Jones Thomas J, Shetty Abhishek, Chalk Caitlin, Dufek Josef, Gonnermann Helge M
Lancaster Environment Centre, Lancaster University, Lancaster, UK.
Rheology Division, Advanced Technical Center, Anton Paar USA Inc, Ashland, VA, USA.
Nat Commun. 2024 May 23;15(1):4401. doi: 10.1038/s41467-024-48612-7.
Pyroclastic density currents (PDCs) are the most lethal of all volcanic hazards. An ongoing challenge is to accurately forecast their run-out distance such that effective mitigation strategies can be implemented. Central to this goal is an understanding of the flow mobility-a quantitative rheological model detailing how the high temperature gas-pyroclast mixtures propagate. This is currently unknown, yet critical to accurately forecast the run-out distance. Here, we use a laboratory apparatus to perform rheological measurements on real gas-pyroclast mixtures at dynamic conditions found in concentrated to intermediate pumice-rich PDCs. We find their rheology to be non-Newtonian featuring (i) a yield stress where deposition occurs; (ii) shear-thinning behavior that promotes channel formation and local increases in velocity and (iii) shear-thickening behavior that promotes decoupling and potential co-PDC plume formation. We provide a universal regime diagram delineating these behaviors and illustrating how flow can transition between them during transport.
火山碎屑密度流（PDCs）是所有火山灾害中最致命的。当前面临的一个挑战是准确预测它们的流动距离，以便能够实施有效的减灾策略。实现这一目标的核心是理解流体流动性——一个详细描述高温气体 - 火山碎屑混合物如何传播的定量流变模型。目前这一点尚不清楚，但对于准确预测流动距离至关重要。在这里，我们使用实验室设备对在浓缩至中等富含浮石的PDCs中发现的动态条件下的真实气体 - 火山碎屑混合物进行流变测量。我们发现它们的流变学是非牛顿型的，其特征包括：（i）发生沉积时的屈服应力；（ii）促进通道形成以及局部速度增加的剪切变稀行为；（iii）促进解耦和潜在的伴生PDC羽状物形成的剪切增稠行为。我们提供了一个通用的状态图，描绘了这些行为，并说明了在运输过程中流体如何在它们之间转变。
