Sedimentary Processes in Pyroclastic Density Currents: Insights From the Deposits of Nevado de Toluca Volcano, Mexico

EAR-0309703Gardner火山碎屑密度流是流动颗粒物质的最大天然例子，并显示出复杂的大小和密度分离模式。该项目将研究它们的矿藏，以深入了解控制混合和分离模式的过程，这些模式在较小规模的颗粒流中很难研究。对块状和层状相的拓扑结构、颗粒大小和密度的分析将被用来重建母流的内部工作。要研究的地点是墨西哥内瓦多德托卢卡的一次爆炸性喷发。将通过地理信息系统数据库的三个子集探索相变化，该数据库将把通过确定成分和粒度分析获得的采样数据与地层柱、全球定位系统坐标和照片相结合。第一个子集将允许确定块状相的沉积机制，整体或沉积。这一步骤将解开托卢卡目前反向粗尾分级的含义，这是一种罕见的沉积模式，引起了广泛的兴趣，因为它与其他火山常见的正常分级相反。第二个子集给出的分层相的局部变化将与不同模型的预测进行比较，以评估涌浪是具有强烈颗粒浓度内部波动的准稳定流，还是受源洞波动控制的非稳定流。这项工作将扩展到其他发生类似沉积过程的危险地球物理流，如雪崩、泥石流和山体滑坡。该结果也将适用于试图避免粉末生产过程中分离的工业、化工和制药应用。

EAR-0309703GardnerPyroclastic density currents are the largest natural examples of flowing granular matter and display complex patterns of size and density segregation. This project will study their deposits to gain insight into processes controlling mixing and segregation patterns difficult to study in smaller-scale granular flows. Analysis of the topology and particle sizes and densities of both massive and stratified facies will be used to reconstruct the internal workings of the parent current. The site to be studied is an explosive eruption of Nevado de Toluca, Mexico. Facies changes that will be explored by the means of three subsets of a GIS database, which will integrate sampling data obtained by determining componentry and grain size analysis with stratigraphic columns, GPS coordinates, and photographs. The first subset will allow determining the depositional mechanism of the massive facies, en masse or aggradation. This step will unlock the meaning of the reverse coarse-tail grading present at Toluca, a rare sedimentary pattern of broad interest because it is the opposite of the normal grading found commonly in other volcanoes. The local variations of the stratified facies given by the second subset will be compared to predictions from various models in order to assess whether surges are quasi-steady currents with strong internal fluctuations in particle concentration, or unsteady currents controlled by fluctuations at the source vent.This work will be extended to other hazardous geophysical flows where similar sedimentation processes occur, such as snow avalanches, debris flows, and landslides. The results will also be applicable to industrial, chemical, and pharmaceutical applications attempting to avoid segregation during powder production.