Near‐surface hydraulic conductivity of northern hemisphere glaciers          下载免费PDF全文

Ian T. Stevens  Tristram D.L. Irvine‐Fynn  Philip R. Porter  Joseph M. Cook  Arwyn Edwards  Martin Smart  Brian J. Moorman  Andy J. Hodson  Andrew C. Mitchell 《水文研究》2018,32(7):850-865

The hydrology of near‐surface glacier ice remains a neglected aspect of glacier hydrology despite its role in modulating meltwater delivery to downstream environments. To elucidate the hydrological characteristics of this near‐surface glacial weathering crust, we describe the design and operation of a capacitance‐based piezometer that enables rapid, economical deployment across multiple sites and provides an accurate, high‐resolution record of near‐surface water‐level fluctuations. Piezometers were employed at 10 northern hemisphere glaciers, and through the application of standard bail–recharge techniques, we derive hydraulic conductivity (K) values from 0.003 to 3.519 m day^?1, with a mean of 0.185 ± 0.019 m day^?1. These results are comparable to those obtained in other discrete studies of glacier near‐surface ice, and for firn, and indicate that the weathering crust represents a hydrologically inefficient aquifer. Hydraulic conductivity correlated positively with water table height but negatively with altitude and cumulative short‐wave radiation since the last synoptic period of either negative air temperatures or turbulent energy flux dominance. The large range of K observed suggests complex interactions between meteorological influences and differences arising from variability in ice structure and crystallography. Our data demonstrate a greater complexity of near‐surface ice hydrology than hitherto appreciated and support the notion that the weathering crust can regulate the supraglacial discharge response to melt production. The conductivities reported here, coupled with typical supraglacial channel spacing, suggest that meltwater can be retained within the weathering crust for at least several days. Not only does this have implications for the accuracy of predictive meltwater run‐off models, but we also argue for biogeochemical processes and transfers that are strongly conditioned by water residence time and the efficacy of the cascade of sediments, impurities, microbes, and nutrients to downstream ecosystems. Because continued atmospheric warming will incur rising snowline elevations and glacier thinning, the supraglacial hydrological system may assume greater importance in many mountainous regions, and consequently, detailing weathering crust hydraulics represents a research priority because the flow path it represents remains poorly constrained.  相似文献   

Prediction of open stope hangingwall stability using random forests     

Qi  Chongchong  Fourie  Andy  Du  Xuhao  Tang  Xiaolin 《Natural Hazards》2018,92(2):1179-1197

Natural Hazards - The prediction of open stope hangingwall (HW) stability is a crucial task for underground mines. In this paper, a relatively novel technique, the random forest (RF) algorithm, is...  相似文献   

Mechanical Study of Shear Failure of Vertical Goaf Drainage Hole     

Khanal  Manoj  Adhikary  Deepak  Balusu  Rao  Wilkins  Andy  Belle  Bharath 《Geotechnical and Geological Engineering》2022,40(4):1899-1920

Geotechnical and Geological Engineering - Most of the published research on goaf-hole failures are performed using 2D numerical analyses. However, 2D analyses of the goaf-hole failure mechanism,...  相似文献   

Thoracican cirripedes (Crustacea) from the Hauterivian (Lower Cretaceous) of Hannover,northern Germany     

Andy Gale 《Proceedings of the Geologists' Association. Geologists' Association》2019,130(6):659-672

Diverse thoracican cirripedes from the Hauterivian of the Hannover district of northern Germany are described, including seven species, belonging to five genera. Of these, a new genus belonging to the Scalpellidae, Jaegerscalpellum, includes one Hauterivian species, J. elegans sp. nov., an Aptian species, J. comptum (Withers, 1910) and an Albian species, J. politum (Darwin, 1851) are also referred to it. A new Cretiscalpellum, C. mutterlosei sp. nov. is described from the Hauterivian, and C. matrioni sp. nov. is described from the Middle Albian of France. The oldest record of the Unilatera Gale, 2018, Pedupycnolepas pulcher sp. nov. is described from the Hauterivian; this displays typical shell structure of the group, retained by living Verrucidae. Finally, four species of Zeugmatolepadidae, subfamily Martillepadinae, are recorded from the Hauterivian, including Martillepas hausmanni (Koch and Dunker, 1836), M. decoratus sp. nov., M. auriculum sp. nov. and Etcheslaepas borealis (Collins, 1990). The Hauterivian fauna from Hannover shows affinities both with Late Jurassic and later Cretaceous (Aptian-Cenomanian) forms, and includes the earliest scalpellids, unilateran (Pedupycnolepas) and Cretiscalpellum species known. It constrains the age of the Cretaceous cirripede evolutionary radiation to the earliest Cretaceous.  相似文献   

SEAWAT‐Based Simulation of Axisymmetric Heat Transport     

Alexander Vandenbohede  Andy Louwyck  Nele Vlamynck 《Ground water》2014,52(6):908-915

Simulation of heat transport has its applications in geothermal exploitation of aquifers and the analysis of temperature dependent chemical reactions. Under homogeneous conditions and in the absence of a regional hydraulic gradient, groundwater flow and heat transport from or to a well exhibit radial symmetry, and governing equations are reduced by one dimension (1D) which increases computational efficiency importantly. Solute transport codes can simulate heat transport and input parameters may be modified such that the Cartesian geometry can handle radial flow. In this article, SEAWAT is evaluated as simulator for heat transport under radial flow conditions. The 1971, 1D analytical solution of Gelhar and Collins is used to compare axisymmetric transport with retardation (i.e., as a result of thermal equilibrium between fluid and solid) and a large diffusion (conduction). It is shown that an axisymmetric simulation compares well with a fully three dimensional (3D) simulation of an aquifer thermal energy storage systems. The influence of grid discretization, solver parameters, and advection solution is illustrated. Because of the high diffusion to simulate conduction, convergence criterion for heat transport must be set much smaller (10^?10) than for solute transport (10^?6). Grid discretization should be considered carefully, in particular the subdivision of the screen interval. On the other hand, different methods to calculate the pumping or injection rate distribution over different nodes of a multilayer well lead to small differences only.  相似文献   

Supraglacial weathering crust dynamics inferred from cryoconite hole hydrology          下载免费PDF全文

Joseph Mitchell Cook  Andy J. Hodson  Tristram D. L. Irvine‐Fynn 《水文研究》2016,30(3):433-446

Water levels in cryoconite holes were monitored at high resolution over a 3‐week period on Austre Brøggerbreen (Svalbard). These data were combined with melt and energy balance modelling, providing insights into the evolution of the glacier's near‐surface hydrology and confirming that the hydrology of the near‐surface, porous ice known as the ‘weathering crust’ is dynamic and analogous to a shallow‐perched aquifer. A positive correlation between radiative forcing of melt and drainage efficiency was found within the weathering crust. This likely resulted from diurnal contraction and dilation of interstitial pore spaces driven by variations in radiative and turbulent fluxes in the surface energy balance, occasionally causing ‘sudden drainage events’. A linear decrease in water levels in cryoconite holes was also observed and attributed to cumulative increases in near‐surface ice porosity over the measurement period. The transport of particulate matter and microbes between cryoconite holes through the porous weathering crust is shown to be dependent upon weathering crust hydraulics and particle size. Cryoconite holes therefore yield an indication of the hydrological dynamics of the weathering crust and provide long‐term storage loci for cryoconite at the glacier surface. This study highlights the importance of the weathering crust as a crucial component of the hydrology, ecology and biogeochemistry of the glacier ecosystem and glacierized regions and demonstrates the utility of cryoconite holes as natural piezometers on glacier surfaces. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Using FTIR spectroscopy to characterise the soil mineralogy and geochemistry of cryoconite from Aldegondabreen glacier,Svalbard     

Harry Langford  Andy Hodson  Steve Banwart 《Applied Geochemistry》2011

Mineralogical and geochemical diversity in cryoconite granules from Aldegondabreen glacier was investigated using FTIR spectroscopy. Results suggest that the technique is an effective tool for investigating mineralogy and identifying spatial differences in geochemistry, based upon characteristic spectral signatures.  相似文献   

Development of Specimen Curing Procedures that Account for the Influence of Effective Stress During Curing on the Strength of Cemented Mine Backfill   总被引：2，自引：1，他引：1  

Martin Fahey  Matthew Helinski  Andy Fourie 《Geotechnical and Geological Engineering》2011,29(5):709-723

Paste backfill used to provide ground support in underground mining is generated from full-stream tailings and is almost always placed underground with cement. For the backfill, both the rate of strength development and the final strength are important considerations for design, particularly when the backfill is subsequently exposed in the stope-mining sequence. There is strong evidence that strengths measured on specimens obtained from coring the in situ cemented backfill are much greater than laboratory-cured specimens with the same cement content. The paper reviews some of the experimental evidence showing that one of the major reasons for the different strength is the difference in effective stress acting on the backfill during curing. Laboratory specimens are (almost) always cured under zero total stress, so no effective stress develops. In contrast, backfill in a stope may cure under high effective stress, which develops due to either “conventional” consolidation in free-draining backfills, or to the so-called “self-desiccation” mechanism in fine-grained fills. Evidence is presented showing how the final strength is affected by applying stress to specimens at different stages of curing and at different rates. It is shown that a fully-coupled analysis of the filling behaviour is required to determine the appropriate effective stress regime to apply in curing laboratory specimens, where “fully-coupled” in this context means taking account of the interaction of consolidation/drainage rate, filling rate and cement hydration rate. Curing protocols for laboratory specimens are proposed, which would ensure that the strengths obtained are representative of in situ conditions.  相似文献   

2.5-D DC Resistivity Modeling Considering Flexibility and Accuracy     

汤井田  王飞燕  肖晓  张林成 《中国地质大学学报(英文版)》2011,(1)

We highlighted the flexibility of using unstructured mesh together with the local refinement by a resistivity model with complicated topography. The effect of topography is emphasized. Based on this, we calculated a specific class of layered models and found that the accuracy is not always satisfactory by utilizing the standard approach. As an improvement, we employed the layered earth as the reference model to calculate the wavenumbers. The comparison demonstrates that the accuracy is considerably improved...  相似文献   

利用有限单元法模拟二维MT倾子响应   总被引：1，自引：0，他引：1  

童孝忠  柳建新  刘颖  甘佳雄  张连伟 《吉林大学学报(地球科学版)》2011,(Z1):349-354

在二维地电模型中,考虑到大地电磁测深(MT)倾子响应依赖于横电(TE)模式的数值模拟问题,笔者采用矩形网格单元和双二次插值对MT的倾子响应进行求解。首先,给出了二维地电条件下的边值问题和变分问题,并通过有限单元法对模型进行单元剖分、插值、积分和整体合成;其次,通过求解复系数方程组得到了每个节点的电场值;最后,采用差分方法求得电场沿横向和垂向的偏导数值,从而计算出二维MT的倾子响应。通过对2个二维地电模型的倾子响应进行数值模拟,获得了倾子响应的实部、虚部和振幅,结果很好地反映了不均匀体的横向分布情况。  相似文献