Gas release rates from pyroclastic flows: a assessment of the role of fluidisation in their emplacement
Gas release rates from pyroclastic flows: a assessment of the role of fluidisation in their emplacement
复制标题
火山碎屑流的气体释放速率：流化在其就位中的作用的评估
DOI：
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发表时间：
1978
期刊：
影响因子：
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通讯作者：
R. S. J. Sparks
中科院分区：
文献类型：
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作者：
R. S. J. Sparks
估计溶解水的释放速率从火山碎屑流中的颗粒扩散。计算了气体从不同厚度火山碎屑流中逸出的速度。对于相当小的残留气体含量（0.2至0.8%H2O），在释放的第一个103秒期间，对于厚度为1至20 m的流，估计气体速度为10至超过100 cm/sec，实验研究表明，这是流化细至中等灰所需的速度。具有高残余气体含量或大体积（厚流）的流很可能被出溶气体充分流化。预计在这样的流中30%至超过60%的颗粒被流化。因此，流化作用被认为是流动的重要机制，并在确定流动性的大规模，史前火山碎屑流，形成广泛的熔结凝灰岩片。然而，在几次历史性喷发中观察到的小火山碎屑流并不被认为是流化的，因为它们的残余气体含量低，体积小，并且在它们的就位过程中发生了大量的冷却。
Estimates are presented for the rates of release of dissolved water from the particles in a pyroclastic flow by diffusion. Velocities of gas escaping from pyroclastic flows of different thicknesses are calculated. For quite small residual gas contents (0.2 to 0.8% H2O), gas velocities of 10 to over 100 cm/sec during the first 103 sec of release are estimated for flows of thickness 1 to 20 m, which experimental studies demonstrate are the velocities required to fluidise fine to medium ash. Flows with high residual gas contents or large volume (thick flows) are likely to be substantially fluidised by exsolving gas. 30% to over 60% of the particles in such flows are predicted to be fluidised. Fluidisation is thus believed to be an important mechanism in the flow and in determining the mobility of the large magnitude, prehistoric pyroclastic flows which formed extensive ignimbrite sheets. Small pyroclastic flows, however, of the magnitude observed in several historic eruptions are not believed to be fluidised, because of their low residual gas contents, small volume, and the substantial amount of cooling that occurs during their emplacement.