Interactions between eruptive activity and sector collapse at Anak Krakatau, Indonesia

2018年12月22日，印度尼西亚Anak Krakatau火山灾难性坍塌，形成山体滑坡引发的海啸，造成周围海岸线400多人死亡。很少有人对这种规模和类型的火山滑坡，即所谓的扇形崩塌进行详细研究。正因为如此，我们对导致部门崩溃的因素的了解仍然相对有限，因此我们预测此类事件及其相关危险的能力仍然有限。尽管历史上很少有大型火山滑坡的例子，但它们在更长的地质时间尺度上很常见，在所有火山环境中都会发生。阿纳克拉喀拉喀托火山的崩塌为我们提高对这一基本火山过程的认识提供了一个重要机会。阿纳克拉喀拉喀托火山是在1883年喀拉喀托火山(又称喀拉喀托火山)毁灭性喷发后形成的火山岛，1929年首次出现在海平面以上。Anak Krakatau空中岛屿的大约一半因最近的扇区坍塌而被拆除。坍塌发生在一次持续的、相对低强度的喷发期间，类似于前几十年的特征活动类型。然而，卫星观测表明，这种活动方式在坍塌前后发生了变化，变成了一次威力更大的爆炸性喷发。这一变化的确切时机，以及它在崩盘中的潜在作用，是我们将在这项研究中详细探讨的问题。坍塌后，爆炸活动继续进行，并可能再次发生变化，因为海水与浅层喷发的岩浆相互作用。这一后期的活动喷发了大量新物质，在崩塌后的几天里迅速填满了山体滑坡的伤疤，并延长了岛屿的海岸线。我们的研究将确定喷发活动在阿纳克拉卡托地区坍塌中的具体作用。我们将解决的问题是，火山喷发行为的变化，包括新岩浆的上升，是在崩塌之前发生并因此起到触发作用；还是崩塌本身导致了强大的爆炸性喷发，通过突然减压储存在火山下面的浅层岩浆。我们还将确定崩塌后立即发生的喷发活动的性质。在喷发的这个阶段，物质似乎以非常高的速度被喷出，我们将检验这样的假设，即坍塌破坏了底层岩浆系统的稳定，导致喷发行为的变化。这种过程在受大范围崩塌影响的火山中可能很常见，形成了破坏和再生周期的一部分，但目前人们对此了解很少。我们的工作将利用横跨崩塌时期的喷发沉积物的详细现场采样。现场数据集将与卫星图像和其他遥感观测、模拟喷发过程的数值模型以及对我们的喷发沉积样品中保存的岩浆过程的化学和结构记录的分析一起进行解释。总之，我们的结果将使我们能够确定不同活动阶段所涉及的岩浆的储存条件、上升速度和喷发行为的变化。我们的结果将使我们能够探索控制部门崩溃的时间，喷发活动在崩溃中的作用，以及崩溃本身对潜在岩浆系统的影响。通过制作Anak Krakatau崩塌和喷发的全面记录，我们将推进我们对火山部门崩塌的总体理解。我们还将更清楚地了解Anak Krakatau的喷发过程和不稳定性，这将为未来随着火山重新生长而可能发生的山体滑坡提供减灾计划。

Anak Krakatau volcano, Indonesia, collapsed catastrophically on 22nd December 2018, forming a landslide-generated tsunami that caused over 400 deaths on surrounding coastlines. Very few volcanic landslides of this size and type, known as sector collapses, have been studied in detail. Because of this, our understanding of the factors that lead to sector collapse, and therefore our capacity to forecast such events and their associated hazards, remains relatively limited. Although there have been few historical examples of large volcanic landslides, they are common on longer, geological timescales and occur across all volcanic settings. The collapse of Anak Krakatau thus provides an important opportunity to improve our knowledge of this fundamental volcanic process.Anak Krakatau is the volcanic island that formed after the devastating eruption of Krakatau (also known as Krakatoa) in 1883, first emerging above sea level in 1929. Approximately half of the subaerial island of Anak Krakatau was removed by its recent sector collapse. The collapse occurred during an ongoing, relatively low-intensity eruption, similar to the type of activity that had characterised previous decades. However, satellite observations suggest that this style of activity changed around the time of the collapse, to a much more powerful explosive eruption. The precise timing of this change, and its potential role in the collapse, is something we will explore in detail in this research. Following the collapse, explosive activity continued and may have changed yet again, as seawater interacted with shallow erupting magma. This later stage of activity erupted large volumes of new material, rapidly filling the landslide scar and extending the island coastline in the days after the collapse.Our research will determine the specific role of eruptive activity in the sector collapse of Anak Krakatau. We will address whether changes in eruption behaviour, involving the ascent of fresh magma, preceded the collapse and thus acted as a trigger; or whether it was the collapse itself which led to the powerful explosive eruption, by suddenly depressurising the shallow magma stored beneath the volcano. We will also define the nature of eruptive activity that took place immediately after the collapse. In this phase of the eruption, material appears to have been ejected at a very high rate, and we will test the hypothesis that the collapse destabilised the underlying magma system, leading to a change in eruption behaviour. Such processes may be common at volcanoes affected by large sector collapses, forming part of a cycle of destruction and regrowth, but are currently poorly understood.Our work will draw upon detailed field sampling of eruption deposits spanning the collapse period. Field datasets will be interpreted alongside satellite imagery and other remote observations, numerical models that simulate eruption processes, and analyses of the chemical and textural record of magmatic processes preserved in our eruption-deposit samples. Together, our results will allow us to identify changes in the storage conditions, ascent rate and eruptive behaviour of magmas involved in different stages of activity. Our results will allow us to explore controls on the timing of the sector collapse, the role of eruptive activity in the collapse, and the impact the collapse itself had on the underlying magma system. By producing a comprehensive record of the Anak Krakatau collapse and eruptions, we will advance our understanding of volcanic sector collapses in general. We will also develop a much clearer picture of eruption processes and instabilities at Anak Krakatau, which will inform hazard mitigation plans for potential future landslides as the volcano regrows.