Understanding the thermo-rheological regime and physical character of lava while it is flowing is crucial if we are to adequately model lava flow emplacement dynamics. We present measurements from simultaneous sampling and thermal imaging across the full width of an active channel at Piton de la Fournaise (La Réunion, France). Our data set involves measurements of flow dynamics at three sites down-channel from the vent. Quantification of flow velocities, cooling rates, sample texture, and rheology allows all thermo-rheological parameters to be linked, and down- as well as cross-channel variations to be examined. Within 150 m from the vent, we recorded an unexpected velocity increase (from 0.07 to 0.1 m/s), in spite of cooling rates of 0.19–0.29 °C/m and constant slope. This change requires a switch from a Newtonian-dominated regime to a Bingham plug–dominated regime. Sample analysis revealed that the plug consists of foam-like lava, and the shear zones involve vesicle-poor (low-viscosity) lava. With distance from the vent, shear zones develop, carrying the vesicular plug between them. This causes flow to initially accelerate, helped by bubble shearing in narrow lateral shear zones, until cooling takes over as the main driver for viscosity increase and, hence, velocity decrease.

中文翻译：

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剪切力如何帮助熔岩流动

如果我们要对熔岩流的位移动力学进行充分的建模，那么了解熔岩流动时的热流变状态和物理特性至关重要。我们介绍了在Piton de la Fournaise（法国留尼汪）活动通道的整个宽度上同时采样和热成像的测量结果。我们的数据集涉及在排气孔下游三个位置的流动动力学测量。流速，冷却速率，样品质地和流变性的定量分析可以链接所有热流变参数，并检查向下和跨通道的变化。尽管冷却速率为0.19–0.29°C / m，且坡度恒定，但在距通风口150 m内，我们仍记录到了意外的速度增加（从0.07到0.1 m / s）。这种变化需要从以牛顿为主的政权转变为以宾汉插头为主的政权。样品分析表明，该栓塞由泡沫状的熔岩组成，剪切带包括囊泡较差的（低粘度）熔岩。随着与排气孔的距离的增加，剪切区域形成，并在它们之间携带囊泡塞。这导致流动最初在狭窄的横向剪切区域中受到气泡剪切的帮助下加速，直到冷却成为粘度增加并因此速度降低的主要驱动力。