Causes and Consequences of Holocene Mafic Explosive Volcanism in Central OR?

智力价值：该项目扩展了私人投资机构关于能够爆发活动(导致火山灾害)的小型“单一”喷发的初步工作，其喷发方式和岩浆演化在很大程度上取决于通过地壳的气体和岩浆运输条件。这项工作提出了关于天然气迁移机制、通过地壳的岩浆输送系统的时间演化以及对结晶镁铁质岩浆破碎的控制等问题。建议通过重点研究两次全新世喷发的产物来研究小型镁铁质系统中活跃的物理和化学过程之间的联系：[1]沙山喷发，OR(年龄=约3500年BP；体积=~0.9千米)。这个喷口产生了一个巨大的火山灰岩层(0.3千米)，沉积的均匀细小的颗粒(1-3毫米)引发了关于岩浆破碎的有趣问题。公元1666年的这次喷发是喀斯喀特山脉中最年轻的一次火山灰锥喷发，是同喷发成分演化的一个例子；此外，火山喷发产生的火山灰可能与特定的熔岩流有关，因此可以评估喷发的物理和化学演化之间的联系。这两个例子代表了用于危险评估的两个末端成员“类型”喷发(见下文)。为了补充拟议的实地研究，将进行模拟实验，以确定控制通过富含晶体的岩浆的气体迁移的三相流动模式，并调查晶体对岩浆膨胀和破碎的影响。最后，将进行实验，以考察对上地壳底床杂岩中临时岩浆储存的控制；这些实验的结果不仅适用于岩石学研究，也适用于火山监测。更广泛的影响：这项工作的一个重要的更广泛的影响将是为中部或更远地区发展一项全面的火山危险评估。这种“以社区为中心”的危险评估将不同于传统的“以火山为中心”的评估，不仅纳入了多个火山源，而且还利用来自两个“类型”喷发的数据，为Bend OR地区预期的各种风条件开发了现实的Tephra扩散模型。存款数据将由Leed PI地质灾害课程的学生以Google Earth(KML)格式汇编。该项目还将部分资助三名研究生完成他们在最初的资助下开始的博士论文：Dan Ruscitto正在分析熔体包裹体成分，作为更大规模研究的一部分，目的是研究OR中部俯冲带熔体的起源(与P.Wallace)；Daniele McKay正在研究Newberry火山和OR Cascade中部的镁铁质喷发的物理火山学、岩石学和危险性(与K.Cashman)；Isolde Belien进行了所有的模拟实验，并将研究富含晶体的岩浆的气体迁移、膨胀和碎裂之间的联系(与K.Cashman和A.Rempel)。此外，麦凯和现金男都在帮助自然和文化历史博物馆(UO)开发一种新的展示，它将纳入这项工作的成果。最后，这项工作涉及与美国地质调查局(Michael Clynne；Cinder Cone)、瑞士日内瓦大学(Costanza Bonadonna；Tephra建模)和英国布里斯托尔大学(Alison Rust；Jeremy Phillips；模拟实验)的同事合作。

Intellectual Merit: This project extends initial work by the PIs on small 'monogenetic' eruptions that are capable of explosive activity (with consequences for volcanic hazards), and for which eruption style and magma evolution depend in large part on the conditions of both gas and magma transport through the crust. This work has raised questions regarding mechanisms of gas migration, temporal evolution of magma delivery systems through the crust, and controls on fragmentation of crystalline mafic magma. It is proposed to examine links between physical and chemical processes active in small mafic systems by focusing on products of two Holocene eruptions: [1] Sand Mountain, OR (age = c. 3500 yr bp; volume = ~ 0.9 km3). This vent produced a large tephra sheet (0.3 km3), and the uniformly fine (1-3 mm) grain size of the deposit raises interesting questions about magma fragmentation.[2] Cinder Cone, CA. This 1666 AD eruption is the youngest scoria cone in the Cascades, and serves as an example of syn-eruptive compositional evolution; moreover, episodes of tephra production can be related to specific lava flows, thus allowing evaluation of links between the physical and chemical evolution of the eruption. These two examples represent two end-member 'type' eruptions for hazard assessment (below). To complement the proposed field studies, analog experiments will be conducted to define three-phase flow regimes that control gas migration through crystal-rich magmas and to investigate the effect of crystals on magma expansion and fragmentation. Finally, experiments will be conducted to examine controls on temporary magma storage in sill complexes within the upper crust; the results of these experiments will have applicability not only to petrologic studies but also to volcano monitoring.Broader Impacts: An important broader impact of this work will be development of a comprehensive volcanic hazard assessment for central OR. This 'community-centric' hazard assessment will differ from traditional 'volcano-centric' assessments not only by incorporating multiple volcanic sources, but also in using data from the two 'type' eruptions to develop realistic tephra dispersion models for the range of wind conditions expected for the Bend OR region. Deposit data will be compiled in Google Earth (kml) format by students in the led PI's Geologic Hazards class. This project will also partially fund three graduate students to complete PhD dissertations that they started under the original grant: Dan Ruscitto is analyzing melt inclusion compositions as part of a larger study of the origin of subduction zone melts in central OR (with P. Wallace); Daniele McKay is studying the physical volcanology, petrology, and hazards of mafic eruptions from both Newberry Volcano and the central OR Cascades (with K. Cashman); Isolde Belien has conducted all analog experiments and will investigate links between gas migration, expansion, and fragmentation of crystal-rich magmas (with K. Cashman and A. Rempel). Additionally, both McKay and Cashman are helping to develop a new display at the Museum of Natural and Cultural History (UO) that will incorporate results from this work. Finally, this work involves collaborations with colleagues from the USGS (Michael Clynne; Cinder Cone), University of Geneva, Switzerland (Costanza Bonadonna; tephra modeling), and the University of Bristol, UK (Alison Rust & Jeremy Phillips; analog experiments).