eclogite and along the contact between eclogite and surrounding schist. Intrusion of the veins at about 42.6 Ma occurred at eclogite-facies metamorphic conditions (480–570°C, >1.3–1.4 GPa) based on textural relations, oxygen isotope thermometry, and geothermobarometry. The timing of eclogite-facies metamorphism in the Monte Rosa nappe determined in this study is identical to that of the Gran Paradiso nappe [Meffan-Main et al. (2004) J Metamorphic Geol 22:261–281], confirming that these two units have shared the same Alpine metamorphic history. Furthermore, the Gran Paradiso and Monte Rosa nappes underwent eclogite-facies metamorphism within the same time interval as the structurally overlying Zermatt-Saas ophiolite [∼50–40 Ma; e.g., Amato et al. (1999) Earth Planet Sci Lett 171:425–438; Mayer et al. (1999) Eur Union Geosci 10:809 (abstract); Lapen et al. (2003) Earth Planet Sci Lett 215:57–72]. The nearly identical P–T–t histories of the Gran Paradiso, Monte Rosa, and Zermatt-Saas units suggest that these units shared a common Alpine tectonic and metamorphic history. The close spatial and temporal associations between high pressure (HP) ophiolite and continental crust during Alpine orogeny indicates that the HP internal basement nappes in the western Alps may have played a key role in exhumation and preservation of the ophiolitic rocks through buoyancy-driven uplift. Coupling of oceanic and continental crust may therefore be critical in preventing permanent loss of oceanic crust to the mantle.  相似文献   

Aspiration and reality: flood policy, economic damages and the appraisal process   总被引：1，自引：0，他引：1  

Clare Johnson  Edmund Penning-Rowsell  Sue Tapsell 《Area》2007,39(2):214-223

Research shows that flood damage potential has increased significantly in the last 15 years. At the same time, flood policy has shifted away from simplistic flood defence towards 'living with floods' and 'making space for water'. This paper explores the mis-match between the aspiration in policy ideals, the reality of rising potential economic damages and the inability of the flood risk appraisal process to match the aspiration with the reality. Unless investment appraisal procedures are changed, the increase in damages will undermine policy changes that seek a different pattern of flood risk management, away from economically dominated decision-criteria towards more sustainable objectives.  相似文献   

Feedbacks between erosion and sediment transport in experimental bedrock channels     

Joel P. Johnson  Kelin X. Whipple 《地球表面变化过程与地形》2007,32(7):1048-1062

Natural bedrock rivers flow in self‐formed channels and form diverse erosional morphologies. The parameters that collectively define channel morphology (e.g. width, slope, bed roughness, bedrock exposure, sediment size distribution) all influence river incision rates and dynamically adjust in poorly understood ways to imposed fluid and sediment fluxes. To explore the mechanics of river incision, we conducted laboratory experiments in which the complexities of natural bedrock channels were reduced to a homogenous brittle substrate (sand and cement), a single sediment size primarily transported as bedload, a single erosion mechanism (abrasion) and sediment‐starved transport conditions. We find that patterns of erosion both create and are sensitive functions of the evolving bed topography because of feedbacks between the turbulent flow field, sediment transport and bottom roughness. Abrasion only occurs where sediment impacts the bed, and so positive feedback occurs between the sediment preferentially drawn to topographic lows by gravity and the further erosion of these lows. However, the spatial focusing of erosion results in tortuous flow paths and erosional forms (inner channels, scoops, potholes), which dissipate flow energy. This energy dissipation is a negative feedback that reduces sediment transport capacity, inhibiting further incision and ultimately leading to channel morphologies adjusted to just transport the imposed sediment load. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献