Surface Morphology of Pyroclasts from Mount St. Helens and Vesuvius: Characterization and Interpretation

该项目将开发和测试一种方法，用于鉴定和分析来自两个经典火山碎屑沉积物的结晶和玻璃状幼年火山碎屑的形态特征：1)1980年圣海伦火山的产物，2)公元79年维苏威火山的沉积物。这两个事件产生了从火山泥流到普林尼式瀑布的各种沉积物。对这两个矿床的地层和喷发现象进行了深入的研究和表征。原始颗粒表面形态的集体特征将根据这两次喷发特征的连续变化来解释。机械和化学过程对颗粒表面的相对影响将通过颗粒的喷发、运输、沉积和冷却来追踪。从这些矿床的每一个主要地层水平收集的足够的火山碎屑数据集将被检查，以确定对解释环境历史有用的关键结构。此外，还将在一个专门设计的装置上进行实验研究，研究热碎片在水中淬灭后的形貌和原生碎屑磨损后产生的织构。火成岩形态调查方法的发展和使用计算机分析结果的验证是本研究的组成部分。将测试各种用于分析样品形态的技术，以确定哪一种最适合从单个成分的特征来确定沉积物的历史。

This project will develop and test a methodology for the identification and analysis of morphological features on crystalline and glassy juvenile tephra from two calssic pyroclastic deposits: 1) the 1980 products of Mount St. Helens, and 2) the A.D. 79 deposits of Vesuvius. A wide range of deposits from lahars to plinian falls were produced by these two events. The stratigraphy and eruptive phenomena of both deposits have been well studied and characterized. Collective features of primary grain-surface morphology will be interpreted in terms of the successive changes in the character of these two eruptions. The relative effects of mechanical and chemical processes on grain surfaces will be traced through the eruption, transportation, deposition and cooling of the tephra. Data sets of sufficient pyroclasts from every major stratigraphic level of these deposits will be examined to identify key textures useful for interpretation of environmental histories. In addition, experimental studies will be done to investigate the morphology of hot fragments quenched in water, and the textures produced by abrasion of primary clasts in a specially designed device. Development of a methodology for pyroclast morphologic investigation and verification of the results using computer analysis are integral parts of this study. Various techniques for analysis of tephra morphologies will be tested to determine which are best suited to determine the history of the deposits from the characteristics of the individual components.