Assessing landslide movements in volcanic islands using near-shore marine geophysical data: south Pico island,Azores

Marine geophysical data from around the submarine flanks of volcanic islands can potentially help to resolve whether large-scale instability of an edifice has been geologically recently active. We use geophysical data to investigate part of the coast of Pico Island of the Azores where, above sea-level, a major slump of Topo volcano has been interpreted previously from arcuate escarpments and a rugged irregular topography seaward of them. Multibeam echo-sounder data collected offshore of this feature show remarkably little evidence for slump fault movements in the island's submarine slope. Mid-slope benches, like those associated with the Hilina Slump of Kilauea, are absent. The high-resolution data extends onto the island's shelf, allowing us to evaluate evidence for continuing activity there. In particular, as the shelf's rock platform will have been last modified by surf erosion during the postglacial period of sea-level transgression, it provides a reference surface of intermediate age (7–19 ka) that can potentially reveal whether any movements occurred in pre-historic times. Where the arcuate escarpments are continued offshore, the modern seabed shows no bathymetric evidence for active faults where the shelf rock platform crops out in the multibeam data. Elsewhere, mobile shelf sediments could be disguising evidence for active faulting so we examined boomer profiles able to image the rock platform beneath them. The data reveal a platform that is steep (6.6°) compared with the dips of platforms that we have studied previously around the coast of adjacent Faial Island and steeper than the platform outside the proposed slump. This suggests that it was created by coastal erosion over a shorter period and hence is consistent with a younger age of the coastline. As with the multibeam data, where escarpments are continued offshore onto the shelf, the rock surface imaged with these boomer data also shows no clear evidence of major slump-related fault displacements. This study therefore illustrates how high-resolution boomer seismic and multibeam data could usefully contribute to hazard assessment of volcanic islands, by helping to evaluate areas with no historical movements. Explanations to reconcile the onshore and offshore data here are also put forward.     

Tellurides from Sunrise Dam gold deposit, Yilgarn Craton, Western Australia: a new occurrence of nagyágite

Summary The Cu–Fe–Au–Mo (W) deposits in southeastern Hubei are an important component of the Middle–Lower Yangtze River metallogenic belt. Molybdenite from the Fengshandong Cu- (Mo), Ruanjiawan W–Cu- (Mo), Qianjiawan Cu–Au, Tongshankou Cu–Mo and Tonglüshan Cu- (Fe) deposits yielded Re–Os ages of 144.0 ± 2.1 Ma, 143.6 ± 1.7 Ma, 137.7 ± 1.7 Ma, 142.3 ± 1.8–143.7 ± 1.8 Ma and 137.8 ± 1.7–138.1 ± 1.8 Ma, respectively. Phlogopite from the Tieshan Fe- (Cu) deposit yielded an Ar–Ar age of 140.9 ± 1.2 Ma. These data and other published isotopic ages (Re–Os molybdenite and Ar–Ar mica ages) for the Cu–Fe–Au–Mo (W) deposits in the Middle–Lower Yangtze River metallogenic belt show that Cu–Fe–Au–Mo (W) mineralisation in the Tongling, Anqing, Jiurui and Edong ore districts developed in a narrow time span between 135.5 and 144.9 Ma, reflecting an important regional metallogenic event. An integrated study of available petrological and geochronological data, together with relationships to magmatism and the regional geodynamic framework, indicate that the Cu–Fe–Au–Mo (W) mineralisation in the Middle–Lower Yangtze River belt occurred during a regime of lithospheric extension. This extension is probably related to Late Mesozoic processes of lower crustal delamination and lithospheric thinning in East China.     

On the sampling of airborne measurements of radiative properties of cloud fields: Results from International Cirrus Experiment (ICE), 1987

Summary During the first pilot phase of the International Cirrus Experiment (ICE) in September/October 1987 radiation measurements were carried out above and below broken cloud fields over the German Bight. Analyses of the measurements of 25.9.1987 (broken cumulus cloud field) showed an unexpected high absorption of solar radiation but not those of 28.9.1987 (stratocumulus/stratus cloud field). This might be explained by a partial negligence of cloud side factor under the viewing geometry of the pyranometer and other reasons. The light guide effect (leakage) within holes can account for the depletion of cloud reflectance and the enhancement of cloud transmittance at large cloud cover, as observed during the measurements on 28.9.1987. The fluctuation of the irradiances, which can be characterized by the intermittency parameter, has been related to the corresponding cloud cover by a regression equation. On the condition of similarity, this scaling parameter derived from sample measurements could be extrapolated to that of the whole cloud field. Thus, the estimation of the irradiance spectrum for the whole cloud field may be possible, from samples taken with aircraft and imaging data.With 5 Figures     

Finite element analysis for a finite conductivity fracture in an infinite poroelastic medium

In the technology of oil recovery, oil production rate can be increased by generation of a vertical conductive fracture adjacent to the well-bore. In this paper the seepage flow and isothermal deformation in both the oil formation and the fracture are studied by modelling the formation as a two-dimensional infinite poroelastic medium and the conductive fracture as a one-dimensional poroelastic material, saturated by a one-phase compressible fluid. The plane strain condition is employed. Solutions for a growing conductive fracture and a stationary conductive fracture in the infinite medium are obtained by means of the finite element method based on a variational principle for the formation which can impose the governing equations of the fracture. Infinite elements are used outside the finite element domain. Numerical results indicate that the injection rate, the applied pressure and the crack mouth opening displacement at the well-bore oscillate during the propagation of the conductive fracture. The production rate of a well with the conductive fracture is compared with that of a well without the conductive fracture. Finally, a new definition of the conductivity coefficient for the conductive fracture is presented. Copyright © 1999 John Wiley & Sons, Ltd.     

The Proterozoic,albitite-hosted,Valhalla uranium deposit,Queensland, Australia: a description of the alteration assemblage associated with uranium mineralisation in diamond drill hole V39

The Valhalla uranium deposit, located 40 km north of Mount Isa, Queensland, Australia, is an albitite-hosted, Mesoproterozoic U deposit similar to albitite-hosted uranium deposits in the Ukraine, Sweden, Brazil and Guyana. Uranium mineralisation is hosted by a thick package of interbedded fine-grained sandstones, arkoses and gritty siltstones that are bound by metabasalts belonging to the ca. 1,780 Ma Eastern Creek Volcanics in the Western Succession of the Mount Isa basin. Alteration associated with U mineralisation can be divided into an early, main and late stage. The early stage is dominated by laminated and intensely altered rock comprising albite, reibeckite, calcite, (titano)magnetite ± brannerite. The main stage of mineralisation is dominated by brecciated and intensely altered rocks that comprise laminated and intensely altered rock cemented by brannerite, apatite, (uranoan)-zircon, uraninite, anatase, albite, reibeckite, calcite and hematite. The late stage of mineralisation comprises uraninite, red hematite, dolomite, calcite, chlorite, quartz and Pb-, Fe-, Cu-sulfides. Brannerite has U–Pb and Pb–Pb ages that indicate formation between 1,555 and 1,510 Ma, with significant Pb loss evident at ca. 1,200 Ma, coincident with the assemblage of Rodinia. The oldest ages of the brannerite overlap with ⁴⁰Ar/³⁹Ar ages of 1,533 ± 9 Ma and 1,551 ± 7 Ma from early and main-stage reibeckite and are interpreted to represent the timing of formation of the deposit. These ages coincide with the timing of peak metamorphism in the Mount Isa area during the Isan Orogeny. Lithogeochemical assessment of whole rock data that includes mineralised and unmineralised samples from the greater Mount Isa district reveals that mineralisation involved the removal of K, Ba and Si and the addition of Na, Ca, U, V, Zr, P, Sr, F and Y. U/Th ratios indicate that the ore-forming fluid was oxidised, whereas the crystal chemistry of apatite and reibeckite within the ore zone suggests that F⁻ and were important ore-transporting complexes. δ¹⁸O values of co-existing calcite and reibeckite indicate that mineralisation occurred between 340 and 380°C and involved a fluid having δ¹⁸O_fluid values between 6.5 and 8.6‰. Reibeckite δD values reveal that the ore fluid had a δD_fluid value between −98 and −54‰. The mineral assemblages associated with early and main stages of alteration, plus δ¹⁸O_fluid and δD_fluid values, and timing of the U mineralisation are all very similar to those associated with Na–Ca alteration in the Eastern Succession of the Mount Isa basin, where a magmatic fluid is favoured for this style of alteration. However, isotopic data from Valhalla is also consistent with that from the nearby Mount Isa Cu deposit where a basinal brine is proposed for the transport of metals to the deposit. Based on the evidence to hand, the source fluids could have been derived from either or both the metasediments that underlie the Eastern Creek Volcanics or magmatism that is manifest in the Mount Isa area as small pegmatite dykes that intruded during the Isan Orogeny.     

An analysis of climatic and human induced determinants of agricultural land use changes in Shupiyan area of Jammu and Kashmir state,India

The economy of the Jammu and Kashmir state depends mostly on traditional forms of occupation. Unaffected and unaltered by modern day industrial developments and changing times, the indigenous traditional occupations of farming, animal husbandry and horticulture forms the backbone of the state economy. But in the last few decades, Agriculture in the state as well as the study area is receiving a set back and Horticulture is flourishing leaps and bounds. The present study aims to analyze various determinants responsible for this change. Climatic as well as field data was thoroughly analyzed to comprehend the situation. A Mann–Kendall test was done on the climatic data to support the hypotheses. It was observed that initially changing climatic trends proved to be the triggering factor supporting this change, but in due course of time, the determinants took an economic and psychological turn. The perusal of Indian Meteorological Data reveals an increasing trend of annual mean maximum temperature from 16.78 °C in 1985 to 17.58 °C in 1995 and an increase from 5.30 °C to 7.00 °C in the annual mean minimum temperature, and as such acting as a triggering factor for the land use conversion. Further, the mean annual rainfall shows a decrease from 100.75 mm in 1981 to 79.43 mm in 1991. The greater economic returns from horticulture as well as the changing behavioral patterns of people over the time further cemented its growth. The farmers have since persisted with the horticulture activity as it has proven to be an economically a much better lucrative enterprise.     

Electrical and electromagnetic surveys to locate possible causes of water seepage to ground surface at a quarry open pit near Helwan city,Egypt

Water seepage to ground surface at a limestone quarry located at Wadi Garawy about 20 km south-east of Helwan city in Egypt posed a real threat to the mining activity at the quarry. The quarry area is known to be very dry for decades and away from water utilities and infrastructures that may cause water leaks to the quarry. Geophysical investigation including 1D Vertical Electrical Sounding (VES), 2D Electrical Resistivity Tomography (ERT) and 1D Transient Electromagnetic (TEM) surveys were conducted to characterize the rock sequence and locate what could be a possible source of water seepage to the quarry. The resistivity profiles generated from the VES and TEM surveys mapped the rock units in the area down to depths exceeded 100 m. The ERT profiles acquired from the quarrying zone close to the water seepage spot have imaged the top of groundwater level at few meters below the ground surface at the quarry open pit. The spot of groundwater seepage seemed to occur at an area of limestone dissolution that were filled by finer sediments. The finer sediments acted as a hydrological conduit that allowed an upward seepage of groundwater to ground surface under the capillary action effect.     

Uncertainty as the overlap of alternate conditional distributions

An important task in modern geostatistics is the assessment and quantification of resource and reserve uncertainty. This uncertainty is valuable support information for many management decisions. Uncertainty at specific locations and uncertainty in the global resource is of interest. There are many different methods to build models of uncertainty, including Kriging, Cokriging, and Inverse Distance. Each method leads to different results. A method is proposed to combine local uncertainties predicted by different models to obtain a combined measure of uncertainty that combines good features of each alternative. The new estimator is the overlap of alternate conditional distributions.     

Temporal and Spatial Dynamics of Diel-Cycling Hypoxia in Estuarine Tributaries

The distribution and intensity of hypoxia (low dissolved oxygen) in estuaries is increasing worldwide due to cultural eutrophication. This study quantifies the strength of associations between the duration of diel-cycling severe hypoxia (≤2 mg O₂ l⁻¹) in bottom water (∼15 cm above bottom) of a shallow (<2 m) coastal lagoon estuary (Delaware, USA) and abiotic environmental variables (water temperature, insolation, tide, streamflow, and wind) and predicts the duration of severe hypoxia given different combinations of these variables. The intensity and spatial extent and dynamics of diel-cycling severe hypoxia events were defined. Vertical variability in dissolved oxygen (DO) concentration during the daytime was also determined. During the summers of 2001–2005, bottom DO data were collected for periods of weeks to months at multiple sites using automated sondes. Multiple linear regression (MLR) and regression tree analysis (RTA) were used to determine the relative importance of the environmental variables in predicting the number of hours of severe hypoxia per day. Key findings of the study were that severe hypoxia events of minutes to hours in duration occurred frequently in all four tributaries sampled, primarily between 0200 and 1000 hours. Severe hypoxia duration and diel-cycling amplitudes of DO concentration increased in the up-tributary direction. Hierarchically, the duration of severe hypoxia was influenced mostly by the mean daily water temperature, then by preceding days’ total insolation, percentage of morning hours (02:00 to 10:00 a.m.) ebb tide, and daily streamflow. Collectively, the variables examined by the MLR and the RTA approaches accounted for 62% and 65% of the variability in the duration of severe hypoxia, respectively. RTA demonstrated that daily mean water temperature above 26.3°C and previous day’s total insolation below 13.6 kW m⁻² were associated with the longest lasting severe hypoxic events (9.56 h). The environmental variables and combinations of conditions that modulate or augment diel-cycling hypoxia presented in this paper enhance understanding of this widespread and growing phenomenon and provide additional insight regarding the extent to which it can impact food webs in very shallow estuarine waters that often serve as nursery habitat.