Reconstructing historic Glacial Lake Outburst Floods through numerical modelling and geomorphological assessment: Extreme events in the Himalaya          下载免费PDF全文

Matthew J. Westoby  Neil F. Glasser  Michael J. Hambrey  James Brasington  John M. Reynolds  Mohamed A. A. M. Hassan 《地球表面变化过程与地形》2014,39(12):1675-1692

Recession of high‐mountain glaciers in response to climatic change frequently results in the development of moraine‐dammed glacial lakes. Moraine dam failure is often accompanied by the release of large volumes of water and sediment, termed a Glacial Lake Outburst Flood (GLOF). Chukhung Glacier is a small (~3 km²) receding valley glacier in Mt. Everest (Sagarmatha) National Park, Nepal. Unlike many Himalayan glaciers, which possess a thick mantle of supraglacial debris, its surface is relatively clean. The glacier terminus has receded 1.3 km from its maximum Holocene position, and in doing so provided the space for an ice‐contact moraine‐dammed lake to develop. The lake had a maximum volume of 5.5 × 10⁵ m³ and drained as a result of breaching of the terminal moraine. An estimated 1.3 × 10⁵ m³ of material was removed from the terminal moraine during breach development. Numerical dam‐breach modelling, implemented within a Generalised Likelihood Uncertainty Estimation (GLUE) framework, was used to investigate a range of moraine‐dam failure scenarios. Reconstructed outflow peak discharges, including failure via overtopping and piping mechanisms, are in the range 146–2200 m³ s^‐1. Results from two‐dimensional hydrodynamic GLOF modelling indicate that maximum local flow depths may have exceeded 9 m, with maximum flow velocities exceeding 20 m s^‐1 within 700 m of the breach. The floodwaters mobilised a significant amount of material, sourced mostly from the expanding breach, forming a 300 m long and 100 m wide debris fan originating at the breach exit. moraine‐dam. These results also suggest that inundation of the entire floodplain may have been achieved within ten minutes of initial breach development, suggesting that debris fan development was rapid. We discuss the key glaciological and geomorphological factors that have determined the evolution of a hazardous moraine‐dammed lake complex and the subsequent generation of a GLOF and its geomorphological impact. © 2014 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

3D Modeling of sediment movement by ships-generated wakes in confined shipping channel     

Shengcheng JI  Abdellatif OUAHSINE  Hassan SMAOUI 《国际泥沙研究》2014,29(1):49-58

Ship-generated waves and return currents are capable of re-suspending significant quantities of bottom and bank sediments.However,most of the previous studies done on the subject do not show how and where sediment is re-suspended by the wakes and the directions of net transport.In this paper,a 3D numerical model based on hydro-sedimentary coupling is presented to search the relationship between the sediment movement,and the pattern of ship-generated waves around and far away from the vessel and the return currents around the ships.The hydrodynamic model is based on 3D Navier-Stokes equations including the standard k-ε model for turbulence processes,and the sediment transport model is based on a 3D equation for the re-suspended sediment transport.The computation results show that the areas of sediment concentration and transport(whether by resuspension or by the bedload) depend mainly on the position,the speed of the ship in the waterways,the kinematics of ship-generated waves and on the return flows.Thus,a map of sediment distribution and the modes of sediment transport generated by the passage of the ship are presented.  相似文献   

Forest cover change assessment in conflict-affected areas of northwest Pakistan: the case of swat and shangla districts   总被引：2，自引：2，他引：0  

Faisal Mueen QAMER  Sawaid ABBAS  Rashid SALEEM  Khurram SHEHZAD  Hassan ALI  Hammad GILANI 《山地科学学报》2012,9(3):297-306

This study examines the spatial and temporal forest cover changes in Swat and Shangla districts to understand the deforestation pattern in context of the recent security conflict in these districts. We used multi-resolution satellite images to assess the long term deforestation from 2001 to 2009 and also to identify episodic forest cutting areas appeared during the conflict period of Oct. 2007 - Oct. 2008. There are only 58 ha of deforestation identified during the conflict period while 1268 ha of gross annual deforestation were assessed during last eight years. Most of the deforestation patches persist around the administrative boundaries at sub-district levels (tehsils) which can be attributed to ambiguity in unclear jurisdiction between the forest official. The results highlight that the forest cutting appeared in Swat and Shangla during the conflict period is not as significant when compared with the long term deforestation pattern in the area. On the one side the results of the study are supportive to the picture that emerges from international studies which report high rate of deforestation in the country and on the other side it negates any relation between the security situation and the increasing deforestation in the north western Pakistan. The study concludes that deforestation assessments require verification by independent sources of data, such as satellite imagery to improve our understanding of deforestation processes.  相似文献   

Agrobiodiversity of Muda Rice Agroecosystem:A case Study in Largest Granary Area of Malaysia     

Amir Shah Ruddin Md Shah　Mashhor Mansor　Shahrul Anuar Mohd Shah　Che Salmah Mohd Rawi　Abu Hassan Ahmad　Ibrahim Jaafar 《湿地科学》2008,6(1):34-44

A survey was carried out at the largest rice cultivation area in Peninsular Malaysia,the Muda rice agroecosystem.The main objective of this study was to document the overall biodiversity associated with this unique agroecosystem by using a combination of sampling techniques in order to record different groups of fauna and flora.The total number of biota recorded and identified from the rice field ecosystem during the study period consisted of 46 species of zooplankton,81 species of aquatic insects,5 species of rodents,7 species of bats,87 species of birds,11 species of fishes and 58 species of weeds.A long-term study should be carried out as more species are expected to be recorded when more of the Muda rice agroecosystem area has been sampled to obtain sufficient information on the Muda rice agrobiodiversity.  相似文献   

Temperature Sensitivity and Soil Organic Carbon Pools Decomposition under Different Moisture Regimes: Effect on Total Microbial and Enzymatic Activity          下载免费PDF全文

Waseem Hassan  Rizwana Bano  Bashir Ullah Khatak  Imtiaz Hussain  Mohummad Yousaf  Julie David 《洁净——土壤、空气、水》2015,43(3):391-398

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Geology and petrography of the Nagar Parkar igneous complex,southeastern Sindh,Pakistan: The Kharsar body     

M. Qasim Jan  M. Hassan Agheem  Amanullah Laghari  Suhail Anjum 《Journal of the Geological Society of India》2017,89(1):91-98

Kharsar hill is one of many granitic plutons comprising the Nagar Parkar igneous complex. The eastern part of the hill is occupied by grey-pink granite (earlier) and the western part by pink granite (later). They are composed of perthite, quartz, and plagioclase, with minor opaque oxide, biotite, titanite, local amphibole, and secondary chlorite, epidote, leucoxene/titanite. The pink granite is characterized by the presence of mafic clots. Both the granitoids are intruded by microgranite/aplite, and porphyritic mafic and rhyolite dykes, locally in swarms. These are abundant in a NE trending 200 m wide zone cutting the entire granite hill. The dykes may extend over 1 km in length and >10 m in thickness, but most are < 100 m in length. The felsic dykes are of several generations; some are associated with the two varieties of granite, others are contemporaneous with the rhyolite and mafic dykes. The mafic dykes can be grouped into two types one of which contains hornblende and the other augite as the principal mafic mineral. Major element analyses suggest that the granitic rocks are metaluminous. The Kharsar granites, like the others in Nagar Parkar, may be an extension of the Malani igneous suite of Rajasthan. The occurrence of bimodal mafic-felsic dykes and petrographic variation in the mafic dykes are briefly discussed.  相似文献   

Use of remote sensing data in comprehending an extremely unusual flooding event over southwest Bangladesh     

Chowdhury  Ehsan H.  Hassan  Quazi K. 《Natural Hazards》2017,88(3):1805-1823

Natural Hazards - Flooding is one of the natural disasters that affect the livelihood of the people living in the floodplains, like Bangladesh. Here, we proposed to employ SAR satellite images in...  相似文献   

Landslide susceptibility analysis with a bivariate approach and GIS in Northern Iran   总被引：3，自引：3，他引：0  

Ataollah Kelarestaghi  Hassan Ahmadi 《Arabian Journal of Geosciences》2009,2(1):95-101

Globally, landslides cause hundreds of billions of dollars in damage and hundreds of thousands of deaths and injuries each year. A landslide susceptibility map describes areas where landslides are likely to occur in the future by correlating some of the principal factors that contribute to landslides with the past distribution of landslides. A case study is conducted in the mountainous northern Iran. In this study, a landslide susceptibility map of the study area was prepared using bivariate method with the help of the geographic information system. Area density (bivariate) method was used to weight landslide-influencing data layers. An overlay analysis is carried out by evaluating the layers obtained according to their weight and the landslide susceptibility map is produced. The study area was classified into five hazard classes: very low, low, moderate, high, and very high. The percentage distribution of landslide susceptibility degrees was calculated. It was found that about 26% of the study area is classified as very high and high hazard classes.  相似文献   

Evaluation of Bioavailability and Partitioning of Aluminum in Sediment Samples of Different Ecosystems by Modified Sequential Extraction Methods     

Sumaira Khan  Tasneem G. Kazi  Muhammad B. Arain  Nida F. Kolachi  Jameel A. Baig  Hassan I. Afridi  Abdul Q. Shah 《洁净——土壤、空气、水》2013,41(8):808-815

Sequential extraction procedures are widely used to characterize the different operational fractions with different potential toxicity of metals in environmental solid samples. The present work describes the application of different analytical approaches for sequential extraction of aluminum to evaluate its mobility, availability, and persistent chemical forms in sediment samples of different fresh water ecosystems (lake, canal, and river). The conventional BCR three‐stage sequential extraction procedure (C‐BCR) was modified at each stage, by applying ultrasonic device (U‐BCR), in order to shorten the required shaking time of 16 h for each three steps (excluding the hydrogen peroxide digestion in step 3, which was not performed with ultrasonic bath), could be completed in 40, 50, and 45 min, respectively. The aluminum in all extracts were determination by atomic absorption spectrometry using nitrous oxide – acetylene flame. The accuracy of results obtained from C‐BCR and proposed U‐BCR was verified with literature reported values of certified sediment sample (BCR 701). The overall recoveries of aluminum obtained by proposed U‐BCR were found in the range of 96.7–113% of those values obtained with C‐BCR for all fractions. Use of ultrasonic device, provided a large saving in extraction time relative to conventional shaking. It was observed that major part of Al in real sediment samples (80–83% of total Al) were bound to residual fraction. The acid soluble fraction of aluminum extracted by 0.11 mol/L CH₃COOH has good correlation with aluminum content in corresponding water samples of each ecosystem.  相似文献   

INCOMING LONGWAVE RADIATION ENHANCEMENT BY CLOUD COVER     

Ibrahim M. Oroud  Hassan A. Nasrallah 《自然地理学》2013,34(3):256-270

The effect of cloud cover on incoming longwave radiation reaching the ground surface is investigated using an analytic procedure. Results show that the contribution of a cloud deck depends not only on cloud type, but also on cloudless emissivity. The widely accepted notion that the enhancement factor for a cloud deck depends only on the cloud type is misleading and could lead to inconsistent results. Results in this paper explain the difference between observed and empirically derived incoming longwave radiation during overcast conditions in cold and mountainous regions. The effect of cloudless emissivity should be taken into account to represent adequately the contribution of cloud cover on incoming longwave radiation. The enhancement factor of all cloud types spans a wide range; it reaches its maximum values during dry atmospheric conditions and diminishes, almost linearly, as atmospheric humidity increases. The difference in the enhancement factor could reach as much as 100%. [Key words: longwave radiation enhancement, cloud contribution, clear-sky emissivity, atmospheric radiation, cloud emissivity.]  相似文献