An Experimental Model of Unconfined Bubbly Lava Flows: Importance of Localized Bubble Distribution
An Experimental Model of Unconfined Bubbly Lava Flows: Importance of Localized Bubble Distribution
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DOI：
10.1029/2022jb024139
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发表时间：
2022-05
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影响因子：
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通讯作者：
A. Namiki;E. Lev;J. Birnbaum;Jasper Baur
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文献类型：
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作者：
A. Namiki;E. Lev;J. Birnbaum;Jasper Baur
大多数熔岩流携带着悬浮的气泡和晶体。从早期的工作，它是已知的，球形气泡增加有效粘度，而气泡变形的快速流动降低it.Changes在空间分布的气泡可以导致可变的流变学和流动局部化，从而修改所产生的熔岩流的结构和形态。为了了解气泡和固相晶体分布的作用，我们进行了一系列高气泡分数悬浮液的模拟实验。我们将模拟熔岩倾倒在倾斜的斜坡上，观察其形状，计算速度场，并监测其局部厚度。在泡状流的中心形成一个局部快速流动和低泡状度的区域，其厚度比周围区域薄。这些特征表明，局部较高的液体分数降低了有效粘度，增加了流体密度，并加速了流动。我们还发现，停止的含颗粒气泡流可以恢复流动。我们将其解释为气泡向上垂直分离的结果，这在流动的底部产生了富液层。在我们的实验中，气泡基本上是球形的，会降低流速，而我们的估计表明，天然熔岩流中的气泡会增加或降低流速。下游流速的降低阻止了气泡变形，并可能导致有效粘度的突然增加。在流速减慢的前缘处液相的垂直分离可能是产生海绵状壳状帕霍埃霍埃的一种方式。
Most lava flows carry bubbles and crystals in suspension. From earlier works, it is known that spherical bubbles increase the effective viscosity while bubbles deformed by rapid flow decrease it. Changes in the spatial distribution of bubbles can lead to variable rheology and flow localization and thus modify the resulting lava flow structure and morphology. To understand the roles of bubble and solid phase crystal distributions, we conducted a series of analog experiments of high bubble fraction suspensions. We poured the analog lava on an inclined slope, observed its shape, calculated the velocity field, and monitored its local thickness. A region of localized rapid flow and low vesicularity, whose thickness is thinner than the surrounding area, develops at the center of the bubbly flows. These features suggest that the locally higher liquid fraction decreases the effective viscosity, increases the fluid density, and accelerates the flow. We also found that a halted particle‐bearing bubbly flow can resume flowing. We interpret this to result from the upward vertical separation of bubbles, which generates a liquid‐rich layer at the bottom of the flow. In our experiment, bubbles are basically spherical and decrease the flow velocity, while our estimate suggests that bubbles in natural lava flows could increase or decrease flow velocity. Downstream decreases in flow velocity stops the bubble deformation and can cause a sudden increase of effective viscosity. The vertical segregation of the liquid phase at the slowed flow front may be a way to generate a cavernous shelly paho’eho’e.