Geomorphic control on the formation of mixed layer clays by progressive degradation of biotite: A case study from Jutulsessen Gjelsvikfjella,East Antarctica     

Kamlesh Verma  Sanjeeb Bhattacharya  A. M. Asim Ansari  Prakash K. Srivastava  Amit Dharwadkar 《Journal of the Geological Society of India》2014,83(5):532-534

Eleven glacial sediment samples collected from different elevation of Jutulsessen Nunatak, Gjelsvikfjella of East Antarctica were studied for the clay mineralogical analysis using X-ray diffraction technique. The result shows prominent peak at 10, and 3.34 Å suggesting the presence of biotite possibly derived from the catchment where biotite rich granite gneisses are exposed. The detailed investigation on the shape of biotite peak of certain samples shows the signs of alteration of biotite in to a mixed layer containing tri-octahedral smectite (low charge vermiculite). The presence of mixed layer along with the biotite is found to be associated with the samples of lower geomorphic level. The progressive alteration of clay sized biotite to form a mixed layer in the lower horizons of Jutulsessen Nunatak is probably due to the periodic accumulation of melt-water during the austral summer.  相似文献   

Spatio-temporal variation in radon concentration in groundwater with respect to rock types: A case study from Chitradurga district,Karnataka   总被引：1，自引：0，他引：1  

P. Ravikumar  Deljo Davis  Sharika Mathew  R. K. Somashekar  K. L. Prakash 《Journal of the Geological Society of India》2014,83(2):156-164

An attempt was made in the present study to delineate how the radon concentrations vary with respect to different geological formations and to evaluate annual effective dose exposure due to ingestion of radon. A total of 60 groundwater samples were collected from layered sequential aquifers in Chitradurga district having major rock types such as Bababudan Group, Charnockite, Chitradurga Group, Closepet granite, migmatites and granodiorite — tonalitic gneisses and Sargur Schist complex during pre-monsoon and post-season of the year 2011. Radon measurement was made using Durridge RAD-7 radon-in-air monitor, connected to RAD H₂O accessory with closed loop aeration concept. In the present study, the radon activity ranged from 0 to 186.6 Bq/L and 0 to 150.6 Bq/L during pre- and post-monsoon seasons of the year 2011, with 56.67 % (17 samples) of samples during both the seasons exceeding the EPA’s MCL value of 11.1 Bq/L. The annual mean radon activity in the groundwater was higher in the area having Chitradurga rock group formations (78.1 Bq/L) followed by Sargur-Satyamangalam schist complex group (56.8 bq/L), migmatites and granodiorite — tonalitic Gneisses group (56.3 Bq/L), Closepet granite (42.7 Bq/L), Charnonkite (29.1 Bq/L) and Bababudan Group (22.2 Bq/L). It is inferred that radon concentration found to depend on the tectonic structure, geology of the area and on the presence of uranium minerals in these rocks. The annual effective dose resulting from radon in groundwater in the Chitradurga district were significantly lower than UNSCEAR and WHO recommended limit of 1 mSv/y.  相似文献   

An assessment of wind forcing impact on a spectral wave model for the Indian Ocean     

P G Remya  Raj Kumar  Sujit Basu 《Journal of Earth System Science》2014,123(5):1075-1087

The focus of the present study is the assessment of the impact of wind forcing on the spectral wave model MIKE 21 SW in the Indian Ocean region. Three different wind fields, namely the ECMWF analyzed winds, the ECMWF blended winds, and the NCEP blended winds have been used to drive the model. The wave model results have been compared with in-situ observations and satellite altimeter data. This study also evaluated the performance of the wind products during local phenomenon like sea breeze, since it has a significant impact on the wave prediction in the Indian coastal region. Hence we explored the possibility of studying the impact of diurnal variation of winds on coastal waves using different wind fields. An analysis of the model performance has also been made during high wind conditions with the inference that blended winds generate more realistic wave fields in the high wind conditions and are able to produce the growth and decay of waves more realistically.  相似文献   

Simulation of severe thunder storm event: a case study over Pune,India     

S. Fadnavis  Medha Deshpande  Sachin D. Ghude  P. Ernest Raj 《Natural Hazards》2014,72(2):927-943

Numerical simulation of a typical tropical thunder storm event at Pune (18.53°N, 73.85°E), India, has been performed using the three nested domain configuration of Weather Research and Forecasting-Advanced Research Weather Model (version 3.2). The model simulations have been compared with observations. Sensitivity to cumulus parameterization schemes, namely Betts–Miller (BM), Grell–Devenyi (GD), and Kain–Fritsch (KF), for simulation of vertical structure and time evolution of weather parameters has been evaluated using observations from automatic weather station and global positioning system radiosonde ascents. Comparison of spatial distribution of 24-h accumulated rain with Tropical Rainfall Measuring Mission data shows that BM scheme could simulate better rain than GD and KF schemes. The BM scheme could well simulate the development of storm and heavy rain as it could generate sufficiently humid and deep layer in the lower and middle atmosphere, along with co-existence of updrafts and downdrafts and frozen hydrometeors at the middle level and rain water near the surface.  相似文献   

Weathering and mineralogical variation in gneissic rocks and their effect in Sangrumba Landslide,East Nepal     

Amar Deep Regmi  Kohki Yoshida  Megh Raj Dhital  Biswajeet Pradhan 《Environmental Earth Sciences》2014,71(6):2711-2727

Sangrumba landslide is one of the largest and the most active landslides in Nepal Himalaya. Geologically the landslide belongs to the Higher Himalaya and consists of Pre-Cambrian biotite–garnet and sillimanite gneiss with some quartzite. The present paper aims at describing various degrees of rock weathering and their effect in Sangrumba landslide. Field study followed by mineralogical, geochemical and geotechnical analyses of the collected rock and soil samples from the landslide zone were used in characterizing weathering degree. The gneisses are intensely weathered while quartzite is unweathered. Petrographical and X-ray diffraction analyses showed that the rocks in the landslide zone had undergone weathering process with the formation of different types of clay minerals as kaolinite, vermiculite, smectite and chlorite. This was further confirmed by the Scan Electron Microscope and Energy Dispersive X-ray analyses. These clay minerals drastically reduced the rock strength facilitating the extensive failure of the Sangrumba landslide. The major and trace element composition of the rock and soil samples was calculated from the XRF analyses. The geochemical analyses and weathering indexes of rocks showed that they are significantly weathered and had a major influence in the formation of the Sangrumba landslide. In addition, mechanical strength measurement of rock/soil showed that the strength drastically decreases as the weathering intensity increases. Rainfall followed by the rock type are the most dominant parameters influencing the weathering process which leads to the formation of large landslide as the present one. These findings can be used in other areas with similar geological and topographical conditions.  相似文献   

GPR survey and physical measurements of sea ice in Quilty Bay,Larsemann hills,East Antarctica and its correlation with local atmospheric parameters     

Mohd Yunus Shah  Kato K. Ayemi  Prakash Kumar Shrivastava 《Journal of the Geological Society of India》2017,90(3):371-377

Sea ice formation in Quilty Bay, East Antarctica shows a strong relationship with climatic conditions and its spatial variation is established by GPR survey over the sea ice during the austral winters. The study also evaluates the variability of sea ice thickness and extent with local weather parameters between 2010 and 2014. Profiling on sea ice in Quilty Bay shows that sea ice thickness decreases gradually towards east. The overall thickness of sea ice is considerably less at the centre of the bay as compared to the coastal side. Two types of fast ice layers have been delineated from GPR surveys i.e. top layer fast ice which incorporates very low density surface snow and underlying high density fast ice i.e. with melt water pockets. Development of sea ice is influenced by persistent easterly winds, temperature fluctuations and ocean currents. Sea ice reveal average annual cyclic trend in Quilty Bay with maximum development in the year 2013 (157.54 cm) and the minimum development has been observed in the year 2010 (99.04 cm).The cyclic pattern of average sea ice accumulation data show perfect inverse correlation with surface air temperature, with measure of reliability R² = 0.93. However, moderate (R² = 0.52) and good (R² = 0.69) degree of inverse relationship is observed with surface snow and overall sea ice (snow and ice) respectively. With 0.46 °C change in temperature, there is 33% change in sea ice condition in Quilty Bay which may remain same as far as ice extents in the region. Besides this easterly winds play a vital role in controlling the snow/ice distribution patterns as reflected by isopach maps.  相似文献   

Shake Table Tests and Numerical Modeling of Liquefaction of Kasai River Sand     

Raj Banerjee  Sanku Konai  Aniruddha Sengupta  Kousik Deb 《Geotechnical and Geological Engineering》2017,35(4):1327-1340

As a part of the seismic safety evaluation of several bridges and other hydraulic structures located on Kasai River bed in India, the liquefaction potential of Kasai River sand is studied in 1-g shake table in laboratory and numerically using a commercial software FLAC 2D. The surface settlement, lateral spreading, predominant frequency, amplification of the ground motion and pore water pressure development in Kasai River sand in dry and liquefied states have been studied when subjected to sinusoidal motions of amplitude 0.35 g at a frequency of 2 Hz. The nonlinear curves used to represent shear strain dependency of stiffness and damping ratio of Kasai River sand are obtained from cyclic triaxial tests. Reasonably good agreement between the experimental and the numerical results is observed. It is found that the settlement and lateral spreading for the liquefied sand is 2.60 and 2.50 times than those of the sand in the dry state. The volumetric strain of the liquefied sand is found to be around 4%, which is significantly higher than 1.53% observed in the dry sand. It is observed that the amplification of the peak ground acceleration for the saturated sand is 1.08 and 1.32 times higher than that for the dry sand from theoretical and experimental results, respectively. The shear strain developed in the liquefied sand is 1.17 times more than that for dry sand. The fundamental and higher modal frequencies of dry sand are found to be 1.13, 1.117 and 1.119 times more than those for the saturated sand, respectively.  相似文献   

Groundwater appraisal of Dhekiajuli,Assam, India: an insight of agricultural suitability and arsenic enrichment     

Latu Khanikar  Rashmi Rekha Gogoi  Nilotpal Das  Jyoti Prakash Deka  Aparna Das  Manish Kumar  K. P. Sarma 《Environmental Earth Sciences》2017,76(15):530

The present work is an effort to develop an appraisal of the hydrogeochemical regime for the aquifers of Dhekiajuli, Sonitpur district, Assam, which is imperative considering: (i) excessive use of groundwater for irrigation; (ii) reported high arsenic (As) contamination; (iii) application of fertilizer is an inevitable process undergoing in this region to achieve higher yield owing to deteriorating water quality; and (iv) study area being the location of many tea estates of Assam, that export tea in many foreign countries. The highest As concentration of 44.39 µg/L was detected in this study (Bachasimalu and Sitalmari region), implying high As-contaminated aquifers being used for drinking and irrigation purposes in the area. The relative abundance pattern of major cations and anions was in the order of Na⁺ > Mg²⁺ > Ca²⁺ > K⁺ and HCO₃ ^? > Cl^? > SO₄ ^2?, respectively. Majority of the samples belong to Na⁺–K⁺–Cl^?–HCO₃ ^? and mixed water type. Closer inspection of Piper plot reveals that a higher As value (>40 µg/L) was prevalent in HCO₃ ^? water type. Results of hydrogeochemical plots suggest silicate and carbonate weathering, ion exchange and anthropogenic activities to be the dominant processes governing groundwater contamination, including As which is further supported from PCA loadings. The Singri area to the east of the affected areas and adjacent to the Brahmaputra River has oxic aquifers owing to the absence of mass deposition of younger sediments, while reducing conditions prevails in the Bachasimalu and Sitalmari region. High positive correlation between As and Fe (r = 0.83**) and a negative correlation between ORP and Fe (r = ?0.68**) further add that Fe (hydr)oxides are the direct source of As release in the affected region, the mechanism being reductive hydrolysis of such (hydr)oxides. The study implies that although groundwater is suitable for irrigation use, there is a high probability of As getting into the food chain through tea and other edible plants irrigated with As-contaminated water; thus, the area has a maximum probability of facing health hazards caused by As-contaminated groundwater.  相似文献   

Diversity,composition and host-species relationships of epiphytic orchids and ferns in two forests in Nepal   总被引：1，自引：0，他引：1  

Yagya P. Adhikari  Anton Fischer  Hagen S. Fischer  Maan B. Rokaya  Prakash Bhattarai  Axel Gruppe 《山地科学学报》2017,14(6):1065-1075

Epiphytic plant species are an important part of biological diversity. It is therefore essential to understand the distribution pattern and the factors influencing such patterns. The present study is aimed at observing the patterns of species richness, abundances and species composition of epiphytic orchids and ferns in two subtropical forests in Nepal. We also studied the relationship of host plants (Schima wallichii and Quercus lanata) and epiphyte species. Data were collected in Naudhara community forest (CF) and the national forest (NF) in Shivapuri Nagarjun National Park. The data were analyzed using univariate and multivariate tests. In total, we recorded 41 species of epiphytes (33 orchid and 8 fern species). Orchid species abundance is significantly higher in CF compared to NF. Orchid species richness and abundance increased with increasing southern aspect whereas it decreased with increasing canopy cover, and fern species richness increased with host bark roughness. Orchid abundance was positively correlated with increasing bark pH, stem size, tree age and tree height and negatively correlated with increasing steepness of the area. Likewise, fern abundances were high in places with high canopy cover, trees that were tall and big, but decreased with increasing altitude and southern aspect. The composition of the orchid and fern species was affected by altitude, aspect, canopy cover, DBH, number of forks and forest management types. We showed that the diversity of orchid and fern epiphytes is influenced by host characteristics as well as host types. The most important pre-requisite for a high epiphyte biodiversity is the presence of old respectively tall trees, independent of the recent protection status. This means: (i) for protection, e.g. in the frame of the national park declaration, such areas should be used which host such old tall trees; and (ii) also in managed forests and even in intensively used landscapes epiphytes can be protected by letting a certain number of trees be and by giving them space to grow old and tall.  相似文献   

A novel insight into vertical ground motion modelling in earthquake engineering     

Luca Prakash Argani  Alessandro Gajo 《国际地质力学数值与分析法杂志》2022,46(1):164-186

Recent observations of failure and damage of buildings and structures under seismic action has led to an increasing interest for an in-depth analysis of the vertical component of site ground motion. In particular, when dealing with saturated soils, the current engineering practice does not usually go beyond the simplified $u$–$p$ formulation of the Biot's equations describing the coupled hydro-mechanical behaviour, thus neglecting some terms of fluid inertial forces, despite the presence of more refined formulations, for example, the $u$–$U$ formulation. Therefore, a theoretical and numerical validation of the $u$–$p$ formulation as compared with the $u$–$U$ formulation is proposed in this work, where the numerical simulations are compared with the analytical solution for the $u$–$p$ formulation, which is also derived and illustrated in this text. The comparison between the two formulations and the analytical solution is provided for different levels of permeability and dynamic actions, which are representative of a wide scenario of site ground properties and seismic hazard in the vertical direction. In particular, the soil response is analysed in terms of acceleration and pore pressure time history, frequency content, acceleration response spectrum, and amplification ratio of acceleration. This study extends the discussion of the limits of applicability of the $u$–$p$ formulation with respect to the rigorous solution of Biot's equations (obtained here with $u$–$U$ formulation) to the context of a complex dynamic regime provided by the vertical components of real earthquake records, and paves the way for further investigations.  相似文献