Constraints on the tempo and magnitude of explosive volcanism: facilitating long-term ash fall hazard assessments

火山爆发对喷口附近地区造成毁灭性影响，在那里，火山碎屑密度流可造成重大生命损失，但大量火山灰注入大气层并随后散布数百至数千公里，造成重大和深远的危害。火山灰是一种严重和广泛的火山灾害;造成屋顶坍塌，健康（呼吸）和农业问题以及基本基础设施的大规模中断。即使是在中等爆炸性喷发中释放的火山灰也会使空中交通瘫痪，2010年冰岛埃亚菲亚德拉火山爆发就是明证。因此，火山灰的广泛散布造成了巨大的经济和社会成本。令人不安的是，全球有8亿人生活在离活火山100公里的范围内，但对全球火山爆发数据库的统计研究表明，对过去火山爆发的记录严重不足。例如，这项分析将表明，VEI 5喷发中多达66%的喷发，相当于1980年的圣海伦火山喷发，在过去20万年的地质记录中消失了。我们对某个火山喷发的规模和频率的了解通常偏向于最近的活动，因为较早的火山喷发记录不完整，往往是由于最近的火山喷发造成的侵蚀和（或）掩埋。然而，保存较好的短期记录并不一定反映火山活动的全部范围或活动克里思的变化。这是长期火山灾害评估的一个主要障碍，并妨碍我们的能力：i）确定随时间变化的喷发率，ii）评价震级-频率关系，iii）预测危险火山灰扩散的复发间隔。这项研究通过重建日本南部和中部火山爆发的全面长期记录克服了这一僵局。这项研究利用了保存在远离火山的海洋和湖泊沉积物岩心密集网络中的火山灰层的未充分利用的记录。这些连续的沉积物序列提供了前所未有的火山灰降落库（以可见和微观沉积物的形式保存），这些火山灰不易受到破坏性近源火山过程的影响。使用最先进的化学“指纹”技术，可以精确定位远端火山灰层的火山源，同时在核心网络中追踪这些火山灰下落事件，为计算建模和绘制过去的火山灰分布提供了机会，并计算喷发幅度。整合尖端的测年技术（40 Ar/39 Ar/14 C）来确定火山灰沉积物的年代，使我们能够揭示单个火山过去爆发的时间和克里思，并重要地确定这些火山广泛危险的火山灰散布的复发间隔。我们在日本南部和中部的研究已经成功地解决了未报告的火山爆发问题，并填补了许多火山喷发记录的空白。在我们研究的下一阶段，我们将扩大我们方法的应用范围，以解决日本东北部和千岛群岛弧的火山问题，利用国际海洋发现计划（IODP）和日本海洋地球科学与技术机构（JAMSTEC）新提供的海洋岩心。此外，利用我们制作全面喷发记录的能力，我们将探索火山与气候的相互作用。将与直接负责个别火山的火山危险评估的人员和在该领域工作的决策者合作，继续审查该项目产生的远距离火山学记录。

Explosive volcanic eruptions have devastating impacts in near-vent areas where pyroclastic density currents can cause significant loss of life, yet the injection of large volumes of ash into the atmosphere and its subsequent dispersal over hundreds to thousands of kilometres, pose significant and far-reaching hazards. Ash fall is a severe and wide-ranging volcanic hazard; causing roof collapse, health (respiratory) and agricultural issues and wide-scale interruptions to essential infrastructure. Even ash emitted during moderately explosive eruptions can ground air traffic as was demonstrated by the 2010 Eyjafjallajökull eruption (Iceland). As such widespread volcanic ash dispersals present huge economic and societal costs. Disturbingly, 800 million people live within 100 km of active volcanoes globally, yet statistical studies of global eruption databases indicate significant under-recording of past volcanic eruptions deeper in time. For instance, this analysis would indicate up to 66% of VEI 5 eruptions, equivalent in scale to the 1980 Mount St Helens eruption, are missing within the geological record spanning the last 200,000 years. Our understanding of the magnitude and frequency of eruptions at a particular volcano is typically skewed to recent activities, because records of older eruptions are fragmentary often owing to erosion and/or burial by more recent eruptions. The better-preserved, shorter-term records, however, do not necessarily reflect the full range of volcanic activity, or variations in the tempo of activity. This is a major obstacle for long-term volcanic hazard assessments and hampers our ability to: i) determine changing eruption-rates through time, ii) evaluate magnitude-frequency relationships and iii) project the recurrence intervals of hazardous ash dispersals. This research has overcome this impasse by reconstruct comprehensive long-term records of explosive volcanism for volcanoes in southern and central Japan. This research exploits the under-utilised record of volcanic ash layers preserved in dense networks of marine and lake sediment cores away from the volcano. These continuous sediment sequences present unprecedented repositories of ash fall (preserved as visible and microscopic deposits), which are not susceptible to destructive near-source volcanic processes. Using state-of-the-art chemical 'fingerprinting' techniques, it is possible to pinpoint the volcanic source of the distal ash layers, whilst tracing these ash fall events across a network of cores provides the opportunity to computationally model and map past ash dispersals, and calculate eruption magnitudes. Integrating cutting-edge dating techniques (40Ar/39Ar/14C) to date the ash deposits, enables us to reveal the timing and tempo of past explosive eruptions at an individual volcano, and importantly determine the recurrence intervals of widespread hazardous volcanic ash dispersals from these volcanoes. Our research in south and central Japan has been successfully tackling eruption un-reporting and plugged the gaps in the eruption records of numerous volcanoes. In the next phase of our research we will expand the application of our methods to address the volcanoes of NE Japan and the Kurile Arc, utilising newly available marine cores from International Ocean Discovery Programme (IODP) and Japan Agency For Marine-Earth Sciences and Technology (JAMSTEC). In addition, using our ability to produce comprehensive eruption records, we will explore volcano-climate interactions. The distal volcanological records generated in this project will continue to be examined in partnership with those directly responsible for volcanic hazard assessments at individual volcanoes, and policy-makers working in the field.