New insights into the deposit architecture and emplacement mechanisms of block-and-ash flows using ground penetrating radar

块状火山灰(BAFs)是地球上最危险的火山现象之一。由于粘性熔岩穹顶的重力或爆炸性坍塌或火山岩型喷发柱的坍塌，BAFF在许多活动俯冲带火山中很常见，包括Colima(墨西哥)、Unzen(日本)、Soufrière Hills(蒙特塞拉特)、Arenal(哥斯达黎加)和Merapi(印度尼西亚)，它们对周围的人口和基础设施构成严重威胁。默拉皮火山是位于印度尼西亚爪哇中部的一座安山岩复合火山，是印尼喷发频率最高的火山之一，火山活动几乎持续不断。生活在火山两侧的110万人中，近一半生活在高危地区。据估计，价值数千万美元的财产位于火山的脆弱区，鉴于当地人口每年3%的增长率，这一数字可能会增加。自15世纪中期以来，默拉皮火山喷发已造成约7000人死亡。最近，1994年的一次小规模喷发导致66人死亡，而2006年的新一轮活动导致更多人死亡，这是一个多世纪以来首次影响到火山南侧人口稠密的地区。这些喷发说明了BAFS的不可预测和仍然鲜为人知的行为，它在被认为相对不受BAFS和相关危险影响的地区造成了严重破坏。此外，它们还表明迫切需要改进对生物燃料燃料的流动性、运输和沉积过程的实际了解，以便改进对其当地潜在危险的评估。传统上，生物滤池的迁移和沉积的定性模型是基于对所产生的沉积物的内部结构的解释而建立的。不幸的是，暴露不良和受未知古地形控制的侧向相快速变化，往往使这种实地研究变得复杂，并阻碍了对侵位机制的详细评估，从而阻碍了这种流动的潜在危险。这一建议旨在通过将探地雷达(GPR)应用于2006年的Merapi BAF矿床来克服这些传统研究的固有局限性，这为这类研究提供了一个独特而理想的天然实验室。探地雷达在火山碎屑矿床中的应用相对较新，该技术能够独立于暴露的存在而系统和快速地收集地下信息。这开启了一种独特的视角，与沿裸露剖面的详细沉积学研究相结合，将提供迄今最完整的BAF矿床三维矿床结构以及这种类型的火山碎屑流是如何侵位的图景。仅靠直接观察技术是不可能达到这样的解释复杂程度的。这项研究的结果将有助于形成对生物曝气生物滤池相关危害的新的、更好的理解，并有助于为与减灾相关的挑战提供可持续的技术解决方案(NERC科学战略计划中强调的一个优先领域)。该项目的关键成果之一是创建了一个独特的、约束良好的数据集，该数据集在质量流动的数值模拟和多相颗粒矿床的侵位动力学方面具有重要的应用。因此，这项工作将直接(在世界上一些最活跃的火山的观测站)或通过遥感和数值模拟技术对参与评估火山危害的所有小组立即受益。

Block-and-ash flows (BAFs) are amongst the most dangerous volcanic phenomena on the planet. Generated by gravitational or explosive collapses of viscous lava domes or by the collapse of vulcanian-type eruption columns, BAFs are common at many active subduction zone volcanoes, including Colima (Mexico), Unzen (Japan), Soufrière Hills (Montserrat), Arenal (Costa Rica) and Merapi (Indonesia), where they pose a severe threat to the surrounding population and infrastructure. Merapi, an andesitic composite volcano located in Central Java (Indonesia), is one of the most frequently erupting volcanoes in Indonesia with nearly persistent volcanic activity. Of the 1.1 million people living on the flanks of the volcano, almost half live in high-risk areas. It is estimated that property worth tens of millions of U.S. dollars lies in the vulnerability zone of the volcano and this amount is likely to increase given a population growth rate of 3% per year in the local area. Since the mid-1500s, eruptions of Merapi have caused ~7000 fatalities. More recently, BAFs from a small-scale eruption in 1994 killed 66 people, whilst the renewed activity of 2006, which, for the first time in more than a century affected densely populated areas on the volcano's southern flank, led to more fatalities. These eruptions illustrate the unpredictable and still poorly understood behaviour of BAFs, which caused havoc in areas considered relatively save from BAFs and related hazards. Furthermore, they have demonstrated the urgent need for an improved physical understanding of the mobility, transport and deposition processes of BAFs in order to improve assessments of their local hazard potential. Traditionally, qualitative models of BAF transport and deposition have been developed based on interpretations of the internal structure from resulting deposits. Unfortunately, a combination of poor exposure and rapid lateral facies variations, controlled by unknown palaeo-topography, have often complicated such field-based studies and have hindered the detailed assessment of emplacement mechanisms and, hence, the hazard potential of such flows. This proposal aims to overcome the inherent limitations of these traditional studies through the application of ground penetrating radar (GPR) to the 2006 Merapi BAF deposits, which provide a unique and ideal natural laboratory for this type of research. The application of GPR to pyroclastic deposits is relatively new and the technique is capable of allowing systematic and rapid collection of sub-surface information independently from the presence of exposures. This opens a unique perspective that, when combined with detailed sedimentological studies along exposed sections, will provide the most complete picture yet of the three-dimensional deposit architecture of BAF deposits and how this type of pyroclastic flows is emplaced. Such a level of interpretational sophistication is impossible to achieve with direct observation techniques alone. The results of this study will be instrumental in formulating a new, improved understanding of BAF-related hazards and help provide sustainable technology solutions to the challenges associated with hazard mitigation (a priority area highlighted in the NERC Strategic Plan for Science). One of the key outcomes of the project is to create a unique, well-constrained data set that has important applications to the numerical modelling of mass flows and the emplacement dynamics of multi-phase granular deposits. Consequently, the work will be of immediate benefit to all groups involved in assessing volcano hazards either directly (at observatories on some of the most active volcanoes around the world) or through remote sensing and numerical modelling techniques.