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位的扩散特征罗德岛大学的Steven Carey EAR-0545112摘要广泛分布的火山灰地层在地质记录中形成了重要的年代地层层位，在与火山学、古气候、大气环流和辐射测年相关的研究中起着至关重要的作用。它们构成了事件视界，允许跨越数万平方公里的空间域进行精确的时间关联。它们形成的许多方面都很清楚，但关键问题仍然是过去发生的非常大的喷发所产生的火山灰的扩散和沉积。它们的分布模式通常在明显的迎风方向上显著延伸，并且它们的宽度相对于历史上较小的尘埃例子来说是较宽的。控制广泛灰层形成的因素将使用拉格朗日颗粒跟踪模型进行调查，该模型最初是根据污染扩散法规制定的。该模型将被修改为：1)考虑大尺度伞状云注入的火山灰；2)考虑粒子沉降变化作为雷诺数的函数；3)考虑平流层输送，包括风随高度和时间的典型变化。将对1991年的火山喷发进行模拟。在菲律宾的Pinatubo，以评估该模型的预测能力。模型结果将与喷发羽流运动和火山灰沉积面积的观测数据进行比较。将对印度尼西亚托巴火山口的两次喷发(最年轻的托巴凝灰岩事件和最古老的托巴凝灰岩事件)进行额外的模拟。这些模拟的结果将被用来评估对流层和平流层输送在产生异常广泛的苔藓层分布方面的作用，这种分布在整个印度洋和南中国海的沉积物中都有。

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.