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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Syneruptive sequential fragmentation of pyroclasts from fractal modeling of grain size distributions of fall deposits: the Cretaio Tephra eruption (Ischia Island, Italy)
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Syneruptive sequential fragmentation of pyroclasts from fractal modeling of grain size distributions of fall deposits: the Cretaio Tephra eruption (Ischia Island, Italy)

机译：从秋季沉积物粒度分布的分形模型出发，解热质的协同顺序破碎：Cretaio Tephra喷发（意大利伊斯基亚岛）

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摘要

In this work we use fractal statistics in order to decipher the mechanisms acting during explosive volcanic eruptions by studying the grain size distribution (GSD) of natural pyroclastic-fall deposits. The method was applied to lithic-rich proximal deposits from a stratigraphic section of the Cretaio Tephra eruption (Ischia Island, Italy). Analyses were performed separately on bulk material, juvenile, and lithic fraction from each pyroclastic layer. Results highlight that the bulk material is characterized by a single scaling regime whereas two scaling regimes, with contrasting power-law exponents, are observed for the juvenile and the lithic fractions. On the basis of these results, we infer that the bulk material cannot be considered as a good proxy for deducing eruption dynamics because it is the result of mixing of fragments belonging to the lithic and juvenile fraction, both of which underwent different events of fragmentation governed by different mechanisms. In addition, results from fractal analyses of the lithic fraction suggest that it likely experienced a fragmentation event in which the efficiency of fragmentation was larger for the coarser fragments relative to the finer ones. On the contrary, we interpret the different scaling regimes observed for the juvenile fraction to be due to sequential events of fragmentation in the conduit, possibly enhanced by the presence of lithic fragments in the eruptive mixture. In particular, collision al events generated increasing amounts of finer particles modifying the original juvenile GSDs and determining the development of two scaling regimes in which the finer fragments record a higher efficiency of fragmentation relative to the coarser ones. We further suggest that in lithic-rich proximal fall deposits possible indications about the original GSDs of the juvenile fraction might still reside in the coarser particles fraction. (C) 2017 Elsevier B.V. All rights reserved.
机译：在这项工作中，我们使用分形统计方法，通过研究天然火山碎屑沉积物的粒度分布（GSD）来解释爆炸性火山喷发过程中的作用机理。该方法应用于来自Cretaio Tephra火山喷发（意大利伊斯基亚岛）地层剖面的富含石块的近端沉积物。分别对每个火山碎屑层的散装物料，幼体和岩屑进行了分析。结果表明，散装材料的特征在于单一的结垢状态，而对于幼虫和石质碎屑则观察到两种具有不同幂律指数的结垢状态。根据这些结果，我们推断散装物质不能被认为是推论喷发动力学的良好替代，因为它是属于石质和少年部分的碎片混合的结果，两种碎片均受到不同的碎片控制。通过不同的机制。另外，对岩屑馏分的分形分析结果表明，它可能经历了一个碎裂事件，其中较粗的碎屑相对于较细的碎屑，碎裂效率更高。相反，我们将观察到的幼体馏分的不同结垢机制解释为是由于导管中连续的碎裂事件所致，可能是由于喷发性混合物中存在碎屑碎片而增强了。特别是，碰撞事件产生了越来越多的细颗粒，这些颗粒修饰了原始的青少年GSD，并决定了两种缩放机制的发展，在这种机制中，较细的片段相对于较粗的片段记录了更高的碎片效率。我们进一步建议，在富含石块的近端秋季沉积物中，有关少年馏分的原始GSD的可能迹象可能仍存在于较粗的颗粒馏分中。 （C）2017 Elsevier B.V.保留所有权利。

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