Pyroclastic surges of the Pleistocene Monte Guardia sequence (Lipari island, Italy): Depositional processes
Pyroclastic surges of the Pleistocene Monte Guardia sequence (Lipari island, Italy): Depositional processes
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DOI：
10.1111/j.1365-3091.1997.tb00423.x
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发表时间：
1997-02-01
期刊：
影响因子：
3.5
通讯作者：
Hiscott, RN
中科院分区：
文献类型：
--
作者：
Colella, A;Hiscott, RN
意大利南部利帕里岛20-16 ka的Monte Guardia层序是一个复杂的火山碎屑潮沉积序列，部分由海平面附近的水岩浆爆发产生。大多数涌浪都指向喷口的东部、东北部和北部，并沿该岛中部蒙特圣安杰洛南坡12度爬升。一系列含有氧化灰和加积火山砾的薄而独特的关键层组允许详细的剖面对比和对全岛单个火山碎屑涌浪沉积物的横向追踪。相分析表明，近端到远端的相变化是不同于以往的研究所建议的基于统计方法的横向相分布。单一的干涌浪沉积物从（1）含有分散块体的无序中粗粒火山砾层，到（2）含有火山灰基质的细粒至粗粒火山砾的二分无序/分层层，到（3）由粗粒火山灰至中粒火山砾形成的沙丘，再到（4）细粒火山砾的平面层，向下流演化。这一相序与已发表的一些韩国涌浪沉积物的模型相似，记录了经历湍流、颗粒浓度和悬浮载荷沉降率下降的下降流以及牵引过程增加的减速涌浪。当蒙特瓜迪亚涌浪爬上蒙特圣安杰洛的相对斜坡时，它们分叉为东舌和西舌。其经历了快速减速，导致快速的顺流变薄和浪涌沉积物的变细。两种流体动力学方法表明，瓜迪亚峰在攀登蒙特圣安杰洛之前的速度超过75-85 m s（-1）。具有这种活力和分布的水流能够摧毁利帕里的动物和植物种群。
The 20-16 ka Monte Guardia sequence of Lipari island, southern Italy, is a complex succession of silicic pyroclastic surge deposits produced, in part, by hydromagmatic explosions near sea level. Most surges were directed to the east, north-east and north of the vent, and climbed the 12 degrees southern slopes of Monte Sant'Angelo in the central part of the island.A series of thin, distinctive key bed-sets containing oxidized ash and accretionary lapilli allow a detailed correlation of sections and the lateral tracing of deposits of single pyroclastic surges across the island. Facies analysis reveals that the proximal-to-distal facies changes are different from those suggested by a previous study based on a statistical approach to lateral facies distribution. Single dry surge deposits evolve downcurrent from (1) beds of disorganized medium- to coarse-grained lapilli containing scattered blocks, to (2) bipartite disorganized/stratified beds of fine- to coarse-grained lapilli with ash matrix, to (3) dunes formed of coarse-grained ash to medium-grained lapilli, to (4) planar beds of fine-grained lapilli. This facies sequence is similar to published models for some Korean surge deposits, and records decelerating surges which experienced a downflow decrease in turbulence, particle concentration and suspended-load fall-out rate, and an increase in traction processes.As the Monte Guardia surges climbed the opposing slopes of Monte Sant'Angelo, they bifurcated into eastern and western tongues, which experienced rapid deceleration leading to a rapid downcurrent thinning and fining of the surge deposits. Two fluid-dynamical approaches suggest that Monte Guardia surges travelled at speeds of more than 75-85 m s(-1) before climbing Monte Sant'Angelo. Flows with this vigour and distribution are capable of destroying animal and plant populations on Lipari.