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221.
M. A. Alam D. Chandrasekharam O. Vaselli B. Capaccioni P. Manetti P. B. Santo 《Journal of Earth System Science》2004,113(4):715-721
Although Barren Island (Andaman Sea, Indian Ocean) witnessed several volcanic eruptions during historic times, the eruptions
that led to the formation of this volcanic island occurred mainly during prehistoric times. It is still active and currently
in the fumarolic stage. Its volcanic evolution appears to be characterized by a constructive phase with the piling up of lava
flows and scoria deposits and Strombolian activities, followed by a sudden collapse of the main cone. Deposits of a possible
caldera-forming eruption were not recognized earlier. After a period of peri-calderic hydromagmatic activity, whose deposits
presently mantle inner and outer caldera walls, a new phase of intracalderic Vulcanian activities took place. A prominent
dyke in the SE inner side of the caldera wall was recognized. Petrographically the lava flows and dyke are similar but they
differ in their chemical composition (viz., SiO2, MgO, Ni, Cr) significantly. Similarity in major, minor and trace element composition (viz., K/La, K/Nb, K/Rb, K/Ti ratios)
of these rocks together with Chondrite normalized trace element (Rb, Ba, Sr, P, Zr, Ti and Nb) and REE (La, Ce, Nd and Y)
patterns of the Barren Island prehistoric lava flows and dyke and low-K lavas of Sunda Arc indicates that Barren Island must
have evolved from a source similar to that of Sunda Arc lavas during the Quaternary Period. 相似文献
222.
Janet M. Sumner 《Bulletin of Volcanology》1998,60(3):195-212
The 1986 eruption of B fissure at Izu-Oshima Volcano, Japan, produced, among other products, one andesite and two basaltic
andesite lava flows. Locally the three flows resemble vent-effused holocrystalline blocky or aa lava; however, remnant clast
outlines can be identified at most localities, indicating that the flows were spatter fed or clastogenic. The basaltic andesite
flows are interpreted to have formed by two main processes: (a) reconstitution of fountain-generated spatter around vent areas
by syn-depositional agglutination and coalescence, followed by extensional non-particulate flow, and (b) syn-eruptive collapse
of a rapidly built spatter and scoria cone by rotational slip and extensional sliding. These processes produced two morphologically
distinct lobes in both flows by: (a) earlier non-particulate flow of agglutinate and coalesced spatter, which formed a thin
lobe of rubbly aa lava (ca. 5 m thick) with characteristic open extension cracks revealing a homogeneous, holocrystalline
interior, and (b) later scoria-cone collapse, which created a larger lobe of irregular thickness (<20 m) made of large detached
blocks of scoria cone interpreted to have been rafted along on a flow of coalesced spatter. The source regions of these lava
flows are characterized by horseshoe-shaped scarps (<30 m high), with meso-blocks (ca. 30 m in diameter) of bedded scoria
at the base. One lava flow has a secondary lateral collapse zone with lower (ca. 7 m) scarps. Backward-tilted meso-blocks
are interpreted to be the product of rotational slip, and forward-tilted blocks the result of simple toppling. Squeeze-ups
of coalesced spatter along the leading edge of the meso-blocks indicate that coalescence occurred in the basal part of the
scoria cone. This low-viscosity, coalesced spatter acted as a lubricating layer along which basal failure of the scoria cone
occurred. Rotational sliding gave way to extensional translational sliding as the slide mass spread out onto the present caldera
floor. Squeeze-ups concentrated at the distal margin indicate that the extensional regime changed to one of compression, probably
as a result of cooling of the flow front. Sliding material piled up behind the slowing flow front, and coalesced spatter was
squeezed up from the interior of the flow through fractures and between rafted blocks. The andesite flow, although morphologically
similar to the other two flows, has a slightly different chemical composition which corresponds to the earliest stage of the
eruption. It is a much smaller lava flow emitted from the base of the scoria cone 2 days after the eruption had ceased. This
lava is interpreted to have been formed by post-depositional coalescence of spatter under the influence of the in-situ cooling
rate and load pressure of the deposit. Extrusion occurred through the lower part of the scoria cone, and subsequent non-particulate
flow of coalesced material produced a blocky and aa lava flow. The mechanisms of formation of the lava flows described may
be more common during explosive eruptions of mafic magma than previously envisaged.
Received: 30 May 1997 / Accepted: 19 May 1998 相似文献
223.
Mary E. MacKay Scott K. Rowland Peter J. Mouginis-Mark Harold Garbeil 《Bulletin of Volcanology》1998,60(4):239-251
We use a digital elevation model (DEM) derived from interferometrically processed SIR-C radar data to estimate the thickness
of massive trachyte lava flows on the east flank of Karisimbi Volcano, Rwanda. The flows are as long as 12 km and average
40–60 m (up to >140 m) in thickness. By calculating and subtracting a reference surface from the DEM, we derived a map of
flow thickness, which we used to calculate the volume (up to 1 km3 for an individual flow, and 1.8 km3 for all the identified flows) and yield strength of several flows (23–124 kPa). Using the DEM we estimated apparent viscosity
based on the spacing of large folds (1.2×1012 to 5.5×1012 Pa s for surface viscosity, and 7.5×1010 to 5.2×1011 Pa s for interior viscosity, for a strain interval of 24 h). We use shaded-relief images of the DEM to map basic flow structures
such as channels, shear zones, and surface folds, as well as flow boundaries. The flow thickness map also proves invaluable
in mapping flows where flow boundaries are indistinct and poorly expressed in the radar backscatter and shaded-relief images.
Received: 6 September 1997 / Accepted: 15 May 1998 相似文献
224.
Using near simultaneously acquired Landsat 7 Enhanced Thematic Mapper Plus (ETM+) and Earth Observing-1 Advanced Land Imager (ALI) data we assess the relative radiant responses over active lava flows from the Mt. Etna July/August 2001 flank eruption. By assessing the extent of saturation between the two instruments and using the dual-band method of extracting sub pixel thermal information, we show that the ALI represents an improvement over the ETM+ in the present ability to assess temperatures of hot active lava flows for a number of reasons. (1) The extra spectral channels provided by ALI compliment the current SWIR channels on ETM+ by providing a greater number of paired channel combinations for input into the dual-band method. Thus, dual-band temperature solutions can be determined for a greater range of lava flow types than previously possible using the two paired channel combinations available with the ETM+. (2) The ALI instrument is less susceptible than ETM+ to saturation within the SWIR, especially when using channels 5, 5p and 4p at wavelengths of 1.65, 1.25 and 0.87 μm respectively. (3) The greater radiometric sensitivity of the ALI 12 bit electronics coupled with a significantly higher signal to noise ratio aid in obtaining successful dual-band solutions. 相似文献
225.
The lava section in the Troodos ophiolite, Cyprus, is chemically stratified and divided into a shallow lava sequence with low TiO2 content and a deeper lava sequence with high TiO2 content. We calculate the viscosity at magmatic temperature based on major element chemistry of lavas in Cyprus Crustal Study Project (CCSP) Holes CY-1 and 1A. We find that typical shallow low-Ti lavas have a magmatic viscosity that is two to three orders of magnitude lower than that of the deeper high-Ti lavas. This implies that, after eruption on-axis, Troodos low-Ti lavas would have been able to flow down the same slope faster and farther than high-Ti lavas. The calculated lava viscosity increases systematically from the lava-sediment interface to the bottom of the composite Hole CY-1/1A. This suggests that an efficient process of lava segregation by viscosity on the upper flanks of the paleo Troodos rise may have been responsible for the chemical stratification in the Troodos lava pile. Calculated magmatic temperature and molar Mg/(Mg+Fe), or Mg#, decrease systematically down-section, while SiO2 content increases. Correlation of Mg# in the lavas with Mg# in the underlying, lower crustal plutonic rocks sampled by CCSP Hole CY-4 shows that the shallow lavas came from a high-temperature, lower crustal magma reservoir which is now represented by high-Mg# pyroxenite cumulates, while the deeper lavas were erupted from a lower-temperature, mid-crustal reservoir which is now represented by gabbroic cumulates with lower Mg#. 相似文献
226.
根据靖宇县政府提供的新资料,结合过去已有资料,经过综合分析,提出了靖宇矿泉水矿田的新认识,并重点介绍了靖宇矿泉水矿田的地质背景,形成分布特征,同时提出了几点开发战略建议,为进一步开发和研究靖宇矿泉水矿田指明了重要的思路和方向。 相似文献
227.
228.
229.
琼北全新世火山区熔岩流流动速度的恢复与火山灾害性讨论 总被引:3,自引:0,他引:3
琼北全新世火山区分为 4个火山系统 ,熔岩流流动距离集中在 4~ 8km之间 ,而熔岩流宽度则以 1.5km左右为常见。根据琼北全新世火山区内熔岩流不同流动单元表面坡度、岩流厚度的调查 ,结合熔岩流温度与密度等物理参数计算恢复的琼北全新世火山区熔岩流流动速度众值在 0 .5 m/ s左右 ,底部剪切力约为 5 0 0 0 Pa。对于厚度巨大的熔岩流 (流动单元厚度 >15 m)流动速度可加快至 5 m/ s,而底部剪切力则可加大至 5 0 0 0 0 Pa。对于一条 8m厚的熔岩流 ,其地表流动时间均在 10 0 h以内 ,而以流动时间在 1d以内为常见。根据熔岩流长度与体积恢复的喷发持续时间对于不同火山系统短至 2个月 ,长达 2年。8km预期熔岩流长度可以作为未来火山喷发时熔岩流火山灾害影响范围的重要参照系数 ,制定的相应减灾措施应该以此作为重要依据之一。琼北近代火山区火山灾害主要表现为熔岩流对农田、林地、道路的毁坏及引发的火灾 相似文献
230.
基于不同岩性、岩相条件从根本上决定了储集空间的发育程度与规模,所以找火山岩的储层集中表现为火山岩相、亚相的识别。文中以松辽盆地庆深气田为例,重点研究了深层火山碎屑熔岩形成机理及其在火山岩地质相和测井相识别中的意义。研究表明,火山碎屑熔岩类火山岩常见火山碎屑流、泡沫熔岩流、岩流自碎作用、近地表隐爆作用、再熔结(胶结)型5种成因类型,且不同成因火山碎屑熔岩具有明显不同的矿物岩石学特征和测井响应特征。根据其形成机理、矿物岩石学特征和FMI成像特征,认为上述5种成因类型的火山碎屑熔岩分别发育于爆发相热碎屑流亚相、介于爆发相和喷溢相之间的爆溢相、喷溢相、火山通道相隐爆角砾岩亚相、火山通道相火山颈亚相或近火山口相。该研究成果对于促进火山岩相、亚相的准确识别和优质储层的有效预测具有重要的指导意义。 相似文献