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131.
Steven B. Meyerhoff Reed M. Maxwell Wendy D. Graham John L. Williams III 《Hydrogeology Journal》2014,22(6):1329-1343
Subsurface heterogeneity is one of the largest sources of uncertainty associated with saturated hydraulic conductivity. Recent work has demonstrated that uncertainty in hydraulic conductivity can impart significant uncertainty in runoff generation processes and surface-water flow. Here, the role of site characterization in reducing hydrograph prediction bias and uncertainty is demonstrated. A fully integrated hydrologic model is used to conduct two sets of stochastic, transient simulation experiments comprising different overland flow mechanisms: Dunne and Hortonian. Conditioning hydraulic conductivity fields using values drawn from a simulated synthetic control case are shown to reduce both mean bias and variance in an ensemble of conditional hydrograph predictions when compared with the control case. The ensemble simulations show a greater reduction in uncertainty in the hydrographs for Hortonian flow. The conditional simulations predict surface ponding and surface pressure distributions with reduced mean error and reduced root mean square error compared with unconditional simulations. Uncertainty reduction in Hortonian and Dunne flow cases demonstrates different temporal signals, with more substantial reduction achieved for Hortonian flow. 相似文献
132.
The Institute of Australian Geographers Urban Study Group and Australian Geographer present the first essay in our Leading Insights/Thinking Space partnership. We discuss Dr Natalie Osborne's 2018 essay, flag Dr Marilu Melo's 2019 essay and talk about creating a thinking space for the rising stars of Australian urban geography. 相似文献
133.
Wei-Ning Xiang Wendy Lee Stratton 《International journal of geographical information science》2013,27(4):499-510
Abstract Mapping variable stream buffers in a vector environment in which buffer width values are delineated often yields inaccurate results. Possible vector solutions are either ineffective or inefficient, An alternate raster approach is presented here in which a buffer effectiveness-achievement function (b-function) is introduced to map desirable buffer zones at an individual cell level based upon areal differentiations in physical and ecological conditions. The implementation of b-function is made feasible by a GIS procedure devised in this article. This tested method can be extended to a variety of variable buffer studies, such as visual buffers, noise buffers, greenways, and urban natural buffers. ‘A robe can never be made of the fur from one fox's axillae’ (A Chinese idiom). 相似文献
134.
Thomas C. B. Hill Wendy A. Woodland Chris D. Spencer Susan B. Marriott David J. Case John A. Catt 《Journal of Paleolimnology》2008,40(1):431-444
The Late-glacial and Holocene environmental history of the Gordano Valley, North Somerset, UK has been reconstructed using
pollen, sediment particle size and mineralogical analyses and radiocarbon dating. A Devensian sediment ridge across the valley
confined the waters of a small lake, within which the initial sedimentation was minerogenic. Radiocarbon dating of overlying
organic-rich deposits suggests that this began late in the Dimlington Stadial c. 18,000–15,000 Cal. BP. Petrographic analyses
indicate the minerogenic sediments were partly wind-blown in origin. Climatic amelioration during the Windermere Interstadial
c. 15,000 Cal. BP encouraged a shift from minerogenic to biogenic sedimentation. A brief return to minerogenic sedimentation
between c. 10,400 and c. 9,520 Cal. BP was followed by uninterrupted fen peat accumulation throughout the Holocene. The later
minerogenic horizon appears to represent the Loch Lomond Stadial. Few stratigraphic sequences preserving the complete Devensian
Late-glacial–Holocene transition exist in southwest Britain, making the sedimentary archive of the Gordano Valley valuable
regionally for reconstructing Late-glacial climate change. 相似文献
135.
Alejandro Cisneros de León Julie C. Schindlbeck-Belo Steffen Kutterolf Martin Danišík Axel K. Schmitt Armin Freundt Wendy Pérez Janet C. Harvey Kuo-Lung Wang Hao-Yang Lee 《第四纪科学杂志》2021,36(2):169-179
The climactic Los Chocoyos (LCY) eruption from Atitlán caldera (Guatemala) is a key chronostratigraphic marker for the Quaternary period given the extensive distribution of its deposits that reached both the Pacific and Atlantic Oceans. Despite LCY tephra being an important marker horizon, a radioisotopic age for this eruption has remained elusive. Using zircon (U–Th)/He geochronology, we present the first radioisotopically determined eruption age for the LCY of 75 ± 2 ka. Additionally, the youngest zircon crystallization 238U–230Th rim ages in their respective samples constrain eruption age maxima for two other tephra units that erupted from Atitlán caldera, W-Fall (130 +16/−14 ka) and I-Fall eruptions (56 +8.2/−7.7 ka), which under- and overlie LCY tephra, respectively. Moreover, rim and interior zircon dating and glass chemistry suggest that before eruption silicic magma was stored for >80 kyr, with magma accumulation peaking within ca. 35 kyr before the LCY eruption during which the system may have developed into a vertically zoned magma chamber. Based on an updated distribution of LCY pyroclastic deposits, a new conservatively estimated volume of ~1220 ± 150 km3 is obtained (volcanic explosivity index VEI > 8), which confirms the LCY eruption as the first-ever recognized supereruption in Central America. 相似文献
136.
Rare dunite and 2-pyroxene gabbro xenoliths occur in banded trachyte at Puu Waawaa on Hualalai Volcano, Hawaii. Mineral compositions suggest that these xenoliths formed as cumulates of tholeiitic basalt at shallow depth in a subcaldera magma reservoir. Subsequently, the minerals in the xenoliths underwent subsolidus reequilibration that particularly affected chromite compositions by decreasing their Mg numbers. In addition, olivine lost CaO and plagioclase lost MgO and Fe2O3 during subsolidus reequilibration. The xenoliths also reacted with the host trachyte to form secondary mica, amphibole, and orthopyroxene, and to further modify the compositions of some olivine, clinopyroxene, and spinel grains. The reaction products indicate that the host trachyte melt was hydrous. Clinopyroxene in one dunite sample and olivine in most dunite samples have undergone partial melting, apparently in response to addition of water to the xenolith. These xenoliths do not contain CO2 fluid inclusions, so common in xenoliths from other localities on Hualalai, which suggests that CO2 was introduced from alkalic basalt magma between the time CO2-inclusion-free xenoliths erupted at 106±6 ka and the time CO2-inclusion-rich xenoliths erupted within the last 15 ka. 相似文献
137.