TILL FABRICS AND SPEED OF MOVEMENT OF THE ARAPAHOE GLACIER,COLORADO     

Stuart A. Harris 《The Professional geographer》1968,20(3):195-198

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Lake basins as archives of continental tectonics and paleoclimate: introduction     

Elizabeth H. Gierlowski-Kordesch  H. Paul Buchheim 《Journal of Paleolimnology》2003,30(2):113-114

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Editorial     

Frances Harris  Chasca Twyman 《The Geographical journal》2003,169(4):326-327

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N-view reconstruction: a new method for morphological modelling and deformation measurement in volcanology     

E. Cecchi  B. van Wyk de Vries  J. -M. Lavest  A. Harris  M. Davies 《Journal of Volcanology and Geothermal Research》2003,123(1-2):181

We present a method of reconstructing volcanic morphology using multiple digital views (N-view), captured at different angles around an object. This approach uses recent advances in the field of Computer Vision to provide accurate 3-D measurements of volcanic surfaces. Videogrammetry (digital image reconstruction) is used, as it is best adapted to numerical processing. The method is tested and now used in the laboratory on analogue volcanic cones. The method begins with calibrating the camera and finding image positions, using an accurate N-view calibration method. This is done by estimating internal and external parameters of the camera using several views of a specially constructed calibration target. The N-view reconstruction of the real object is then done by iteratively deforming an initial theoretical model of the surface. Laboratory tests show that reconstruction accuracy is about 10⁻⁴ m for a distance between the object and the camera of 0.5 m, and is potentially several orders of magnitude higher for surfaces of finer texture and using higher precision sensors. This is easily high enough to be useful for the accuracy required for morphological studies. It is also sufficient for monitoring most types of volcano deformation. The technique has the potential to detect morphology changes of the order of mm. Use of the method in the field requires a slightly different approach from that in the laboratory: textures and lighting are more variable, and the sensor and ground control point location and model calibration must be done differently. We provide case studies from laboratory tests and qualitative image analysis for two field cases: Piton de la Fournaise (Indian Ocean) and Santaguito (Guatemala). These illustrate the technique’s potential and explore problems of field application. Using current sensors, the method has the potential to provide sufficient precision for fine (mm–cm) scale reconstruction, and will represent a valuable, simple and flexible tool when compared with classical stereophotogrammetry techniques.  相似文献   

Gelifluction: viscous flow or plastic creep?     

Charles Harris  Michael C. R. Davies  Brice R. Rea 《地球表面变化过程与地形》2003,28(12):1289-1301

This paper reports results from two scaled centrifuge modelling experiments, designed to simulate thaw‐related geli?uction. A planar 12° prototype slope was modelled in each experiment, using the same natural ?ne sandy silt soil. However two different scales were used. In Experiment 1, the model scale was 1/10, tested in the centrifuge at 10 gravities (g) and in Experiment 2, the scale was 1/30, tested at 30 g. Centrifuge scaling laws indicate that the time scaling factor for thaw consolidation between model and prototype is N², where N is the number of gravities under which the model was tested. However, the equivalent time scaling for viscous ?ow is 1/1. If geli?uction is a viscosity‐controlled ?ow process, scaling con?icts will therefore arise during centrifuge modelling of thawing slopes, and rates of displacement will not scale accurately to the prototype. If, however, no such scaling con?icts are observed, we may conclude that geli?uction is not controlled by viscosity, but rather by elasto‐plastic soil deformation in which frictional shear strength depends on effective stress, itself a function of the thaw consolidation process. Models were saturated, consolidated and frozen from the surface downwards on the laboratory ?oor. The frozen models were then placed in the geotechnical centrifuge and thawed from the surface down. Each model was subjected to four freeze–thaw cycles. Soil temperatures and pore water pressures were monitored, and frost heave, thaw settlement and downslope displacements measured. Pore water pressures, displacement rates and displacement pro?les re?ecting accumulated shear strain, were all similar at the two model scales and volumetric soil transport per freeze–thaw cycle, when scaled to prototype, were virtually identical. Displacement rates and pro?les were also similar to those observed in earlier full‐scale laboratory ?oor experiments. It is concluded therefore that the modelled geli?uction was not a time‐dependent viscosity‐controlled ?ow phenomenon, but rather elasto‐plastic in nature. A ?rst approximation ‘?ow’ law is proposed, based on the ‘Cam Clay’ constitutive model for soils. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

The relationship between phytolith- and plant-water δO values in grasses     

Elizabeth A. Webb  Fred J. Longstaffe 《Geochimica et cosmochimica acta》2003,67(8):1437-1449

Information regarding climatic conditions during plant growth is preserved by the oxygen-isotope composition of biogenic silica (phytoliths) deposited in grasses. The O-isotope compositions of phytoliths and the plant water from which they precipitate are dependent on soil-water δ¹⁸O values, relative humidity, evapotranspiration rates, and temperature. Plant water and phytoliths from two grass species, Ammophila breviligulata (C₃) and Calamovilfa longifolia (C₄) at Pinery Provincial Park in southwestern Ontario, Canada, were examined to determine the variability in their δ¹⁸O values. Stem water was unfractionated from soil-water in oxygen isotopic composition and the δ¹⁸O values of stem silica provide a good proxy for the soil water available to roots during the growing season. Greater spatial and temporal variation in the δ¹⁸O values of water in the top 5 cm of the soil, and their enhanced sensitivity to evaporative ¹⁸O enrichment, are reflected in the generally higher δ¹⁸O values of water in the shallow roots and rhizomes of these grasses. Water within the sheath and lower and upper leaf tissues experiences continual evaporation, becoming progressively enriched in ¹⁸O as it moves towards the tip of the leaf. However, the water from which leaf silica precipitates has not acquired the extreme ¹⁸O enrichment predicted using steady-state models, or measured for midday or average daily leaf water. Possible explanations for this behaviour include preferential deposition of silica at night; the existence of a secluded water fraction within the leaf, which experiences smaller diurnal variations in isotopic composition than leaf water at sites of evaporation; kinetic isotope effects during rapid precipitation of leaf silica; and incomplete exchange between the oxygen in the silicic acid and the leaf water.  相似文献   

Amazonian climate: results and future research   总被引：1，自引：0，他引：1  

J. H. C. Gash  C. Huntingford  J. A. Marengo  R. A. Betts  P. M. Cox  G. Fisch  R. Fu  A. W. Gandu  P. P. Harris  L. A. T. Machado  C. von Randow  M. A. Silva Dias 《Theoretical and Applied Climatology》2004,78(1-3):187-193

Summary Some of the results from the climate component of the Large Scale Biosphere-Atmosphere Experiment in Amazonia (LBA), which are presented in this Special Issue are summarised. Recent advances in Amazonian climate modelling are also discussed. There is a range of papers which fall into three groups: surface fluxes and boundary layer growth; convection, clouds and rainfall; and climate modelling. The new insight given by this work is discussed and an argument is made for future research to employ a wider approach to Amazonian climate modelling.  相似文献   

Numerical Simulations of Large Earthquakes: Dynamic Rupture Propagation on Heterogeneous Faults   总被引：1，自引：0，他引：1  

Ruth A. Harris 《Pure and Applied Geophysics》2004,161(11-12):2171-2181

— Our current conceptions of earthquake rupture dynamics, especially for large earthquakes, require knowledge of the geometry of the faults involved in the rupture, the material properties of the rocks surrounding the faults, the initial state of stress on the faults, and a constitutive formulation that determines when the faults can slip. In numerical simulations each of these factors appears to play a significant role in rupture propagation, at the kilometer length scale. Observational evidence of the earth indicates that at least the first three of the elements, geometry, material, and stress, can vary over many scale dimensions. Future research on earthquake rupture dynamics needs to consider at which length scales these features are significant in affecting rupture propagation.  相似文献   

Geology-exploration endowment models for simultaneous estimation of discoverable mineral resources and endowment     

Guocheng Pan  DeVerle P. Harris 《Mathematical Geology》1991,23(4):507-540

A new type of model, referred to as a geology-exploration endowment model, is proposed in this paper. These models differ from conventional ones in that they simultaneously estimate discoverable mineral resources and endowment by extracting and utilizing geoscience information from both geological features and exploration factors. Geological measurements describe mineral endowment, while exploration variables describe the completeness of exploration, and together, they explain discoverable resources. Without incorporation of exploration factors to geological-endowment models, the estimation of endowment is generally biased. This paper presents two variations of such hybrid nonlinear models: Poisson-logistic (PL) and exponential-logistic (EL) for estimation of number of mineral deposits or prospects based upon the Arps and Roberts' discovery process model and assumptions of endowment distributions. The PL model is obtained by assuming that endowment follows a Poisson distribution and that the probability of mineral occurrences ( 1) is a logistic function with geological arguments. The EL model is derived similarly, except that endowment is assumed to be exponentially distributed. The PL model is demonstrated on both a synthetic example and a case study of epithermal gold-silver vein deposits in the Walker Lake quadrangle of Nevada and California. A map containing the estimated numbers of gold-silver mineral occurrences potentially discoverable in the Walker Lake quadrangle is produced. The parameter estimates for the PL model based on the Levenberg-Marquardt iterative algorithm are validated by using several statistical measures, such as theT-statistic, Box's bias, and goodness of fit. Both a synthetic example and a case study suggest that the Box's bias measure is useful for validation of the nonlinear estimates.  相似文献   

The Mineralogy of gold and its relevance to gold recoveries     

D. C. Harris 《Mineralium Deposita》1990,25(1):S3-S7

Processing of most gold ores, other than placers, involves conventional gravity separation and direct cyanidation. The difficult (or refractory) gold ores are not amenable to direct cyanidation and these ores require detailed mineralogical investigations to assist in determining the recovery processes. There are six mineralogical factors that can contribute to poorer recoveries. These are 1. the nature of the gold-containing minerals, 2. the grain size of the gold minerals, 3. the nature of the gangue minerals, 4. the associated sulfide minerals, 5. coatings on gold, and 6. chemically bound or invisible gold.Geological Survey of Canada Contribution Number 13089  相似文献