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1.
2.
Andrew J. L. Harris Anna L. Butterworth Richard W. Carlton Ian Downey Peter Miller Pedro Navarro David A. Rothery 《Bulletin of Volcanology》1997,59(1):49-64
Satellite data offer a means of supplementing ground-based monitoring during volcanic eruptions, especially at times or locations
where ground-based monitoring is difficult. Being directly and freely available several times a day, data from the advanced
very high resolution radiometer (AVHRR) offers great potential for near real-time monitoring of all volcanoes across large
(3000×3000 km) areas. Herein we describe techniques to detect and locate activity; estimate lava area, thermal flux, effusion
rates and cumulative volume; and distinguish types of activity. Application is demonstrated using data for active lavas at
Krafla, Etna, Fogo, Cerro Negro and Erebus; a pyroclastic flow at Lascar; and open vent systems at Etna and Stromboli. Automated
near real-time analysis of AVHRR data could be achieved at existing, or cheap to install, receiving stations, offering a supplement
to conventional monitoring methods.
Received: 21 January 1997 / Accepted: 3 April 1997 相似文献
3.
An Example of Island-Arc Petrogenesis: Geochemistry and Petrology of the Southern Luzon Arc, Philippines 总被引:7,自引:1,他引:6
DEFANT MARC J.; MAURY REN? C.; RIPLEY EDWARD M.; FEIGENSON MARK D.; JACQUES DARIO 《Journal of Petrology》1991,32(3):455-500
Volcanism throughout the Luzon arc is associated with eastwardsubduction of the South China Sea floor along the Manila Trench.The southern section of the arc, the focus of this study, extendsfrom the Lingayen-Dingalan fault to the small islands just southof Luzon. Two segments appear to exist along this section ofthe arc the northern Bataan and southern Mindoro segments whichare separated by the Macolod Corridor. The volcanic rocks have typical arc phenocryst mineralogies:olivine, clinopyroxene, plagioclase, and titanomagnetite inthe most mafic rocks and clinopyroxene, plagioclase, orthopyroxene,titanomagnetite, ? amphibole in the more felsic samples. Complexzoning, sieve textures, and decoupling of incompatible traceelements suggest that processes such as assimilation have takenplace. The rocks from the study area range from basalts to rhyolitesand show typical calc-alkaline features. The rocks of the MacolodCorridor and Mindoro segment are particularly enriched in largeion lithophile elements (LILE), light rare earth elements (LREE),and radiogenic Sr compared with the Bataan segment. The datafall within the mantle array on Sr-Nd isotopic diagrams andgrade toward higher Sr and lower Nd isotopic values from northto south. A likely source for the volcanics of this study is either amid-ocean ridge basalt (MORB)-type mantle that undergoes higherdegrees of partial melting than regions involved in MORB generationor a previously depleted source. We suggest that the high fieldstrength element (HFSE) anomalies have been derived throughdifferential element partitioning during fluid transport fromthe subducted lithosphere to the mantle wedge. Continental crustal material seems to play a significant roleparticularly in the Macolod Corridor and the Mindoro segment,based on the high LILE, La/Sm ratios, radiogenic Sr isotopes,and 18O values. The Macolod Corridor and the Mindoro segmenthave undergone source contamination by crustal material fromthe North Palawan-Mindoro crustal block either during the collisionof this block with the Manila Trench or by subduction of sedimentsrich in this crustal material. A similar component has alsobeen detected in the Bataan segment but in minor amounts. Thetrace element and isotopic differences between the northernand southern sections of the arc are interpreted in terms ofvariable composition (i. e., variable amounts of a crustal componentintroduced from the Palawan-Mindoro crustal terrain) of themetasomatic fluids released into the source. 相似文献
4.
Unconsolidated sand, gravel and clay deposits near Beihai and in the Leizhou Peninsula in southern China form an unconfined
aquifer, aquitard and a confined aquifer. Water and soil samples were collected from the two aquifers in the coastal Beihai
area for the determination of chemical compositions, minerals and soluble ions. Hydrogeochemical modeling of three flow paths
through the aquitard are carried out using PHREEQC to determine water–rock interactions along the flow paths. The results
indicate that the dissolution of anorthite, fluorite, halite, rhodochrosite and CO2, and precipitation of potash feldspar and kaolinite may be occurring when groundwater leaks through the aquitard from the
unconfined aquifer to the confined aquifer. Cation exchanges between Na and Ca can also happen along the flow paths. 相似文献
5.
Pedro J. Marenco Frank A. Corsetti Douglas E. Hammond Alan J. Kaufman David J. Bottjer 《Chemical Geology》2008,247(1-2):124-132
The sulfur isotopic composition of carbonate associated sulfate (CAS) has been used to investigate the geochemistry of ancient seawater sulfate. However, few studies have quantified the reliability of δ34S of CAS as a seawater sulfate proxy, especially with respect to later diagenetic overprinting. Pyrite, which typically has depleted δ34S values due to authigenic fractionation associated with bacterial sulfate reduction, is a common constituent of marine sedimentary rocks. The oxidation of pyrite, whether during diagenesis or sample preparation, could thus adversely influence the sulfur isotopic composition of CAS. Here, we report the results of CAS extractions using HCl and acetic acid with samples spiked with varying amounts of pyrite. The results show a very strong linear relationship between the abundance of fine-grained pyrite added to the sample and the resultant abundance and δ34S value of CAS. This data represents the first unequivocal evidence that pyrite is oxidized during the CAS extraction process. Our mixing models indicate that in samples with much less than 1 wt.% pyrite and relatively high δ34Spyrite values, the isotopic offset imparted by oxidation of pyrite should be much less than ? 4‰. A wealth of literature exists on the oxidation of pyrite by Fe3+ and we believe this mechanism drives the oxidation of pyrite during CAS extraction, during which the oxygen used to form sulfate is taken from H2O, not O2. Consequently, extracting CAS under anaerobic conditions would only slow, but not halt, the oxidation of pyrite. Future studies of CAS should attempt to quantify pyrite abundance and isotopic composition. 相似文献
6.
Quantitative sinkhole hazard assessments in karst areas allow calculation of the potential sinkhole risk and the performance
of cost-benefit analyses. These estimations are of practical interest for planning, engineering, and insurance purposes. The
sinkhole hazard assessments should include two components: the probability of occurrence of sinkholes (sinkholes/km2 year) and the severity of the sinkholes, which mainly refers to the subsidence mechanisms (progressive passive bending or
catastrophic collapse) and the size of the sinkholes at the time of formation; a critical engineering design parameter. This
requires the compilation of an exhaustive database on recent sinkholes, including information on the: (1) location, (2) chronology
(precise date or age range), (3) size, and (4) subsidence mechanisms and rate. This work presents a hazard assessment from
an alluvial evaporite karst area (0.81 km2) located in the periphery of the city of Zaragoza (Ebro River valley, NE Spain). Five sinkholes and four locations with features
attributable to karstic subsidence where identified in an initial investigation phase providing a preliminary probability
of occurrence of 0.14 sinkholes/km2 year (11.34% in annual probability). A trenching program conducted in a subsequent investigation phase allowed us to rule
out the four probable sinkholes, reducing the probability of occurrence to 0.079 sinkholes/km2 year (6.4% in annual probability). The information on the severity indicates that collapse sinkholes 10–15 m in diameter
may occur in the area. A detailed study of the deposits and deformational structures exposed by trenching in one of the sinkholes
allowed us to infer a modern collapse sinkhole approximately 12 m in diameter and with a vertical throw of 8 m. This collapse
structure is superimposed on a subsidence sinkhole around 80 m across that records at least 1.7 m of synsedimentary subsidence.
Trenching, in combination with dating techniques, is proposed as a useful methodology to elucidate the origin of depressions
with uncertain diagnosis and to gather practical information with predictive utility about particular sinkholes in alluvial
karst settings: precise location, subsidence mechanisms and magnitude, and timing and rate of the subsidence episodes. 相似文献
7.
Diel patterns in the chlorophyll a specific absorption coefficient of surface picoplankton, a*pico (γ) (m2·[mg chlorophyll a]−1), were studied at 7 stations under daily cycle of in situ light condition in the western subarctic Pacific and Japan Sea. All the data were normalized by dividing the anomaly with daily averaged a*pico (γ). Opposite diel patterns were observed for the normalized a*pico (443) and a*pico (675) with maximum toward dawn or dusk and minimum toward midday at 4 stations under low-irradiance (LI) conditions and vice versa at 3 stations under high-irradiance (HI) conditions. The absorption efficiency factors at red absorption peak, Q
a (675), were determined by reconstruction with intracellular chlorophyll a concentration and cell diameter. The normalized Q
a (675) also showed diel pattern with maximum toward midday and minimum toward dawn or dusk under LI. The diel pattern in a*pico (675) and Q
a (675) were primarily caused by changes in intracellular chlorophyll a concentration due to photoadaptation under LI. The diel pattern in a*pico (443) was influenced by pigmentation, as recognized by blue to red ratio [a*pico (443)/a*pico (675)] under HI. This study proposed that the opposite diel pattern in a*pico (γ) might occur for a wide range of algal species. The results presented here have important consequences for the interpretation of diel variations in optical properties observed in the open ocean. 相似文献
8.
Toru?Iwata Keiko?Yoshikawa Katsutoshi?Nishimura Yoshihisa?Higuchi Takao?Yamashita Shigeru?Kato Eiji?OhtakiEmail author 《Journal of Oceanography》2004,60(6):995-1000
The measurements of the vertical transport of CO2 were carried out over the Sea of Japan using the specially designed pier of Kyoto University on September 20 to 22, 2000. CO2 fluxes were measured by the eddy correlation and aerodynamic techniques. Both techniques showed comparable CO2 fluxes during sea breeze conditions: −0.001 to −0.08 mg m−2s−1 with the mean of −0.05 mg m−2s−1. This means that the measuring site satisfies the fetch requirement for meteorological observations under sea breeze conditions. Moreover, the eddy diffusivity coefficient used in the aerodynamic technique is found to be consistent with the coefficient used in the eddy correlation technique. The present result leads us to conclude that the aerodynamic technique may be applicable to underway CO2 flux measurements over the ocean and may be used in place of the bulk technique. The important point is the need to maintain a measuring accuracy of CO2 concentration difference of the order of 0.1 ppmv on the research vessels or the buoys. 相似文献
9.
Monthon?Ganmanee Teruyoshi?Narita Hideo?SekiguchiEmail author 《Journal of Oceanography》2004,60(6):1071-1083
Based on our long-term data from megabenthos sampling from 1993 to 2002 in Ise Bay, central Japan, we examined spatio-temporal variations in taxon composition, species richness and its distribution of megabenthos in the bay in relation to the occurrence of the oxygen-poor water (i.e. oxygen content less than 3 ppm) in bottom waters of the bay. A total of 261 species were identified including 6 cnidarians, 1 tentaculate, 5 annelids, 71 molluscs, 72 crustaceans, 16 echinoderms, 12 urochordates and 78 pisces. Of the most abundant 10 megabenthos species, the following 4 species of echinoderms made up more than the half of megabenthos biomass: Luidia quinaria, Echinocardium cordatum, Asterias amurensis and Astropecten scoparius. Species richness of megabenthos varied significantly between seasons and among stations. The severity and period of occurrence of the oxygen-poor water developing every summer play an important role in determining spatial distributions of species richness in the bay. 相似文献
10.
Tatsuya?IwataEmail author Yoshiko?Shinomura Yuta?Natori Yasumasa?Igarashi Rumi?Sohrin Yoshimi?Suzuki 《Journal of Oceanography》2005,61(4):721-732
We investigated the water structure and nutrient distribution in the Suruga Bay from April 2000 to July 2002, especially the Offshore Water, which occupies a large part of the bay. The maximum salinity in the upper 200 m varied between 34.49 and 34.71, indicating a temporal change in the influence of Kuroshio Water on the Offshore Water. Seasonal variation in nutrient concentrations was largest from surface to 50 m. On the other hand, the variance in nutrient concentrations within each season was largest in the subsurface layer of 100–300 m in spring, summer and fall. In the Offshore Water, the change of nutrients was negatively correlated with that of salinity in each season. This suggests that an increasing intrusion of saline water brings about a lower nutrient concentration in the Offshore Water. Likewise, negative correlations were observed between the change of the maximum salinity and chlorophyll a (Δ [chl.a-int])/nutrients integrated in the upper 200 m. Δ[chl.a-int] was significantly correlated with the changes of nitrate and phosphorus, but there were no significant correlations between Δ[chl.a-int] and the change of silicate. These results suggest that the concentrations of chlorophyll a and nutrients in the Offshore Water were decreased due to the increasing intrusion of Kuroshio Water. The Offshore Water is likely to be related to the regulation of primary production by nitrate. 相似文献