The August 2019 Tongan 18.325oS/174.365oW submarine volcanic eruption: eruptive processes and pumice raft formation and evolution

2019年8月汤加18.325oS/174.365oW海底火山喷发：喷发过程和浮石筏的形成和演化

• 批准号: NE/T010916/1
• 负责人: Isobel Yeo
• 金额: $ 8.35万
• 依托单位: NATIONAL OCEANOGRAPHY CENTRE
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2019
• 资助国家: 英国
• 起止时间: 2019 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FT010916%2F1
• 关键词: August; 2019; Tongan; 18.325oS; 174.365oW

The August 7th 2019 eruption of Volcano 0403-091, a shallow submarine volcano near Tonga, produced a 200 km2 raft of pumice - a highly porous, buoyant volcanic rock that can float in water for many weeks, during which time it is dispersed around the oceans as it drifts in the direction of winds and currents. This floating pumice raft has already reached Fiji and is expected to reach Vanuatu, New Caledonia and ultimately Australia in the coming months. Pumice rafts provide a home for numerous marine species that begin to colonise the drifting pumice, and this raft has sparked global interest because of its potential to transport species, including corals, as far as the Australian Great Barrier Reef. Pumice rafts are also of interest to scientists and society because of their potential to damage ships: past rafts have demonstrated that they can abrade hulls, jam or damage propellers and rudders, and block water intakes (causing engine failure) - even for large cargo ships. A future pumice raft that enters a major shipping lane could therefore cause severe economic disruption, just like the 2010 European aviation ash crisis. To prepare hazard mitigation strategies for such an event, we need to better understand what kinds of eruptions (hence which volcanoes) can create floating pumice, and improve our ability to forecast where rafts will travel to via ocean currents. This eruption has provided us with a unique opportunity to gain crucial data that will help us to understand how pumice rafts are formed, how their physical characteristics change as they drift across the ocean, and how pumice raft-producing eruptions impact ecosystems and biogeochemical processes both at the eruption site and in distant regions reached by the raft. We propose to visit the volcano and perform a seafloor survey of the eruptive vent and shallow volcano summit using a Remotely Operated Vehicle (ROV) that records video and collects samples, as well as additional sample collection from deeper locations using a dredge system with attached camera. This will enable us to map the new morphology and seafloor deposits of the volcano, and document the species living on the volcano and how they have been affected by the eruption and hydrothermal activity. Samples of seafloor eruptive products from near the vent (which never floated) and up to 6 km away (which floated some way before sinking) will be compared with samples of floating raft pumice collected by sailors within one week of the eruption. By analysing the chemistry (magma composition, gas contents) and comparing the physical characteristics (clast size, bubble connectivity) of these different samples we can investigate the eruption processes that control whether a volcano can produce a floating pumice raft. We also intend to sample raft pumice when it washes up on nearby coastlines (e.g. Fiji, New Caledonia) after several weeks of floating. This will reveal how pumice characteristics (e.g. size, shape, buoyancy) change during dispersal, which will help us improve models of pumice raft dispersal and hazard assessment. It will also reveal the temporal change in the number and type of marine species that colonise the raft, allowing us to assess which species may be transported to the Australian Great Barrier Reef. It is important to undertake this survey and sampling as soon as possible after the eruption, before the shallow vent can be altered by wave/cyclonic action (which can erode and redistribute eruption products) and while the seafloor ecosystem is still in a state of responding to the eruption and hydrothermal activity. This eruption and its raft have been unusually well documented e.g. we have clear satellite images of raft dispersal, whereas past rafts have been hidden by clouds. It is therefore an extremely rare and valuable opportunity to obtain both seafloor and floating samples with excellent constraints; a quality of opportunity that is unlikely to occur again in coming decades.

2019年8月7日火山爆发0403-091是汤加附近的浅海底火山，产生了200 km2筏的浮石 - 一种高度多孔的，浮动的火山岩，可以漂浮在水中数周，在此期间，它散布在海洋周围，随着风的方向散落。这种浮动的浮石筏已经到达斐济，预计将在未来几个月内到达瓦努阿图，新喀里多尼亚和澳大利亚。 Pumice Rafts为众多海洋物种提供了一个家园，这些海洋物种开始定居漂浮的浮石，并且这种木筏引发了全球的兴趣，因为就其在澳大利亚的大屏障礁方面，其运输物种（包括珊瑚）的潜力。浮力石筏也引起了科学家和社会的兴趣，因为它们的潜力损坏了船只：过去的筏子表明，它们可以磨损船体，果酱或损坏的螺旋桨和舵，并阻止摄入量（导致发动机故障） - 即使是大型货船也是如此。因此，进入大型运输车道的未来浮石筏可能会造成严重的经济破坏，就像2010年欧洲航空灰烬危机一样。为了为此类事件制定缓解危险策略，我们需要更好地了解哪种喷发（因此火山）可以产生浮动浮游生物，并提高我们预测木筏将通过洋流前往的预测能力。 这次喷发为我们提供了一个独特的机会来获得关键数据，这将帮助我们了解浮华筏的形成方式，它们的物理特征在遍布海洋时如何变化以及如何影响生态系统和生物地球化学过程，这两者都在爆发和延误的地区均可通过Raptaft。我们建议使用远程操作的车辆（ROV）来参观火山，并对爆发通风口和浅火山峰会进行海底调查，该车辆记录视频并收集样品，并使用带有附件的疏水器系统从更深层次的位置收集了其他样品。这将使我们能够绘制火山的新形态和海底沉积物，并记录生活在火山上的物种以及它们如何受到喷发和热液活动的影响。从通风口附近（从未漂浮）和距离6公里（在下沉之前漂浮的）海底喷发产品样品将与喷发后一周内的水手收集的漂浮木pumice样品进行比较。通过分析化学（岩浆成分，气体含量），并比较这些不同样品的物理特征（碎屑大小，气泡连接性），我们可以调查控制火山是否可以产生浮动pumice筏的喷发过程。我们还打算在几周的浮动后在附近的海岸线（例如斐济，新喀里多尼亚）上洗涤时进行采样。这将揭示分散期间的浮石特征（例如尺寸，形状，浮力）变化，这将有助于我们改善Pumice Raft Explersal和危险评估模型。它还将揭示定植筏的海洋物种数量和类型的时间变化，从而使我们能够评估哪些物种可以运输到澳大利亚大堡礁。在喷发后尽快进行此调查和采样非常重要，然后在通过波/环环（Wave/Cyclonic）作用（可能会侵蚀和重新分配喷发产物）改变浅水发泄之前，而海底生态系统仍处于对喷发和水热活动的反应状态。这种喷发及其木筏的文献异常很好，例如我们有清晰的木筏散布卫星图像，而过去的木筏被云掩盖了。因此，这是一个极为罕见且宝贵的机会，可以获得具有良好限制的海底和浮动样品。未来几十年的机会不太可能再次发生。

项目成果

The 2019-2020 volcanic eruption of Late'iki (Metis Shoal), Tonga.

• DOI: 10.1038/s41598-022-11133-8
• 发表时间: 2022-05-06
• 期刊: Scientific reports
• 影响因子: 4.6
• 作者: Yeo IA;McIntosh IM;Bryan SE;Tani K;Dunbabin M;Metz D;Collins PC;Stone K;Manu MS
• 通讯作者: Manu MS