Volatile Clues to the Initial Controls on Large Explosive Volcanic Eruptions

大规模火山喷发初步控制的不稳定线索

• 批准号: 1524824
• 负责人: Paul Wallace
• 金额: $ 31万
• 依托单位: University of Oregon Eugene
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-07-01 至 2020-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1524824&HistoricalAwards=false
• 关键词: Volatile; Clues; Initial; Controls; Large

The goal of this project is to better understand how large explosive volcanic eruptions start and the timescales (days or weeks or more) of precursory activity that might serve as a warning sign of an impending eruption. Enormous explosive eruptions (known as supereruptions) have occurred in the recent geologic past that are many times larger than any eruptions that have taken place in historic times. Some of the best and youngest examples, at Yellowstone, in eastern California, and in New Zealand will be studied in this project. A primary goal is to determine if external factors, like an earthquake and movement along a fault, can cause such eruptions to start, or whether instead, they start when a magma body in the earth?s crust becomes overpressured and bursts, like a ruptured balloon. The project will involve chemical analysis of ash and pumice deposits that were created during the opening stages of the eruptions because these preserve a record of information about how and why the eruptions started and how long it took for magma to move to the Earth's surface. This project will test some fundamental ideas about how large explosive rhyolitic eruptions start and when caldera collapse occurs. Despite many important advances in modeling of these processes, there is a surprising lack of geochemical data on the very earliest deposits from large explosive eruptions that could inform the debate about eruption triggering. A quantitative record of magma decompression and ascent rates shortly before and during the opening stages of these eruptions will be obtained by measuring concentrations and gradients of volatiles (H2O, CO2, Cl, S, F) in melt inclusions and reentrants (unsealed inclusions) in quartz and the OH contents of plagioclase. Because magma ascent rates reflect the extent of overpressure in the underlying magma body, constraining ascent rates for the earliest materials from an eruption using diffusive loss of volatiles can provide insight into whether internal (magma overpressure) or external (little or no overpressure) triggers were involved. Based on preliminary results for the Huckleberry Ridge fall deposit (Yellowstone), such data appear to provide a unique record of the processes and timescales of vent development just prior to and during the opening phases of an eruption, with implications for when and why caldera collapse develops and how magma bodies were configured in the upper crust. The results of this investigation will provide quantitative information about how rapidly supereruptions begin and will contribute data to models of geophysical signals that could precede them. This project involves collaborations with other scientists in the U.S. and New Zealand for some of the specialized chemical analyses that will be done and for computer modeling using the results.

该项目的目标是更好地了解大规模火山爆发如何开始以及可能作为即将爆发的警告信号的火山活动的时间尺度（天或周或更长）。巨大的爆炸性喷发（称为超级喷发）发生在最近的地质过去，比历史上发生的任何喷发都大很多倍。 一些最好的和最年轻的例子，在黄石公园，在东部加州，并在新西兰将在这个项目中进行研究。 一个主要的目标是确定外部因素，如地震和沿沿着的运动，是否会导致这种喷发的开始，或者相反，它们是否会在地球上的岩浆体开始时发生？地壳变得超压和爆裂，就像一个破裂的气球。该项目将涉及对火山爆发初期阶段产生的火山灰和浮石沉积物进行化学分析，因为这些沉积物保存了关于火山爆发如何和为什么开始以及岩浆移动到地球表面需要多长时间的信息记录。这个项目将测试一些基本的想法如何大爆炸流纹岩喷发开始，当破火山口崩溃发生。尽管在这些过程的建模方面取得了许多重要进展，但令人惊讶的是，缺乏关于大型爆炸性喷发最早期沉积物的地球化学数据，这些数据可以为有关喷发触发的辩论提供信息。通过测量熔融包裹体和石英中的折返物（未封闭包裹体）中挥发分（H2O、CO2、Cl、S、F）的浓度和梯度以及斜长石中OH的含量，可以定量记录这些喷发前不久和喷发过程中的岩浆减压和上升速率。由于岩浆上升速率反映了底层岩浆体超压的程度，因此使用挥发物的扩散损失来限制喷发最早期物质的上升速率可以深入了解是否涉及内部（岩浆超压）或外部（很少或没有超压）触发因素。根据哈克贝里岭瀑布存款（黄石公园）的初步结果，这些数据似乎提供了一个独特的记录的过程和时间尺度的喷口发展之前和期间的喷发的开放阶段，与何时和为什么破火山口崩溃的发展和岩浆体是如何配置在地壳上部的影响。这项调查的结果将提供有关超级喷发开始有多快的定量信息，并将为可能先于它们的地球物理信号模型提供数据。该项目涉及与美国和新西兰的其他科学家合作，进行一些专门的化学分析，并使用结果进行计算机建模。