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: 1220511
• 负责人: Kimberly Genareau
• 金额: $ 19.92万
• 依托单位: Lehigh University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-08-01 至 2013-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1220511&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.

2010年10月火山爆发。默拉皮，印度尼西亚的一个？世界上最活跃的火山，显示了世界各地活跃的成层火山系统即使是中等到小规模的爆发也可能造成人类生命的破坏和突然损失。观测默拉皮火山目前活动的能力，以及长期活动所产生的保存完好的喷发序列的存在，使得能够详细研究熔岩穹丘生长和重大穹丘坍塌事件期间的挥发性脱气动力学。 它还提供了一个机会，以制定一个一般模型，这些系统如何随着时间的推移而演变。因为熔岩穹丘的生长和坍塌是产生危险和不可预测的火山现象的主要机制（例如，火山碎屑密度流、火山灰降落）对当地和区域人口具有毁灭性影响，因此，了解触发圆顶坍塌事件和影响火山碎屑灾害产生的物理参数，对于改进这一持续活跃的成层火山的减灾战略至关重要。在探索安山质成层火山重大穹丘坍塌事件的原因时，该项目寻求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，目的是确定熔岩渗出期间挥发性脱气的动力学如何有助于产生火山碎屑密度流和火山灰坠落危害的特定特征。 从默拉皮收集的现有样本将有针对性地进行一系列有重点的分析，以限制单一喷发事件之间特定特征的相似性或差异以及喷发活动长期过程中的时间变化，包括：1.在火山灰最有效破碎的部分内的落流单元和灰粒形态的粒度分布。熔岩样品中的微晶数量密度和微晶形态，斜长石斑晶边缘成分，边缘结构和角闪石反应边缘厚度。3)熔岩囊泡，囊泡形态，气泡大小分布，以及圆顶生长过程中气体逸出的可渗透网络的发展。4)在岩浆上升和穹隆喷发过程中矿物和熔体中挥发性元素（H2O，CO2，Li）的行为。通过比较几个圆顶生产的事件随着时间的推移在一个单一的层状火山系统，这项研究旨在量化的流变参数导致主要的圆顶倒塌事件，试图解释为什么这些倒塌事件发生，为什么他们发生在可变的时间尺度上，以及如何挥发性元素的行为和这些元素的脱气将影响火山碎屑灾害的特性。 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重大圆顶坍塌事件，将使研究人员能够更准确地建模（并最终预测）火山行为。 这将导致改进的危险评估战略，不仅是默拉皮火山，这对印度尼西亚国家来说是一个重大的火山危险，而且是世界各地其他100个活跃的层状火山中心，表现出类似的行为。