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首页> 外文期刊>Journal of Volcanology and Geothermal Research2012V243-244NOCT,15 >Geological and geotechnical characterization of the debris avalanche and pyroclastic deposits of Cotopaxi Volcano (Ecuador). A contribute to instability-related hazard studies
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Geological and geotechnical characterization of the debris avalanche and pyroclastic deposits of Cotopaxi Volcano (Ecuador). A contribute to instability-related hazard studies

机译：科托帕希火山（厄瓜多尔）的碎屑雪崩和碎屑沉积物的地质和岩土特征。有助于与不稳定相关的危害研究

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摘要

The huge volcanic debris avalanche occurred at 4.5 ka is a major event in the evolution of the Cotopaxi volcano, Ecuador. The present volcanic hazard in the Cotopaxi region is related to lahars generated by volcanic eruptions and concurrent ice melting. This paper presents the geological and geotechnical field and laboratory characterization of the 4.5 ka Cotopaxi debris avalanche deposit and of the younger unconsolidated pyroclastic deposits, representing the probable source of future shallow landslides. The debris avalanche formed a deposit with a well-developed hummocky topography, and climbed a difference in height of about 260 m along the slopes of the adjacent Sincholagua volcano. The debris avalanche deposit includes four lithofacies (megablock, block. mixed, and sheared facies) that represent different flow regimes and degrees of substratum involvement. The facies distribution suggests that, in the proximal area, the debris avalanche slid predominantly confined to the valleys along the N and NE flank of the volcanic cone, emplacing a stack of megablocks. When the flow reached the break in slope at the base of the edifice, it became unconfined and spread laterally over most of the area of the Rio Pita valley. A dynamic block fragmentation and dilation occurred during the debris avalanche transport, emplacing the block facies. The incorporation of the older Chalupas lgnimbrite is responsible for the mixed facies and the sheared facies. Geotechnical results include a full-range grain size characterization, which enabled to make broader considerations on possible variability among the sampled facies. Consolidated drained triaxial compression tests, carried out on the fine fraction <4.76 mm, point out that shear strength for cohesionless sandy materials is only due to effective friction angle, and show a quite homogeneous behaviour over the set of tested samples.
机译：发生在4.5 ka处的巨大火山碎片雪崩是厄瓜多尔科托帕希火山演变中的重要事件。科托帕希地区目前的火山灾害与火山喷发和同时发生的冰融化所产生的拉哈斯有关。本文介绍了4.5 ka Cotopaxi碎片雪崩矿床和较年轻的未固结火山碎屑矿床的地质和岩土工程领域以及实验室特征，它们代表了未来浅层滑坡的可能来源。碎屑雪崩形成了一个具有发达的山形地形的沉积物，并且沿着相邻的Sincholagua火山的斜坡爬了大约260 m的高度差。碎屑雪崩沉积包括四个岩相（巨块，块状，混合和剪切相），代表了不同的流动方式和基底受侵程度。相分布表明，在近端区域，碎屑雪崩主要沿着火山锥的N和NE侧面滑落在山谷中，形成了一叠巨型区块。当水流到达建筑物底部的坡度折断处时，它变得不受限制，并在里约皮塔河谷的大部分地区横向扩散。在碎片雪崩运输过程中发生了动态的块碎裂和扩张，形成了块状相。较早的Chalupas辉绿岩的合并是造成混合相和剪切相的原因。岩土工程结果包括全范围的晶粒尺寸表征，这使得可以对采样相之间的可能变化进行更广泛的考虑。对＜4.76 mm的细颗粒进行的排水三轴固结压缩试验表明，无粘性砂质材料的剪切强度仅归因于有效摩擦角，并且在一组测试样品中表现出相当均匀的行为。

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