Constraints on cooling rates and permeabilities of pumice in an explosive eruption jet from colour and magnetic mineralogy     

S. Tait  R. Thomas  J. Gardner  C. Jaupart 《Journal of Volcanology and Geothermal Research》1998,86(1-4)

In explosive volcanic eruptions, vesicular magma droplets, produced by fragmentation, are propelled into the atmosphere where they are chilled to form pumices. The thermal history of droplets and the permeability of their internal bubble networks determine how much they are deformed in the eruption jet, and hence what information pumices record about the state of the magma at fragmentation. We study these aspects of the `Minoan' plinian eruption of Santorini Volcano by quantifying the rate of oxidation reactions that took place when air entered the hot magma fragments. In our experiments white Minoan pumices were heated for minutes to hours between 600 and 850°C, either in air, or in an atmosphere with an oxygen fugacity at the Ni–NiO buffer. Pumices were unchanged by heating at Ni–NiO. Those heated in air often became pink to dark pink, depending on heating time, and their Curie temperatures, as determined by magnetic susceptibility measurements, increased. We use oxidation rates deduced from these experiments, in conjunction with calculations of the rate of conductive cooling and of the rate at which air can enter a pumice, to constrain the conditions experienced by pumices during the eruption. Natural Minoan pumices less than about 5 cm in radius are white, whereas larger ones often have white rims and pink interiors with Curie temperatures higher than those of white material. We infer that small pumices were cooled before being oxidized, and that oxidation of the interiors of large clasts mostly took place during flight, at temperatures within a few tens of degrees of magmatic values. White rims of large pumices, despite being permeable, were cooled before oxidation could occur. Permeability developed in the liquid state, but did not develop early enough, with respect to cooling, or was not large enough to allow extreme oxidation. We give measurements of pumice permeabilities that should be close to magmatic values.  相似文献   

浮石及其开发利用研究进展   总被引：3，自引：0，他引：3  

钱装志 《矿物岩石》1998,18(2):110-114

随着非金属矿市场的发展,目前浮石的应用领域正在拓宽和变化,相关研究亦在不断深入之中。本文在总结浮石一般特征和用途基础上,重点介绍了有关浮石气孔构造及相关特性、利用实验等方面研究的一些主要进展。  相似文献   

Seismic bearing capacity of shallow foundations near rock slopes using the generalized Hoek–Brown criterion     

Z. Saada  S. Maghous  D. Garnier 《国际地质力学数值与分析法杂志》2011,35(6):724-748

The seismic bearing capacity of shallow foundations resting on a modified Hoek–Brown rock mass is investigated within the framework of the kinematic approach of limit analysis theory. The analysis focuses on evaluating the reduction in bearing capacity induced by seismic loading and by the proximity of a rock slope. A pseudo‐static approach is adopted to account for the earthquake effects for the seismic bearing capacity evaluations. At the rock material level, the closed‐form expressions previously obtained for the support functions of the rock failure criterion allow the implementation of different failure mechanisms families, and thus to derive rigorous upper bounds estimates of the load‐bearing capacity in both static and seismic conditions. The effects of geometrical, strength and loading parameters are assessed through a large number of parametric computations. Finally, design tables are presented for practical use in rock engineering. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

A quantitative estimation of the energetic cost of brown ring disease in the Manila clam using Dynamic Energy Budget theory     

Jonathan Flye-Sainte-Marie  Fred Jean  Christine Paillard  Sebastiaan A.L.M. Kooijman 《Journal of Sea Research》2009,62(2-3):114

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Pseudo‐static analysis of tunnel face stability using the generalized Hoek–Brown strength criterion     

Z. Saada  S. Maghous  D. Garnier 《国际地质力学数值与分析法杂志》2013,37(18):3194-3212

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The Quetzalapa Pumice: a voluminous late Pleistocene rhyolite deposit in the eastern Trans-Mexican Volcanic Belt     

Sergio-Raúl Rodríguez  Claus Siebe  Jean-Christophe Komorowski  Michael Abrams 《Journal of Volcanology and Geothermal Research》2002,113(1-2)

The study area is located in the east part of the Trans-Mexican Volcanic Belt, in the Las Cumbres Volcanic Complex (LCVC) which lies between two large stratovolcanoes: Pico de Orizaba (5700 m a.s.l.) to the south, and Cofre de Perote (4200 m a.s.l.) to the NNE. The most conspicuous structure of the LCVC is a 4-km-diameter circular crater with a dacitic dome in the center, which constitutes the remains of a destroyed stratovolcano.The Quetzalapa Pumice (QP) was produced by a plinian eruption that was dated by the ¹⁴C method at 20 000 yr. BP. The eruptive sequence consists predominantly of pumice fall deposits and scarce intra-plinian pyroclastic flow deposits, which crop out on the west flank of the LCVC. The absence of post-plinian ignimbrite deposits is striking.The deposits are well sorted, clast-supported with reverse grading at the base, with a medium to high accessory lithics content. The maximum average thickness of the deposit in the proximal areas is about 15 m and has been divided into three members: the Basal Member (BM), 2 m thick with four submembers (BMf₁, BMf₂, BMf₃, and BMafl), the Intermediate Member (IM), 10 m thick with two submembers (IMpf and IMaf), and the Upper Member (UM), 3 m thick with four submembers (UMpl, UMsdf, UMwaf, and UMpls).The predominant component of the fall deposits is a white, highly vesiculated pumice with 71% SiO₂ content. Plagioclase is the most abundant mineral followed by 1–3-mm-long biotite phenocrysts. The accessory lithics are lavas mostly of andesitic composition. Their abundance increases toward the uppermost levels of the sequence.We calculate a minimum volume of 8.4 km³ (2.22 km³ dense rock equivalent), for the entire QP deposit. Isopach and isopleth maps show that the IM deposit has an elongated distribution with a NNE–SSW direction, whereas the UM deposit has a circular distribution.We estimate a maximum eruptive column height for the IM of 20 km. Field studies and isopach and isopleth maps indicate that the eruptive column was affected by a strong wind.Previous studies located the QP source in the Las Cumbres crater. However, based on the isopach and isopleth distribution, and the lack of pumice fall deposits inside the Las Cumbres crater, we consider that the QP emission center is located on the west flank of the LCVC, and was buried by its own pumice fall deposits. It coincides with an explosion crater called La Capilla formed during the closing phase of the QP eruption.A ‘pumice fountain’ model is proposed to explain the observed sequence of deposits. According to this model, the material was emitted through a ‘hose-type’ conduit during a monogenetic eruption of rhyolitic composition. This kind of volcanic activity is not extensively reported in the literature.  相似文献   

桂林布朗李花果期气象条件分析   总被引：2，自引：1，他引：1  

蒋珍姣  龙凤翔  李艳玉  陈桂莲 《气象研究与应用》2011,32(2):47-48,51

通过对桂林市布朗李花果期气象条件分析,得出影响桂林布朗李花果期主要气候特征,并提出相应的种植措施。  相似文献   

~5.9 cal ka bp Towada-Chuseri tephra from Towada volcano: a mid-Holocene marker layer from Japan to northeast China     

Chunqing Sun  Gill Plunkett  Zeyang Zhu  Lei Zhang  Bin Zhang  Di Zhang  Qian Mao  Haitao You  Luo Wang  Guoqiang Chu  Jiaqi Liu 《第四纪科学杂志》2021,36(7):1143-1148

Far-travelled ash layers from explosive volcanic eruptions can provide invaluable marker horizons for dating and correlating regional to global sedimentary archives. Here, we present a new cryptotephra associated with the ~5.9 cal ka bp Towada-Chuseri eruption (To-Cu) in a peat sediment record from northeast China. This tephra exhibits a rhyolitic glass composition that can be distinguished from other widespread tephra layers around the region of Japan and northeast China. Our findings extend the known range of this ash significantly, making it now traceable about 1200 km from its source, Towada volcano, Japan. Notably, this tephra provides an important isochron for synchronising palaeoenvironmental studies during the mid-Holocene period from the western Pacific, central Japan, Japan Sea and northeast China.  相似文献   

Predicting presence and absence of trout (Salmo trutta) in Iran     

《Limnologica》2014

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STATE PARKS AND JIM CROW IN THE DECADE BEFORE BROWN v. BOARD OF EDUCATION     

WILLIAM E. O'BRIEN 《Geographical review》2012,102(2):166-179

African Americans had access to only a small number of state parks in the Jim Crow South. Between the end of World War II and the U.S. Supreme Court's 1954 Brown v. Board of Education decision, however, state park officials oversaw a relative expansion in the construction of facilities available to southern blacks. Emphasizing developments leading up to that landmark court ruling, I note that this trend did not indicate waning support for segregation among whites. Rather, this relative expansion was part of a strategy to protect Jim Crow by demonstrating that the “separate‐but‐equal” principle was being successfully achieved by southern park agencies. This intensified construction was largely a reaction to increasingly successful legal action in federal courts by the naacp generally; and officials in the state agencies hoped—unsuccessfully—to avoid challenges to state park segregation. After the Brown decision, several border states integrated their park systems, but most agencies displayed the reactionary defiance that characterized most white Southerners as the civil rights movement grew.  相似文献