Evolution of West Rota Volcano, an extinct submarine volcano in the southern Mariana Arc: Evidence from sea floor morphology, remotely operated vehicle observations and ⁴⁰Ar–³⁹Ar geochronological studies     

Robert J.  Stern  Yoshihiko  Tamura  Robert W.  Embley  Osamu  Ishizuka  Susan G.  Merle  Neil K.  Basu  Hiroshi  Kawabata  Sherman H.  Bloomer 《Island Arc》2008,17(1):70-89

Abstract West Rota Volcano (WRV) is a recently discovered extinct submarine volcano in the southern Mariana Arc. It is large (25 km diameter base), shallow (up to 300 m below sealevel), and contains a large caldera (6 × 10 km, with up to 1 km relief). The WRV lies near the northern termination of a major NNE‐trending normal fault. This and a second, parallel fault just west of the volcano separate uplifted, thick frontal arc crust to the east from subsiding, thin back‐arc basin crust to the west. The WRV is distinct from other Mariana Arc volcanoes: (i) it consists of a lower, predominantly andesite section overlain by a bimodal rhyolite‐basalt layered sequence; (ii) andesitic rocks are locally intensely altered and mineralized; (iii) it has a large caldera; and (iv) WRV is built on a major fault. Submarine felsic calderas are common in the Izu and Kermadec Arcs but are otherwise unknown from the Marianas and other primitive, intraoceanic arcs. ⁴⁰Ar–³⁹Ar dating indicates that andesitic volcanism comprising the lower volcanic section occurred 0.33–0.55 my ago, whereas eruption of the upper rhyolites and basalts occurred 37–51 thousand years ago. Four sequences of rhyolite pyroclastics each are 20–75 m thick, unwelded and show reverse grading, indicating submarine eruption. The youngest unit consists of 1–2 m diameter spheroids of rhyolite pumice, interpreted as magmatic balloons, formed by relatively quiet effusion and inflation of rhyolite into the overlying seawater. Geochemical studies indicate that felsic magmas were generated by anatexis of amphibolite‐facies meta‐andesites, perhaps in the middle arc crust. The presence of a large felsic volcano and caldera in the southern Marianas might indicate interaction of large normal faults with a mid‐crustal magma body at depth, providing a way for viscous felsic melts to reach the surface.  相似文献   

Structural, tectonic and glaciological controls on the evolution of fjord landscapes     

Neil F. Glasser  Matías C. Ghiglione 《Geomorphology》2009,105(3-4):291-302

The fjord landscape of South America, stretching ~ 1500 km between Golfo Corcovado (~ 43°S) and Tierra del Fuego (~ 56°S), is the largest continuous fjord landscape on Earth. This paper presents the results of new structural geological and geomorphological mapping of this landscape using optical satellite images and digital elevation models. First-order geological structures are represented by strike-slip faults forming lineaments up to hundreds of kilometres long. The strike-slip faulting has been active since Late Cretaceous times and is responsible for the presence of a conspicuous structural cleavage visible as lineaments up to ~ 10 km long. A detailed analysis of these second-order lineaments from digital image data was carried out in three sectors. In Sector 1, located northwest of the North Patagonian Icefield, there are three distinct mean orientations, characterized by a main nearly orogen-parallel orientation (az. ~ 145°) and two orogen-oblique secondary orientations (az. ~ 20° and az. ~ 65°). In Sector 2, located west of the South Patagonian Icefield, there are also three separate mean orientations, with most of the lineaments concentrated between azimuths 0° and 80° (mean at ~ 36°); and two other orogen-oblique means at azimuth ~ 122° and ~ 163°. In Sector 3, around the Cordillera Darwin, there is a single main orogen-parallel mean at ~ 100–115°. In all three sectors, mapped fjord orientations bear a striking similarity to the structural data, with fjords orientated preferentially in the same direction as structural lineaments. We infer that successive glaciations followed the same ice-discharge routes, widening and deepening pre-existing geological structures at the expense of the surrounding terrain to create the fjord landscape. This study has broader implications for ice sheet reconstructions and landscape evolution beneath ice sheets because we demonstrate that the primary control on fjord development in glaciated areas is geological and not glaciological.  相似文献   

The impact of upland land management on flooding: results from an improved pasture hillslope   总被引：1，自引：0，他引：1  

Miles R. Marshall  Oliver J. Francis  Zoe L. Frogbrook  Bethanna M. Jackson  Neil McIntyre  Brian Reynolds  Imogen Solloway  Howard S. Wheater  Joanne Chell 《水文研究》2009,23(3):464-475

In response to growing concern about impacts of upland agricultural land management on flood risk, an intensely instrumented experimental catchment has been established at Pontbren, a sheep‐farmed headwater catchment of the River Severn, UK. Primary aims are to develop understanding of the processes governing flood generation and the associated impacts of land management practices, and to bridge the gap between process understanding and ability to predict effects on downstream flooding. To achieve this, the experiment is designed to operate at plot (～100 m²), hillslope (～0·1 km²) and small catchment scale (～10 km²). Hillslope‐scale data, from an under‐drained, agriculturally ‘improved’ pasture, show that drain flow is a dominant runoff process. However, depending on antecedent moisture conditions, overland flow may exceed drain flow rates and can be an important contributor to peak flow runoff at the hillslope‐scale. Flow, soil tension data and tracer tests confirm the importance of macropores and presence of perched water tables under ‘normal’ wet conditions. Comparisons of pasture runoff with that from within a 10 year‐old tree shelterbelt show significantly reduced overland flow due to the presence of trees and/or absence of sheep. Comparisons of soil hydraulic properties show significant increases in hydraulic conductivity and saturated moisture content of soil under trees compared to adjacent improved pasture. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

法理地震学与全面禁止核试验条约     

David Bowers  Neil D.Selby  王兴臣  郭志伟  杨婷  吴清  常莹 《国际地震动态》2009,(10):1-22

法理地震学的用途之一就是帮助核查“全面禁止核试验条约”的执行情况。法理地震学家面临的一个重要挑战是将每年发生的成千上万次天然地震与可能违反条约的地下爆破区别开来。识别方法主要有4种：（a）体波与面波的震级比,（b）高频P波与S波能量比,（c）基于模型的方法,（d）震源深度。方法（a）和（b）有经验基础。方法（a）～（c）的不足是对全球地质学介质范围内激发的地下爆破缺少一个等效的弹性震源。可靠的常规震源深度的确定已被证明非常困难。然而,过去的十几年获得的在识别可疑震源方面的经验说明,尽管没有单一的方法能够长期奏效,但巧妙地独创性地应用各种互补方法通常能够解决可疑震源识别问题。  相似文献   

Calibration of an estuarine sediment transport model to sediment fluxes as an intermediate step for simulation of geomorphic evolution     

Neil K. Ganju  David H. Schoellhamer 《Continental Shelf Research》2009

Modeling geomorphic evolution in estuaries is necessary to model the fate of legacy contaminants in the bed sediment and the effect of climate change, watershed alterations, sea level rise, construction projects, and restoration efforts. Coupled hydrodynamic and sediment transport models used for this purpose typically are calibrated to water level, currents, and/or suspended-sediment concentrations. However, small errors in these tidal-timescale models can accumulate to cause major errors in geomorphic evolution, which may not be obvious. Here we present an intermediate step towards simulating decadal-timescale geomorphic change: calibration to estimated sediment fluxes (mass/time) at two cross-sections within an estuary. Accurate representation of sediment fluxes gives confidence in representation of sediment supply to and from the estuary during those periods. Several years of sediment flux data are available for the landward and seaward boundaries of Suisun Bay, California, the landward-most embayment of San Francisco Bay. Sediment flux observations suggest that episodic freshwater flows export sediment from Suisun Bay, while gravitational circulation during the dry season imports sediment from seaward sources. The Regional Oceanic Modeling System (ROMS), a three-dimensional coupled hydrodynamic/sediment transport model, was adapted for Suisun Bay, for the purposes of hindcasting 19th and 20th century bathymetric change, and simulating geomorphic response to sea level rise and climatic variability in the 21st century. The sediment transport parameters were calibrated using the sediment flux data from 1997 (a relatively wet year) and 2004 (a relatively dry year). The remaining years of data (1998, 2002, 2003) were used for validation. The model represents the inter-annual and annual sediment flux variability, while net sediment import/export is accurately modeled for three of the five years. The use of sediment flux data for calibrating an estuarine geomorphic model guarantees that modeled geomorphic evolution will not exceed the actual supply of sediment from the watershed and seaward sources during the calibration period. Decadal trends in sediment supply (and therefore fluxes) can accumulate to alter decadal geomorphic change. Therefore, simulations of future geomorphic evolution are bolstered by this intermediate calibration step.  相似文献   

Patterns of surface downwearing on shore platforms in eastern Canada     

Neil J. Porter  Alan S. Trenhaile  Kyle Prestanski  Jacob I. Kanyaya 《地球表面变化过程与地形》2010,35(15):1793-1810

Downwearing rates were measured on shore platforms at about 200 transverse micro‐erosion meter (TMEM) stations, over periods ranging from 2 to 6 years. There were seven study areas in eastern Canada. The platforms were surveyed and a Schmidt Rock Test Hammer was used to measure rock hardness. More than 1200 rock samples from three of the study areas were also subjected each day, over a 3 year period, to two tidal cycles of immersion and exposure, which simulated the central intertidal zone. A further 840 samples were subjected to longer periods of exposure and immersion, over a 1 year period, which represented different elevations within the upper and lower intertidal zone, respectively. These experiments suggested that tidally generated weathering and debris removal is an effective erosional mechanism, particularly at the elevation of the lowest high tides. In the field, mean rates of downwearing for each study area ranged from 0·24 mm yr^?1 to more than 1·5 mm yr^?1. Rates tended to increase with elevation in the field, with maxima in the upper intertidal zone. This trend in the field cannot be attributed entirely to the tidally induced weathering processes that were simulated in the laboratory, and must reflect, in part, the effect of waves, frost, ice, and other mechanisms. It is concluded that there are no strong spatial downwearing patterns on shore platforms, and that downwearing rates in the intertidal zone are the result of a number of erosional mechanisms with different elevation‐efficacy characteristics. Furthermore, even if only one or two mechanisms were dominant in an area, any resulting relationship between downwearing rates and elevation would be obscured or eliminated by the effect of variations in the chemical and physical characteristics of the rocks. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Linking neo- and palaeolimnology: a case study using crater lake diatoms from central Turkey     

Jessie Woodbridge  Neil Roberts 《Journal of Paleolimnology》2010,44(3):855-871

Palaeoenvironmental interpretations from analyses of lake sediment archives are dependent on our understanding of the modern lake environment and the link between neo- and palaeolimnology. Diatom assemblages represent different lake habitats and vary in species composition and abundance on seasonal and annual timescales. These factors, along with mixing at the mud-water interface, alter the information recorded in the sedimentary archive and the resulting interpretation of environmental variables in the past. Nar Gölü (central Turkey), a crater lake with annually laminated sediments, is used to investigate the link between modern and palaeo diatom assemblages. Information about the modern diatom population has been gathered through sampling of different lake habitats (1999–2009) and installing seston sediment traps in the water column (2002–2007). The palaeo diatom assemblage has been analysed through annual-resolution percentage counts and biovolume calculations on core sediments (1927–2006), along with identification of sub-annual assemblage changes through microscopic analysis of core thin sections. Comparisons of data collected using these different methods has shown a good correspondence between sediment trap and core results, but revealed that blooms of two diatom species (Nitzschia paleacea and Synedra acus), in each case occurring on average 1 year in five, can have major impacts on percentage calculations and may result in distorted and misleading palaeoenvironmental interpretations. These two species distort the average signal and may bloom for short periods of time as a result of short duration changes in lake water chemistry, such as following fresh-water input from snow melt. Blurring of sedimentary records through mixing at the sediment–water interface can mask the full magnitude of environmental variation and low sampling resolution may fail to capture high amplitude events of short duration.  相似文献   

Contemporary rural geographies: Land,property and resources in Britain: Essays in honour of Richard Munton     

Neil Argent 《New Zealand geographer》2008,64(3):244-245

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From mimeos to E-copy--a tribute to Professor R B (Bob) Clark,founding editor of the Marine Pollution Bulletin     

Wells P  Baker J  Chapman P  Elliott M  Hutchings P  Mann K  Olive P  Pearce J  Phillips D  Sheppard C 《Marine pollution bulletin》2003,46(9):1051-1054

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Kinetic analysis of the photodegradation of polycyclic aromatic hydrocarbons in aqueous solution     

Matthew?P.?Fasnacht  Neil?V.?BloughEmail author 《Aquatic Sciences - Research Across Boundaries》2003,65(4):352-358

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