Laser depolarization studies of simulated crystallized H2O/H2SO4 clouds

Laboratory experiments were carried out to investigate the linear depolarization ratios (LDRs) of crystallized H₂O/H₂SO₄ acid clouds at angles of 45°, 135° and 157° to the forward direction. LDR is the ratio of the returned energies in the planes of polarization perpendicular and parallel to that of the source (Sassen, 1974). Experiments were carried out for different concentrations of aqueous solution of sulfuric acid. A cloud of supercooled droplets is formed inside an experimental chamber kept in a walk-in cold room by heating an aqueous solution of sulfuric acid, and the ice crystal formation is initiated by momentarily introducing a rod dipped in liquid nitrogen into the cloud. A 2-mW polarized He:Ne laser beam is directed through the cloud and a photomultiplier tube measures the scattered intensity. It is found that the scattered energy is higher in the direction of 157° and 135° than that at 45°. Microscopic examination of the crystals formed from acid concentrations above 50% shows dark fuzzy spots on the surface of the ice crystals suggesting that this could be a film of acid drops. This film also alters the shape of the crystals, and the crystal boundaries are no longer sharp and well defined like that observed for pure water clouds and this is found to influence the LDR.     

Earthquakes associated with the Clark Hill reservoir, South Carolina — A case of induced seismicity

Following the McCormick County, South Carolina, local magnitude 4.3 earthquake on August 2, 1974, continuous seismic activity has been observed in the area. The epicenters are located within 3 km from the Clark Hill reservoir. The shallow seismic activity appears to be related to water level fluctuations in the reservoir, and follows them by about two days. The frequency of earthquakes is related to the rate of change of water level, while the energy release is seen to depend on the water level itself. Pore pressure fluctuations at focal depths in a regime of high tectonic stresses is the suggested cause for the triggering of earthquakes.     

Estimation of Columbia River virgin flow: 1879 to 1928

The Columbia River is a major source of and conduit for Pacific Northwest economic activity, and is one of the more heavily modified rivers in North America. Understanding human and climate‐induced changes in its hydrologic properties is, therefore, vital. Long streamflow records are essential to determining how runoff has changed over time, and Columbia River daily streamflow record at The Dalles began in 1878. To understand and separate anthropogenic and climate effects, however, it is also necessary to have a basin‐scale estimate of virgin or naturalized flow. The United States Geological Survey has calculated a monthly averaged adjusted river flow at The Dalles for 1879–1999 that accounts for the effects of flow regulation. The Bonneville Power Administration has estimated the monthly averaged virgin flow at The Dalles, i.e. the flow in the absence of both flow regulation and irrigation depletion for 1929–89. We have estimated the monthly virgin flow of the Columbia River at The Dalles from records of irrigated area for the missing early years, i.e. for the period 1879–1928. In addition, to allow hindcasting of a virgin flow sediment transport for the system, a daily virgin flow index with realistic higher moments and spectral properties has been calculated. Examination of the virgin flow record shows that climate change since the late 19th century has decreased annual average flow volume by > 7%; irrigation depletion has reduced the flow by another ∼7%. Copyright © 2005 John Wiley & Sons, Ltd.     

Hydromechanics of the Koyna–Warna Region, India

Continuous reservoir-induced seismicity has been observed in the Koyna–Warna region in western India following the beginning of impoundment of Koyna and Warna Reservoirs in 1961 and 1985, respectively. This seismicity includes 19 events with M ≥ 5.0 which occurred in 7 episodes (I–VII) between 1967 and 2005 at non-repeating hypocentral locations. In this study, we examined the first six episodes. The seismicity occurs by diffusion of pore pressures from the reservoirs to hypocentral locations along a saturated, critically stressed network of NE trending faults and NW trending fractures. We used the daily lake levels in the two reservoirs, from impoundment to 2000, to calculate the time history of the diffused pore pressures and their daily rate of change at the hypocentral locations. The results of our analysis indicate that Episodes I and IV are primarily associated with the initial filling of the two reservoirs. The diffused pore pressures are generated by the large (20–45 m) annual fluctuations of lake levels. We interpret that critical excess pore pressures >~300 kPa and >~600 kPa were needed to induce Episodes I–III and Episodes IV–VI, respectively, suggesting the presence of stronger faults in the region. The exceedance of the previous water level maxima (stress memory) was found to be the most important, although not determining factor in inducing the episodes. The annual rise of 40 m or more, rapid filling rates and elevated dp/dt values over a filling cycle, contributed to the rapid increase in pore pressure.     

Tectonic Setting of the Kadiri Schist Belt, Andhra Pradesh, India

Plate tectonic activity has played a critical role in the development of petrotectonic associations in the Kadiri schist belt. The calc alkaline association of basalt, andesite, dacite and rhyolite(BADR) is the signature volcanic rock suite of the convergent margin. The N-S belt has gone below the unconformity plane of Cuddapah sediments. In the northern part geochemical and structural attributes of the Kadiri greenstone belt is studied along with microscopic observations of selected samples. Harker diagram plots of major elements generally indicate a liquid line of descent from a common source, such that BADR rocks are derived from a common parent magma of basaltic to andesitic composition. These calc-alkaline volcanic rocks are formed at convergent margins where more silicic rocks represent more highly fractionated melt. All the litho-units of this greenstone belt indicate crush and strain effects. The stretched pebbles in the deformed volcanic matrix with tectonite development along with associated greenschist facies metamorphism, alteration and hydration is remarkable. Flow foliation plane with N-S strike and very low angle(5° to 10°) easterly dip and N-S axial planar schistosity formed due to later phase isoclinal folding can be clearly identified in the field. Basic intrusives are quite common in the surrounding area. All the observations including the field setting and geochemistry clearly demonstrate ocean-continent subduction as the tectonic environment of the study area.     

Sugarcane crop identification from LISS IV data using ISODATA,MLC, and indices based decision tree approach

Image classification is one of the crucial techniques in detecting the crops from remotely sensed data. Crop identification and discrimination provide an important basis for many agricultural applications with various purposes, such as cropping pattern analysis, acreage estimation, and yield estimation. Accurate and faster estimation of crop area is very essential for projecting yearly agriculture production for deciding agriculture policies. Remote sensing is a technique that allows mapping of large areas in a fast and economical way. In many applications of remote sensing, a user is often interested in identifying the specific crop only while other classes may be of no interest. Indian Remote Sensing Satellite (IRS-P6) LISS IV sensor image of spatial resolution 5.8 m has been used to identify the sugarcane crop for the Chhapar village of Muzaffarnagar District, India. Classification of satellite data is one of the primary steps for information extraction for crop land identification. In recent years, decision tree approach to image analysis has been developed for the assessment and improvement of traditional statistically based image classification. In this study, ISODATA, MLC, and vegetation indices based decision tree approaches are used for classifying LISS IV imagery. The 11 vegetation index images have been generated for decision tree classification. All the three methods are compared and it is found that the best performance is given by the decision tree method. Vegetation indices based decision tree method for sugarcane classification, the user’s accuracy, producer’s accuracy, overall accuracy, and kappa coefficient were found 88.17, 86.59, and 87.93% and 0.86 respectively.     

Rapid visual screening of different housing typologies in Himachal Pradesh,India

Natural Hazards - Methods capable of assessing the vulnerability of houses for future earthquakes are of fundamental importance for the safety and development of an area. As the detailed assessment...     

Predictive modelling of rainfall-induced landslide hazard in the Lesser Himalaya of Nepal based on weights-of-evidence

Landslide hazard mapping is a fundamental tool for disaster management activities in mountainous terrains. The main purpose of this study is to evaluate the predictive power of weights-of-evidence modelling in landslide hazard assessment in the Lesser Himalaya of Nepal. The modelling was performed within a geographical information system (GIS), to derive a landslide hazard map of the south-western marginal hills of the Kathmandu Valley. Thematic maps representing various factors (e.g., slope, aspect, relief, flow accumulation, distance to drainage, soil depth, engineering soil type, landuse, geology, distance to road and extreme one-day rainfall) that are related to landslide activity were generated, using field data and GIS techniques, at a scale of 1:10,000. Landslide events of the 1970s, 1980s, and 1990s were used to assess the Bayesian probability of landslides in each cell unit with respect to the causative factors. To assess the accuracy of the resulting landslide hazard map, it was correlated with a map of landslides triggered by the 2002 extreme rainfall events. The accuracy of the map was evaluated by various techniques, including the area under the curve, success rate and prediction rate. The resulting landslide hazard value calculated from the old landslide data showed a prediction accuracy of > 80%. The analysis suggests that geomorphological and human-related factors play significant roles in determining the probability value, while geological factors play only minor roles. Finally, after the rectification of the landslide hazard values of the new landslides using those of the old landslides, a landslide hazard map with > 88% prediction accuracy was prepared. The methodology appears to have extensive applicability to the Lesser Himalaya of Nepal, with the limitation that the model's performance is contingent on the availability of data from past landslides.     

VLA Observations of Angular Broadening Close to the Sun

We present synthesis imaging of scatter-broadening of radio sources carried out using the Very Large Array (VLA) at six radio frequencies during the period of solar minimum. Three compact radio sources were observed from 2 to 16 solar radii around the sun. The data indicate highly anisotropic scattering. The scatter-broadening was estimated from the area of the scattered image and was found to be factor of two lower and orientation of magnetic fields was closer to the radial direction. Present observations confirm the variation of scatter-broadening with solar elongation. This revised version was published online in July 2006 with corrections to the Cover Date.     

A Petrological and Geochemical Account of Subsurface Noritic Intrusion in the Western Part of Bundelkhand Massif,Shivpuri District,M.P.

Subsurface exploration for uranium in the northwestern part of Bundelkhand massif, near Khor area, Shivpuri dist., M.P., resulted in intercepting a substantial thickness of mafic rock within Bundelkhand granitoid. Intercepts of this mafic rock at various levels in the boreholes, indicate that the rock mainly occurs as dykelike intrusion and fracture-fills within Bundelkhand granite. It is essentially composed of hypersthene and plagioclase, with or without olivine, leading to the characterisation as hypersthene microdolerite, noritic dolerite and norite (±olivine), depending on the grainsize and variation from intergranular to ophitic texture. Chemically, the rock is characterised by av. 49.09% SiO₂, 2.46%TiO₂, 2.33 Fe₂O₃, 9.45% FeO, 5.75% MgO, 8.37% CaO and 0.96% K₂O. The normative composition ranges from 3.53% quartz, 46.86% plagioclase, 12.58% diopside, 19.24% hypersthene. The olivine normative samples show av. 5.65% olivine. Geochemical plots indicate an intra-plate affinity along with oceanic signature, while presence of mineralogical and normative olivine, together with the REE pattern, point towards a lower crustal or mantle source. The mineralogical and normative presence of either quartz or olivine in these mafic rocks implies that it has an intermediate character between the tholeiitic dolerite dykes and the komatiite-type ultramafics reported from Bundelkhand craton. The complex geochemical signature of the rocks also reveals that both intra-continental as well as a mixture of oceanic- to upper mantle signatures are evident. The present study is a first time report of the occurrence of this hitherto unknown noritic body at depth within the Bundelkhand granite, which has no visible surface expression. The findings may strengthen the existing concept of a continuum between Rajasthan craton in the west and Bundelkhand craton in the east, as a single protocontinent.