Episodes of cyclic Vulcanian explosive activity with fountain collapse at Soufriere Hills Volcano, Montserrat
Episodes of cyclic Vulcanian explosive activity with fountain collapse at Soufriere Hills Volcano, Montserrat
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DOI：
10.1144/gsl.mem.2002.021.01.13
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发表时间：
2002-01-01
期刊：
影响因子：
--
通讯作者：
Voight, B
中科院分区：
文献类型：
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作者：
Druitt, TH;Young, SR;Voight, B
1997年，蒙特塞拉特的Soufriére Hills火山发生了88次火山爆炸：其中13次发生在8月4日至12日，75次发生在9月22日至10月21日。每一集之前都有一个巨大的圆顶坍塌，使管道减压，并导致爆炸破碎的条件。爆炸发生的时间间隔为2.5至63小时，平均为10小时，属于暂时性事件，最初的高强度阶段持续数十秒，而低强度的减弱阶段持续1至3小时。除了一次爆炸外，喷泉在最初的10-20秒内坍塌产生了火山碎屑涌流，在放样之前席卷了1-2公里，以及高浓度的浮质火山碎屑流，沿着圆顶周围的所有主要排水系统流动了6公里。浮力羽流上升3-15公里进入大气层，在那里它们以伞状云的形式展开。大部分伞状云被高空(8-18公里)风吹向北部或西北方向，而低层(<；5公里)风将较低、逐渐减弱的羽流分散到西部或西北方向。从视频中测得的出口速度在40到140ms−1之间，弹道块被抛到距离圆顶1.7千米的地方。每一次爆炸平均释放3×105m~3的岩浆，约1/3形成尘埃，2/3形成火山碎屑流和涌流，并将管道排空至0.5-2公里或更深。在爆炸地震信号中区分出两个重叠的分量：一个是由爆炸本身引起的低频分量(c.1 Hz)，另一个是由喷泉坍塌、弹道撞击和火山碎屑流引起的高频分量(>；2 Hz)。在许多爆炸中，爆炸开始和火山碎屑流信号开始之间的延迟(通常为10-20秒)记录了弹道和坍塌喷泉撞击地面所需的时间。8月份的爆炸伴随着地震活动的循环模式和由于上部管道反复加压而导致的建筑物变形。许多散落浮石的棱角状、表格状表明，它们保存了破碎后获得的气孔和形状，并表明爆炸是由超压岩浆泡沫的脆性破碎驱动的，在每个事件之前，上部导管中至少存在55%的气泡。
In 1997 Soufriére Hills Volcano on Montserrat produced 88 Vulcanian explosions: 13 between 4 and 12 August and 75 between 22 September and 21 October. Each episode was preceded by a large dome collapse that decompressed the conduit and led to the conditions for explosive fragmentation. The explosions, which occurred at intervals of 2.5 to 63 hours, with a mean of 10 hours, were transient events, with an initial high-intensity phase lasting a few tens of seconds and a lower-intensity, waning phase lasting 1 to 3 hours. In all but one explosion, fountain collapse during the first 10–20 seconds generated pyroclastic surges that swept out to 1–2 km before lofting, as well as high-concentration pumiceous pyroclastic flows that travelled up to 6 km down all major drainages around the dome. Buoyant plumes ascended 3–15 km into the atmosphere, where they spread out as umbrella clouds. Most umbrella clouds were blown to the north or NW by high-level (8–18 km) winds, whereas the lower, waning plumes were dispersed to the west or NW by low-level (< 5 km) winds. Exit velocities measured from videos ranged from 40 to 140 ms− 1 and ballistic blocks were thrown as far as 1.7 km from the dome. Each explosion discharged on average 3× 10 5 m 3 of magma, about one-third forming fallout and two-thirds forming pyroclastic flows and surges, and emptied the conduit to a depth of 0.5–2 km or more. Two overlapping components were distinguished in the explosion seismic signals: a low-frequency (c. 1 Hz) one due to the explosion itself, and a high-frequency (> 2 Hz) one due to fountain collapse, ballistic impact and pyroclastic flow. In many explosions a delay between the explosion onset and start of the pyroclastic flow signal (typically 10–20 seconds) recorded the time necessary for ballistics and the collapsing fountain to hit the ground. The explosions in August were accompanied by cyclic patterns of seismicity and edifice deformation due to repeated pressurization of the upper conduit. The angular, tabular forms of many fallout pumices show that they preserve vesicularities and shapes acquired upon fragmentation, and suggest that the explosions were driven by brittle fragmentation of overpressured magmatic foam with at least 55 vol% bubbles present in the upper conduit prior to each event.