Contributions of the IGU and ICA commissions in population studies

This paper surveys the contributions of the International Geographic Union (IGU) and the International Cartographic Association (ICA) to the field of population studies over the past 3 decades. Reviewing the various focal themes of conferences sponsored by the organizations since the 1960s, the author examines the evolution of population studies in IGU and ICA. During the 1960s, IGU began holding symposia addressing the issue of population pressure on the physical and social resource in developing countries. However, it wasn't until 1972, at a meeting in Edmonton, Canada, when IGU first addressed the issue of migration. But since then, migration has remained on the the key concerns of IGU. In 1978, the union hosted a symposium on Population Redistribution in Africa -- the first in a series of conferences focusing on the issue of migration. As an outgrowth of migration, the IGU also began addressing the related issue of population education. The interest in migration has continued through the 1980s. In addition to studies of regional migration, the IGU has also focused on conceptual issues such as migrant labor, environmental concerns, women and migration, and urbanization. In 1984, IGU began cooperating with ICA in the areas of census cartography and population cartography. The author concludes his review of IGU and ICA activities by discussing the emerging trends in population studies. The author foresees a more refined study of migration and more sophisticated population mapping, the result of better study techniques and the use of computer technology.     

Influence of rock types and structures in the development of drainage network in hard rock area

Remote sensing techniques has proved to be an extremely useful tool in morphometric analysis and groundwater studies. Remote sensing techniques with an emphasis on lineament identifications can play a great role in groundwater prospecting in semi-arid hard rock areas of Purulia district. In the present study, morphometric analysis using remote sensing technique has been carried out in parts of Baghmundi block, Purulia district, West Bengal. The parameters worked out include Bifurcation ratio (R_b), Stream length (L_u), Form factor (R_c), Circulatory ratio (R_c), and Drainage density (D). The morphometric analysis suggests that fractured, resistant, permeable rocks cover the area, the drainage network not so affected by tectonic disturbances. Using satellite imageries of two dates of IRS, different hydrogeomorphological units have been delineated. Among different hydrogeomorphic units (i) very shallow weathered pediment and (ii) Structural hills/ residual hills/inselbergs have very poor ground water prospects, while moderately weathered pediplains and valley fills are good prospective zones for groundwater exploration.     

Periodicity in the Basal Component of Radio Emission During Maximum and Minimum Solar Activity

The basal component of radio emission is the radio intensity obtained after subtracting the sunspot-dependent (magneto-active) component from the observed flux and finally deducting the steady part from this subtracted value. The periodicity of this basal component of solar radio emission in the frequency band 0.245–15.4 GHz was studied both for the solar maximum (1980 and 1991) and minimum (1975 and 1986) periods. A constant periodicity of 35 days was observed in the entire radio band under study during the periods of maximum solar activity, whereas the periodicity fluctuates harmonically with frequency during the minimum periods, giving rise to an average time period of approximately 54 days.     

On the propagation of Rayleigh waves in three dimensions in alluvial soils

Summary The propagation of Rayleigh waves in three dimensions in alluvial soils which do not behave like ordinary isotropic elastic solids have been discussed in this paper. The frequency equation has been solved for different soil constants.     

Application of lineament density and hydrogeomorphology to delineate groundwater potential zones of Baghmundi block in Purulia District, West Bengal

Groundwater being a valuable resource in today’s world needs proper evaluation and management for overall development within the region for its judicious use. The Baghmundi Block of Purulia district, West Bengal is within the hard rock terrain of Ayodhya hills and Matha Protected forest. The groundwater in this region is confined within the fracture zones and weathered residuum. Hydrogeomorphologically, the entire area is classified into following categories such as - i) Very shallow weathered pediment, ii) Moderately weathered pediment, iii) Valley fills, iv) Erosional gullies, v) Lateritic Upland and vi) Accumulation gullies. The hydrogeomorphic map of the area prepared by Department of Science and Technology, Govt. of West Bengal has been digitized for the present study. The lineament map has been prepared from the satellite imagery. The lineament map has also been digitized for the present study. From this the lineament density contour map has been prepared. An integrated remote sensing and Geographic Information System (GIS) based methodology has been used for the delineating Groundwater potential zones in the study area. Here the Geomorphology and Lineament density maps are overlaid following the Weighted Index Overlay Method, which delineates groundwater potential zones.     

Alkaline basic intrusives of Elchuru,Prakasam District,Andhra Pradesh,India

The igneous alkaline rocks at Elchuru start from a parent ijolite-melteigite association to basic malignite, melalusitanite and shonkinite followed by nepheline syenites and then biotite lamprophyres (as dykes) at the waning phase of the evolutionary course of the complex. The distinct alkalinity of the rocks is manifested by the development of modal nepheline and calcic amphibole (kaersutite). For both the basic rocks,i.e. alkali gabbro and biotite lamprophyre, the percentages of normative nepheline are always higher than modal nepheline, indicating silica deficiency and alkali enrichment of the mafics. It is evident from detailed petrological and geochemical studies that the two basic members are very much akin to each other and there is no major deviation in their bulk chemistry.     

Volcanology and lava flow morpho-types from the Koyna-Warna region,western Deccan Traps,India

Flow mapping and physical volcanology of 15 basaltic lavas exposed in three critical road pass sections (ghats) in the Koyna-Warna region of the western Deccan Traps is presented in this paper. Transitional lavas like rubbly pahoehoe are most common morpho-type exposed in these ghat sections. Sinking of rubbly breccia into flow interiors and formation of breccia-cored rosette are common in some lava flows. Few rubbly lavas exhibit slabby tendencies. The amount and nature of the associated rubble is variable and result from the mechanical fracturing and auto-brecciation of the upper vesicular crust in response to distinctive stages in the cooling, crystallization and emplacement history of individual lava flows. Occurrence of aa and pahoehoe morpho-types in the lava flow sequence is subordinate. Three prominent pahoehoe flows separated by red bole horizons are seen in the upper parts of the Kumbharli ghat. These are thick, P-type sheet pahoehoe. The pahoehoe lavas represent compound flow fields that grew by budding, endogenous lava transfer and inflation. Presence of pahoehoe lavas in the Koyna-Warna region hints at possible hitherto unrecorded southern extension of Bushe-like flow fields. This study reconfirms the existence of pahoehoe-slabby-rubbly-aa flow fields and transitions even in the upper echelons of the Deccan Trap stratigraphy. The study of morphology and internal structure of lava flows exposed at the ghat sections in the Koyna-Warna region could guide subsurface core-logging that is critical in deciphering the physical volcanology and emplacement dynamics of basaltic lava flows penetrated by drill holes sunk under the scientific deep drilling programme.