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的一级挑战-了解在最危险的火山喷发期间对喷发方式和强度转变的控制。大多数硅质火山爆发始于高能量、高危险的爆炸阶段，然后减弱并停止，或者过渡到混合和喷涌行为，产生相对较短的熔岩流，危险潜力要小得多。了解这些转变的时间，以及火山喷发结束的时间，是影响危害评估和火山喷发应对的主要挑战。现有的模型假设，岩浆上升速率的变化或加压气体的渗透释放，有效地“化解”了爆炸的潜力，从下面驱动了从爆炸到喷涌行为的转变。然而，这些自下而上的模型未能解释硅火山作用的两个基本方面：(i)在2011-12年智利Cordon Caulle火山喷发期间直接目睹并随后在其他地方推断的同时发生的爆炸-喷涌行为，以及（ii）在这些喷发类型的所有阶段的沉积物中保存的管道内火山碎屑烧结的广泛记录证据。项目团队成员利用这一证据开发了一种新的范例，用于研究硅喷发中的爆炸性-喷涌过渡（Wadsworth等人，2020），其中过渡是由破碎岩浆的浅层焊接和浅层管道的闭塞从上方驱动的。在这种“隐裂”范式中，所有的硅质喷发在深度上都是爆炸性的，即使在表面上明显是渗出的。这个新观点要求对硅质火山系统进行全面的重新评估。我们的新模型提出，表面上喷涌的熔岩是由火山喷发直接产生的，由热火山灰和浮石在地壳最浅部分的火山导管中的粘性混合-烧结而成（见CfS）。隐裂模型是根据贫晶硅体系的证据而发展起来的。在这项新的研究中，我们进一步提出，该模型也适用于富含晶体的中间系统，这种中间系统更为常见，并构成全球危害。这一假设是基于来自富含晶体的系统的大量证据，类似于上面总结的。该项目将提供：(1)利用来自多个实验室的现有样本，对全球范围内的圆顶形成和富含晶体的熔岩进行新的分析。我们将限制地质体中的结构——重点关注指示烧结岩石成因的孔隙结构——以及与破裂和烧结相关的宏观结构，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，将支持我们将隐裂模型扩展到含晶岩浆系统。(2)一套全面的新的火山学实验测量多相岩浆颗粒-含晶体玻璃的烧结速率。依靠PI大量的实验和理论烧结工作，我们将开发新的实验验证模型，用于在高压、岩浆挥发物存在和剪切应力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，并允许首次定量测试火山的烧结速率。(3)我们将这些烧结速率方程应用于过去在收集样品组的同一地点的含晶体活性火山喷发，重点是科利马火山（墨西哥），通过与火山观测站的利益相关者的接触。隐裂模型参考：Wadsworth， f.b., Llewellin, e.w., Vasseur， J, Gardner， J.E. and Tuffen， H., 2020。由烧结引起的爆发性-喷涌性火山喷发过渡。科学进展，6(39),p.eaba7940