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The interaction between concentrated pyroclastic density currents and snow: a case study from the 2008 mixed-avalanche from Volcán Llaima (Chile)
Bulletin of Volcanology ( IF 3.5 ) Pub Date : 2020-10-29 , DOI: 10.1007/s00445-020-01413-4
E. C. P. Breard , Eliza S. Calder , Dawn C.S. Ruth

The incorporation of snow and ice by pyroclastic density currents (PDCs) can generate mixed-avalanches and pose significant hazards at snow-clad volcanoes. Commonly, the poor preservation of these thin deposits, combined with the subtle characteristics of PDC-snow interaction, has limited their recognition in the geological record. A small-volume (2.5 × 105 m3), basaltic-andesite, mixed-avalanche deposit formed during the 2008 eruption of Volcán Llaima (Chile) provides insight into PDC and snow interactions. Pyroclasts accumulated on the crater rim and collapsed to form a flow that swept up to 2.8 km from source and spread across 6.09 × 105 m2 of the snow-clad slopes. The PDC-snow interaction at the crater rim or during flow propagation resulted in distinct deposit and pyroclast textures. These included abundant blocky non-vesicular cauliflower clasts and blocky poorly vesicular scoria. The thin and sheet-like mixed-avalanche deposit had a lumpy surface, lacked marginal levees, was very loose, and fine ash depleted. Although the flow likely incorporated snow and/or ice mechanically, the overall coarseness of the mixture precluded effective fluidization related to vaporization. Many of the features described herein are distinctive features of other mixed-avalanche deposits worldwide and should be considered key indicators of PDC-snow interaction.

中文翻译:

集中火山碎屑密度流与雪之间的相互作用:来自 Volcán Llaima(智利)的 2008 年混合雪崩的案例研究

火山碎屑密度流 (PDC) 将冰雪结合在一起会产生混合雪崩,并对积雪覆盖的火山造成重大危害。通常,这些薄层沉积物保存不佳,再加上 PDC 与雪相互作用的微妙特征,限制了它们在地质记录中的识别。在 2008 年 Volcán Llaima(智利)喷发期间形成的小体积(2.5 × 105 m3)玄武岩-安山岩混合雪崩沉积物提供了对 PDC 和雪相互作用的深入了解。火山碎屑堆积在火山口边缘并坍塌形成一股气流,从源头扫过 2.8 公里,并蔓延到 6.09 × 105 平方米的积雪斜坡。PDC-雪在火山口边缘或流动传播过程中的相互作用导致了不同的沉积物和火山碎屑纹理。这些包括大量块状非水泡花椰菜碎屑和块状差水泡碎屑。薄而片状的混合雪崩沉积物表面凹凸不平,缺乏边缘堤防,非常松散,细灰已枯竭。虽然流动可能会机械地包含雪和/或冰,但混合物的整体粗糙程度妨碍了与汽化相关的有效流化。此处描述的许多特征是世界范围内其他混合雪崩矿床的独特特征,应被视为 PDC 与雪相互作用的关键指标。混合物的整体粗糙阻止了与汽化相关的有效流化。此处描述的许多特征是世界范围内其他混合雪崩矿床的独特特征,应被视为 PDC 与雪相互作用的关键指标。混合物的整体粗糙阻止了与汽化相关的有效流化。此处描述的许多特征是世界范围内其他混合雪崩矿床的独特特征,应被视为 PDC 与雪相互作用的关键指标。
更新日期:2020-10-29
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