Degassing Dynamics that Lead to Repeated Lava Dome Growth and Collapse at Persistently Active Stratovolcanoes

导致持续活跃的成层火山熔岩穹丘反复生长和塌陷的排气动力学

• 批准号: 1358886
• 负责人: Kimberly Genareau
• 金额: $ 11.65万
• 依托单位: University of Alabama Tuscaloosa
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-08-01 至 2015-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1358886&HistoricalAwards=false
• 关键词: Degassing; Dynamics; Lead; Repeated; Lava

The October 2010 eruption of Mt. Merapi, one of Indonesia?s most active volcanoes, demonstrates the devastation and sudden loss of human life that can result from even moderate to small eruptions of active stratovolcanic systems throughout the world. The ability to observe current activity on Merapi, and the existence of preserved erupted sequences resulting from long-lived activity, allow for a detailed examination of volatile degassing dynamics during lava dome growth and major dome collapse events. It also provides an opportunity to formulate a general model of how such systems evolve over time. Because lava dome growth and collapse is a dominant mechanism for the production of dangerous and unpredictable volcanic phenomena (e.g., pyroclastic density currents, ash fall) that have devastating effects on both local and regional populations, understanding the physical parameters that trigger dome collapse events and influence the generation of pyroclastic hazards is paramount to improving the hazard mitigation strategies at this persistently active stratovolcano. In exploring the causes of major dome collapse events at andesitic stratovolcanoes, this project seeks evidence for geochemical and textural signals for these impending events in erupted products, with the objective of determining how the dynamics of volatile degassing during lava effusion contributes to particular characteristics of resulting pyroclastic density currents and ash fall hazards. Existing samples collected from Merapi will be targeted by a focused range of analyses in order to constrain similarities or differences in particular characteristics between single eruptive events and temporal variations over the long-term course of eruptive activity, including: 1. Grain size distributions of fall and flow units and ash grain morphologies within the most efficiently fragmented portion of the tephra.2. Microlite number density and microlite morphology within lava samples, plagioclase phenocryst rim compositions, rim textures, and amphibole reaction rim thicknesses. 3) Lava vesicularity, vesicle morphology, bubble size distributions, and development of permeable networks for gas escape during dome growth. 4) Behavior of volatile elements (H2O, CO2, Li) in minerals and melts during magma ascent and dome effusion. By comparing several dome-producing events over time within a single stratovolcanic system, this study seeks to quantify the rheological parameters leading up to major dome collapse events, attempting to explain why these collapse events occur, why they occur on variable time scales, and how the behavior of volatile elements and the degassing of these elements will influence the resulting characteristics of pyroclastic hazards. Quantifying the physical parameters within volcanic conduits and understanding how these parameters vary over time to cause major dome collapse events will allow researchers to more accurately model (and ultimately, forecast) volcanic behavior. This will lead to improved hazard assessment strategies for not only Merapi, which represents a significant volcanic hazard for the nation of Indonesia, but for the other 100 active stratovolcanic centers throughout the world that display similar behavior.

印度尼西亚最活跃的火山之一默拉皮火山 2010 年 10 月的喷发表明，全世界活跃的层状火山系统即使是中度到小规模的喷发也可能造成破坏和突然的人员伤亡。观察默拉皮岛当前活动的能力，以及长期活动所导致的保存完好的喷发序列的存在，可以详细检查熔岩穹顶生长和主要穹顶塌陷事件期间的挥发性脱气动态。 它还提供了一个机会来制定此类系统如何随时间演变的通用模型。由于熔岩穹顶生长和塌陷是产生危险且不可预测的火山现象（例如火山碎屑密度流、火山灰坠落）的主要机制，对当地和区域人口产生破坏性影响，因此了解触发穹顶塌陷事件并影响火山碎屑灾害产生的物理参数对于改善这座持续活跃的成层火山的灾害缓解策略至关重要。在探索安山质成层火山主要穹顶塌陷事件的原因时，该项目寻找喷发产物中这些即将发生的事件的地球化学和结构信号的证据，目的是确定熔岩喷出过程中挥发性脱气的动态如何影响所产生的火山碎屑密度流和火山灰坠落危险的特定特征。 从默拉皮收集的现有样本将进行一系列集中分析，以限制单次喷发事件与喷发活动长期过程中时间变化之间特定特征的相似或差异，包括： 1. 火山灰最有效破碎部分内的坠落和流动单元以及灰粒形态的粒度分布。 2.熔岩样品内的微晶石数密度和微晶石形态、斜长石斑晶边缘成分、边缘纹理和角闪石反应边缘厚度。 3）熔岩囊泡性、囊泡形态、气泡尺寸分布以及穹顶生长过程中气体逸出的可渗透网络的发展。 4）岩浆上升和穹顶喷发过程中矿物和熔体中挥发性元素（H2O、CO2、Li）的行为。通过比较单个成层火山系统内随时间推移发生的几次穹顶生成事件，本研究试图量化导致主要穹顶塌陷事件的流变参数，试图解释这些塌陷事件发生的原因、它们在不同时间尺度上发生的原因，以及挥发性元素的行为和这些元素的脱气将如何影响火山碎屑危害的最终特征。 量化火山管道内的物理参数并了解这些参数如何随时间变化而导致主要的穹顶塌陷事件将使研究人员能够更准确地模拟（并最终预测）火山行为。 这不仅会改进默拉皮火山的危害评估策略（默拉皮火山对印度尼西亚来说是一个重大的火山灾害），而且也会改进全世界其他 100 个表现出类似行为的活跃层火山中心的危害评估策略。