The Verification and Significance of Three Approaches to Longitudinal Stresses in High–resolution Models of Glacier Flow     

Alun Hubbard 《Geografiska Annaler: Series A, Physical Geography》2000,82(4):471-487

With the purpose of improving the ice physics underpinning time–dependent glacier flowline models, three independent approaches for solving longitudinal stresses in glaciers are discussed and verified by application to Haut Glacier d'Arolla. To highlight any shortcomings, the reduced and much utilised driving stress approximation is also applied and compared. Modelled velocity patterns using the three full stress schemes exhibit consistency with one another and good coincidence with observed velocities for the 1991 summer melt season. Furthermore, these stress patterns indicate that longitudinal stresses are significant and of a similar order of magnitude as the basal shear stress components. However, the driving stress approximation yields erratic fluctuations in the stress and velocity fields which are neither realistic in terms of mass continuity nor agree with observations. Basal decoupling experiments indicate a complex relationship between basal velocity and englacial stresses with considerable dampening of any basal perturbation occurring as it is dissipated towards the surface and transferred throughout the ice mass. The driving stress approximation fails to account at all for any such coupling. Experiments to identify the length scale over which longitudinal effects operate indicate that they are significant even up to 10 ice thicknesses. The implication here is that longitudinal stresses play a significant role in determining glacier dynamics on length scales up to at least 2 km and that the predictive power of models of glacier flow based purely on the driving stress approximation is therefore subject to significant limitations. Inclusion of longitudinal stresses overcomes one of the main limitations imposed on such models and, given the potential ease of incorporation of the schemes described here, this deficiency may readily be resolved.  相似文献   

IN SITU MEASUREMENTS OF BASAL WATER QUALITY AND PRESSURE AS AN INDICATOR OF THE CHARACTER OF SUBGLACIAL DRAINAGE SYSTEMS     

DAN B. STONE  GARRY K. C. CLARKE 《水文研究》1996,10(4):615-628

Continuous subglacial measurements of turbidity and electrical conductivity — two indicators of basal water quality — can be used to help characterize subglacial drainage systems. These indicators of water quality yield information that complements that provided by water pressure measurements. Quantitative attributes of subglacial drainage systems, such as water velocity and subglacial residence time, as well as qualitative behaviour — for example, spatial and temporal variations in system morphology — can be deduced using water quality measurements. Interpretation is complicated by the many potential influences on turbidity and electrical conductivity, but when these complications are appreciated a richer interpretation results. To demonstrate the utility of basal water quality measurements, observations from Trapridge Glacier, Yukon Territory, Canada were examined. The data reveal complex behaviour of the drainage system, but constraints imposed by basal water quality measurements help to clarify the nature of the subglacial flow system. The measurement and interpretation methods described and demonstrated are applicable to other glaciers. As such, they should prove useful for characterizing different subglacial drainage configurations and behaviours, thereby improving our general understanding of the hydrology and dynamics of wet-based glaciers.  相似文献   

沼泽湿地垦殖对土壤碳动态的影响   总被引：20，自引：7，他引：13  

张金波  宋长春  杨文燕 《地理科学》2006,26(3):340-344

在中国科学院三江平原湿地生态试验站选取相邻的、土壤类型相同的小叶章沼泽化草甸以及不同开垦殖年限的已垦湿地农田,综合运用多种微生物指标,全面地评价沼泽湿地垦殖后土壤有机碳的动态。结果表明,沼泽湿地垦殖初期(1~3年),土壤微生物量碳(MBC)、微生物商以及基础呼吸(BR)都迅速降低,而代谢商(qCO₂)、PR/BR和PR/MBC比值却不断升高。表明湿地垦殖后,有机碳的可利用性下降,微生物对碳源的利用效率降低,造成土壤有机碳的大量损失。各种微生物指标之间有密切的相关关系,综合这些微生物指标能够全面地、准确地评价沼泽湿地垦殖后土壤有机碳的动态。  相似文献   

2003年10～11月的大磁暴   总被引：5，自引：2，他引：3  

李琪  高玉芬 《地震地磁观测与研究》2006,27(2):43-47

分析了引起2003年10～11月发生的3个特大磁暴的太阳活动、行星际扰动以及中国东部地磁台链记录到的地面磁场变化。结果表明,这3个特别大的磁暴是由太阳质量抛射事件引起的。太阳向着地球喷发出的大量等离子体引起的强烈太阳风扰动和持续长时间的南向行星际磁场与磁层相互作用形成了特别大的磁暴。ACE卫星、GOES卫星以及地面地磁台站较完整地记录了这3次日地扰动传输过程。对于每一个磁暴,中国东部地磁台链记录到的H分量变化形态一致,纬度最高的满洲里地磁台H幅度最大,而其他台站的幅度与纬度无明显关系,这表明磁暴的发展不完全由赤道环电流引起,在这样强烈的磁暴期间,磁层内的电流体系非常复杂。  相似文献   

关于水资源总量计算的探讨     

段乔文  李林涛  俞富有  何继永 《地质灾害与环境保护》2006,17(3):14-16

一个地区的水资源量,相对来说无论是地表水资源还是地下水资源均处于相对动态平衡之中。天然状态下,水资源总量等于地表水径流量与地下水天然排泄量之和,再减去地下水枯月天然排泄量(即地下水恒转化为河川基流量的部分)。  相似文献   

新疆东部地区大地构造问题探讨   总被引：5，自引：0，他引：5  

张德润 《新疆地质》1990,(2)

根据最新的航磁资料,主要探讨了新疆东部基底性质及岩相分区,指出在天山地区除普通存在古生界浅变质基底外,于吐鲁番—哈密盆地中南部深层还存在强磁性基底.库鲁克塔格地区由于元古界多为弱磁性或无磁性岩石,因而显示负磁场面貌,该区与南天山、塔里木盆地北部为区域负背景异常,推测它们为同一深部因素控制的构造区.磁场资料可清楚地圈定出塔里木地台东部边界.文中还对原中天山隆起带出现的升高变化异常提出了解释依据.  相似文献   

白坪井田太原组上段底部砂岩沉积环境分析及其意义     

刘庆献 《中国煤炭地质》2008,20(1):1-2,36

白坪井田太原组上段主要由三层灰岩（L7、L8、L9）、泥岩和薄煤层组成,L7灰岩位于该段底部,是一7煤层顶板。根据井田西部钻孔资料,相当于L7灰岩层位,往往相变为砂岩。该砂岩以中、粗粒砂岩为主,向上渐变为细砂岩,正粒序特征明显,具板状交错层理和波状层理,底部多为粗砂岩,见冲刷面,其厚度与L7灰岩厚度相当,剖面上砂体呈连续的透镜状,与两侧的L7灰岩呈突变接触关系,砂岩体平面上呈条带状分布,与地层走向垂直,综合分析认为该砂体属潮道沉积相,是在潮坪上潮汐通道部位形成的砂质沉积属潮道沉积相。对该砂体分布的圈定,意味着一7煤在此范围的缺失,这一结论有助于解决太原组煤岩层的对比问题。  相似文献   

面部和颅底骨折的CT分析     

许家亮  李恒国 《CT理论与应用研究》1997,6(2):15-17

为了提高对面部和颅底骨折的认为。本组７４例，男性６３例，女性１１例，年龄２－７１岁，车祸外伤６４例，拳击伤５例，铁棍击伤２例，从高处跌下３例，全部病例均采用轴位ＣＴ平扫。眶内壁骨折２０例，其中爆裂骨的１１例，直接骨折８例，１列同时受直接和间接外力作用；眶下壁骨折１例，为爆裂骨折；眶外后壁骨折１例，眶顶壁骨折９例，均为直接骨折；其他骨折３３例；蝶窦内液平为颅底骨折的重要间接征象。ＣＴ检查可确定骨折类  相似文献   

陈家庄铀矿同位素地质年代学特征   总被引：2，自引：0，他引：2  

刘德成 《矿物岩石》1991,11(1):73-79

陈家庄铀矿床铀单矿物U-Pb及黑云母K-Ar、全岩Rb-Sr同位素定年结果,成矿时期为423—382Ma,主成矿年龄406Ma,矿床形成至今仍保持半封闭系统,未遭受明显后期改造。本区早古生代时期发生的区域动力热流变质作用的年龄为457Ma,热液活动的上限为378Ma,冷却年龄为373—350Ma,伟晶状花岗岩原岩丰龄452Ma。并提出了本区主要地质事件时序及演化模式。  相似文献   

利用遥感技术进行大熊猫栖息环境的调查研究   总被引：2，自引：0，他引：2  

李芝喜 《遥感学报》1990,(2)

本文利用陆地卫星图像和航空像片判读,结合地面采样调查,对既能从遥感图像上提取又是影响大熊猫主食竹类生长的环境因子,建立多元回归的数学模型。根据多元回归求算各个地块的得分值,以评价主食竹类的立地质量等级。得出位于中高海拔东北向缓坡下部兼有针阔混交林覆盖的厚土层地段,是主食竹类的最适生长环境和大熊猫的最佳栖息环境。因此,利用遥感技术进行立地质量分类和编制大熊猫环境质量分布图,将对恢复和改善其栖息环境以及管理保护工作起到积极的作用。  相似文献