Collaborative Research: Recharge, Mixing and Eruption Triggering Mechanisms at Chaos Crags and 1915 Eruptions, Lassen Volcanic Center, California

合作研究：混沌峭壁和 1915 年火山喷发的补给、混合和喷发触发机制，拉森火山中心，加利福尼亚州

• 批准号: 1250294
• 负责人: Lisa Hammersley
• 金额: $ 2.05万
• 依托单位: University Enterprises, Incorporated
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-01-01 至 2015-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1250294&HistoricalAwards=false
• 关键词: Collaborative; Research; Recharge; Mixing; Eruption

This project will produce advances in pure science with broader impacts in public safety and education. The Lassen volcanic center had its last major eruption in 1915 at Lassen Peak, and it is located beneath many of the flight paths of airlines that connect cities in the western U.S. An understanding of how and why volcanic eruptions are triggered at Lassen Peak thus will play a key role in future hazards assessments. Our study brings together researchers with a wide variety of expertise to examine several processes operating prior to eruption, including eruption triggers and magma storage. For example, prior work shows several mechanisms by which an eruption even may be triggered. One line of thought is that eruptions are triggered soon after new magma is introduced into a magma reservoir beneath a volcano, as new magmas mix with magmas already present in a shallow chamber. Alternatively, new magma inputs may need to cool, and partially crystallize before an eruption occurs. This cooling drives water into the remaining uncrystallized magma, which increases pressure within the magmatic system if enough water is concentrated into the magma to form a vapor phase. Expansion of the vapor phase may crack the overlying rock and allow an eruption to occur. Lassen provides an important testing ground for these ideas because the two most recent eruptive episodes (1915 at Lassen Peak, and the earlier eruption at approximately 1144 AD at Chaos Crags) both show evidence for pre-eruption magma inputs, but those fresh inputs acted very differently in the two cases. Thus a comparison of the two eruptions will provide insight into the importance of different triggering mechanisms in the Lassen magma system. This study will bring together researchers and students across the spectrum of universities, with representatives from major research institutions, state service universities and a liberal arts college. This will enhance the education of many students, as it provides valuable opportunities to support under-represented groups (Hispanics and women) at both the undergraduate and graduate level, to work in laboratories and with researchers across the globe. In addition, many undergraduates at CSU Fresno will participate in the research as research projects are routinely integrated into the laboratory requirements for core courses.To attack the research problems outlined above, we will perform a collaborative study of the relationships between magma recharge (fresh inputs of magma), magma mixing and eruption, in the Chaos Crags and 1915 eruptions of the Lassen Volcanic Center, California. The study will use a combination of textural studies to assess crystallization processes, U-series (radiometric) and diffusion profile methods for age dating, and mineral-melt and fluid inclusion studies to delimit pressures and temperatures of magma storage. The specific targets of investigation are the 6 domes of Chaos Crags (denoted as A to F), and the more well-mixed 1915 eruptive products at Lassen Peak. At Lassen Peak, magmas mixed intimately prior to eruption, while at Chaos Crags, mixing was for some reason inhibited. Does this contrast reflect (a) the timing between fresh magma inputs and eruption; (b) contrasts in temperatures and depths of magma storage/interaction or; (c) the relative amounts of hot fresh magma inputs compared to the cooler magmas that already inhabit the chamber (left-over from some prior magmatic episode)? The Chaos Crags units are of special interest because Dome A shows little evidence of mixing?and so yields the most extreme felsic and mafic compositions; all other domes, and the 1915 lavas, fall between these extremes. Dome A thus provides access to end-member magmas. The Chaos Crags and Lassen Peak suites also expose interesting textural contrasts as the Chaos Crags rocks are more crystalline, and their enclaves show a greater variety of quenching textures, which suggests a relationship between mixing and recharge. Key questions include: (1) Does recharge of a chamber with mafic magma trigger mixing (and eventually, eruption), or is there a time lag between recharge and mixing? (2) What effect does a time lag between the initial intrusion of felsic magma and the later intrusion of mafic recharge magma have on the efficacy of mixing and the time scale of eruption? (3) Does the ratio of mafic recharge/resident felsic magma affect mixing and/or the timing of eruption? (4) Do the depths and temperatures of magma storage affect the mixing/eruption process?

该项目将在纯科学方面产生进步，并在公共安全和教育中产生更大的影响。拉森火山中心于1915年在拉森峰（Lassen Peak）举行了最后一次重大爆发，它位于连接美国西部城市的许多航空公司的飞行路径下，了解在拉森峰（Lassen Peak）如何以及为什么在Lassen Peak触发火山喷发未来危害评估的关键作用。 我们的研究汇集了具有各种专业知识的研究人员，以检查喷发前运行的几个过程，包括喷发触发器和岩浆存储。例如，先前的工作显示了几种机制，甚至可以触发喷发。一条思路是，在将新岩浆引入火山下的岩浆储层之后，爆发很快就会触发，因为新的岩浆与已经存在于浅室内的岩浆的新岩浆混合在一起。另外，新的岩浆输入可能需要冷却，并在发生喷发之前部分结晶。这种冷却将水驱动到其余未结合的岩浆中，如果足够的水集中在岩浆中以形成蒸气相，则会增加岩浆系统内的压力。蒸气相的膨胀可能会破裂上覆的岩石并允许发生喷发。 Lassen为这些想法提供了重要的测试场，因为两个最新的爆发性发作（1915年在Lassen Peak，较早的爆发，大约在Chaos Crags的公元约1144年）都显示出爆发前岩浆输入的证据，但是那些新鲜的投入非常行动。在这两种情况下的情况有所不同。因此，对两次爆发的比较将洞悉拉森岩浆系统中不同触发机制的重要性。这项研究将与主要研究机构，州服务大学和一所文科学院的代表一起将研究人员和学生召集在一起。这将增强许多学生的教育，因为它提供了宝贵的机会，以支持本科和研究生层面的代表性不足的群体（西班牙裔和妇女），以在实验室和全球研究人员工作。此外，CSU Fresno的许多大学生将经常纳入核心课程的实验室要求，以攻击上面概述的研究问题，我们将对Magma Recharge之间的关系进行协作研究（新的投入（新的投入）岩浆），岩浆混合和喷发，在加利福尼亚州拉森火山中心的混乱岩壁和1915年的爆发中。该研究将使用纹理研究的组合来评估年龄约会的结晶过程，U系列（辐射学）和扩散曲线方法，以及矿物融合和流体包容性研究，以界定岩浆存储的压力和温度。调查的具体目标是6个混乱岩岩的圆顶（称为a至f），以及拉森峰的1915年爆发产物。 在拉森峰（Lassen Peak），岩浆在爆发之前紧密混合，而在混乱岩壁上，混合是由于某种原因而抑制的。这种对比反映了（a）新鲜岩浆输入和喷发之间的时机吗？ （b）在岩浆存储/相互作用的温度和深度中对比； （c）与已经居住在腔室的凉爽岩浆相比，热的新鲜岩浆输入的相对量（从以前的岩浆发作中剩下的）？混乱的岩壁单元具有特殊的兴趣，因为圆顶A很少显示混合的证据？因此产生了最极端的Felsic和Mafic组成。所有其他圆顶和1915年的熔岩都介于这些极端之间。圆顶A因此提供了对最终会员岩浆的访问。混乱的岩壁和拉森峰套件也揭示了有趣的质地对比，因为混乱的岩石岩石更晶体，它们的飞地显示出更大的淬火质地，这表明混合与补给之间存在关系。关键问题包括：（1）用镁铁质岩浆触发混合（最终是喷发）补给腔室，还是充电与混合之间有时间滞后？ （2）长英质岩浆的初始侵入与后来的镁铁质补给岩浆对混合功效和喷发时间尺度的侵入之间有什么影响？ （3）镁铁质充电/常驻长英质岩浆的比率是否会影响混合和/或喷发时间？ （4）岩浆存储的深度和温度是否会影响混合/喷发过程？