Urgency Response to the 15 January 2022 Hunga Tonga - Hunga Ha'apai Volcanic Eruption -understanding the Volcanic Mechanism and Impact of the tsunami

2022年1月15日，位于太平洋西南部汤加岛弧的Hunga Tonga - Hunga Ha'apai火山爆发一个月后，发生了一次短暂的（两小时），极高强度的爆炸性喷发，摧毁了火山建筑物的大部分陆上部分。由此产生的压力波和海啸影响是局部和全球性的，是自1883年喀拉喀托火山爆发以来影响最深远的一次。海啸波袭击附近（65公里）汤加塔普岛的低洼海岸，高达15米。由于组织良好的早期预警和疏散，死亡人数很少（3人），但沿海地区沿着有重大破坏。更远的诺穆卡群岛的低洼岛屿完全被淹没，村庄被摧毁。在汤加群岛更远的地方，海啸是由巨大的大气压力波引起的，这是第一次有仪器记录的这种规模的火山爆发事件，它影响了整个全球大气层和电离层，造成了观测到的次声波和不寻常的长周期地震共振。Hunga Tonga - Hunga Ha'apai火山爆发是一个重大的意外事件，袭击附近汤加群岛海岸的当地海啸的机制和产生仍然存在很大的不确定性，考虑了三种可能性：1）爆炸造成的50公里高的灰柱坍塌造成的火山碎屑密度流，2）与火山建筑物破坏有关的海底块状沉积物运动，和/或3）海水进入破裂的火山破火山口时，由蒸汽岩浆爆炸产生的巨大冲击波。因此，拟议研究的目的是从甚高分辨率（1米）卫星图像中确定火山爆发的机制和海啸对附近汤加群岛的影响（淹没、高度和破坏）。为了实现这些目标，我们将利用卫星图像：1）绘制洪加汤加-洪加哈派火山在喷发前和喷发期间的形态变化图; 2）作为观测喷发机制及其影响的基础，特别是关于事件发生时间的信息; 3）确定海啸对汤加群岛的高度和淹没程度以及所造成的破坏。在最近的海啸之后，例如2018年印度尼西亚的海啸，多国团队在现场工作后不久就绘制了沿海地区的影响，记录了破坏和洪水。然而，Hunga Tonga - Hunga Ha'apai事件的一个主要挑战是持续缺乏关于汤加海啸影响的信息，因为火山爆发破坏了连接该国与外界的互联网通信电缆-因此自火山爆发以来，岛国王国在很大程度上被孤立。这也是因为汤加处于新型冠状病毒封锁状态，外国（非汤加）游客无法进入。因此，我们使用卫星图像来绘制海啸影响图是一种新颖的方法，以前没有在事件发生后立即绘制海啸淹没图。这次火山爆发导致了一个重大的科学研究计划，由许多科学组织实施，我们正在与他们协调。我们亦正尽可能与本地科学家协调，他们会提供有关海啸影响的观测数据，以证实卫星数据的解释。除了验证海啸模型外，这些解释还将用于支持减轻海啸影响。

On January 15th, 2022, a month into the eruption of Hunga Tonga - Hunga Ha'apai volcano, located in the Tonga Island arc in the southwest Pacific, there was a short lived (two hour), extremely high intensity explosive eruption that destroyed most of the subaerial parts of the volcanic edifice. The resulting pressure wave and tsunami impacts were local and global, and the most far-reaching since the eruption of Krakatau volcano in 1883. Tsunami waves striking the nearby (65 km) low-lying coasts of Tongatapu Island, were up to 15 m high. Because of well organised early warning and evacuation, there were very few (three) fatalities, although there was significant destruction along coastal areas. The low-lying islands of the more distant Nomuka Group were completely overwhelmed, and villages destroyed. Farther afield from the Tongan islands, the tsunamis were caused by the massive atmospheric pressure wave, that is the first instrumentally recorded eruption-generated event of this scale, which affected the entire global atmosphere and ionosphere, causing the observed infrasound waves and unusual long-period seismic resonances. The Hunga Tonga - Hunga Ha'apai eruption was a major surprise and there remains a major uncertainty over the mechanism(s) and the generation of the local tsunamis striking the nearby Tongan islands coasts, with three possibilities considered 1) pyroclastic density currents resulting from the collapse of the 50 km high ash column resulting from the explosion, 2) submarine mass sediment movements associated with the destruction of the volcanic edifice, and/or, 3) the massive shock wave resulting from a phreatomagmatic explosion as sea water entered the fractured volcanic caldera. The objectives of the proposed research, therefore, are to identify from very high resolution (one metre) satellite images the volcanic mechanism (s) of the eruption and the impact (inundation, height, and destruction) of the tsunami on the nearby Tonga islands. To achieve these aims, we will use the satellite imagery, 1) to map the morphological changes of Hunga Tonga - Hunga Ha'apai volcano in the build-up to and during the eruption; 2) as basis for observations on the eruption mechanism and its impacts, particularly information on the timing of the events, and 3) identify the height and inundation of the tsunami on the Tongan islands together the resulting destruction. After previous recent tsunamis, such as those of 2018 in Indonesia, the impacts on coastal areas were mapped soon after the event from field work by multinational teams that recorded the destruction and inundation. A major challenge with the Hunga Tonga - Hunga Ha'apai event, however, is the ongoing lack of information on the tsunami impact from Tonga because the eruption fractured the internet communications cable connecting the country to the outside world - so since the eruption the Island Kingdom has been largely isolated. It is also because Tonga is in Covid lockdown, with no access for foreign (non-Tongan) visitors. Our use of satellite imagery to map the tsunami impact, therefore, is a novel approach, not used previously in mapping tsunami inundation immediately after an event. The eruption has resulted in a major programme of scientific research carried out by many scientific organisations with who we are co-ordinating. We are also co-ordinating as far as possible, with local scientists, who will provide observational information on the tsunami impact to validate the interpretations of satellite data. These interpretations, in addition to validating the tsunami modelling, will also be used to underpin mitigation of the tsunami impact.