Peak discharge of a Pleistocene lava-dam outburst flood in Grand Canyon, Arizona, USA   总被引：1，自引：0，他引：1  

Cassandra R. Fenton  Robert H. Webb 《Quaternary Research》2006,65(2):324-335

The failure of a lava dam 165,000 yr ago produced the largest known flood on the Colorado River in Grand Canyon. The Hyaloclastite Dam was up to 366 m high, and geochemical evidence linked this structure to outburst-flood deposits that occurred for 32 km downstream. Using the Hyaloclastite outburst-flood deposits as paleostage indicators, we used dam-failure and unsteady flow modeling to estimate a peak discharge and flow hydrograph. Failure of the Hyaloclastite Dam released a maximum 11 × 10⁹ m³ of water in 31 h. Peak discharges, estimated from uncertainty in channel geometry, dam height, and hydraulic characteristics, ranged from 2.3 to 5.3 × 10⁵ m³ s⁻¹ for the Hyaloclastite outburst flood. This discharge is an order of magnitude greater than the largest known discharge on the Colorado River (1.4 × 10⁴ m³ s⁻¹) and the largest peak discharge resulting from failure of a constructed dam in the USA (6.5 × 10⁴ m³ s⁻¹). Moreover, the Hyaloclastite outburst flood is the oldest documented Quaternary flood and one of the largest to have occurred in the continental USA. The peak discharge for this flood ranks in the top 30 floods (>10⁵ m³ s⁻¹) known worldwide and in the top ten largest floods in North America.  相似文献   

城市河岸土地利用对河流廊道功能影响初探——以上海苏州河为例   总被引：1，自引：0，他引：1  

陈婷  杨凯 《世界地理研究》2006,15(3):82-87

城市河岸土地利用往往改变河岸的自然地理条件,对城市河流功能产生影响。通过总结城市河岸廊道功能以及国内外城市河岸规划土地利用的实践,分析了河岸土地利用对城市河流廊道功能的影响,并以上海苏州河为例进行了实证分析。结果表明,苏州河河岸规划土地利用方式提高了河岸开放带宽度,改善了河岸舒适性,控制了河岸建筑高度,有利于保护和开发苏州河河流的景观、遗产和经济廊道的功能。干流河岸在自然廊道功能方面,仍存在一定缺陷,与支流的部分河段相比仍有差距。  相似文献   

Precambrian fluvial deposits: Enigmatic palaeohydrological data from the c. 2–1.9 Ga Waterberg Group, South Africa     

Patrick G. Eriksson  Adam J. Bumby  Jacobus J. Brümer  Markus van der Neut 《Sedimentary Geology》2006,190(1-4):25-46

Precambrian fluvial systems, lacking the influence of rooted vegetation, probably were characterised by flashy surface runoff, low bank stability, broad channels with abundant bedload, and faster rates of channel migration; consequently, a braided fluvial style is generally accepted. Pre-vegetational braided river systems, active under highly variable palaeoclimatic conditions, may have been more widespread than are modern, ephemeral dry-land braided systems. Aeolian deflation of fine fluvial detritus does not appear to have been prevalent. With the onset of large cratons by the Neoarchaean–Palaeoproterozoic, very large, perennial braided river systems became typical. The c. 2.06–1.88 Ga Waterberg Group, preserved within a Main and a smaller Middelburg basin on the Kaapvaal craton, was deposited largely by alluvial/braided-fluvial and subordinate palaeo-desert environments, within fault-bounded, possibly pull-apart type depositories.

Palaeohydrological data obtained from earlier work in the Middelburg basin (Wilgerivier Formation) are compared to such data derived from the correlated Blouberg Formation, situated along the NE margin of the Main basin. Within the preserved Blouberg depository, palaeohydrological parameters estimated from clast size and cross-bed set thickness data, exhibit rational changes in their values, either in a down-palaeocurrent direction, or from inferred basin margin to palaeo-basin centre. In both the Wilgerivier and Blouberg Formations, calculated palaeoslope values (derived from two separate formulae) plot within the gap separating typical alluvial fan gradients from those which characterise rivers (cf. [Blair, T.C., McPherson, J.G., 1994. Alluvial fans and their natural distinction from rivers based on morphology, hydraulic processes, sedimentary processes, and facies assemblages. J. Sediment. Res. A64, 450–489.]). Although it may be argued that such data support possibly unique fluvial styles within the Precambrian, perhaps related to a combination of major global-scale tectono-thermal and atmospheric–palaeoclimatic events, a simpler explanation of these apparently enigmatic palaeoslope values may be pertinent. Of the two possible palaeohydrological formulae for calculating palaeoslope, one provides results close to typical fluvial gradients; the other formula relies on preserved channel-width data. We suggest that the latter will not be reliable due to problematic preservation of original channel-widths within an active braided fluvial system. We thus find no unequivocal support for a unique fluvial style for the Precambrian, beyond that generally accepted for that period and discussed briefly in the first paragraph.  相似文献   

The Usage of Ground Penetrating Radar (GPR) in Designing Blast Pattern     

G. U. Aldas  S. Kadioglu  E. Ulugergerli 《Rock Mechanics and Rock Engineering》2006,39(3):281-290

  相似文献   

R＆D投入的区位模式与区域经济发展   总被引：2，自引：1，他引：2  

姜怀宇  李铁立 《地理科学》2006,26(1):13-19

基于对中国R＆D投入的区位模式的实证检验，从投入一产出绩效的角度认为集中投入的区位模式具有较强的适宜性。利用聚类分析技术，按照R＆D的投入强度和及其对经济的带动效应、科技化效应、产业化效应将中国各省区划分为6类地区，具有代表性的是科技化模式和产业化模式。其中前者适合于技术存置较高的少数地区，而后者具有较强的借鉴意义。  相似文献   

Fan beheading and drainage diversion as evidence of a 3200-2800 BP earthquake event in the Esmeraldas-Tumaco seismic zone: A case study for the effects of great subduction earthquakes   总被引：1，自引：0，他引：1  

J.F. Dumont  E. Santana  F. Valdez  J.P. Tihay  P. Usselmann  D. Iturralde  E. Navarette 《Geomorphology》2006,74(1-4):100-123

The San Lorenzo area belongs to the Esmeraldas–Tumaco seismic zone where some of the strongest earthquakes of South America occurred during the 20th century. This paper provides evidence for a succession of geomorphic changes characterized by the disruption of the Quaternary drainage network and the reshaping of the Cayapas–Santiago estuary. The rise of the La Boca uplift bordered by the La Boca and San Lorenzo faults is responsible for the southward diversion of the Palabi, Tululbi, Bogotá and Carolina rivers toward the Santiago and Cayapas rivers. The increase of the discharge directed to the Cayapas River generated the change of the channel pattern downstream from the confluence, and the avulsion of a new estuary through the coastal plain. According to the dating of beach ridges the avulsion occurred in the period 3200–2800 BP. This period corresponds also to a faster accretion of the beach ridge margin, interpreted as a response to a small uplift of the shore. The coherency of the three morphologic evidences—diversion of drainage network, avulsion and increase of coastal accretion—suggest a unique morphotectonic event, in relation with the activity of the Esmaraldas–Tumaco seismic zone. The opening of a direct communication through the mangrove margin may have brought favorable conditions for the development of the La Tolita archaeological site after 3000 BP.  相似文献   

Assessing potential abiotic and biotic complications of crayfish-induced gravel transport in experimental streams     

Bernhard Statzner  Odile Peltret 《Geomorphology》2006,74(1-4):245-256

Biogeomorphology adds the element “biological dynamics” (of populations or communities) to chemical and physical geomorphic factors and thus complicates the framework of geomorphic processes. Such biological complications of the animal-induced transport of solids in streams should be particularly important in crayfish, as crayfish affect this transport through their overall activity and intraspecific aggression levels, which could be modified by shelter availability or the establishment of dominance hierarchies among individuals not knowing each other. Using experimental streams, we tested these hypotheses by measuring how shelter availability or residential crayfish group invasion by unknown individuals affected the impact of the crayfish Orconectes limosus on the (i) transport of gravel at baseflow (during 12 experimental days); (ii) sediment surface characteristics (after 12 days); and (iii) critical shear stress causing incipient gravel motion during simulated floods (after 12 days). The two potentially important factors shelter availability or residential group invasion negligibly affected the crayfish impact on gravel sediments, suggesting that habitat unfamiliarity (a third potentially important factor affecting crayfish activity) should increase the crayfish-induced sediment transport. Because habitat unfamiliarity is associated with sporadic long-distance migrations of a few crayfish individuals, this third factor should play a minor role in real streams, where crayfish biomass should be a key factor in relations with crayfish effects on sediments. Therefore, we combined the results of this study with those of previous crayfish experiments to assess how crayfish biomass could serve in modelling the gravel transport. Crayfish biomass explained 47% of the variability in the baseflow gravel transport and, in combination with the coefficient of variation of the bed elevation and algal cover, 72% of the variability in the critical gravel shear stress. These results encourage more research on the topic, as an increasing number of eliminations of abiotic and biotic factors that could complicate the animal-induced sediment transport in streams would facilitate the use of biological variables (e.g., bioturbator biomass) in future modelling of the transport of solids.  相似文献   

华南地区晚二叠和晚三叠世煤中稀土元素特征研究   总被引：2，自引：0，他引：2  

杜美霞  庄新国 《中国煤田地质》2006,18(2):22-26

在华南地区贵州六盘水、江西乐平、露庆和湖北黄石矿区晚二叠和晚三叠世煤层的稀土元素ICP—MS分析数据的基础上，系统研究了研究区煤中稀土元素的含萤分布特征、赋存特征、配分模式以及地质控制因素。含量分布表明晚二叠世稀土元素含量总体高于晚三叠世；煤中稀土元素与灰分成正相关关系，部分煤样品由于有富稀土元素的重矿物组合的存在而出现稀土元素的异常高值；同一矿区、同一时代煤中稀土元素的配分模式具有一定的相似性，而不同地区同一时代和同一地区不同时代煤中稀土元素的配分模式具有较大差异；煤的沉积环境，煤中无机矿物组成以及海水的影响是控制煤中稀土元素含量和配分模式的主要地质因素。  相似文献   

淮北煤田孙庄勘探区煤层气赋存规律及影响因素分析     

樊爱英 《中国煤田地质》2006,18(5):25-27

通过对淮北煤田孙庄勘探区地质构造、沉积特征、煤层煤质及煤层气赋存特征的分析，研究认为有利于本区煤层气赋存的主要因素是较大的埋藏深度、较高的壳质组＋镜质组、较高的变质程度、较大的煤层厚度、低透气性的盖层、较缓的地层倾角和封闭性较好的构造条件，推测煤田深部可能具有一定工业价值的煤层气资源。  相似文献   

新疆巴喀勒萨依地区含铜砂岩及其铜矿床特征     

凌联海  楼法生  刘春根  肖晓林  程春华  于成涛 《华东地质学院学报》2006,29(2):115-120

近年来在新疆巴喀勒萨依地区发现一套含少量火山碎屑岩的含铜砂岩地层,由于该地层位于近东西向的断裂夹块中,其含矿层位的确定就成了难题。在该地层中发现了一些腕足类、珊瑚、腹足类、植物化石,经中国科学院南京地质古生物研究所鉴定,时代属晚石炭世晚期。介绍了巴喀勒萨依地区晚石炭世伊什基里克组含铜砂岩剖面及铜矿特征,并获得铜资源量19 797 t,银铜资源量371 t,提出了该区铜、银富集在红色含铜砂岩中有机质聚集处的新观点。  相似文献