Generation of a debris avalanche and violent pyroclastic density current on 26 December (Boxing Day) 1997 at Soufrière Hills Volcano, Montserrat
Generation of a debris avalanche and violent pyroclastic density current on 26 December (Boxing Day) 1997 at Soufrière Hills Volcano, Montserrat
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1997 年 12 月 26 日（节礼日）蒙特塞拉特岛苏弗里耶尔山火山发生碎片雪崩和剧烈的火山碎屑密度流
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发表时间：
2002
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通讯作者：
Andrew W. Woods
中科院分区：
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作者：
R. Sparks;J. Barclay;E. Calder;R. Herd;J. Komorowski;R. Luckett;G. Norton;L. Ritchie;B. Voight;Andrew W. Woods
摘要蒙特塞拉特火山苏弗里埃山的安山质熔岩穹丘于1995年11月开始生长，引起火山热液蚀变侧翼的不稳定。1997年12月26日，即首次发现不稳定性14个月后，发生了灾难性的故障。在破裂前两个月，一个圆顶突出于不稳定区域，到1997年12月25日，其体积为113 x 106 m3。在当地时间03：01，侧翼岩石和一些圆顶岩堆破裂，产生了碎片雪崩（体积为46 x 106 m3）。35至45 x106立方米的圆顶随后坍塌，产生了猛烈的火山碎屑密度流，摧毁了蒙特塞拉特南部10平方公里的地区。侧翼和拱顶的破坏形成两个相邻的碗状塌陷凹陷。最强烈的活动持续约11.6分钟。丘状岩屑崩落存款是由混合域的杂岩角砾岩。火山碎屑异重流的估计峰值速度为80-90 ms-1，最小通量为108 kgs 1。海流主要侵蚀陆地，大部分沉积在海上。破坏性影响包括房屋、树木和大型车辆被移走，并形成一层薄薄的（3-4毫米）焦油层使被冲刷的表面变黑。火山碎屑密度流形成两个离散的沉积单元，每个单元具有下部粗粒层和上部细粒层状层。这些沉积物上覆有与水流浮力抬升有关的落灰层。侧翼破坏是由于加载的热液弱化岩石的圆顶。火山碎屑密度流的产生是由于破裂和爆炸解体的圆顶，涉及释放和剧烈膨胀的气体最初在高孔隙压力。
Abstract Growth of an andesitic lava dome at Soufriere Hills Volcano, Montserrat, beginning in November 1995, caused instability of a hydrothermally altered flank of the volcano. Catastrophic failure occurred on 26 December 1997, 14 months after the instability was first recognized. Two months before failure a dome lobe had extruded over the unstable area and by 25 December 1997 this had a volume of 113 x 106m3. At 03:01 (local time) the flank rocks and some dome talus failed and generated a debris avalanche (volume 46 x 106 m3). Between 35 and 45 x 106 m3 of the dome then collapsed, generating a violent pyroclastic density current that devastated 10 km2 of southern Montserrat. The failure of the flank and dome formed two adjacent bowl-shaped collapse depressions. The most intense activity lasted about 11.6 minutes. The hummocky debris avalanche deposit is composed of a mixture of domains of heterolithic breccia. The pyroclastic density current had an estimated peak velocity of 80-90 ms-1, and minimum flux of 108 kgs1. The current was largely erosional on land with most deposition out at sea. Destructive effects included removal of houses, trees and large vehicles, and formation of a scoured surface blackened by a thin (3-4 mm) layer of tar. Two discrete depositional units formed from the pyroclastic density current, each with a lower coarse-grained layer and an upper fine-grained stratified layer. These deposits are overlain by an ashfall layer related to buoyant lofting of the current. Flank failure is attributed to loading of hydrothermally weakened rocks by the dome. The generation of the pyroclastic density current is attributed to failure and explosive disintegration of the dome, involving release and violent expansion of gases initially at high pore pressures.