Measuring the size of non-spherical particles and the implications for grain size analysis in volcanology
Measuring the size of non-spherical particles and the implications for grain size analysis in volcanology
复制标题
DOI：
10.1016/j.jvolgeores.2021.107257
复制
发表时间：
2021-05-04
影响因子：
2.9
通讯作者：
Engwell, Samantha L.
中科院分区：
文献类型：
--
作者：
Buckland, Hannah M.;Saxby, Jennifer;Engwell, Samantha L.
为了量化tephra的尺寸，必须解决两个实际挑战：广泛的粒径范围(10（-8)10(1)m）以及颗粒形状、密度和光学性质的多样性。在这里，我们使用动态图像分析（DIA）来同时表征Mazama山、Krafla山、St. Helens山和Campi Flegrei山的麻风样品的大小和形状。本研究使用的Camsizer X2仪器的测量范围为0.8 μ m - 8 mm，避免了对细（125 μ m）粒径的不同测量方法和原理的重叠。重要的是，DIA不需要假设粒子的性质。DIA还允许使用多种尺寸定义来测量粒度分布（gsd）。例如，通过粒子长轴和面积等效球直径进行定量，使DIA GSDs与激光衍射和筛分等其他方法的输出兼容。平行的基于质量（筛分）和基于体积（DIA）的GSDs强调了颗粒密度变化对粒度分析方法的影响；特别是在一个狭窄的尺寸范围内，密集晶体的浓度会影响基于质量的gsd及其解释。我们还发现，颗粒形状对远端tephra的表观晶粒尺寸有重要影响。极端的颗粒形状，如典型的远坎帕系Ignimbrite沉积物的板状玻璃碎片，如果根据颗粒长轴量化大小，可能比其他远端tephras显得更粗。这些结果对灰分散模型具有重要意义，其中输入gsd假设报告的测量结果是体积等效球体直径。我们得出的结论是，DIA方法不仅适合于同时表征火山灰颗粒的大小和形状，而且还提供了对颗粒特性的新见解，这些特性对火山灰分散建模和爆炸性火山作用的研究都很有用。(C) 2021作者。Elsevier B.V.出版
To quantify the size of tephra, two practical challenges must be addressed: the wide range of particle sizes (10(-8) 10(1) m) and the diversity of particle shape, density and optical properties. Here we use dynamic image analysis (DIA) to simultaneously characterise the size and shape of tephra samples from Mount Mazama, Krafla, Mount St. Helens and Campi Flegrei. The Camsizer X2 instrument used in this study, which has a measurement range of 0.8 mu m - 8 mm, avoids the need to overlap different measurement methods and principles for fine (125 mu m) particle sizes. Importantly, DIA does not require an assumption of particle properties. DIA also allows the measurement of grain size distributions (GSDs) using multiple size definitions. Quantification by particle long axis and the area equivalent sphere diameter, for example, make DIA GSDs compatible with the outputs of other methods such as laser diffraction and sieving. Parallel mass-based (sieving) and volume-based (DIA) GSDs highlight the effects of particle density variations on methods of size analysis; concentrations of dense crystals within a narrow size range, in particular, can affect mass-based GSDs and their interpretations. We also show that particle shape has an important effect on the apparent grain size of distal tephra. Extreme particle shapes, such as the platy glass shards typical of the distal Campanian Ignimbrite deposits, can appear coarser than other distal tephras if size is quantified according to the particle long axis. These results have important implications for ash dispersion models, where input GSDs assume that reported measurements are for volume-equivalent sphere diameters. We conclude that DIA methods are not only suitable for characterising, simultaneously, the size and shape of ash particles but also provide new insights into particle properties that are useful for both ash dispersion modelling and studies of explosive volcanism. (C) 2021 The Author(s). Published by Elsevier B.V.