Population pressure in rural Kenya

As an international problem of continuing significance in the underdeveloped world, population pressure foreshadows the future of many Third World countries. Kenya is one such country. Its deteriorating population-resource balances are set against a limited resource base and a demographically explosive growth rate. Although population pressure has yet to be surveyed fully, landlessness, soil erosion, deforestation, overgrazing and river siltation indicate worsening man-land relationships throughout rural Kenya. In an effort to determine the magnitude and extent of population pressure and to find solutions to its manifold consequences, the Kenya Rural Population Pressure Study will conduct an intensive two year program of research.     

Systematic use of trace element in igneous process

This paper describes an extended application of the Rayleigh distillation law to trace element behavior in a fractional crystallization sequence. Using a trace element with a very low bulk partition coefficient as a reference (as suggested by Anderson and Greenland, 1969, and extended by Treuil and Varet, 1973), we can derive bulk partition coefficients for other elements and, in turn, the mineralogical composition of the cumulates. Trace elements with large D, such as Ni and Cr, further constrain the system, and we can deduce the initial composition of the magma. An example of this technique is shown for Terceira Island in the Azores.Contribution IPGNS no 229Now at Dept. of Geological Sciences, California Institute of Technology, Pasadena, California, USA     

PbSrNd isotopic data of Indian Ocean ridges: new evidence of large-scale mapping of mantle heterogeneities

A PbSrNd isotope study of South West and East Indian Ridges confirms that the Indian Ocean belongs to a specific regional isotopic domain, as previously suggested by the results from islands of this ocean. The isotopic domain defined by the Indian MORB is indeed different from that of the North Atlantic and East Pacific Oceans. This demonstrates that the convective circulation of the upper mantle does not allow a rapid homogenization from one region to the other.The isotopic data of the Indian ridges can be interpreted by a contamination model, in which the depleted upper mantle (identical to that under the North Atlantic) is contaminated by two different types of contaminant, one corresponding to the source of the “central Indian Ocean” islands (Amsterdam, St. Paul, Marion, Prince Edward, Réunion, Rodriguez, Mauritius), and the other to a source similar to that of Walvis or Ninety East aseismic ridges. These two contaminants would have contributed to the ridge volcanism in different proportions over time.     

Natural gas seepage in the Gulf of Mexico

Hydrocarbon compositions and δ¹³C values for methane of fourteen natural seep gases and four underwater vents in the northwestern Gulf of Mexico are reported. The C₁/(C₂ + C₃) ratios of the seep gas samples ranged from 68 to greater than 1000, whereas δ_PDB¹³C values varied from ?39.9 to ?65.5‰. Compositions suggest that eleven of the natural gas seeps are produced by microbial degradation whereas the remaining three have a significant thermocatalytically produced component. Contradictions in the inferences drawn from molecular and isotopic compositions make strict interpretation of the origins of a few of the samples impossible.     

Characteristic distributions of angel echoes in the lower atmosphere and their meteorological implications

Analysis of a vast series of angel echo observations made by a millimetric vertically-pointing radar reveals four major types of echo organization on height-time recordings. The relationship between the formation and development of these structures and the thermodynamic state of the atmosphere is clarified. The meteorological indicator role played by angel echoes is then discussed. In particular it is shown that in certain conditions, angel echoes can delineate the boundaries of small cumulus.This work was sponsored by the Direction des Recherches et Moyens d'Essais, under contract 72.426 by the Délégation Générale à la Recherche Scientifique et Technique under contract 71.72.680.     

The Amsterdam-St. Paul volcanic province,and the formation of low Al tholeiitic andesites

The island of St. Paul in the Indian Ocean is located on the axis of the southeastern branch of the Indian Ocean Rise, as is the similar volcano of Amsterdam, 80 km to the north. Both volcanoes and possibly part of the local ridge are formed of a high-alumina plagioclase tholeiite making this a distinctive volcanic province. Lavas with Al₂O₂ contents of 12 to 22% are directly related by plagioclase fractionation. Residual rocks are a distinctive low silica, low alumina, potassic andesite with andesine and even olligoclase feldspar. Parallel lines of evolution exist in the sea floor plagioclase tholeiites, which differ only in slightly lower tenor of Sr and potassium group elements, and in the Steens Mountain tholeiites of Oregon, which differ in their significantly higher Sr and K group elements     

A morphometric analysis of terrace gravels in Santa Ynez basin,Santa Barbara County,California

An analysis of 6,300 pebbles from eighteen river terraces within the five subareas of the Santa Ynez River basin has revealed significant differences in particle sphericity and roundness of the various terrace gravels.Using the Cailleux technique of pebble measurement, Krumbein's sphericity ratio formula (Y) and the author's own roundness ratio or the I/L¹ ratio (R) the computed values derived for $\text{Y}$ range from 0.92 to 1.11, and for $\text{R}$ from 0.66 to 0.79 on these benches.An analysis of variance, based on the F-test applied to samples has established that: (a) gravel sphericity and roundness increase significantly from upstream to the river mouth; (b) in the subareas themselves pebble sphericity and roundness vary significantly from bench to bench indicating varied energy conditions of deposition; (c) all terrace gravels measured show higher sphericity and roundness than the underlying Orcutt gravels. This suggests a reworking of the latter by the Santa Ynez River.