Explosive-effusive volcanic eruption transitions caused by pyroclast sintering

火山碎屑烧结引起的爆炸-喷发火山喷发转变

• 批准号: NE/X015440/1
• 负责人: Fabian Wadsworth
• 金额: $ 107.35万
• 依托单位: Durham University
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2023
• 资助国家: 英国
• 起止时间: 2023 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FX015440%2F1
• 关键词: Explosive; effusive; volcanic; eruption; transitions

This project will address a first-order challenge in volcanology - understanding the controls on transitions in eruption style and intensity during the most hazardous eruptions. Most silicic eruptions begin with a high-energy, high-hazard explosive phase, then either wane and stop, or transition to hybrid and effusive behaviour that produces relatively short-range lava flows with much lower hazard potential. Understanding the timing of these transitions, and of the end of an eruption, is a major challenge that impacts hazard assessment and eruption response. Existing models assume that a transition from explosive to effusive behaviour is driven from below by a change in either the magma ascent rate or by the permeable release of pressurised gas, effectively 'defusing' the explosive potential. However, these bottom-up models fail to explain two fundamental aspects of silicic volcanism: (i) simultaneous explosive-effusive behaviour that was witnessed directly during the 2011-12 eruption of Cordon Caulle (Chile) and subsequently inferred elsewhere, and (ii) widely documented evidence for in-conduit pyroclast sintering preserved in the deposits from all phases of these eruption types. Members of the project team have used this evidence to develop a new paradigm for explosive-effusive transitions in silicic eruptions (Wadsworth et al., 2020) in which transitions are driven from above by shallow welding of fragmented magma and occlusion of the shallow conduit. In this 'cryptic fragmentation' paradigm, all silicic eruptions are explosive at depth, even when apparently effusive at the surface. This new idea demands a wholesale re-evaluation of silicic volcanic systems.Our new model proposes that apparently effusive lava is generated directly from explosive volcanism, assembled by the viscous amalgamation - sintering - of hot volcanic ash and pumice in the volcanic conduit in the shallowest parts of the Earth's crust (see CfS). The cryptic fragmentation model was developed in response to evidence from crystal-poor silicic systems. In this new study we go further, and propose that the model also applies to crystal-rich intermediate systems, which are much more common, and pose a global hazard. This hypothesis is based on abundant evidence from crystal-rich systems, similar to that summarized above. This project will deliver:(1) New analysis of dome-forming and crystal-rich lavas worldwide using existing samples from multiple laboratories. We will constrain the textures in the groundmass - with a focus on pore-textures indicative of sintering petrogenesis - and macro-scale textures associated with breaking and sintering, such as fractures will with partially sintered particles. This new textural work, coupled with analytical and petrophysical measurements, will underpin our extension of the cryptic fragmentation model to crystal-bearing magma systems. (2) A comprehensive suite of new experimental volcanology measurements of sintering rates with multiphase magmatic particles - glass with crystals. Relying on the PI's large body of experimental and theoretical sintering work, we will develop new experimentally-validated models for sintering rates with crystals in systems under elevated pressures, in the presence of magmatic volatiles, and under shear stresses. For the first time, this will push sintering theory to magmatic conditions and allow the first quantitative test of sintering rates at volcanoes. (3) We will apply these sintering rate equations to active crystal-bearing volcanic eruptions of the past at the same sites from which the sample suites were collected, with a focus on Colima volcano (Mexico) via engagement with stakeholders at volcano observatories.Cryptic fragmentation model reference:Wadsworth, F.B., Llewellin, E.W., Vasseur, J., Gardner, J.E. and Tuffen, H., 2020. Explosive-effusive volcanic eruption transitions caused by sintering. Science advances, 6(39), p.eaba7940

该项目将解决火山学中的首要挑战——了解最危险的喷发期间对喷发类型和强度转变的控制。大多数硅质喷发始于高能、高危险的爆炸阶段，然后减弱并停止，或者过渡到混合和喷发行为，产生相对短程的熔岩流，潜在危险要低得多。了解这些转变的时间以及喷发结束的​​时间是影响灾害评估和喷发响应的重大挑战。现有模型假设，从爆炸行为到喷发行为的转变是由岩浆上升速率的变化或加压气体的渗透性释放从下方驱动的，从而有效地“化解”了爆炸潜力。然而，这些自下而上的模型无法解释硅质火山活动的两个基本方面：(i) 在 2011-12 年 Cordon Caulle（智利）喷发期间直接目睹并随后在其他地方推断的同时爆发-喷流行为，以及 (ii)这些喷发类型所有阶段的沉积物中都保存了广泛记录的管道内火山碎屑烧结的证据。项目团队成员利用这一证据开发了硅质喷发中爆炸-喷流转变的新范例（Wadsworth 等人，2020），其中转变是通过碎片岩浆的浅焊接和浅管道的闭塞从上方驱动的。在这种“神秘碎片”范式中，所有硅质喷发在深处都是爆炸性的，即使在地表表面明显喷发也是如此。这个新想法需要对硅质火山系统进行全面的重新评估。我们的新模型提出，明显喷出的熔岩是直接由爆发性火山活动产生的，是由最浅火山管道中的热火山灰和浮石的粘性混合-烧结而成的。地壳的一部分（参见 CfS）。神秘的碎裂模型是根据贫晶硅质系统的证据而开发的。在这项新研究中，我们更进一步，提出该模型也适用于富含晶体的中间系统，这种系统更为常见，并构成全球性危害。该假设基于来自富含晶体的系统的大量证据，与上面总结的类似。该项目将实现：(1) 使用多个实验室的现有样本对全球圆顶形成和富含晶体的熔岩进行新分析。我们将限制基质中的纹理 - 重点关注指示烧结成岩作用的孔隙纹理 - 以及与破碎和烧结相关的宏观尺度纹理，例如部分烧结颗粒的裂缝。这项新的结构工作，加上分析和岩石物理测量，将支持我们将神秘碎裂模型扩展到含晶体岩浆系统。 (2) 一套全面的新实验火山学测量方法，用于测量多相岩浆颗粒（含晶体的玻璃）的烧结速率。依靠 PI 大量的实验和理论烧结工作，我们将开发新的经过实验验证的模型，用于在高压、存在岩浆挥发物和剪切应力的情况下系统中晶体的烧结速率。这将首次将烧结理论推向岩浆条件，并首次对火山的烧结速率进行定量测试。 (3) 我们将通过与火山观测站的利益相关者合作，将这些烧结率方程应用于过去在收集样本组的同一地点的活跃的含晶体火山喷发，重点关注科利马火山（墨西哥）。Cryptic碎片模型参考：Wadsworth, F.B., Llewellin, E.W., Vasseur, J., Gardner, J.E. and Tuffen, H., 2020. 烧结引起的爆炸-喷发火山喷发转变。科学进展，6(39)，p.eaba7940