Longitudinal distributions of river flood power: the combined automated flood,elevation and stream power (CAFES) methodology     

Douglas M. Barker  Damian M. Lawler  Donald W. Knight  David G. Morris  Helen N. Davies  Elizabeth J. Stewart 《地球表面变化过程与地形》2009,34(2):280-290

Stream power can be an extremely useful index of fluvial sediment transport, channel pattern, river channel erosion and riparian habitat development. However, most previous studies of downstream changes in stream power have relied on field measurements at selected cross‐sections, which are time consuming, and typically based on limited data, which cannot fully represent important spatial variations in stream power. We present here, therefore, a novel methodology we call CAFES (combined automated flood, elevation and stream power), to quantify downstream change in river flood power, based on integrating in a GIS framework Flood Estimation Handbook systems with the 5 m grid NEXTMap Britain digital elevation model derived from IFSAR (interferometric synthetic aperture radar). This provides a useful modelling platform to quantify at unprecedented resolution longitudinal distributions of flood discharge, elevation, floodplain slope and flood power at reach and basin scales. Values can be resolved to a 50 m grid. CAFES approaches have distinct advantages over current methodologies for reach‐ and basin‐scale stream power assessments and therefore for the interpretation and prediction of fluvial processes. The methodology has significant international applicability for understanding basin‐scale hydraulics, sediment transport, erosion and sedimentation processes and river basin management. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Surge in sulphur and halogen degassing from Ambrym volcano,Vanuatu     

Philipson Bani  Clive Oppenheimer  Vitchko I. Tsanev  Simon A. Carn  Shane J. Cronin  Rachel Crimp  Julie A. Calkins  Douglas Charley  Michel Lardy  Tjarda R. Roberts 《Bulletin of Volcanology》2009,71(10):1159-1168

Volcanoes provide important contributions to atmospheric budgets of SO₂ and reactive halogens, which play significant roles in atmospheric oxidative capacity and radiation. However, the global source strengths of volcanic emissions remain poorly constrained. These uncertainties are highlighted here by the first measurements of gas emission rates from Ambrym volcano, Vanuatu. Our initial airborne ultraviolet spectroscopic measurements made in January 2005 indicate fluxes of 18–270 kg s^-1 of SO₂, and 62–110 g s^-1 of BrO, into the atmosphere, placing Ambrym amongst the largest known contemporary point sources of both these species on Earth. We also estimate high Cl and F fluxes of ~8–14 and ~27–50 kg s^-1, respectively, for this period. Further observations using both airborne and spaceborne remote sensing reveal a fluctuating SO₂ output between 2004 and 2008, with a surge in the first half of 2005, and underline the substantial contribution that a single passively degassing volcano can make to the atmospheric budget of sulfur and halogens.  相似文献   

Late Cenozoic structural and stratigraphic evolution of the northern Chinese Tian Shan foreland   总被引：1，自引：1，他引：0  

Honghua Lu  Douglas W. Burbank  Youli Li  Yunming Liu 《Basin Research》2010,22(3):249-269

Three successive zones of fault‐related folds disrupt the proximal part of the northern Tian Shan foreland in NW China. A new magnetostratigraphy of the Taxi He section on the north limb of the Tugulu anticline in the middle deformed zone clarifies the chronology of both tectonic deformation and depositional evolution of this collisional mountain belt. Our ～1200‐m‐thick section encompasses the upper Cenozoic terrigenous sequence within which ～300 sampling horizons yield an age span of ～8–2 Ma. Although the basal age in the Taxi He section of the Xiyu conglomerate (often cited as an indicator of initial deformation) is ～2.1 Ma, much earlier growth of the Tugulu anticline is inferred from growth strata dated at ～6.0 Ma. Folding of Neogene strata and angular unconformities in anticlines in the more proximal and distal deformed zones indicate deformation during Miocene and Early Pleistocene times, respectively. In the Taxi He area, sediment‐accumulation rates significantly accelerate at ～4 Ma, apparently in response to encroaching thrust loads. Together, growth strata, angular unconformities, and sediment‐accumulation rates document the northward migration of tectonic deformation into the northern Tian Shan foreland basin during the late Cenozoic. A progradational alluvial–lacustrine system associated with this northward progression is subdivided into two facies associations at Tugulu: a shallow lacustrine environment before ～5.9 Ma and an alluvial fan environment subsequently. The lithofacies progradation encompasses the time‐transgressive Xiyu conglomerate deposits, which should only be recognized as a lithostratigraphic unit. Along the length of the foreland, the locus of maximum shortening shifts between the medial and proximal zones of folding, whereas the total shortening across the foreland remains quite homogeneous along strike, suggesting spatially steady tectonic forcing since late Miocene times.  相似文献   

中国大别山双河超高压变质大理岩的氧、碳同位素   总被引：7，自引：1，他引：6  

王清晨  Douglas Rumble 《中国科学D辑》1999,29(3):18

中国大别山双河超高压变质岩板中发育了一系列大理岩层和透镜体 ,其δ18O值介于 1 1 1‰～ 2 0 5‰ (SMOW)间 ,δ13 C值介于 1 .0‰～ 5 .7‰ (PDB)间 .详细调查表明 ,大理岩的氧、碳同位素值在厘米尺度上表现出均一化 ,但在大于1m的范围内则不均一 .与已经同地幔中的碳发生均一化的挪威榴辉岩相大理岩不同 ,双河超高压大理岩的碳同位素则保留了沉积碳酸盐岩的特征 ,而且表现出白云石含量与δ13 C间的负相关关系 .与原岩相比 ,双河大理岩18O有所亏损 .这种亏损来自 3种可能的地质过程 :( 1 )在超高压变质作用前曾与亏损18O的水发生过氧同位素交换 ;( 2 )在超高压变质过程中发生过脱碳酸盐作用 ;( 3)在退变质过程中与围岩片麻岩在接触部位发生过有限的氧同位素交换 .氧、碳同位素研究表明 ,超高压变质岩的俯冲和折返过程历时较短 ,且在该过程中 ,流体的活动性极为有限 .  相似文献   

Paleoecology and its application to fire and vegetation management in Kootenay National Park, British Columbia     

Douglas Hallett  Robert Walker 《Journal of Paleolimnology》2000,24(4):401-414

High-resolution analysis of macroscopic charcoal and pollen ratios were used to reconstruct a 10,000 yr history of fire and vegetation change around Dog Lake, now in the Montane Spruce biogeoclimatic zone of southeastern British Columbia. Lake sediment charcoal records suggest that fire was more frequent in the early Holocene from 10,000 to 8200 calendar yrs BP, when climate was warmer and drier than today and forest fuels were limited. Fire frequency increased and reached its maximum during the early to mid-Holocene from 8200 to 4000 calendar yrs BP, corresponding to the dry and warm Hypsithermal period in the Rocky Mountains. During the Hypsithermal period forests around Dog Lake were dominated by Pseudotsuga/Larix,Pinus and open meadows of Poaceae that were subject to frequent fire. From 4000 calendar yrs BP to present, fires became less frequent with the onset of cooler and wetter Neoglacial climate and an increase in wet-closed Picea and Abies forests in the valley. Changes in fire frequency are supported by dry-open/wet-closed pollen ratio data indicating that forest type and disturbance regimes vary with changing climate. The fire frequency and forest cover reconstructions from Dog Lake are a first attempt at defining a range of natural variability for Montane Spruce forests in southeastern British Columbia. Fire and vegetation management in Kootenay National Park can now use this century to millennial-scale range of variability to define the context of current forest conditions and potential changes under global warming scenarios.  相似文献   

Reappraisal of surface wave magnitudes in the Eastern Mediterranean region and the Middle East     

N. Ambraseys  & J. Douglas 《Geophysical Journal International》2000,141(2):357-373

We report on a detailed palaeomagnetic study of the Miocene Farellones volcanic formation in the Chilean Andes near Santiago (two sections, 37 sites, about 400 orientated cores). Petrological observations show evidence of low-grade metamorphism increasing downwards through the volcanic sequence. Optical observations of opaque minerals and magnetic experiments suggest that in many cases maghemitization is associated with hydrothermal alteration. However, thermal demagnetization data indicate that the low-grade metamorphism did not significantly modify the direction of the primary remanent magnetization recorded at the time of emplacement of the volcanic lava flows. Four intervals of polarity with two intermediate palaeodirections were observed in the ~650-m-thick composite section. According to the dispersion of flow average directions, palaeosecular variation was slightly larger than that observed in general during the Upper Cenozoic. The site mean directions obtained in this study differ significantly from the expected Miocene direction. Clockwise rotations of up to 20° of small blocks are probably associated with the deformation of the Andean Cordillera since middle Miocene times. Geomagnetic palaeointensity data were obtained, using the Thellier method, on 24 samples from eight distinct lava flows. The flow mean VDM varies from 1.4 to 4.0 × 10²² A m⁻². Altogether, our data seem to suggest the existence of a relatively low geomagnetic field undergoing large fluctuations. Although a linear relationship was observed between the natural remanent magnetization and the thermal remanent magnetization acquired during the Thellier–Thellier experiments, undetected chemical alteration of the magnetic minerals during hydrothermalism may also explain the unusually low palaeointensity obtained.  相似文献   

Random variation of fabric eigenvalues: implications for the use of a‐axis fabric data to differentiate till facies†     

Douglas I. Benn  Trevor J. Ringrose 《地球表面变化过程与地形》2001,26(3):295-306

Fabric ‘shape’, based on the relative values of three eigenvalues calculated from fabric data, has been used to differentiate sediment facies and infer deformation histories. The eigenvalues are based on samples drawn from parent populations, and as such are subject to statistical variance due to sampling effects. In this paper, the degree of statistical variance in fabric data for two types of subglacial till from Breidamerkurjøkull, Iceland, is investigated using ‘bootstrapping’ techniques, in which empirical ‘confidence regions’ are built up by repeated resampling of the original data. The experiments show that, for each till type, the observed between‐sample variability in the fabrics lies within the boundaries associated with random variations, indicating that the observed range of fabric shapes within each till type is likely to be entirely the product of sampling effects. Differences in fabric shape between till types are generally greater than that associated with random variations, indicating that their fabric shape characteristics, as measured by eigenvalues, are significantly different. Nevertheless, the results suggest that great care should be exercised when using a‐axis fabric data to differentiate sedimentary facies, or to infer subtle differences in physical processes or conditions. Copyright © 2001 John Wiley & ­Sons, Ltd.  相似文献   

Orbital resonances in the inner neptunian system: I. The 2:1 Proteus-Larissa mean-motion resonance     

Ke Zhang  Douglas P. Hamilton 《Icarus》2007,188(2):386-399

We investigate the orbital resonant history of Proteus and Larissa, the two largest inner neptunian satellites discovered by Voyager 2. Due to tidal migration, these two satellites probably passed through their 2:1 mean-motion resonance a few hundred million years ago. We explore this resonance passage as a method to excite orbital eccentricities and inclinations, and find interesting constraints on the satellites' mean density () and their tidal dissipation parameters (Qs>10). Through numerical study of this mean-motion resonance passage, we identify a new type of three-body resonance between the satellite pair and Triton. These new resonances occur near the traditional two-body resonances between the small satellites and, surprisingly, are much stronger than their two-body counterparts due to Triton's large mass and orbital inclination. We determine the relevant resonant arguments and derive a mathematical framework for analyzing resonances in this special system.  相似文献   

Glacial deposits at the Boyne Bay Limestone Quarry,Portsoy, and their place in the late Pleistocene history of northeast Scotland     

J. Douglas Peacock  Jon W. Merritt 《第四纪科学杂志》2000,15(5):543-555

The glacial deposits at the Boyne Bay Limestone Quarry near Portsoy, a key Quaternary Site of Special Scientific Interest, comprise (i) a sandy, partly weathered diamicton (Craig of Boyne Till Formation, CBTF) resting on decomposed bedrock, (ii) a central, variably glaciotectonised assemblage of dark clay, diamicton and sand, with rafts of sand and weathered diamicton (Whitehills Glacigenic Formation, WGF), and (iii) an upper dark sandy diamicton (Old Hythe Till Formation, OHTF). The CBTF was probably derived from the west or southwest, and the WGF from seawards. Structures within the OHTF conform to deposition by east‐ or southeast‐moving ice from the Moray Firth, but some erratics indicate derivation from the south. The CBTF is believed to pre‐date the last (lpswichian) interglacial, but the WGF and OHTF both post‐date the early Middle Devensian, and are probably of Late Devensian age. It is proposed that the OHTF was deposited by ice from inland which was directed eastwards near the coast by a vigorous glacier in the Moray Firth, and that the complex, Late Devensian glacial history of the south coast of the Moray Firth as a whole is the result of the interplay of these two contemporary ice‐masses. British Geological Survey. © NERC 2000.  相似文献   

Simultaneous photometry and spectroscopy of the newly discovered γ Doradus variable HR 8330=HD 207223     

Anthony B. Kaye  Gregory W. Henry  Francis C. Fekel  Douglas S. Hall 《Monthly notices of the Royal Astronomical Society》1999,308(4):1081-1086

We present BV photometry and simultaneous high-resolution, high signal-to-noise ratio spectroscopy of the newly-discovered γ Doradus variable HR 8330 taken during the 1997 and 1998 observing seasons. We calculate power spectra for the B - and V -band data sets and for the time series defined throughout the observing season at each point across the Fe  ii λ 4508.289 and the Ti  ii λ 4501.278 line profiles to search for periodic variability. Period analysis reveals a single, 2.6-d period in both the photometric and the spectroscopic data, with a 237° phase lag between them. Based on the location of HR 8330 in the HR diagram and the characteristics of its photometric and spectroscopic variations, we conclude that HR  8330 is a bona fide γ Doradus-type pulsating variable.  相似文献