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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Towards fast and routine analyses of volcanic ash morphometry for eruption surveillance applications
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Towards fast and routine analyses of volcanic ash morphometry for eruption surveillance applications

机译：进行火山灰形态分析的快速常规分析，以用于喷发监测应用

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The morphometry of volcanic ash produced by explosive eruptions yields ample information on fragmentation processes (e.g. magmatic vs magma-water interactions), and on transport and sedimentation mechanisms. Most previous works on volcanic clast morphometry focused on the Apparent (2D-)Projected shape of ASH grains, here termed APASH, to infer processes and eruptive styles. However, textural analyses of ash grains has remained a long and tedious task that made such approaches inappropriate for eruption surveillance duties. In this work we show that new technological advances on automated dispersion of granular materials imaged with a camera-coupled microscope and enhanced computer capabilities enable fast and high resolution image acquisition of thousands of ash grains that resolve this limitation. With a morpho-grainsizer designed for such fast and routine measurements we perform a series of APASH analyses on selected ash fractions of tephra deposits from known eruptive styles. We record the size, aspect ratio, circularity and convexity of APASH images and assess resolution, reproducibility, minimum population size, and total analytical duration, and offer recommendations for the reporting of APASH data for inter-laboratory comparisons. To avoid fractal geometry concerns, our analyses are carried out at constant size range (250-300 mu m) and optical magnification (x5) on similar to 3000 grains per samples collected from homogenized samples. Results from the andesitic 1999-ongoing eruption of Tungurahua volcano (Ecuador) show that ash particles from the moderate 2001 phase are relatively equant and convex in shape, while the stronger 2006 subplinian phase produced ash grains with more elongated, less circular and less convex APASH signatures. Ash grains from a basaltic scoria cone-forming eruption show even more ragged APASH characteristics. Overall, our protocol allows obtaining accurate and reproducible morphometric measurements that reveal subtle variations of the morphological signature, and the short duration (1.8 hours) of the whole analytical process renders high resolution analyses of ash shape achievable for volcano surveillance applications. This research ultimately aims to set up a morphometric database of APASH results for well-defined eruptive styles, in order to interpret on a short term basis any APASH data from active volcanoes for monitoring purposes. (C) 2015 Published by Elsevier B.V.
机译：爆炸性喷发产生的火山灰的形态学产生了关于破碎过程（例如岩浆与岩浆-水的相互作用）以及运输和沉积机制的大量信息。以前有关火山岩地貌形态学的大多数工作都集中在ASH颗粒的表观（二维）投影形状（这里称为APASH）上，以推断出过程和喷发样式。然而，灰烬的质地分析仍然是一项漫长而繁琐的任务，这使得此类方法不适用于喷发监测工作。在这项工作中，我们证明了利用相机耦合显微镜成像的粒状材料自动分散和增强的计算机功能方面的新技术进步，可以快速，高分辨率地采集数千种灰烬颗粒，从而解决了这一局限性。使用专为这种快速和常规测量而设计的形态粒度分析仪，我们对来自已知喷发方式的提夫拉沉积物的选定灰分进行了一系列APASH分析。我们记录APASH图像的大小，纵横比，圆度和凸度，并评估分辨率，可重复性，最小人口规模和总分析时间，并为报告APASH数据进行实验室间比较提供建议。为避免出现分形几何问题，我们的分析在恒定大小范围（250-300μm）和光学放大倍数（x5）下进行，每个样品均质样品均采集3000个颗粒。通古拉瓦火山（厄瓜多尔）的安山岩1999年持续喷发的结果表明，中度2001年相的火山灰颗粒相对均匀且呈凸形，而2006年次亚平相较强的火山灰产生的灰烬具有更长的伸长度，较小的圆形度和较少的凸度APASH签名。玄武岩锥状喷发形成的灰烬颗粒显示出更加粗糙的APASH特征。总体而言，我们的协议允许获得准确且可重现的形态测量结果，以揭示形态特征的细微变化，并且整个分析过程的持续时间短（1.8小时）使火山监测应用可以实现高分辨率的灰分形状分析。这项研究最终旨在为定义明确的喷发样式建立APASH结果的形态计量数据库，以便在短期基础上解释来自活火山的APASH数据以进行监测。 （C）2015由Elsevier B.V.发布

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