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

印度尼西亚喀拉喀托火山于2018年12月22日灾难性崩塌，形成山体滑坡引发的海啸，造成周边海岸线400多人死亡。很少有这种规模和类型的火山滑坡，被称为扇形崩塌，被详细研究过。正因为如此，我们对导致行业崩溃的因素的理解，以及我们预测此类事件及其相关危害的能力，仍然相对有限。虽然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，并且发生在所有的火山环境中。因此，喀拉喀托火山的崩塌提供了一个重要的机会来提高我们对这一基本火山过程的认识。喀拉喀托火山是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上。在最近的板块崩溃中，大约有一半的喀拉喀托陆上岛屿消失了。这次崩塌发生在一次持续的、强度相对较低的喷发期间，类似于过去几十年的活动类型。然而，卫星观测表明，这种活动方式在崩溃前后发生了变化，变成了更强大的爆炸性喷发。这种变化的确切时间，以及它在崩溃中的潜在作用，是我们将在这项研究中详细探讨的。在崩塌之后，爆炸活动继续进行，并且可能再次发生变化，因为海水与浅层喷发的岩浆相互作用。这一活动的后期爆发了大量的新物质，迅速填满了滑坡的疤痕，并在崩塌后的几天里延伸了岛屿的海岸线。我们的研究将确定火山喷发活动在喀拉喀托火山板块崩塌中的具体作用。我们将探讨喷发行为的变化，包括新鲜岩浆的上升，是否先于崩塌，从而成为触发因素；或者是火山崩塌本身突然使储存在火山下面的浅层岩浆减压，从而导致了强大的爆炸性喷发。我们还将定义在崩塌后立即发生的喷发活动的性质。在喷发的这一阶段，物质似乎以非常高的速度喷射出来，我们将测试这样的假设，即塌陷破坏了潜在的岩浆系统，导致喷发行为的变化。这种过程可能在受大板块崩塌影响的火山中很常见，形成了破坏和再生循环的一部分，但目前对其了解甚少。我们的工作将借鉴详细的实地取样喷发沉积物跨越崩溃时期。现场数据集将与卫星图像和其他远程观测数据、模拟喷发过程的数值模型以及对保存在喷发沉积物样本中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岩浆的储存条件、上升速率和喷发行为的变化。我们的研究结果将使我们能够探索对板块崩塌时间的控制，火山喷发活动在崩塌中的作用，以及崩塌本身对下伏岩浆系统的影响。通过对喀拉喀托崩塌和喷发的全面记录，我们将提高我们对火山板块崩塌的总体理解。我们还将更清楚地了解喀拉喀托火山的喷发过程和不稳定性，这将为火山重新生长时未来可能发生的山体滑坡制定减灾计划提供信息。

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.