Sedimentary peels from pyroclastic density current deposits: revealing basal flow-boundary processes.

稀薄火山碎屑密度流(PDC)代表了在火山爆发期间发生的一些最具流动性和危险性的事件。它是一种低浓度气体和颗粒混合物的输运过程，属于颗粒密度流的范畴。它们可以从喷口直接排放，也可以从密集的火山碎屑流中剥离出来，在距离喷发中心几公里的地方产生。它们的低密度是它们高流动性的原因，使它们能够克服地形障碍，而且到目前为止，人们对它们的内部动力学知之甚少。在稀释的PDC中，颗粒既起到驱动动量的作用，又构成了生成的沉积物。因此，对稀释的PDC留下的交错层状沉积物的沉积学研究是这些流动的最丰富和最具启发性的自然数据来源。通过在广泛的实地活动中用固化树脂浸渍2006年(厄瓜多尔)通古拉瓦火山喷发的沉积物，现在已经获得了一个独特的高分辨率数据集。这项技术允许生产既保留原始颗粒组织又保留地层的沉积皮。由此产生的数据集是用于精细调查和教育目的的罕见工具。作为对沉积剥层的补充，两项探地雷达调查和地面激光扫描仪测绘提供了关于矿床内部和地表的三维几何图形的额外信息。我们计划通过实验室表征结合特别设计的、有针对性的模拟实验对这些数据集进行详细的调查。我们的目标是对稀相颗粒的动力学和颗粒在流动床界面的形态动力学有独到的见解。PEELL数据集还将作为学生、研究人员和公众教育传播工具的核心部分。

Dilute pyroclastic density currents (PDCs) represent some of the most mobile and dangerous events occurring during explosive volcanic eruptions. They are a transport process of gas and particle mixtures at low concentration that belong to the class of particulate density currents. They can be directly emitted from a vent or be produced kilometres away from the eruptive centre by flow stripping from dense pyroclastic flows. Their low density is responsible for their high mobility, allowing them to overcome topographic obstacles and to date, little is known of their internal dynamics.In a dilute PDC, particles play the role of both driving momentum and make up the resultant deposit. Sedimentological studies on the cross-bedded deposits left by dilute PDCs thus represent the richest and most revealing source of natural data for these flows. A unique high-resolution dataset has now been acquired by impregnating the deposits of the 2006 eruption of Tungurahua volcano (Ecuador) with a solidifying resin during extensive field campaigns. This technique permits to produce sedimentary peels that preserve both the original grain organization and stratification. The resulting data-set is a rare tool for fine-scale investigation and educational purposes. As a complement to the sedimentary peels, two surveys of ground penetrating radar and terrestrial laser scanner mapping provide additional information on the three dimensional geometry of the deposits, both internal and surficial. We plan a detailed investigation of these datasets through laboratory characterisation in combination with specially designed, targeted, analogue experiments. Our goal is to gain unique insights into the dynamics of dilute PDCs and the morphodynamics of grain transport at the flow-bed interface. The peel dataset will also serve as the central piece of an educational dissemination tool for students, researchers, and the public.