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首页> 外文期刊>Journal of Volcanology and Geothermal Research2012V243-244NOCT,15 >Pyroclast cooling and saturation in water
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Pyroclast cooling and saturation in water

机译：Pyroclast冷却和水中饱和

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In the submarine setting pyroclast cooling and saturation, by controlling the buoyancy of individual clasts and surrounding fluid, exert fundamental controls on the dispersal and fate of volcanic material. In this study we use laboratory experiments to understand and quantify how hot and air-filled pyroclasts cool and saturate in liquid water. By measuring internal temperature and clast submerged weight in over thirty experiments, we find that pumice cools and saturates in two stages. We observe that the first stage is marked by much higher rates of cooling and saturation than the second stage and that the transition between stages is sharp. We propose conceptual and quantitative models for each stage of pyroclast cooling and saturation. Specifically we argue that the first stage is defined by the presence of internal steam. That is, hot pyroclasts ingest liquid water and generate steam. Once a clast's internal pore space is filled with steam, heat loss to the surroundings causes condensation of internal vapor and clast saturation. Stage 1 ends when all internal steam has condensed. We test this idea with a Stefan Model with advection and conclude that heat loss, rather than permeability, controls the saturation of pyroclasts above the boiling temperature. We find that permeability matters for air-filled clasts with initial temperatures below the boiling point. Stage 2 begins after all internal vapor has condensed and we propose that stage 2 cooling and saturation are controlled by heat conduction and thermal contraction of trapped gas, respectively. From our understanding of the processes that govern the stage 1 to 2 transition, we derive an empirical average pyroclast cooling rate of q = 7.5 +/- 0.5 W cm(-2). Finally, we develop quantitative models for cooling-controlled porous clast saturation and for buoyant clast rise to the ocean surface. We find that meter size clasts stay buoyant for more than 10 min - long enough to reach the surface from a depth of 1000 m. The models developed here test our understanding of clast-scale processes and demonstrate that - in hot and porous clasts - the details of internal texture do not matter because clast saturation, and thus buoyancy and fate in the water column, are governed by heat transfer. (C) 2018 Elsevier B.V. All rights reserved.
机译：在海底环境中，火山碎屑的冷却和饱和度通过控制单个碎屑和周围流体的浮力，对火山物质的扩散和命运进行了基本控制。在这项研究中，我们使用实验室实验来了解和量化液体中热的和充满空气的热解麦芽浆如何冷却和饱和。通过在三十多个实验中测量内部温度和大量浸没重量，我们发现浮石分两个阶段冷却和饱和。我们观察到，第一阶段的冷却和饱和速率比第二阶段高得多，并且各阶段之间的过渡非常明显。我们提出了对于破骨细胞冷却和饱和的每个阶段的概念和定量模型。具体来说，我们认为第一阶段是由内部蒸汽的存在定义的。即，热的火山灰质吸收液态水并产生蒸汽。一旦碎屑的内部孔隙空间充满蒸汽，热量散失到周围环境就会导致内部蒸气凝结和碎屑饱和。当所有内部蒸汽凝结后，阶段1结束。我们用具有对流的Stefan模型测试了这个想法，并得出结论，热损失而不是渗透率控制着破火细胞在沸腾温度以上的饱和度。我们发现，对于初始温度低于沸点的充气填充物，渗透率很重要。第2阶段在所有内部蒸汽冷凝后开始，我们建议第2阶段的冷却和饱和分别受捕获气体的热传导和热收缩控制。从我们对控制阶段1到阶段2过渡的过程的理解中，我们得出q = 7.5 +/- 0.5 W cm（-2）的经验平均焦破石冷却速率。最后，我们开发了用于冷却控制的多孔碎屑饱和度和浮力碎屑上升到海面的定量模型。我们发现，米级碎屑保持漂浮的时间超过10分钟-足够长，可以从1000 m的深度到达水面。此处开发的模型检验了我们对碎屑尺度过程的理解，并证明了-在热碎屑和多孔碎屑中-内部纹理的细节并不重要，因为碎屑饱和度以及水柱中的浮力和结实受传热控制。 （C）2018 Elsevier B.V.保留所有权利。

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