Interpreting the Dispersal Characteristics of Widespread Volcanic Ash Marker Horizons in the Geologic Record

解释地质记录中广泛分布的火山灰标志层的分散特征Steven Carey，University of Rhode Islande-0545112摘要广泛分布的火山灰层在地质记录中形成重要的年代地层层位，并且在与火山学、古气候、大气环流和放射性测年相关的研究中至关重要。它们构成了事件视界，使数万平方公里的空间域之间具有精确的时间相关性。它们形成的许多方面已经很好地了解，但关于过去发生的最大规模喷发的火山灰的散布和沉积仍然存在关键问题。它们的分布模式往往明显地向上风方向延伸，相对于历史上较小的沉降物来说，它们的宽度很宽。控制广泛灰层形成的因素将使用拉格朗日粒子跟踪模型进行调查，该模型最初是根据污染扩散代码制定的。将对模型进行修改，以便：1）考虑到大规模伞云的火山灰喷射; 2）将颗粒沉降变化视为雷诺数的函数; 3）考虑到平流层传输，包括作为高度和时间函数的典型风变化。模拟将在1991年的火山喷发进行。皮纳图博在菲律宾，以评估该模型的预测能力。将把模型结果与关于喷发羽流移动和火山灰沉积区的观测数据进行比较。将对印度尼西亚多巴火山口的两次喷发（最年轻的多巴凝灰岩和最古老的多巴凝灰岩事件）进行额外的模拟。这些模拟的结果将被用来评估对流层与平流层的运输在产生异常广泛的分布的火山灰层，在整个印度洋和中国南海的沉积物中发现的作用。

Interpreting the dispersal characteristics of widespread volcanic ash markerhorizons in the geologic recordSteven Carey, University of Rhode IslandEAR-0545112Abstract Widespread volcanic ash layers form important chrononstratigraphic horizons in the geologic record and have been critical in studies related to volcanology, paleoclimate, atmospheric circulation, and radiometric dating. They constitute event horizons that allow for precise temporal correlation across spatial domains of several tens of thousands of km2. Many aspects of their formation are well understood but critical questions remain about the dispersal and deposition of volcanic ash from the very largest eruptions that have occurred in the past. Their distribution patterns often extend significantly in an apparent upwind direction and their widths are wide relative to smaller historic examples of fallout. The factors that control the formation of widespread ash horizons will be investigated using a Lagrangian particle tracking model that was originally formulated from a pollution dispersal code. The model will be modified to 1) account for injection of volcanic ash from large-scale umbrella clouds, 2) treat particle settling variations as functions of the Reynolds number, and 3) account for stratospheric transport, including the typical variation of wind as a function of altitude and time. Simulations will be carried out on the 1991 eruption of Mt. Pinatubo in the Philippines in order to evaluate the predictive capability of the model. Model results will be compared with observational data on the movement of the eruption plume and the area of ash deposition. Additional simulations will be carried out on two eruptions of the Toba caldera in Indonesia (Youngest Toba Tuff and Oldest Toba Tuff events). Results of these simulations will be used to assess the role of tropospheric versus stratospheric transport in producing the exceptionally wide distribution of the tephra layers that are found in sediments both throughout the Indian Ocean and South China Sea.