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

学术价值：玄武岩火山活动最常见的是熔岩渗出，轻度爆炸性的斯特龙堡活动或夏威夷火喷泉喷发。然而，一些玄武岩喷发现在被认为是非常猛烈的，即产生广泛的呼吸岩浆，下普林尼纪和普林尼纪的瀑布沉积，这些包括基拉韦厄火山（夏威夷），埃特纳火山（意大利）和塔拉韦拉火山（新西兰）的历史喷发。这些喷发特别危险，因为玄武岩岩浆在喷发前的上升速度可能非常高（即，警告时间可能只有几个小时），而且它们的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，对喷发前的上升和脱气条件进行了限制，这些条件允许玄武岩岩浆以普林尼强度喷发。抑制或延迟开放系统行为和促进气体和熔体之间扩展耦合的机制对于允许玄武岩岩浆的普林尼期喷发是必不可少的。我们将在德克萨斯大学对公元前122年的埃特玛熔岩进行减压实验，并将实验产物与自然样品进行结构和化学比较，以限制岩浆上升和起泡的条件和速率。我们将使用三种不同的技术量化爆发的矿渣和实验电荷中的囊泡和微岩石种群的范围，以确保可靠的数据集，并允许对技术进行关键的比较。最后，我们将测量喷发前和喷发后同一火山碎屑中熔融相的挥发性含量。更广泛的影响：我们的目标是了解玄武岩普林尼火山爆发的机制，长期目标是应用这种理解来提高对大型玄武岩火山未来爆发的准备。特别是有证据表明，在埃特纳火山最近的历史中，有几次大的次普林尼火山爆发。很可能会发生另一次大规模的爆炸性喷发，并影响到大量人口。由于埃特纳火山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，因此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讲习班上向应急管理机构介绍结论和影响的摘要，然后于2007年在埃特纳为学生和研究人员举办一个重点讲习班。我们的研究结果还将通过夏威夷大学、德克萨斯大学和意大利INGV主办的链接网站，以及意大利语和英语DVD的形式，在互联网上广泛传播。

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.