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331.
The distribution, stratigraphic relationships and fragmental components of the May 8 and 20, 1902, pyroclastic flows from Mt. Pelée, Martinique, together with eyewitness accounts, suggest the following explanation for those eruptions. The eruptions were vertically directed magmatic (perhaps initiated phreatically), and contained abundant juvenile lithics from congealed magma of the dome and neck. This resulted in a two-part eruption column having (1) a dense, lithic-charged part which collapsed into the crater and flowed out of a pre-existing notch in its side, giving rise to pyrochlastic flows, and (2) a magmatically derived column containing gases, juvenile vitric material and crystals which largely by-passed the neck and dome and escaped into the atmosphere. All of the energy of the flows was apparently focused through the notch. They emerged fully turbulent and flowed down Rivière Blanche. Gravity segregation of large and abundant fragments soon resulted in a dense, high-concentration, poorly fluidized block-and-ash flow confined to the valley, leaving above a fully turbulent, high-energy ash-cloud surge. As the ash-cloud surge moved down the mountain, it continued to expand outward. The process of gravity segregation continued as the ash-cloud surge expanded, resulting in secondary block-and-ash underflows. Toward St. Pierre, the secondary block-and-ash flows developed on a gently sloping upland surface 100 m or more above the valley of Rivière Blanche. The turbulent, fragment-depleted surges above the secondary block-and-ash flows maintained sufficient energy to devastate the landscape outward to about 3000 m, including St. Pierre. The surges refracted around obstacles and in one place, moved up a small valley in a direction opposite to the main flows. 相似文献
332.
333.
334.
Brian Fry Richard S Scalan J.Kenneth Winters Patrick L Parker 《Geochimica et cosmochimica acta》1982,46(6):1121-1124
Stable sulfur isotope analyses show that rooted estuarine plants growing in anoxic sediments incorporate substantial amounts of 34S-depleted sulfides, or oxidation products thereof. In roots, this incorporation predominates over sulfate uptake from interstitial porewater. Either the plants incorporate normally toxic sulfides, or they are creating and using a specialized nutrient pool of oxidized sulfides at the root-sediment interface. 相似文献
335.
Solvent extractions were done on the carbonaceous chondrites Murray, Murchison, Orgueil and Renazzo, using CCl4 and CH3OH. Between 2 and 10% of the total carbon in these meteorites is extractable by ordinary techniques, most of it in CH3OH. After demineralization with HF, perhaps as much as 30% of the total carbon in Murray may be extractable with CH3OH. The extracts from Renazzo have isotopic ratios which suggest that they are mainly terrestrial organic matter, with lesser contributions from indigenous organics. The CH3OH-soluble organic matter from Murchison and both untreated and HF-treated Murray has δ13C values of about +5 to + 10%. and δ15N values of about +90 to +100%., both of which are significantly higher than the bulk meteorite values. The Orgueil CH3OH-extract also has a δ15N value well above the value in residual organic matter. Values for δD of +300 to +500%. are found for the CH3OH-soluble organic matter. The combined data for C, H and N isotopes makes it highly unlikely that the CH3OH-soluble components are derivable from, or simply related to, the insoluble organic polymer found in the same meteorites. A relationship is suggested between the event that formed hydrous minerals in CI1 and CM2 meteorites and the introduction of water-soluble (methanol-soluble) organic compounds. Organic matter soluble in CCl4 has essentially no nitrogen, and δ3C and δD values are lower than for CH3OH-soluble phases. Either there are large isotopic fractionations for carbon and hydrogen between different soluble organic phases, or the less polar components are partially of terrestrial origin. 相似文献
336.
Compositions of chrome-spinels in peridotites from the layered igneous rocks of Rhum and of the Ben Buie intrusion, Mull, show evidence of post-depositional reaction relationships with the cumulus olivine and/or the intercumulus liquid. Some seam-forming spinels in the Ben Buie intrusion are highly aluminous, more so than those in the Rhum intrusion. Occasional zoned spinels, in both intrusions, show enrichment in Al towards their rims. The evidence suggests that the spinel reaction trend involving Cr-Al exchange proceeds in the direction of Al-enrichment. Equilibrium between chrome-spinel and cumulus olivine appears to have been attained rarely, thus limiting the application of the olivine-spinel geothermometer. 相似文献
337.
A deposit of Fe-rich, Al-poor, hydrothermal nontronite was recovered from the Juan de Fuca Ridge. Analyses show the deposit to be mineralogically and chemically similar to nontronite described at other oceanic localities. The deposit is located near the tip of a propagating segment of the Juan de Fuca Ridge. Rare earth elements and Sr isotopes indicate that the nontronite precipitated from seawater. A formation temperature of 57°C is suggested by oxygen isotopic composition. The low-temperature nontronite deposits apparently form from newly established hydrothermal systems associated with the propagating rift segment. More mature hydrothermal systems that deposit sulfide on the seafloor may develop from these low-temperature systems. 相似文献
338.
Richard W Gossett Harold W Puffer Robert H Arthur David R Young 《Marine pollution bulletin》1983,14(2):60-65
In 1978 the California Department of Fish and Game carried out a major, independent sportfishing survey in southern California. The results of that survey indicated that approximately one million angler-trip hours per year were spent fishing and that one in three fish caught was a white croaker (Genyonemus lineatus). There was no attempt by the Department of Fish and Game to determine the disposition of caught fish. We conducted a subsequent survey in 1980 which included 12 popular sportfishing sites in the Los Angeles area. Our results also indicated that one in three fish caught was a white croaker. In addition our survey showed that 82% of the sportfishermen ate the white croaker they caught and the median consumption was 14.8 g day?1 person?1. White croaker were then sampled by hook-and-line from 11 of the 12 survey sites plus two control sites and analysed for PCB, DDT and BaP. Median PCB levels ranged from 0.014 to 0.41 mg wet kg?1; median DDT from 0.059 to 7.5 mg wet kg?1 and BaP was below detectable limits of 1 ng for all sites. 相似文献
339.
Sensible heat flux data obtained from the U.S. Environmental Protection Agency's Regional Air Pollution Study in St. Louis, Missouri are presented and discussed. Large spatial variations exist in heat flux on both a land-use scale and the urban scale. Arguments based upon empirical data and sampling theory show that estimates of heat flux representative of an upwind fetch l
x
require a minimum observation height proportional to z
3/4. The influence of advection on the magnitude of the heat flux is also explored for both the urban and sub-urban or land-use scales. The data clearly indicate that advection can strongly modulate and even dominate the vertical heat flux above surfaces in areas which maintain large horizontal temperature gradients. The advection contribution is positive for cold air advection and negative for warm air advection, and may result from either the urban heat island or land-use mesoscale features. The depth of advective influence is directly proportional to the horizontal scale of the phenomenon and inversely proportional to horizontal temperature gradient. 相似文献
340.