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The summer 2019 basaltic Vulcanian eruptions (paroxysms) of Stromboli
Bulletin of Volcanology ( IF 3.5 ) Pub Date : 2020-12-03 , DOI: 10.1007/s00445-020-01423-2
G. Giordano , G. De Astis

Stromboli is an active, open conduit mafic volcano, whose persistent mild Strombolian activity is occasionally punctuated by much stronger explosions, known as paroxysms. During summer 2019, the volcano unexpectedly produced one such paroxysm on July 3, followed by intense explosive and intermittent effusive activity culminating in a second paroxysm on August 28. Visual observations and the analysis of the fall deposits associated with the two paroxysms allowed us to reconstruct ballistic exit velocities of up to 160 m s−1. Plume heights of ~ 8.4 km and 6.4 km estimated for the two events correspond to mass eruption rates of 1.1 × 106 kg s−1 and 3.6 × 105 kg s−1, respectively. This is certainly an underestimate as directional pyroclastic flows into which mass was partitioned immediately formed, triggering small tsunamis at the sea entrance. The mass of ballistic spatters and blocks erupted during the July 3 event formed a continuous cover at the summit of the volcano, with a mass calculated at ~ 1.4 × 108 kg. The distribution of fall deposits of both the July 3 and August 28 events suggests that pyroclasts characterized by terminal fall velocities < 10–20 m s−1 remained fully suspended within the convective region of the plume and did not fall at distances closer than ca 1700 m to the vent. Based on the impulsive, blast-like phenomenology of paroxysms as well as the deposit distribution and type, paroxysms are classified as basaltic Vulcanian in style. The evolution of the summer 2019 eruptive events was not properly captured within the framework of the alert level system which is focused on tsunamigenic processes, and this is discussed so as to provide elements for the implementation of the reference scenarios and an upgrade of the system to take into account such events. In particular we find that, although still largely unpredictable, at least at operational time scales, and not necessarily tsunamigenic, Vulcanian eruptions and the subsequent evolution of the eruptive phenomena should be considered for the alert level system. This serves as a warning to the implementation of alert systems where the unexpected needs to be taken into account, even at systems that are believed to be relatively “predictable” as is the case at many persistently active, open vent mafic systems.

中文翻译:

2019 年夏季斯特龙博利玄武岩火山喷发(发作)

斯特龙博利是一座活跃的、开放的管道基性火山,其持续的温和斯特龙博利活动偶尔会被更强烈的爆炸打断,称为发作。2019 年夏季,火山在 7 月 3 日出人意料地产生了一次这样的发作,随后发生了强烈的爆发性和间歇性喷发活动,最终在 8 月 28 日发生了第二次发作。目视观察和对与两次发作相关的秋季沉积物的分析使我们能够重建弹道出口速度高达 160 ms-1。两次事件估计的约 8.4 公里和 6.4 公里的羽流高度分别对应于 1.1 × 106 kg s-1 和 3.6 × 105 kg s-1 的大规模喷发率。这当然是低估了,因为定向火山碎屑流立即形成,质量被分割成碎片,在入海口引发小海啸。7 月 3 日事件期间爆发的大量弹道飞溅物和块体在火山顶形成了一个连续的覆盖层,质量计算为 ~ 1.4 × 108 kg。7 月 3 日和 8 月 28 日事件的坠落沉积物分布表明,以最终坠落速度 < 10-20 ms-1 为特征的火山碎屑仍然完全悬浮在羽流的对流区域内,并且不会在距离约 1700 m 更近的地方坠落到通风口。根据阵发的脉冲、爆炸现象以及沉积物分布和类型,阵发在风格上被归类为玄武岩火山。2019 年夏季喷发事件的演变没有在专注于海啸过程的警报级别系统的框架内正确捕捉,对此进行了讨论,以便为参考场景的实施和系统升级提供元素,以将此类事件考虑在内。特别是我们发现,虽然在很大程度上仍然不可预测,至少在操作时间尺度上,不一定是海啸,但火神的喷发和随后的喷发现象的演变应该被考虑用于警报级别系统。这可以作为警报系统实施的警告,其中需要考虑意外情况,即使在被认为相对“可预测”的系统中也是如此,就像许多持续活跃的开放式通风铁质系统的情况一样。至少在操作时间尺度上,不一定是海啸,火山喷发和喷发现象的后续演变应该被考虑用于警报级别系统。这可以作为警报系统实施的警告,其中需要考虑意外情况,即使在被认为相对“可预测”的系统中也是如此,就像许多持续活跃的开放式通风铁质系统的情况一样。至少在操作时间尺度上,不一定是海啸,火山喷发和喷发现象的后续演变应该被考虑用于警报级别系统。这可以作为警报系统实施的警告,其中需要考虑意外情况,即使在被认为相对“可预测”的系统中也是如此,就像许多持续活跃的开放式通风铁质系统的情况一样。
更新日期:2020-12-03
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