Collaborative Research: Violent Basaltic Explosive Volcanism II: Constraints and Conditions of Basaltic Plinian Eruptions

智力优势：玄武岩火山最常产生熔岩喷出、温和的爆发性斯特龙博尔活动或夏威夷喷泉喷发。然而，一些玄武岩喷发现在被认为是极其猛烈的，即产生了广泛的岩浆、次普里尼亚和普利尼亚秋季沉积，其中包括在基拉韦厄(夏威夷)、埃特纳(意大利)和塔拉韦拉(新西兰)的历史喷发。这些喷发特别危险，因为喷发前玄武岩岩浆的上升率可能非常高(即警告时间短至几个小时)，而且其前兆可能被忽视或误解。我们主要以公元前122年埃特纳火山喷发为例，着手限制允许玄武岩岩浆以普林尼安强度喷发的喷发前上升和脱气的条件。抑制或延缓开放系统行为和促进气体和熔体之间扩大耦合的机制是允许普林尼期玄武岩岩浆喷发的关键。我们将在德克萨斯大学对公元前122年的埃特马熔体进行减压实验，并将实验产品与自然样品进行结构和化学上的比较，以期限制岩浆上升和囊泡形成的条件和速率。我们将使用三种不同的技术来量化喷发的渣土和实验药包中的囊泡和微晶种群的范围，以确保可靠的数据集，并允许对这些技术进行关键的比较。最后，我们将测量同一火山碎屑中熔体相在喷发前和喷发后的挥发分含量。更广泛的影响：我们的目标是了解玄武岩普林尼安火山喷发的机制，长期目标是应用这种理解来改善对未来大型玄武岩火山喷发的准备。特别是，在埃特纳的近代史上，有证据表明有几次从底板到普林尼期的大型喷发。很可能会发生另一次大规模爆炸性喷发，并影响到大量人口。由于埃特纳周围的现代人口要多得多，而且有人居住的地区向火山侧翼延伸得更远，未来的喷发会带来重大的潜在危险。我们将在意大利的一个研讨会上向应急管理机构介绍结论和影响的摘要，随后将于2007年在Etna为学生和研究人员举办一个重点研讨会。我们的成果还将通过互联网广泛传播，使用由夏威夷大学、德克萨斯大学和意大利INGV主办的链接网站，并以意大利语和英语DVD的形式发布。

Intellectual Merit: Basaltic volcanism most commonly produces effusion of lava, mildly explosive Strombolian activity or Hawaiian fire fountain eruptions. However, some basaltic eruptions are now recognized as extremely violent, i.e. generating widespread phreatomagmatic, subplinian and Plinian fall deposits, these include historical eruptions at Kilauea (Hawaii), Etna (Italy) and Tarawera (New Zealand). These eruptions are particularly dangerous because the ascent rate of basaltic magma prior to eruption can be very high (i.e., warning times as little as a few hours) and because their precursors may be ignored or misunderstood. We set out to constrain the conditions of pre-eruptive ascent and degassing that permitted basaltic magma to erupt at Plinian intensity, principally using the example of the 122 BC eruption of Mt Etna. Mechanisms to suppress or delay open-system behavior and promote extended coupling between gas and melt are essential to permit Plinian eruptions of basaltic magma. We will look to constrain conditions and rates of magma ascent and vesiculation by performingdecompression experiments on the 122 BC Etma melt at University of Texas and comparing experimental products with natural samples, texturally and chemically. We will quantify the range of vesicle and microlite populations in the erupted scoria and experimental charges using three different techniques, to ensure reliable data sets, and to allow critical comparison of the techniques. Finally we will measure pre- and post-eruptive volatile contents of the melt phases in the same pyroclasts. Broader impacts: Our goal is to understand the mechanisms for basaltic Plinian eruptions, with a long-term aim of applying such understanding to improve preparedness for future eruptions at large basaltic volcanoes. In particular there is evidence for several large subplinian to Plinian eruptions in Etna's recent history. It is likely that another large explosive eruption will happen and affect a large population. Because the modern population surrounding Etna is much greater and the inhabited area extends farther up the volcano's flanks, future eruptions pose significant potential hazards. We will present a summary of conclusions and impacts to emergency management agencies at a workshop in Italy followed by a focused workshop for students and researchers at Etna in 2007. Our results will also be widely disseminated via the Internet using linked web sites hosted by University of Hawaii, University of Texas and INGV, Italy and in the form of a DVD in Italian and English.