Impact of lightning on organic matter-rich soils: influence of soil grain size and organic matter content on underground fires

A detailed study was carried out on a piece of land that had been struck by lightning during the violent rainstorm that raged over the Island of S?o Miguel (Azores Archipelago) in late October 2006. Temperature and gas measurements (CO₂, CO, H₂S and CH₄) were performed in four study trenches, dug in an area of ∼3 m², where an underground fire had been initiated by the impact with a lightning stroke, followed by the emission of a column of gases and smoke. The soil under study was originally a well-pedogenized about 80 cm thick bed, made of volcanic clayey to silty tephra fallouts and contained 5.5–9.7% of organic matter. The underground fire was monitored for one week and revealed a peak release of 404 ppm CO and 3.4% CO₂ originating from a horizon located about 45 cm under the soil surface. Measurements of temperature, performed one week after the impact, indicated a maximum value of 326°C inside the soil, while 516.5°C were measured on the surface of a lava block interred about 20 cm under the surface. Subsequently, a stratigraphic and sedimentologic study proved the role of the grain-size of the soil and of the organic matter content of the different horizons of the impact area, in determining the ratio between anoxic/oxidised combustion conditions and in the progress of the process itself. It was also noticed that combustion was not total all over in the soil bed and that the process had slightly migrated toward SW during the observation period. The combustion process went on for about ten days, in spite of several other violent rainstorms, until it was artificially extinguished through the excavations made to obtain study trenches. This particular circumstance evidenced the potential natural hazard represented by this kind of atmospheric event, especially in a land where the volcanic nature of the soil may easily mislead inexperienced observers and, consequently, delay proper action.     

Rain-induced debris and mudflow triggering factors assessment in the Santiago cordilleran foothills,Central Chile

Debris and mudflows are some of the main geological hazards in the mountain foothills of the Chilean capital city of Santiago. There, the risk of flows triggered in the basins of ravines that drain the range into the city increases with time due to the city growth. A multivariate statistical study based on the logistic regression method is presented. The model provides equations that allow the computation of combined meteorological triggering factors associated with a probability of rain-induced flow occurrence. Daily rainfall, accumulated rainfall and the snowfall level, traditionally considered as the relevant factors, are analysed for a 25-year period. The results show a strong relevance of the rainfall on the day of the flow event over the other factors. However, the relatively low probabilities returned for some real flow events suggest that the model does not capture all the significant variables and the problem is more complex than as it has been traditionally assumed, and further investigations are needed to develop predictive models of flow triggering.     

Methodology of hydrogeological characterization of deep carbonate aquifers as potential reservoirs of groundwater. Case of study: the Jurassic aquifer of <Emphasis Type="Italic">El Maestrazgo</Emphasis> (Castellón,Spain)

A methodology for the characterization of deep carbonate aquifers has been developed and applied to El Maestrazgo Jurassic aquifer in Castellón, Spain. Characterization of these aquifer formations, located at more than 300 m deep, consisted of a previous phase of compilation, analysis and synthesis of the existing information about the area, followed by a coordinated combination of different speciality studies: geology, stratigraphy, structural analysis, hydrogeology, hydrochemistry, geophysics and remote sensing. Geological studies included geological mapping, definition of stratigraphical units and facies and structural analysis. The aim of the hydrogeology study was to define aquifer formations, recharge area, aquifer points inventory and groundwater flow directions for the establishment of piezometric and water quality observation nets. Special techniques were applied, like thermal infrared aerial images and the evaluation of submarine groundwater discharge by means of natural radium isotopes. Hydrochemical techniques, including majority elements characterization and stable isotopes (¹⁸O, ²H and ³H) determination, allowed classifying hydrochemical facies and establishing a renewal pattern for water within the system. Geophysics was useful in determining the aquifer geometry, the features of the basement and the petrophysical characteristics of the geological formations. Preliminary results show an important tectonic complexity and the possibilities for groundwater uses in the area of study.     

基于主成分分析的东江流域水资源承载能力评价

本文分别介绍了主成分分析法的原理和算法,并将其运用到东江流域水资源承载能力评价中,并且与模糊综合评价结果进行比较。结果表明：两评价方法的评价结果都是东江流域水资源承载能力呈现中上游高下游低的分布趋势,对此提出水资源可持续利用的对策,以促进流域水资源与社会经济的协调发展。     

Ermittlung der QNH-werte aus dem luftdruckfeld der synoptischen bodenkarte

Резюме Дабление воздуха, переснитанное иа уровень моря по стандартной атмосфере в Q-коде обозчачается через QNH. Давление воздуха пересчитанное на уровень моря по высотной барометрической формуле обознаеается через QFF. Для целей авиационной службы погоды должны быть известны значения QNH, однако Зе барическое поле на синоптических картах выражается через QFF. С помощью рис. 1 для соответствующей температуры воздуха на станцин и ее высоты н. у. м. можно определить разность значений QFF—QNH при давленин QFF=1000мб. Далее по табл. 2 можно определить поправку для каждого значения QFF отличного от значения QFF при ином давлении, чем 1000мб путем умножения табулированного значения ва разность QFF—1000мб и его алгебраического сложения со значением, полученным по рис. 1.      

Geomagnetic multipoles, 1829 to 1960

Summary Using the results of spherical harmonic analyses of the geomagnetic field for some fourteen different epochs, includingGauss' first analysis for epoch 1835, and theErman-Petersen analysis for epoch 1829, the strength and axes of geomagnetic multipoles have been computed. In particular, a dipole from the three first order spherical harmonic coefficients, a quadrupole from five second order coefficients, and an octupole from seven third order coefficients. The axes of the quadrupole and octupole have moved quite rapidly when compared with movements of the dipole axis, and show a general movement westwards. Although the strength of the dipole has generally diminished, the strengths of the quadrupole and octupole have generally increased.On leave National University of La Plata, Argentina     

Diurnal changes in the bio-optical properties of the phytoplankton in the Alborán Sea (Mediterranean Sea)

The changes in the phytoplankton absorption properties during a diurnal cycle were investigated at one station located in the north-western area of the Alborán Sea. The experiment was performed in spring when the water column was strongly stratified. This hydrological situation permitted the establishment of a deep chlorophyll a (chl a) fluorescence maximum (DFM) which was located on average close to the lower limit of the mixed layer and the nutricline. The relative abundance of pico-phytoplankton (estimated as its contribution to the total chl a) was higher in the surface, however, micro-phytoplankton dominated the community at the DFM level. Chl a specific absorption coefficient (a*(λ)) also varied with optical depth, with a* (the spectrally average specific absorption coefficient) decreasing by 30% at the DFM depth with respect to the surface. A significant negative correlation between the contribution of the micro-phytoplankton to the total chl a and a* was obtained indicating that a* reduction was due to changes in the packaging effect. Below the euphotic layer, a* increased three-fold with respect to the DFM, which agrees with the expected accumulation of accessory pigments relative to chl a as an acclimation response to the low available irradiance. The most conspicuous change during the diurnal cycle was produced in the euphotic layer where the chl a concentration decreased significantly in the afternoon (from a mean concentration of 1.1 μg L⁻¹ to 0.7 μg L⁻¹) and increased at dusk when it averaged 1.4 μg L⁻¹. In addition, a* and the blue-to-red absorption band ratio increased in the afternoon. These results suggest that a*(λ) diurnal variability was due to increase in photo-protective and accessory pigments relative to chl a. The variation ranges of a*(λ) at 675 and 440 nm (the absorption peaks in the red and blue spectral bands, respectively) in the euphotic layer were 0.01–0.04 and 0.02–0.10 m² mg⁻¹ chl a, respectively. Approximately 30% out of this variability can be attributed to the diurnal cycle. This factor should therefore be taken into account in refining primary production models based on phytoplankton light absorption.     

Inhomogeneous substrate analysis using EM300 backscatter imagery

Backscatter reflectivity from multibeam echo-sounders provides a powerful tool to efficiently characterize seafloor substrates. A comprehensive EM300 bathymetric and backscatter survey has been completed of Cook Strait, in central New Zealand. This paper presents a detailed analysis of the realtime corrections applied to the raw EM300 multibeam data and additional corrections required to compute angular variations of the backscatter strength. The corrections, including the local absorption coefficient, the influence of seafloor topography and sound refraction in the water column, are determined for different Cook Strait seafloor substrates. Modifying MB-System software code, we extracted the backscatter signal parameters in order to quantify the raw backscatter strength and apply additional processing. Profiles of backscatter strength versus incidence angle were computed for a variety of sites characterized by flat seafloor and homogeneous substrates, and for which ground-truth data were available. For each homogeneous site, different but characteristic backscatter profiles are observed that can be interpreted in terms of sediment facies. To analyze heterogeneous substrates, we present a statistical technique, based on a 3-dimensional distribution of (incidence angle, backscatter strength) couples that preserves geological information of the substrate components. This analysis, using backscatter data acquired on a submarine volcano, north of New Zealand, clearly differentiates soft sediments and lava flows within a heterogeneous substrate.     

Thickening of the oceanic layer in the Pacific Ocean

A statistical analysis of published seismic refraction results in the Pacific Ocean confirms the existence of a progressive thickening of the oceanic layer with age, following an inverse exponential law. There is no strong indication in the Pacific data of an increase in the thickness of layer 2 with decreasing spreading rate.Contribution No. 93 of the Département Scientifique of the Centre Océanologique de Bretagne, B.P. 337, 29200, Brest, France.