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441.
Laura Rosales Lagarde Penelope J. Boston Andrew R. Campbell Louise D. Hose Gary Axen Kevin W. Stafford 《Hydrogeology Journal》2014,22(6):1447-1467
Conspicuous sulfide-rich karst springs flow from Cretaceous carbonates in northern Sierra de Chiapas, Mexico. This is a geologically complex, tropical karst area. The physical, geologic, hydrologic and chemical attributes of these springs were determined and integrated into a conceptual hydrogeologic model. A meteoric source and a recharge elevation below 1,500 m are estimated from the spring-water isotopic signature regardless of their chemical composition. Brackish spring water flows at a maximum depth of 2,000 m, as inferred from similar chemical attributes to the produced water from a nearby oil well. Oil reservoirs may be found at depths below 2,000 m. Three subsurface environments or aquifers are identified based on the B, Li+, K+ and SiO2 concentrations, spring water temperatures, and CO2 pressures. There is mixing between these aquifers. The aquifer designated Local is shallow and contains potable water vulnerable to pollution. The aquifer named Northern receives some brackish produced water. The composition of the Southern aquifer is influenced by halite dissolution enhanced at fault detachment surfaces. Epigenic speleogenesis is associated with the Local springs. In contrast, hypogenic speleogenesis is associated with the brackish sulfidic springs from the Northern and the Southern environments. 相似文献
442.
M’hamed El Janati Abderrahmane Soulaimani Hassan Admou Nasrrddine Youbi Ahmid Hafid Kevin Patrick Hefferan 《Arabian Journal of Geosciences》2014,7(6):2407-2422
Satellite remote sensing is shown to provide critical support for geological and structural mapping in semiarid and arid areas. In this work, Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data were used to clarify the geological framework of the Precambrian basement of the Iguerda Proterozoic inlier in the Moroccan Central Anti-Atlas. In this study, the interpretation of the processed digital data has been ground truthed with geological field data collected during a reconnaissance-mapping program in the Central Anti-Atlas. The Iguerda inlier offers a deeply eroded Precambrian massif dominated by a Paleoproterozoic basement composed of supracrustal metasedimentary units intruded by various Eburnian granitoids. Impressive mafic dyke swarms mainly of Proterozoic age crosscut this basement. Eburnian basement rocks are unconformably overlain by Lower Ediacaran volcanosedimentary rocks of the Ouarzazate Group and Upper Ediacaran–Lower Cambrian carbonates. The applied ASTER analyses are particularly effective in the lithological differentiation and discrimination of geological units of the Iguerda inlier. The spectral information divergence (SID) classification algorithm coupled with spectral angle mapper and maximum likelihood classification effectively discriminates between metamorphic rocks, granitoid bodies, and carbonate cover. SID classification improves geologic map accuracy with respect to the spatial distribution of plutonic bodies and metamorphic units. In addition, Paleoproterozoic granitoids have been well discriminated into separate distinct suites of porphyritic granites, granodiorites, and peraluminous leucogranite suites. This discrimination was initially identified via remote sensing analysis and later ground truthed in the field. This methodology enhances geological mapping and illustrates the potential of ASTER data to serve as a vital tool in detailed geologic mapping and exploration of well-exposed basement of arid regions, such as the Proterozoic of the Anti-Atlas Mountains of Morocco. 相似文献
443.
Palynological research is increasingly revealing the landscape impacts of Norse colonisation in southern Greenland. Typically, although not exclusively, these studies are from depositional environments with highly localised pollen source areas close to fjord-side centres of medieval power. In contrast, this paper presents data from Vatnahverfi, an inland district of the Eastern Settlement, and explores the emergence of a cultural landscape through three pollen sequences at variable distances from Norse farms. Two are from mires with small pollen source areas close to (< 100 m) and distant from (≥ 1500 m) probable farming activities. The other provides a more regional signal of vegetation change, albeit one located close to a Norse settlement. Landnám is marked primarily through an increase in microscopic charcoal and the appearance of pollen from Rumex acetosella, although significant differences between profiles are noted. Close to Norse ruins, pollen productivity from grassland communities increases and woodland and scrub representation declines. Further from archaeological remains, palynologically inferred human activity is primarily characterised by decreased productivity, notably declining influx from woodland and scrub species, reflecting grazing herbivores or coppicing. Abandonment of Vatnahverfi is indicated from the late 14th to early 15th century AD. 相似文献
444.
Community perception of forest–water relationship was gathered using participatory rural appraisal tools in four watersheds of the Blue Nile River Basin in Ethiopia. These were compared and contrasted with the observational records of forest cover and water flow. Upstream and downstream communities were assessed separately to check for differences in perception based on location within a watershed. The key result of the study was that people in the study watersheds had a range of perceptions about the forest–water relationship which were watershed specific. The perceptions were generally consistent with observational evidence from the same watersheds. This study highlighted the need for locale-specific approaches to land and water management in the Basin, as well as the potential value of using community perceptions to complement the observational records which can have spatial and temporal limitations. 相似文献
445.
446.
Classroom responses of New Zealand school teachers following the 2011 Christchurch earthquake 总被引:1,自引:1,他引:0
Following a damaging magnitude 6.3 earthquake in Christchurch, New Zealand on February 22, 2011, an unprecedented number of displaced school children were enrolled temporarily or permanently in new schools throughout New Zealand. This study utilized accounts from primary school teachers in New Zealand, derived from focus groups scheduled in March and April 2011 for an evaluation of a disaster preparedness teaching resource, to examine how these disasters impacted individuals and schools outside of Christchurch. The educators’ focus group accounts provide an illustration of classroom responses including providing emotional support to displaced children, informal classroom discussions, curricular responses, addressing disaster rumors, and information seeking through peers. Some recommendations are provided on ways to support teachers’ important roles in disaster recovery, including targeting evidence-based guidance and teaching resources to schools enrolling displaced children, dispelling disaster rumors through schools and facilitating peer mentoring among teachers. An overarching lesson is that communities would benefit from teachers being better equipped to provide emotional support and responsive disaster education to children after disasters. 相似文献
447.
Dennis M. Staley Jason W. Kean Susan H. Cannon Kevin M. Schmidt Jayme L. Laber 《Landslides》2013,10(5):547-562
Rainfall intensity–duration (ID) thresholds are commonly used to predict the temporal occurrence of debris flows and shallow landslides. Typically, thresholds are subjectively defined as the upper limit of peak rainstorm intensities that do not produce debris flows and landslides, or as the lower limit of peak rainstorm intensities that initiate debris flows and landslides. In addition, peak rainstorm intensities are often used to define thresholds, as data regarding the precise timing of debris flows and associated rainfall intensities are usually not available, and rainfall characteristics are often estimated from distant gauging locations. Here, we attempt to improve the performance of existing threshold-based predictions of post-fire debris-flow occurrence by utilizing data on the precise timing of debris flows relative to rainfall intensity, and develop an objective method to define the threshold intensities. We objectively defined the thresholds by maximizing the number of correct predictions of debris flow occurrence while minimizing the rate of both Type I (false positive) and Type II (false negative) errors. We identified that (1) there were statistically significant differences between peak storm and triggering intensities, (2) the objectively defined threshold model presents a better balance between predictive success, false alarms and failed alarms than previous subjectively defined thresholds, (3) thresholds based on measurements of rainfall intensity over shorter duration (≤60 min) are better predictors of post-fire debris-flow initiation than longer duration thresholds, and (4) the objectively defined thresholds were exceeded prior to the recorded time of debris flow at frequencies similar to or better than subjective thresholds. Our findings highlight the need to better constrain the timing and processes of initiation of landslides and debris flows for future threshold studies. In addition, the methods used to define rainfall thresholds in this study represent a computationally simple means of deriving critical values for other studies of nonlinear phenomena characterized by thresholds. 相似文献
448.
449.
Jason W. Barnes Jacob Bow Jacob Schwartz Robert H. Brown Jason M. Soderblom Alexander G. Hayes Graham Vixie Stéphane Le Mouélic Sebastien Rodriguez Christophe Sotin Ralf Jaumann Katrin Stephan Laurence A. Soderblom Roger N. Clark Bonnie J. Buratti Kevin H. Baines Philip D. Nicholson 《Icarus》2011,216(1):136-140
We report the discovery of organic sedimentary deposits at the bottom of dry lakebeds near Titan’s north pole in observations from the Cassini Visual and Infrared Mapping Spectrometer (VIMS). We show evidence that the deposits are evaporitic, making Titan just the third known planetary body with evaporitic processes after Earth and Mars, and is the first that uses a solvent other than water. 相似文献
450.
Sarah V. Badman Chihiro Tao Adrian Grocott Satoshi Kasahara Henrik Melin Robert H. Brown Kevin H. Baines Masaki Fujimoto Tom Stallard 《Icarus》2011,216(2):367-375
The intensity of Saturn’s infrared aurora is investigated using Cassini VIMS images acquired during October 2006–February 2009. Polar and main oval auroral regions were defined in both hemispheres, which extend between 0–10° and 10–25° co-latitude, respectively. Average intensities were computed for these regions and compared. While the northern and southern main oval regions covered a similar range of intensities, the southern main oval was on average more intense by a factor of ∼1.3. The emission from the southern polar region was usually less intense than the main oval emissions, while this was only the case for approximately half of the northern hemisphere images. The northern hemisphere polar region displayed intensities more than twice as high as those in the south and the difference between the two hemispheres was most pronounced on the dayside. In general, more intense polar emissions were accompanied by more intense main oval emissions. Possible explanations for the hemispheric and latitudinal differences are discussed in terms of particle energies and fluxes, ionospheric conductivity, temperature and magnetic field strength. 相似文献