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111.
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
112.
113.
Eruption dynamics of Hawaiian-style fountains: the case study of episode 1 of the Kīlauea Iki 1959 eruption 总被引:1,自引:1,他引:0
Wendy K. Stovall B. F. Houghton H. Gonnermann S. A. Fagents D. A. Swanson 《Bulletin of Volcanology》2011,73(5):511-529
Hawaiian eruptions are characterized by fountains of gas and ejecta, sustained for hours to days that reach tens to hundreds
of meters in height. Quantitative analysis of the pyroclastic products from the 1959 eruption of Kīlauea Iki, Kīlauea volcano,
Hawai‘i, provides insights into the processes occurring during typical Hawaiian fountaining activity. This short-lived but
powerful eruption contained 17 fountaining episodes and produced a cone and tephra blanket as well as a lava lake that interacted
with the vent and fountain during all but the first episode of the eruption, the focus of this paper. Microtextural analysis
of Hawaiian fountaining products from this opening episode is used to infer vesiculation processes within the fountain and
shallow conduit. Vesicle number densities for all clasts are high (106–107 cm−3). Post-fragmentation expansion of bubbles within the thermally-insulated fountain overprints the pre-fragmentation bubble
populations, leading to a reduction in vesicle number density and increase in mean vesicle size. However, early quenched rims
of some clasts, with vesicle number densities approaching 107 cm−3, are probably a valid approximation to magma conditions near fragmentation. The extent of clast evolution from low vesicle-to-melt
ratio and corresponding high vesicle number density to higher vesicle-to-melt ratio and lower vesicle-number density corresponds
to the length of residence time within the fountain. 相似文献
114.
Martin Sharp Keith Richards Ian Willis Neil Arnold Peter Nienow Wendy Lawson Jean-Louis Tison 《地球表面变化过程与地形》1993,18(6):557-571
As part of an integrated study of the hydrology, meltwater quality and dynamics of the Haut Glacier d'Arolla, Switzerland, the glacier's drainage network structure was determined from patterns of dye recovery in 342 injection experiments conducted from 47 moulins distributed widely across the glacier. This structure was compared with theoretical predictions based upon reconstructed patterns of water flow governed by (a) the subglacial hydraulic potential surface, and (b) the subglacial bedrock surface. These reconstructions were based on measurements of ice surface and bedrock topography obtained by a combination of ground survey and radio-echo sounding techniques. The two reconstructions simulate the drainage system structures expected for (a) closed channels, in which water is pressurized by the overlying ice, and (b) gravity-driven, open-channel flow. The closed-channel model provides the best fit to the observed structure, even though theoretical calculations suggest that, under summer discharge conditions, open-channel flow may be widespread beneath the glacier. Possible reasons for this apparent discrepancy are discussed. 相似文献
115.
Li Zhong Huang Guohe Huang Wendy Lin Qianguo Liao Renfei Fan Yurui 《Theoretical and Applied Climatology》2018,132(3-4):1029-1038
Theoretical and Applied Climatology - Apparent changes in the temperature patterns in recent years brought many challenges to the province of Ontario, Canada. As the need for adapting to climate... 相似文献
116.
In groundwater of the Trans-Pecos region of West Texas, unexpectedly high levels of nitrate (NO3 ?) are documented in four basins: Red Light Draw, Eagle Flats, Wild Horse and Michigan Flats, and Lobo and Ryan Flats. NO3 ? concentrations are changing over time in the majority (82.8 %) of wells and are increasing in most (69.8 %). The temporal change raises questions about the potential sources of NO3 ? and about flow dynamics in these basins. Presence of NO3 ? and temporal variability in concentration has implications beyond contamination risk because it indicates relatively rapid recharge (<60 years) to the basin groundwaters which was not expected based on previous estimates from chloride mass balance models and groundwater age-dating techniques. This research combines existing data ranging back to the 1940s with data collected in 2011 to document a multi-decadal trend of overall increasing NO3 ? concentration in deep basin groundwaters. Chlorofluorocarbon analyses of groundwater collected during 2011 indicate the presence of young (<70 years) water in the basins. The authors infer from these data that there are mechanism(s) by which relatively rapid and widespread recharge occurs on the basin floors; that recharge is spatially and temporally variable and that it results from both anthropogenic (irrigated agriculture) and natural (precipitation) sources. In light of these observations, fundamental conceptual models of flow in these basins should be re-evaluated. 相似文献
117.
Natural Hazards - Emergency evacuation is the immediate escape of people away from a place of an imminent threat to a place of safety. The ability of the households to evacuate is a crucial... 相似文献
118.
This study applies a spatial fuzzy multi‐criteria evaluation model to determine agricultural feasibility in China based on physical variables (accumulated temperature, sunshine, precipitation, hydrology, elevation and soil properties). The resulting agricultural feasibility index layer is combined with nightlight images (1992‐2013) to determine the spatiotemporal variation of urban encroachment on feasible agriculture land. It reveals the severity of agricultural land losses to urbanization. 相似文献
119.
Chan Faith Ka Shun Gu Xinbing Qi Yunfei Thadani Dimple Chen Yongqin David Lu Xiaohui Li Lei Griffiths James Zhu Fangfang Li Jianfeng Chen Wendy Y. 《Natural Hazards》2022,110(3):2397-2404
Natural Hazards - Frequent typhoons significantly affect many coastal cities via intensive rainstorms, tidal surges and strong wind. Natural factors induced by human disturbance such as climate... 相似文献
120.
Net accumulation measurements from two glaciers located on opposite sides of the New Zealand Southern Alps were used to explore processes controlling spatial variability. The degree of variability, as measured by the spatial variogram, differed in each of the three successive years, but the lowest variance occurred on both glaciers in March 2008, after a hot and dry summer. Strong relationships between net accumulation and elevation within the accumulation area were only found on Franz Josef Glacier (FJG), despite this being the primary control used in glacier mass balance modelling. Interaction between wind and topography was found to be important to the distribution of net accumulation on both glaciers. The crevasse stratigraphy method is an ideal way to gain good spatial coverage of net accumulation, and particularly suited to glaciers with high annual precipitation. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献