Magma ascent and eruption in the Aleutian arc

阿留申岛弧的岩浆上升和喷发阿留申岛弧是世界上火山活动最活跃的地区之一。阿留申火山频繁喷发的高灰云对当地社区和来自北美、欧洲和亚洲的旅行者构成了重大危险。为了减轻这一危害，阿拉斯加火山观测站利用地震数据、大地测量数据和卫星图像对阿拉斯加火山进行广泛监测。这些技术在预测火山爆发方面基本上是成功的;然而，人们对火山爆发的前兆信号（从地震和大地测量数据推断）与火山爆发方式之间的联系知之甚少。被认为在控制火山爆发的活力方面起作用的因素包括岩浆的挥发性含量、岩浆在火山管道中的上升速度以及岩浆的温度。这些参数很难直接测量，但可以从喷发物质的分析中推断出来。拟议工作的目标是测量三个阿留申弧火山喷发的晶体和玻璃中水和其他化学物质的梯度。这些化学梯度是岩浆上升、脱气和冷却的标志。最近开发的解释这种化学梯度的技术将用于限制岩浆在喷发前几分钟到几小时的上升速率和温度。这些测量将进一步加深我们对火山管道在喷发形成过程中的作用的理解，并将为实时火山监测数据提供一个物理框架。拟议的研究整合了最近开发的岩石学方法，用于确定三个阿留申弧火山喷发的岩浆的上升速率和同喷发热历史（Okmok，Seguam和Pavlof）与对比爆炸性（火山爆炸性指数，VEI，1？3）。将使用三种独立的技术计算三次喷发中每次喷发的岩浆上升速率：（1）不同大小的橄榄石熔融包裹体的水分损失;（2）橄榄石中的水分分带;（3）单斜辉石中的水分分带。上升和喷发过程中的岩浆冷却历史将计算内橄榄石托管熔融包裹体使用MgO浓度梯度。整合这些技术的样品从不同的喷发风格的火山将允许岩浆挥发物浓度，上升速率，热历史，和喷发风格之间的关系进行识别。拟议的分析将提高我们的理解的行为的水和其他挥发性元素的橄榄石托管熔融包裹体和弧火山更广泛，他们将使更可靠和准确的测定喷发前的挥发性浓度从橄榄石托管熔融包裹体。

Magma ascent and eruption in the Aleutian arcThe Aleutian arc is one of the most volcanically active regions of the world. Frequent eruptions of tall ash clouds by Aleutian volcanoes present a significant hazard to local communities and to travelers flying from North America, Europe, and Asia. In order to mitigate this hazard, Alaskan volcanoes are extensively monitored by the Alaska Volcano Observatory (AVO), using seismic data, geodetic data and satellite imagery. These techniques are largely successful in enabling the prediction of volcanic eruptions; however, the links between precursor signals of an eruption (as inferred from seismic and geodetic data) and eruptive style are poorly understood. Factors that are thought to play a role in controlling the vigor of a volcanic eruption include the volatile content of the magma, the ascent rate of the magma in the volcanic conduit, and the temperature of the magma. These parameters are difficult to measure directly, but they can be inferred a posteriori from the analysis of erupted materials. The goal of the proposed work is to measure gradients of water and other chemical species in erupted crystals and glasses from three Aleutian arc volcanoes. These chemical gradients are signatures of magma ascent, degassing, and cooling. Recently developed techniques for interpreting such chemical gradients will be used to constrain ascent rates and temperatures of magmas in the minutes to hours prior to their eruption. Such measurements will further our understanding of processes operating in the volcanic conduit in the build-up to an eruption, and will provide a physical framework in which to place real-time volcano monitoring data.The proposed study integrates recently developed petrologic methods for determining the ascent rates and syneruptive thermal histories of magmas erupted at three Aleutian arc volcanoes (Okmok, Seguam, and Pavlof) with contrasting explosivities (Volcanic Explosivity Index, VEI, of 1 ? 3). Magma ascent rates for each of the three eruptions will be calculated using three independent techniques: (1) water loss from olivine-hosted melt inclusions of different sizes; (2) water zonation in olivine; and (3) water zonation in clinopyroxene. Magma cooling histories during ascent and eruption will be calculated using MgO concentration gradients inside olivine-hosted melt inclusions. Integration of these techniques on samples from volcanoes with different eruptive styles will allow identification of relationships between magma volatile concentrations, ascent rate, thermal history, and eruptive style. The proposed analyses will enhance our understanding of the behavior of water and other volatile elements in olivine-hosted melt inclusions and in arc volcanoes more broadly, and they will enable more reliable and accurate determination of pre-eruptive volatile concentrations from olivine-hosted melt inclusions.