Oxygen, hydrogen, and helium isotopes for investigating groundwater systems of the Cape Verde Islands, West Africa

Stable isotopes (δ¹⁸O, δ²H), tritium (³H), and helium isotopes (³He, ⁴He) were used for evaluating groundwater recharge sources, flow paths, and residence times of three watersheds in the Cape Verde Islands (West Africa). Stable isotopes indicate the predominance of high-elevation precipitation that undergoes little evaporation prior to groundwater recharge. In contrast to other active oceanic hotspots, environmental tracers show that deep geothermal circulation does not strongly affect groundwater. Low tritium concentrations at seven groundwater sites indicate groundwater residence times of more than 50 years. Higher tritium values at other sites suggest some recent recharge. High ⁴He and ³He/⁴He ratios precluded ³H/³He dating at six sites. These high ³He/⁴He ratios (R/R_a values of up to 8.3) are consistent with reported mantle derived helium of oceanic island basalts in Cape Verde and provided end-member constraints for improved dating at seven other locations. Tritium and ³H/³He dating shows that São Nicolau Island’s Ribeira Fajã Basin has groundwater residence times of more than 50 years, whereas Fogo Island’s Mosteiros Basin and Santo Antão Island’s Ribeira Paul Basin contain a mixture of young and old groundwater. Young ages at selected sites within these two basins indicate local recharge and potential groundwater susceptibility to surface contamination and/or salt-water intrusion.     

A thick lens of fresh groundwater in the southern Lihue Basin,Kauai, Hawaii,USA

A thick lens of fresh groundwater exists in a large region of low permeability in the southern Lihue Basin, Kauai, Hawaii, USA. The conventional conceptual model for groundwater occurrence in Hawaii and other shield-volcano islands does not account for such a thick freshwater lens. In the conventional conceptual model, the lava-flow accumulations of which most shield volcanoes are built form large regions of relatively high permeability and thin freshwater lenses. In the southern Lihue Basin, basin-filling lavas and sediments form a large region of low regional hydraulic conductivity, which, in the moist climate of the basin, is saturated nearly to the land surface and water tables are hundreds of meters above sea level within a few kilometers from the coast. Such high water levels in shield-volcano islands were previously thought to exist only under perched or dike-impounded conditions, but in the southern Lihue Basin, high water levels exist in an apparently dike-free, fully saturated aquifer. A new conceptual model of groundwater occurrence in shield-volcano islands is needed to explain conditions in the southern Lihue Basin. Electronic Publication     

Analysis of an unconfined aquifer subject to asynchronous dual-tide propagation

Most published solutions for aquifer responses to ocean tides focus on the one-sided attenuation of the signal as it propagates inland. However, island aquifers experience periodic forcing from the entire coast, which can lead to integrated effects of different tidal signals, especially on narrow high-permeability islands. In general, studies disregard a potential time lag as the tidal wave sweeps around the island. We present a one-dimensional analytical solution to the ground water flow equation subject to asynchronous and asymmetric oscillating head conditions on opposite boundaries and test it on data from an unconfined volcanic aquifer in Maui. The solution considers sediment-damping effects at the coastline. The response of Maui Aquifers indicate that water table elevations near the center of the aquifer are influenced by a combination of tides from opposite coasts. A better match between the observed ground water head and the theoretical response can be obtained with the proposed dual-tide solution than with single-sided solutions. Hydraulic diffusivity was estimated to be 2.3 × 10⁷ m²/d. This translates into a hydraulic conductivity of 500 m/d, assuming a specific yield of 0.04 and an aquifer thickness of 1.8 km. A numerical experiment confirmed the hydraulic diffusivity value and showed that the y -intercepts of the modal attenuation and phase differences estimated by regression can approximate damping factors caused by low-permeability units at the boundary.     

全球构造地貌中的大悬崖(英文)

高大并且广泛分布的构造悬崖是全球构造地貌的重要组成部分,是南方大陆和次大陆边缘的基本构造地形类型,同时也发育在亚洲东部的陆-洋过渡区。它们位于大陆边缘区的后缘,其地球动力学作用以大陆架、大陆斜坡和边缘海沉降区域的裂谷作用为特征。大悬崖的形成始于大陆岩石圈的变薄和裂解,持续发育过程较长,期间经历一系列的平行后退过程——即所谓构造夷平作用,导致大陆架沉积基准面的形成。大悬崖见于被动大陆边缘以及西太平洋陆-洋过渡带后缘。在陆内区域大悬崖不常见,而是在陆地升、降交界边缘区域出现其他的地貌构造特征。     

Geotechnogenesis problems

Geotechgjgensis is mineralogical geochemical transformation of minerals, rocks, and ores as consequence of impact on them in the process of performing geological-exploration and irrigation works, extracting and processing mineral resources, constructing transport, civil and military objects. These effects lead to discontinuity and moving different scale fragments ofuppor part of lithospere and conjugate hydro-and biosphere zones. Discontinuity predttermines the disturbance of matural systems dynamic equilibriu and acceleration of mftter transformation and migration processes. The final aim of studying geotechnogenesis minseralogy and geochemistry is the establishment of scientific foundations for developing ecological safety measures including also utilization fo geotechnogene deposits.     

The far ultraviolet spectrum of the sun

Predictions of solar flux and limb darkening calculated from the Utrecht Reference Model, the Mutschlecner model, and the Bilderberg Continuum Atmosphere are compared with the rocket ultraviolet observations. The calculations employ recent experimental and theoretical determinations of metallic photo-ionization cross-sections. The spectral region between the continuous absorption edge from the first excited level of silicon at 1680 Å and the ground-state absorption edge at 1525 Å proves particularly significant for an investigation of the solar temperature minimum. The analysis indicates that the solar temperature minimum is relatively broad and flat, having a nearly constant temperature over somewhat more than a scale height, and that the chromospheric rise occurs just above 5000 = 10^–4 or so. Within the assumptions of the present models, a satisfactory interpretation of the ultraviolet spectrum can be reached with a temperature minimum of 4600° ± 100 °K.     

The Harvard-Smithsonian reference atmosphere

We present a model of the solar atmosphere in the optical depth range from ₅₀₀₀ = 10^–8 to 25. It combines an improved model of the photosphere that incorporates recent EUV observations with a new model of the quiet lower chromosphere. The latter is based on OSO 4 observations of the Lyman continuum, on infrared observations, and on eclipse electron densities.Our model differs from the Bilderberg Continuum Atmosphere (BCA) in the low chromosphere (₅₀₀₀ < 10^–4), where deviations from local thermodynamic equilibrium in hydrogen and carbon have been taken into account. It also differs in the transition region between the chromosphere and the photosphere (10^–4 < ₅₀₀₀ < 10^–2), where the temperature is lower than in the BCA, and in the convective region (₅₀₀₀ 2), where the temperature is higher than in the BCA.     

Examining the Variability of Crossing Times for Canadian Trucks at the Three Major Canada–U.S. Border Crossings

Land borders connecting Canada and the United States are vital transportation facilities for the two countries. Truck crossing times at these facilities can have a significant impact on the performance of the economy. To date, knowledge about border crossing times has been limited due to lack of detailed data on the Canadian border. This article explores and models the patterns of crossing times at the three major land crossings connecting Canada to the United States: Ambassador Bridge, Blue Water Bridge, and Peace Bridge. The analysis is based on 387,775 border crossing truck trips that were generated between Canada and the United States over a course of twelve months. Seemingly unrelated regression (SUR) models are estimated to evaluate the seasonal and hourly crossing times of Canada- and U.S.-bound trips on each border crossing, controlling for traffic intensity in the models. The SUR modeling approach is chosen to control for potential cross-model correlations. The results suggest that crossing times at the border vary by season and hour of the day. Crossing times also vary by direction of traffic and by type of day (i.e., weekday vs. weekend). Traffic intensity has a significant influence on crossing times at two of the crossings but not the Blue Water Bridge. Finally, crossing times are more variable during the summer season and tend to be higher during the late evening hours and past midnight.     

Global Change and Regional Landscape Response and Desertification in Siberia

Climate changes and associated natural and anthropogenic processes have manifested themselves particularly clearly during the last two decades. The study of consequences of these changes has become one of the central scientific, social and political issues of our time (Pilot 2000; UNEP 2007).     

Estimating hydraulic properties from tidal attenuation in the Northern Guam Lens Aquifer, territory of Guam, USA

Tidal-signal attenuations are analyzed to compute hydraulic diffusivities and estimate regional hydraulic conductivities of the Northern Guam Lens Aquifer, Territory of Guam (Pacific Ocean), USA. The results indicate a significant tidal-damping effect at the coastal boundary. Hydraulic diffusivities computed using a simple analytical solution for well responses to tidal forcings near the periphery of the island are two orders of magnitude lower than for wells in the island’s interior. Based on assigned specific yields of ～0.01–0.4, estimated hydraulic conductivities are ～20–800 m/day for peripheral wells, and ～2,000–90,000 m/day for interior wells. The lower conductivity of the peripheral rocks relative to the interior rocks may best be explained by the effects of karst evolution: (1) dissolutional enhancement of horizontal hydraulic conductivity in the interior; (2) case-hardening and concurrent reduction of local hydraulic conductivity in the cliffs and steeply inclined rocks of the periphery; and (3) the stronger influence of higher-conductivity regional-scale features in the interior relative to the periphery. A simple numerical model calibrated with measured water levels and tidal response estimates values for hydraulic conductivity and storage parameters consistent with the analytical solution. The study demonstrates how simple techniques can be useful for characterizing regional aquifer properties.