Assessing magma fragmentation processes from the characteristics of volcanic ash

上下文火山是世界上最大的自然灾害之一。加拿大有200多座潜在的活火山，并受到美国火山的危害。火山产生的颗粒大小不等;直径2毫米或更小的颗粒构成火山灰，通常在爆炸性喷发中形成，这是最危险的。岩浆破碎是由于气泡的增长和加速岩浆在管道中，而蒸汽岩浆破碎发生在响应爆炸性岩浆-水的相互作用。这些不同类型的碎裂与不同的危险有关。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，不同的工作者使用了非常不同的方法，这使得不同研究之间的比较非常困难。我已经开发了一个标准化的协议来描述火山灰与几个国际合作者。 目标.该研究方案的长期目标是发展从火山灰的特性评估岩浆碎裂过程的能力。最终结果将是一套“碎裂图”，其中将为不同类型的岩浆碎裂和不同的喷发风格定义字段。对于不同的岩浆成分，将产生不同的图解。 科学的方法。为了绘制碎裂图，国际火山学界需要从岩浆成分和喷发风格的整个光谱中确定火山灰的特征。我的小组在未来5年的贡献将涉及玄武岩单成火山（火山渣锥和玛耳）和相关的喷发风格。我们将从火山和实验室实验中收集火山灰，并用标准化的协议分析这些火山灰。 新奇。该研究方案将产生以下新的产出： (i)碎裂图上的一个或几个岩浆碎裂场，主要基于玄武岩火山渣锥周围的火山灰毯; (ii)碎裂图上的一个或多个蒸汽岩浆场，基于玄武质玛阿尔和凝灰岩锥; (iii)岩浆泡状度（气泡含量）对玄武岩岩浆和蒸汽岩浆破碎作用影响的实验研究。 预期意义。科学成果将是采取明确步骤，以便能够利用火山灰的特性解释无人目睹的火山爆发的碎裂机制。这将有助于更好地预测未来的活动，并更好地减轻活火山的危害。对加拿大的具体好处将是更好地了解不列颠哥伦比亚省未来的火山渣锥喷发可能是什么样子，以及培训8名HQP，他们将能够在资源部门、地质调查或大学中找到工作。

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.