Volcanic threat in developing countries of the Asia�CPacific region: probabilistic hazard assessment, population risks, and information gaps

The importance of disaster reduction has gained increased awareness within the international development community and thereby highlighted a need for a preliminary assessment of natural hazard risk in developing countries of the Asia?CPacific, including that for volcanic eruption. In this paper, we present a key component of such an assessment, which involved qualifying the frequency and potential consequences of large??Volcanic Explosivity Index of four or more??volcanic eruptions. The frequencies of large eruptions from volcanoes grouped by region were determined from frequency?Cmagnitude plots using data provided by the Smithsonian Institution??s Global Volcanism Program. However, calculated frequencies represent only minimum values due to an incomplete eruption record. Unfortunately, limited data precluded the calculation of eruption frequencies for the Solomon Islands, Fiji and Samoa. A first-order analysis of the populations potentially impacted by large volcanic eruptions suggest that (1) volcanic disasters affecting populations of >100,000 can be expected at least every decade in Indonesia and once every few decades in the Philippines and (2) a volcanic disaster impacting >1% of the population can be expected twice a century in Vanuatu, twice a millennium for Indonesia and the Philippines, and around every millennium in Papua New Guinea and Tonga.     

Infill-sampling design and the Cost of classification errors

The criterion used to select infill sample locations should depend on the sampling objective. Minimizing the global estimation variance is the most widely used criterion and is suitable for many problems. However, when the objective of the sampling program is to partition an area of interest into zones of high values and zones of low values, minimizing the expected cost of classification errors is a more appropriate criterion. Unlike the global estimation variance, the cost of classification errors incorporates both the sample locations and the sample values into an objective infill-sampling design criterion.     

Soil and water conservation measures improve soil carbon sequestration and soil quality under cashews

Land degradation is becoming a serious problem in the west coast region of India where one of the world's eight biodiversity hotspots,the‘Western Ghats’,is present.Poor land management practices and high rainfall have led to increasing problems associated with land degradation.A long-term(13-year)experiment was done to evaluate the impact of soil and water conservation measures on soil carbon sequestration and soil quality at three different depths under cashew nut cultivation on a 19%slope.Five soil and water conservation measures-continuous contour trenches,staggered contour trenches,halfmoon terraces,semi-elliptical trenches,and graded trenches all with vegetative barriers of Stylosanthes scabra and Vetiveria zizanoides and control were evaluated for their influence on soil properties,carbon sequestration,and soil quality under cashews.The soil and water conservation measures improved significantly the soil organic carbon,soil organic carbon stock,carbon sequestration rate and microbial activity compared to the control condition(without any measures).Among the measures tested,continuous contour trenches with vegetative barriers outperformed the others with respect to soil organic carbon stock,sequestration rate,and microbial activity.The lower metabolic quotient with the measures compared to the control indicated alleviation of environmental stress on microbes.Using principal component analysis and a correlation matrix,a minimum dataset was identified as the soil available nitrogen,bulk density,basal soil respiration,soil pH,acid phosphatase activity,and soil available boron and these were the most important soil properties controlling the soil quality.Four soil quality indices using two summation methods(additive and weighted)and two scoring methods(linear and non-linear)were developed using the minimum dataset.A linear weighted soil quality index was able to statistically differentiate the effect of soil and water conservation measures from that of the control.The highest value of the soil quality index of 0.98 was achieved with continuous contour trenches with a vegetative barrier.The results of the study indicate that soil and water conservation measures for cashews are a potential strategy to improve the soil carbon sequestration and soil quality along with improving crop productivity and reducing the erosion losses.     

Lithogeochemical exploration for komatiite-associated Ni-sulfide deposits: strategies and limitations

Summary Lithogeochemistry of komatiites can be useful in exploration for nickel sulfides in two distinct ways: indirectly, through identification of favourable volcanic environments, and more directly, through identification of signatures of crustal contamination and sulfide liquid segregation. However, the discrimination between mineralised and unmineralised sequences is not straightforward.Komatiite chemistry is influenced by a variety of primary magmatic variables, overprinted to various degrees for various elements by the effects of metasomatic alteration. Once highly metasomatised samples have been filtered, primary magmatic signatures are largely retained for the elements Mg, Fe, Si, Al, Ti and Cr, even in cases of extensive CO₂ metasomatism and talc-carbonate alteration. Incompatible trace elements such as Zr and REE are modified to some degree by alteration, particularly in cumulate rocks, but there is evidence for some retention of primary signatures.Favourable volcanic environments, i.e. those containing large-volume lava pathways, can be identified on the basis of their distribution and ratios of whole rock Mg, Fe, Ni, Cr and Ti. Nickel depletion can be recognised in some cases of large mineralised systems where large volumes of sulfide formed at low silicate:sulfide (R) ratios, but is not effective in finding small high-grade ore shoots. PGE in low-S rocks do not appear to be an effective discriminant, owing to the local scale of S-saturation.Crustal contamination is indicated in some mineralised suites on the basis of enriched ratios of strongly to weakly incompatible lithophile elements in fractionated lavas, but the effects of alteration are significant and may be misleading. On the whole, mineralised sequences tend to have more enriched signatures than unmineralised ones, but there may be many false positives and negatives, and if the most CO₂-metasomatised suites are discounted the contrast largely disappears. Overall, the presence of Ni-enriched sulfides is by far the best lithogeochemical indicator there is, and it may be the only really effective one.     

An Overview of Existing Algorithms for Resolving the 180° Ambiguity in Vector Magnetic Fields: Quantitative Tests with Synthetic Data

We report here on the present state-of-the-art in algorithms used for resolving the 180° ambiguity in solar vector magnetic field measurements. With present observations and techniques, some assumption must be made about the solar magnetic field in order to resolve this ambiguity. Our focus is the application of numerous existing algorithms to test data for which the correct answer is known. In this context, we compare the algorithms quantitatively and seek to understand where each succeeds, where it fails, and why. We have considered five basic approaches: comparing the observed field to a reference field or direction, minimizing the vertical gradient of the magnetic pressure, minimizing the vertical current density, minimizing some approximation to the total current density, and minimizing some approximation to the field's divergence. Of the automated methods requiring no human intervention, those which minimize the square of the vertical current density in conjunction with an approximation for the vanishing divergence of the magnetic field show the most promise.     

Dense Spot Coverage and Polar Caps on SV Cam

We have used spectrophotometric data from nine Hubble Space Telescope orbits to eclipse-map the primary component of the RS CVn binary SV Cam. From these observations and its HIPPARCOS parallax we find that the surface flux in the eclipsed low-latitude region is about 30 % lower than computed from the best fitting PHOENIX model atmosphere. This flux deficit can only be accounted for if about a third of the primary's surface is covered with unresolved spots. Even when we extend the spottedness from the eclipsed region to the entire surface, there still remains an unaccounted flux deficit. This remaining flux deficit is explained by the presence of a large polar spot extending down to latitude 42 ±6 °.Marie Curie Intra-European Fellow