Offshore hazard cascades from the largest volcanic eruption this century

海洋环境中的火山喷发造成各种危害，包括由喷发直接和间接造成的危害。2022年1月，部分淹没在汤加火山匈牙利汤加-匈牙利-哈阿派火山经历了数十年来最强烈的火山事件之一，引发的海啸对当地和数千公里外的海岸线都造成了破坏，断裂了连接汤加与世界其他地区的唯一海底电信电缆，造成了9040万美元的损失，相当于汤加国内生产总值的18.5%。电缆的损坏严重阻碍了在灾难发生后立即联系和援助汤加的努力，而且在撰写本报告时(2022年2月16日)尚未修复；这实际上意味着105 000名汤加公民一个多月来不得不依靠低带宽、高延迟的卫星通信。当地的海啸和电缆断裂都是不寻常的。首先，虽然汤加一些地区的当地海啸浪高达15米，但这场近场海啸比其他地方的类似事件(如2018年较小的Anak Krakatau火山海啸)规模更小，造成的破坏也更小。其次，虽然火山的爆炸事件发生在世界协调时4点14分，但海底电缆故障直到世界协调时5点40分才发生，90分钟后。这项建议将审查这些事件是由次生海底山体滑坡或其他过程引起的，并将描述它们的位置、动态和强度。为了解决这些重要问题，我们将于2022年4月在该区域收集新的高分辨率多波束测深数据，与喷发前的现有高分辨率数据进行比较。这一比较将使我们能够确定匈牙利-汤加-匈牙利哈阿派造成的海底变化，绘制其位置和范围，并计算在这一事件期间增加或调动的材料数量。这项研究还将提供一个新的基线，未来可以在此基础上对这一潜在的范式转换喷发进行更大规模的研究，所产生的产品将有助于限制未来海啸模拟的边界条件。为了使数据准确和有用，必须在喷发后尽快收集这些数据。海底非常动态(如对较小离岸火山的重复调查所表明的那样)，大量物质可以在短时间内沉积，现有的浅层沉积物可以被海浪和风暴重新抬高。这一机会是独一无二的，这既是因为这次活动的规模，也因为可以对其进行研究的高质量数据(预先存在的水深测量、有线电视运营商的合作、严格限制的喷发时间和过程)，还利用了延长附近预定的研究巡航的优势，显著减少了相关成本和二氧化碳排放。有线电视公司可以分享断层和修复的数据，但他们的船只没有配备执行详细海底调查所需的多波束声纳；因此，断层的原因、喷发事件的性质尚不清楚，也无法通过卫星数据解决。匈牙利-汤加-匈牙利-哈阿派并不是独一无二的；托夫亚弧和世界各地都有许多类似的火山。然而，其中很少有监测，而且大多数调查很差；因此，它们构成的风险尚不清楚。这一及时的项目将为如此大规模的海上喷发提供第一次详细的延时调查，从而使人们在理解超大型喷发的动态以及它们如何通过海啸或断裂的关键海底电信电缆产生次生危害方面发生重大变化，这些电缆承载着全球99%的数字流量。时间至关重要；进行快速反应调查(通过延长已安排的靠近该地区的巡航)将为海底火山喷发及其相关危险的基本问题提供强有力的答案。

Volcanic eruptions in marine settings pose a diverse range of hazards, both directly and indirectly caused by the eruption. In January 2022 the partially-submerged Tongan volcano Hunga Tonga - Hunga-Ha'apai experienced one of the most powerful volcanic events seen in decades, generating a tsunami that caused damage both locally and on shorelines thousands of km away, breaking the only seafloor telecommunications cables that connect Tonga to the rest of the world and causing $90.4M of damage, equivalent to 18.5% of Tonga's Gross Domestic Product. The damage to the cable both severely hampered efforts to contact and assist Tonga in the immediate aftermath of the disaster and the time of writing (16th Feb 2022) had not yet been repaired; effectively meaning that 105,000 Tongan citizens have had to rely on low bandwidth, high latency satellite communication for over a month. Both the local tsunami and the cable break were unusual. First, while local tsunami waves ran up to 15m in some parts of Tonga, this near field tsunami was smaller and caused less damage than similar events elsewhere e.g. smaller 2018 Anak Krakatau volcanic-tsunami. Second, while the explosive event at the volcano occurred at 04:14 UTC the seabed cable faults did not occur until 05:40 UTC, 90 minutes later. This proposal will examine whether these events were caused by secondary submarine landslides or other process and will characterise their locations, dynamics and magnitudes. In order to address these important questions we will collect new high-resolution multibeam bathymetric data in April 2022 over the region to compare with existing high-resolution data from before the eruption. This comparison will allow us to identify seafloor changes caused by Hunga Tonga -Hunga Ha'apai, map their locations and extents and calculate the volumes of material added or mobilised during this event. This study will also provide a new baseline from which future larger studies of this potentially paradigm-shifting eruption can be based and the products generated will help to constrain the boundary conditions for future tsunami modelling. In order for data to be accurate and useful they must be collected as soon as is feasible after the eruption. The seafloor is extremely dynamic (as shown by repeat surveys at smaller offshore volcanoes), large volumes of material can be deposited over short timescales and existing shallow sediments can be remobilised by waves and storms. This opportunity is unique both because of the scale of the event and because of the high-quality data available to study it (pre-existing bathymetry, cooperation from cable operators, well constrained eruption timings and processes) and also takes advantage of extending a scheduled research cruise nearby, significantly reducing the associated costs and CO2 outputs. Cable companies can share data from the faults and repair, but their vessels are not equipped with multibeam sonars required to perform detailed seafloor surveys; hence the causes of faults, the nature of the eruptive event are unclear and cannot be addressed by satellite data either. Hunga Tonga-Hunga Ha'apai is far from unique; there are numerous similar volcanoes both in the Tofua Arc and worldwide. However, very few of these are monitored and most are poorly surveyed; hence the risk they pose is unclear. This timely project will provide the first detailed time-lapse surveys for such a large offshore eruption, and thus enables major step changes in understanding the dynamics of extremely large eruptions, and how they generate secondary hazards, via tsunami or breaking critical seabed telecommunication cables that carry >99% of all digital traffic globally. Time is of the essence; performing a rapid response survey (by extending an already scheduled cruise that will travel close to the area) will provide robust answers to fundamental questions about submarine volcanic eruptions and their linked hazards.