The Dec. 22, 2018 lateral collapse of the Anak Krakatau (AK) volcano in the Sunda Straits of Indonesia discharged volcaniclastic material into the 250 m deep caldera southwest of the volcano and generated a large tsunami, causing runups of up to 85 m in the near-field, and 13.5 m in the far-field, on the nearby coasts of Sumatra and Java. The tsunami caused 437 fatalities, the greatest number from a volcanically-induced tsunami since the catastrophic explosive caldera-forming eruption of Krakatau in 1883 and the sector collapse of Ritter Island in 1888. For the first time in over 100 years, the 2018 AK event provides an opportunity to study a major volcanically-generated tsunami that caused widespread loss of life and significant damage. Here, we present numerical simulations of the collapse and tsunami generation, propagation, and coastal impact, with state-of the-art numerical models, using both a new parametrization of the collapse and a near-field bathymetric dataset based on our 2019 field surveys and satellite images. These subaerial and submarine data sets are used to constrain the geometry and magnitude of the landslide mechanism, which show that the primary landslide scar bisected the AK edifice, cutting behind the central vent and removing 50% of its subaerial volume. The primary landslide volume is estimated to range from 0.175–0.313 km³, based on uncertainties in the shape of the submerged part of the failure plane. This is supported by an independent estimate of the primary landslide deposit volume of 0.214 ± 0.036 km³. Given uncertainties in the failure volume, we define a range of potential failure surfaces that span these values in 4 collapse scenarios of volume ranging from 0.175 to 0.313 km³. These AK collapses are modeled, assuming either a granular or viscous fluid rheology, together with their corresponding tsunami generation and propagation. Observations of a single tsunami, with no subsequent waves, are consistent with our interpretation of landslide failure in a rapid, single phase of movement rather than a more piecemeal process, generating a tsunami which reached nearby coastlines within ~30 min. For both modeled rheologies, the 0.224 km³ collapse (second and preferred scenario) most successfully reproduces the near- and far-field tsunami flow depth and runup observed in all post-event field survey results, tide gauge records, and eyewitness reports to date, suggesting our estimated landslide volume range is appropriate. This event highlights the significant hazard posed by relatively small-scale lateral volcanic collapses, which can occur en-masse, without any precursory signals, and are an efficient and unpredictable tsunami source. Our successful simulations demonstrate that current numerical models can accurately forecast tsunami hazards from these events. In cases such as Anak Krakatau's, the absence of precursory warning signals, together with the short travel time following tsunami initiation present a major challenge for mitigating tsunami coastal impact, stressing the need to develop and install early warning systems for such events.

2018 年 12 月 22 日印度尼西亚巽他海峡的 Anak Krakatau (AK) 火山横向坍塌，将火山碎屑物质排放到火山西南 250 m 深的火山口中，并产生了巨大的海啸，造成高达 85 m 的爬升。近场，远场 13.5 m，位于苏门答腊和爪哇附近海岸。海啸造成 437 人死亡，这是自 1883 年喀拉喀托发生灾难性爆炸性火山口形成喷发和 1888 年里特岛部门崩溃以来火山引发的海啸造成的死亡人数最多的一次。 2018 年 AK 事件是 100 多年来的首次提供了研究造成广泛生命损失和重大破坏的主要火山产生的海啸的机会。在这里，我们展示了坍塌和海啸产生、传播和沿海影响的数值模拟，使用最先进的数值模型，使用新的坍塌参数化和基于我们 2019 年实地调查和卫星图像的近场测深数据集。这些地面和海底数据集用于约束滑坡机制的几何形状和大小，这表明主要滑坡疤痕将 AK 建筑物一分为二，在中央通风口后面切割并去除了其地下体积的 50%。主要滑坡体积估计范围为 0.175-0.313 公里 这表明主要的滑坡疤痕将 AK 大厦一分为二，在中央通风口后面切割并移除了其地下体积的 50%。主要滑坡体积估计范围为 0.175-0.313 公里 这表明主要的滑坡疤痕将 AK 大厦一分为二，在中央通风口后面切割并移除了其地下体积的 50%。主要滑坡体积估计范围为 0.175-0.313 公里³，基于破坏平面的淹没部分形状的不确定性。这得到了对 0.214 ± 0.036 km ³的主要滑坡沉积体积的独立估计的支持。鉴于故障体积的不确定性，我们定义了一系列潜在故障面，这些值跨越 4 个体积范围从 0.175 到 0.313 km ^{3 的}坍塌场景中的这些值. 这些 AK 坍塌被建模，假设是颗粒状或粘性流体流变学，以及它们相应的海啸产生和传播。对没有后续波浪的单一海啸的观察与我们对快速、单一运动阶段而非更零碎过程中的滑坡破坏的解释一致，产生了在约 30 分钟内到达附近海岸线的海啸。对于两种模拟流变学，0.224 km ³坍塌（第二个也是首选的场景）最成功地再现了迄今为止在所有事后现场调查结果、潮汐测量记录和目击者报告中观察到的近场和远场海啸流量深度和爬高，表明我们估计的滑坡体积范围是合适的. 这一事件凸显了规模相对较小的横向火山崩塌所带来的重大危害，这种崩塌可能会大规模发生，没有任何先兆信号，并且是有效且不可预测的海啸源。我们成功的模拟表明，当前的数值模型可以准确地预测这些事件造成的海啸灾害。在 Anak Krakatau 等案例中，由于缺乏预警信号，加上海啸爆发后的短途旅行时间，对减轻海啸沿海影响构成了重大挑战，强调需要为此类事件开发和安装预警系统。