Assessing magma fragmentation processes from the characteristics of volcanic ash

上下文。火山是世界范围内的主要自然灾害之一。加拿大有200多座潜在的活火山，并暴露在美国火山的危险中。火山产生的颗粒大小不一；直径2毫米或更小的颗粒构成火山灰，通常在最危险的爆炸性喷发期间形成。岩浆破碎是由于管道中气泡的生长和岩浆的加速，而熔岩破碎是由于岩浆-水的爆炸性相互作用而发生的。这些不同类型的碎片化与不同的危险相关。对岩浆破碎过程的解释主要基于火山灰颗粒的形状、表面特征和结构特征。然而，不同的研究人员使用的方法千差万别，这使得不同研究之间的比较非常困难。我已经与几个国际合作者一起制定了一项描述火山灰特征的标准化方案。 目标。该研究计划的长期目标是发展根据火山灰的特征评估岩浆破碎过程的能力。最终的结果将是一套“碎片图”，其中将为不同类型的岩浆碎裂和不同的喷发风格定义区域。不同的岩浆成分会产生不同的图解。 科学的方法。为了构建碎裂图，国际火山界需要从岩浆成分和喷发类型的整个光谱来表征火山灰。我的团队在未来5年的贡献将与玄武岩单生火山(斯科尔山、圆锥山和马阿尔火山)和相关的喷发风格有关。我们将从火山和实验室实验中收集不同泡泡的玄武岩岩浆的火山灰，并用标准化的方案分析这些火山灰。 新奇。该研究计划将产生以下新的成果： (I)破碎图上的一个或几个岩浆碎裂场(S)，主要基于玄武岩斯科石锥体周围的特弗拉毯子； (2)基于玄武岩岩浆和凝灰岩锥体的碎裂图上的一个或几个岩浆场； (3)岩浆气泡性质(气泡含量)对玄武岩岩浆和镜质岩浆破碎作用影响的实验研究。 意料之中的意义。科学成果将是为能够利用火山灰的特性解释未见过的火山喷发的碎裂机制而采取的明确步骤。这将使活火山能够更好地预测未来的活动和更好地减轻灾害。对加拿大的具体好处将是更好地了解未来不列颠哥伦比亚省的蝎子锥喷发可能是什么样子，以及培训8名HQP，他们将处于有利地位，在资源部门、地质调查或大学寻找工作。

CONTEXT. Volcanoes are one of the major natural hazards worldwide. Canada has more than 200 potentially active volcanoes, and is exposed to hazards from volcanoes in the USA. Volcanoes produce particles from a range of sizes; those 2 mm across or less constitute volcanic ash and typically form during explosive eruptions, the most dangerous ones. Magmatic fragmentation is due to the growth of gas bubbles and acceleration of magma in the conduit, whereas phreatomagmatic fragmentation occurs in response to explosive magma-water interaction. These different types of fragmentation are associated with distinct hazards. Interpretation of magma fragmentation processes is based largely on the shapes, surface features and textural characteristics of ash particles. However extremely variable methodologies have been used by different workers, which makes comparisons between different studies very difficult. I have developed a standardized protocol to characterize volcanic ash with several international collaborators. OBJECTIVES. The long-term objective of the research program is to develop the capability to assess magma fragmentation processes from the characteristics of volcanic ash. The end-result will be a set of “fragmentation diagrams”, where fields will be defined for different types of magma fragmentation, and different eruptive styles. Different diagrams will be produced for different magma compositions. SCIENTIFIC APPROACH. To construct the fragmentation diagrams, the international volcanological community needs to characterize ash from the whole spectrum of magma compositions and eruptive styles. The contribution of my group over the next 5 years will relate to basaltic monogenetic volcanoes (scoria cones and maars) and related eruptive styles. We will collect ash from volcanoes and from laboratory experiments with variably bubbly basaltic magma, and analyze this ash with the standardized protocol. NOVELTY. The research program will produce the following novel outputs: (i) One or several magmatic fragmentation field(s) on fragmentation diagrams, based mostly on tephra blankets around basaltic scoria cones; (ii) One or several phreatomagmatic fields on fragmentation diagrams, based on basaltic maars and tuff cones; (iii) An experimental study on the influence of magma vesicularity (content in gas bubbles) on the magmatic and phreatomagmatic fragmentation of basalt. EXPECTED SIGNIFICANCE. The scientific outcome will be the clear steps taken towards being able to interpret the fragmentation mechanism for unwitnessed volcanic eruptions using the characteristics of volcanic ash. This will allow better prediction of future activity and better hazard mitigation at active volcanoes. Specific benefits for Canada will be a better understanding of what a future scoria cone eruption would potentially look like in BC, and the training of 8 HQP, who will then be well placed to seek employment in the resource sector, geological surveys or universities.