On December 22, 2018, the eruption and flank collapse of the Anak Krakatau volcano generated a tsunami in the Sunda Strait causing catastrophic damage to uninhabited coastlines proximal to the source. Along the heavily populated shores of Banten and Lampung provinces in Java and Sumatra, tsunami waves caused severe damage, extensive inundation and more than 430 deaths. An international tsunami survey team (ITST) deployed 6 weeks after the event documented the tsunami effects including runup heights, flow depths and inundation distances, as well as sediment deposition patterns and impacts on infrastructure and the natural environment. The team also interviewed numerous eyewitnesses and educated residents about tsunami hazards. This ITST was the first to visit and document the extreme tsunami effects on the small islands in the Sunda Strait closest to Anak Krakatau (Rakata, Panjang, Sertung, Sebesi and Panaitan). Along the steep slopes of Rakata and Sertung islands, located less than 5 km from and facing directly towards the southwest flank of Anak Krakatau, all of the dense coastal vegetation was stripped to bare earth up to elevations of more than 80 m, while on the northeast tip of Sertung Island, facing away from the source, a single tree remained standing after flow depths of > 11 m above ground struck there. The runup distributions on the islands encircling Anak Krakatau highlight the directivity of the tsunami source suggesting that the collapse occurred towards the southwest. This manifested as tsunami runup of < 10 m on Sebesi Island, located 15 km northeast of the source, contrasting with tsunami flow heights > 10 m that stripped away coastal forests to bare rock for up to 400 m inland in the Ujung Kulon National Park, located 50 km to the south-southwest. Inundation and damage were mostly limited to within 400 m of the shoreline, likely the result of the relatively short wavelengths caused by the landslide generated tsunami. A significant variation in tsunami impact was observed along the shorelines of the Sunda Strait, with runup heights rapidly decreasing with distance from the inferred tsunami source. To model the event we applied a hot-start initial condition that roughly reproduced the measured tsunami runup heights along Rakata and Sertung. The waveforms were then propagated through the Sunda Straight using a Boussinesq-type wave model. The results showed a good fit to the observed heights along the Java and Sumatra coastlines, the northern coast of Panaitan Island and Ujung Kulon Nation Park. The model also produced an acceptable fit to the observed amplitudes at tide gauges. Despite the regional volcanic and tsunamigenic history of the region, and 6-months of eruptive activity prior to the event, the tsunami largely caught the local population off guard. This further highlights the need for community-based education and awareness programs as essential to save lives in locales at risk from locally generated tsunamis.

中文翻译：

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2018 年 12 月 22 日 Anak Krakatau 海啸的现场调查和数值模拟

2018 年 12 月 22 日，Anak Krakatau 火山的喷发和侧翼坍塌在巽他海峡引发了海啸，对源头附近无人居住的海岸线造成了灾难性的破坏。在爪哇和苏门答腊的万丹省和楠榜省人口稠密的海岸，海啸造成了严重破坏、大面积淹没和 430 多人死亡。事件发生 6 周后，一个国际海啸调查小组 (ITST) 部署记录了海啸影响，包括上升高度、流动深度和淹没距离，以及沉积物沉积模式以及对基础设施和自然环境的影响。该团队还采访了许多目击者，并就海啸危害对居民进行了教育。该 ITST 首次访问并记录了最靠近 Anak Krakatau 的巽他海峡小岛（拉卡塔、班让、塞尔通、塞贝西和帕奈丹）受到的极端海啸影响。沿着拉卡塔岛和塞尔通岛的陡坡，距离喀拉喀托岛西南侧不到 5 公里，所有茂密的沿海植被都被剥光，海拔超过 80 m，而在Sertung 岛的东北端背离源头，在距离地面 > 11 m 的水流冲击那里后，一棵树仍然屹立不倒。环绕喀拉喀托的岛屿上的爬升分布突出了海啸源的方向性，表明坍塌发生在西南方向。这表现为Sebesi岛上<10 m的海啸上升，位于源头东北 15 公里处，相比之下，位于西南偏南 50 公里的乌戎库隆国家公园内，海啸流高度 > 10 米，将沿海森林剥落成裸露的岩石，长达 400 米。淹没和破坏大多限于海岸线 400 m 以内，这可能是滑坡产生的海啸造成的波长相对较短的结果。沿巽他海峡海岸线观察到海啸影响的显着变化，上升高度随着与推断的海啸源的距离而迅速降低。为了模拟事件，我们应用了热启动初始条件，该条件大致再现了沿 Rakata 和 Sertung 测量的海啸上升高度。然后使用 Boussinesq 型波模型将波形传播通过巽他海峡。结果显示，与爪哇和苏门答腊海岸线、帕奈坦岛北部海岸和乌戎库隆国家公园沿线的观测高度非常吻合。该模型还对测潮仪观测到的振幅产生了可接受的拟合。尽管该地区有火山和海啸的历史，以及事件发生前 6 个月的喷发活动，但海啸在很大程度上让当地居民措手不及。这进一步突出了基于社区的教育和意识计划的必要性，这对于在当地产生的海啸风险中拯救生命至关重要。尽管该地区有火山和海啸的历史，以及事件发生前 6 个月的喷发活动，但海啸在很大程度上让当地居民措手不及。这进一步突出了基于社区的教育和意识计划的必要性，这对于在当地产生的海啸风险中拯救生命至关重要。尽管该地区有火山和海啸的历史，以及事件发生前 6 个月的喷发活动，但海啸在很大程度上让当地居民措手不及。这进一步突出了基于社区的教育和意识计划的必要性，这对于在当地产生的海啸风险中拯救生命至关重要。