Engineering aspects of obtaining clear seawater from the muddy shores

On some shores the seawater is muddy, contaminated with fine silt and clay in suspension. If it became necessary to use such seawater it would be essential either to resort to filtration or to allow for settling of soil sediments. The present scheme was undertaken with a view to providing clear seawater for experimentation in growing crops and plants with seawater. The system consisted of a filtration unit embedded in the shore over which the tidal water passes. The clear water is run through a conveying assembly and is stored in a sump for end uses. The design, construction materials and construction operation of such a device on coastal sand dunes has been described in detail. The precautions to be taken under such circumstances are also given.     

Rounding of pumice clasts during transport: field measurements and laboratory studies

Volcanic clasts in many pyroclastic density current deposits are notably more round than their counterparts in corresponding fall deposits. This increase in roundness and sphericity reflects different degrees of comminution, abrasion and breakup during transport. We performed experimental measurements to determine an empirical relationship between particle shape and mass loss caused by particle–particle interactions. We consider, as examples, pumice from four volcanoes: Medicine Lake, California; Lassen, California; Taupo, New Zealand; Mount St Helens, Washington. We find that average sample roundness reaches a maximum value once particles lose between 15% and 60% of their mass. The most texturally homogeneous clasts (Taupo) become the most round. Crystal-rich pumice abrades more slowly than crystal-free pumice of similar density. Abrasion rates also decrease with time as particles become less angular. We compare our experimental measurements with the shapes of clasts in one of the May 18, 1980 pyroclastic density current units at Mount St Helens, deposited 4–8 km from the vent. The measured roundness of these clasts is close to the experimentally determined maximum value. For a much smaller deposit from the 1915 Lassen eruption, clast roundness is closer to the value for pumice in fall deposits and suggests that only a few volume percent of material was removed from large clasts. In neither field deposit do we see a significant change in roundness with increasing distance from the vent. We suggest that this trend is recorded because much of the rounding and ash production occur in proximal regions where the density currents are the most energetic. As a result, all clasts that are deposited have experienced similar amounts of comminution in the proximal region, and similar amounts of abrasion as they settle through the dense, near-bed region prior to final deposition.     

Stratigraphy and Sedimentology of Middle Jurassic Sequence of Chorar Island,Patan District,Kachchh Basin,Gujarat

Chorar Island exposes ～109 m thick middle Jurassic (Bathonian-Callovian) succession in the eastern most part of the Kachchh Basin, Patan District, Gujarat and is divided into two, Khadir and Gadhada formations. It mainly comprises of mixed siliciclastic-carbonate sediments and limestones; the shales dominate the lower part of the succession while the top of the succession is marked by ferruginous sandstone which also forms the vast, prominent peripheral zone of the Chorar dome. The field and laboratory analysis of the succession reveals nine lithofacies which includes ferruginous sandstone, cross bedded white sandstone, micritic sandstone, allochemic sandstone, sandy micrite, mudstone, sandy allochemic limestone, coralline limestone and shale. The mix siliciclastic-carbonate sediments and ferruginous facies are fossiliferous in nature and display sedimentary structures, like ripple marks, cross- and planar- lamination with biogenic sedimentary structures. Coralline limestone facies comprise of large size (>1m diameter) corals, which are diagenetically modified severely and have lost its original internal structures. The sediment characteristics and associated bioclasts indicates low to moderate wave and current energy in shoreface-offshore subsequently changing to wave dominated shoreface during the deposition of the middle Jurassic sediments of the Chorar Island.     

Spitzer space telescope observations of SGR and AXP environments

Both Anomalous X-ray Pulsars (AXPs) and Soft Gamma Repeaters (SGRs) are thought to be manifestations of magnetars. However, the specific physical characteristics that differentiate the two classes of objects remain unclear. There is some evidence that the progenitors of these sources and/or the environment in which they form might influence the type of phenomena the resulting magnetar displays. Several of the AXPs appear to be associated with supernova remnants, while embedded clusters of massive stars have been found in the immediate vicinity of some SGRs. Since both AXPs and SGRs are distributed close to the Galactic plane, high extinction makes studies in the optical difficult. We present early results from our Spitzer program aimed at probing the environmental factors that might contribute to the difference in the observed characteristics between AXPs and SGRs.     

Breccia-cored columnar rosettes in a rubbly pahoehoe lava flow,Elephanta Island,Deccan Traps,and a model for their origin

Rubbly pahoehoe lava flows are abundant in many continental flood basalts including the Deccan Traps. However, structures with radial joint columns surrounding cores of flow-top breccia (FTB), reported from some Deccan rubbly pahoehoe flows, are yet unknown from other basaltic provinces. A previous study of these Deccan “breccia-cored columnar rosettes” ruled out explanations such as volcanic vents and lava tubes, and showed that the radial joint columns had grown outwards from cold FTB inclusions incorporated into the hot molten interiors. How the highly vesicular (thus low-density) FTB blocks might have sunk into the flow interiors has remained a puzzle. Here we describe a new example of a Deccan rubbly pahoehoe flow with FTB-cored rosettes, from Elephanta Island in the Mumbai harbor. Noting that (1) thick rubbly pahoehoe flows probably form by rapid inflation (involving many lava injections into a largely molten advancing flow), and (2) such flows are transitional to ‘a’ā flows (which continuously shed their top clinker in front of them as they advance), we propose a model for the FTB-cored rosettes. We suggest that the Deccan flows under study were shedding some of their FTB in front of them as they advanced and, with high-eruption rate lava injection and inflation, frontal breakouts would incorporate this FTB rubble, with thickening of the flow carrying the rubble into the flow interior. This implies that, far from sinking into the molten interior, the FTB blocks may have been rising, until lava supply and inflation stopped, the flow began solidifying, and joint columns developed outward from each cold FTB inclusion as already inferred, forming the FTB-cored rosettes. Those rubbly pahoehoe flows which began recycling most of their FTB became the ‘a’ā flows of the Deccan.     

Plug shaped burrows <Emphasis Type="Italic">Conichnus - Conostichus</Emphasis> from the Late Cretaceous of Bagh Group,Gujarat, western India

Plug-shaped ichnofossils Conichnus conicus, Conostichus broadheadi and C. stouti are found in the intercalated micritic sandstone and sandy allochemic limestone shale sequence of Bagh Group, Narmada district, Gujarat. These ichnospecies occur at two stratigraphic levels and shows distinct morphological features interpreted as resting/dwelling structures of sea anemone. The occurrence of these ichnospecies along with oyster fossils genera like Bosostrea and Indostrea indicate shallow marine environment.     

Exhumation and its mechanisms: A review of exhumation studies in the Himalaya

Exhumation has been recognised as a key factor in understanding the dynamics of a mountain belt. Normal faulting, erosion and ductile thinning are the three basic mechanisms to exhume the deeper high grade metamorphic rocks to the surface. Convergent orogenic belts are characterised by over-thickening of the crust due to thrusting and folding. The interplay of uplift due to over-thickening of crust and climatic-erosion is the most plausible mechanism of exhumation as suggested by the numerical models and analogue experiments. The analysis of 534 thermo-chronological dates through 1D-thermal numerical model in the Himalaya suggest that the exhumation is dominantly due to erosion but the pattern of erosion is controlled by local tectonic activities in different sector of the Himalaya since Miocene, indicating that tectonic force as the prime mechanism of exhumation in Himalaya.     

National Wheat Acreage Estimation for 1995-96 Using Multi-Date IRS-1C WiFS Data

I he aim of the piesent study was to suggest an approach for national level acreage estimation for wheat using satellite remote sensing data and demonstrate its perfromantee Multi-date moderate resolution (188 m) IRS-IC WiFS data sets were used as the core data Sampie segment approach with stratified random sampling was used for the data analysis For making meaningful comparisons over time, multi-date sets were geometncally registered and radiometrically normalised by extracting pseudo-invariant Features and performing regression analysis on the digital numbers of such features The corrected multi-temporal data sets were used in hierarchical classification scheme. The results of this exercise are presented. It appeals that there is an overestimatoin of wheat acreage The sampling effieieney was also low, indicating need to improve sampling strategy Some of the problems encountered and the corrections planned to overcome them are also discussed