Volcano-hydrologic hazards associated with the April 2015 eruption of Calbuco volcano, Chile

火山在不同的时间尺度上产生了广泛的危害。除了与喷发活动相关的对生命和基础设施的更熟悉的主要危害（例如灰烬坠落、火成碎屑密度流（热气和带电颗粒雪崩）和熔岩流）之外，在许多情况下，由于松散的喷发物的再活动而产生的次要危害在喷发结束后，雨水和流水对松散的喷发物的破坏性更大、持续时间更长，并且影响范围更远。火山泥流是由重力驱动的火山碎屑和水流，由于其爆发迅速、流动性强、能量高，并能够影响远离已知危险区的地区，因此特别令人关切。自公元1600年以来，火山泥流造成的死亡人数占火山活动死亡人数的17%，火山泥流要么直接由火山活动触发（即火山口湖喷出或火山碎屑流融化山顶冰盖），要么间接作为次要事件（即降雨重新动员新鲜火山碎屑沉积物或火山堰塞湖爆发）。然而，由于这些现象的复杂性和不可预测性，这些现象是所有火山灾害中最不为人所知的，阻碍了旨在减少其造成损失或损害的可能性的战略。提高我们对火山泥流的理解和知识的关键在于基于实地的研究，这些研究限制了它们的源条件和起始，以及它们在下游流动过程中如何演变，沿着沿着拾取和丢弃沉积物负荷，并与通道边缘相互作用。2015年4月22日至23日，智利南部安第斯山脉的卡尔布科火山最近爆发，为研究火山泥流提供了一个机会。卡尔布科是安第斯山脉南部已知的66座活火山之一，该地区拥有智利80%的人口。该地区历史上的火山喷发伴随着多次火山喷发和降雨引发的火山泥流，造成了该地区世纪大部分与火山喷发有关的死亡。随着该地区经济的持续增长，越来越多的人口和基础设施受到这些灾害的影响，迫切需要更好地量化和了解这些事件，我们将进行实地工作，绘制和测量在最初爆发阶段发生的、摧毁了山区周围一些河谷中的桥梁和基础设施的、由火山爆发引发的原始热泥流的沉积物。火山爆发还在卡尔布科陡峭的、季节性积雪覆盖的上斜坡和附近的奥索尔诺火山锥上沉积了一层厚厚的火山灰和火山砾，使该地区在即将到来的南半球冬季期间进入了一个由降雨引发的强烈再动员阶段，届时该地区将获得大部分的年降雨量。我们将在一系列地点测量火山灰沉积物的性质，并在关键监测点配备延时摄像机和雨量计，使我们能够跟踪火山灰层对降雨事件的反应及其在拉哈尔形成中的综合作用。重复测量将记录灰层随着时间的推移而退化和侵蚀的演变。在下游，我们将测量拉哈尔通道的尺寸和几何形状，并使用传感器对其进行仪器测量，这些传感器可以检测和记录流动事件引起的地面震动，使我们能够测量它们的时间，幅度，速度和位置。定时和触发式摄像机将记录有关水流深度和泥沙浓度的重要信息。这些数据的组合将首次允许在拉哈尔源区的条件和所产生的流动之间建立直接的相关性。将利用遥感卫星数据，包括高分辨率光学和多光谱图像以及哨兵-1 X雷达干涉测量数据，绘制拉哈尔路径随时间的演变图，并建立高分辨率数字高程模型。

Volcanoes generate a wide range of hazards across a variety of timescales. In addition to the more familiar primary hazards to life and infrastructure associated with eruptive activity, such as ashfall, pyroclastic density currents (hot gas and particle-charged avalanches) and lava flows, in many cases the secondary hazards that arise from the remobilisation of the loose erupted material by rain and running water after the eruption is over are more devastating, longer-lasting, and reach further afield. Lahars, gravity-driven flows of volcanic debris and water, are of particular concern due to their rapid onset, mobility, high energy, and ability to impact areas far removed from perceived zones of hazard. Since 1600 AD, lahars have been responsible for 17% of all deaths due to volcanic activity, being triggered either directly by volcanic activity (i.e. by ejection of a crater lake or melting of a summit ice cap by pyroclastic flows) or indirectly as secondary events (i.e. by rainfall remobilisation of fresh pyroclastic deposits or break-outs from volcanically-dammed lakes). However, these phenomena are amongst the most poorly understood of all volcanic hazards because of their complexity and unpredictability, hampering strategies designed to militate against their potential to cause loss or damage. A key to improving our understanding and knowledge of lahars lies in field-based studies that constrain their source conditions and initiation, and how they evolved during downstream flow, picking up and dropping sediment-load along the way and interacting with the channel margins.The recent eruption of Calbuco volcano on 22-23 April 2015, in the Southern Andes of Chile, offers an opportunity to study lahars as they happen. Calbuco is one of more than 66 known active volcanoes in the southern Andes, an area that hosts 80% of Chile's population. Historic eruptions in the area have been accompanied by multiple eruption- and rain-triggered lahars, causing most the region's eruption-related deaths in the 20th Century. As economic growth in the area continues, an increasing population and infrastructure base is becoming exposed to these hazards, creating an urgent need for better quantification and understanding of such events.We will undertake fieldwork to map and characterise the deposits of the primary, eruption-triggered hot lahars that occurred during the initial eruptive phase and destroyed bridges and infrastructure in a number of river valleys around the mountain. The eruptions also deposited a thick layer of ash and lapilli on the steep, seasonally snow-clad upper slopes of Calbuco, and the nearby cone of Osorno volcano, priming the region for an intense phase of rain-triggered remobilisation during the impending Southern Hemisphere winter when the region receives most of its annual rainfall. We will measure the properties of the ash deposits in a range of locations and instrument key monitoring sites with time-lapse cameras and rain gauges to enable us to track the response of the ash layer to rain-fall events and their combined role in lahar initiation. Repeat measurements will document the evolution of the ash layer as it degrades and is eroded over time. Further downstream, we will measure the dimensions and geometry of the lahar channels and instrument them with sensors that detect and record the ground-shaking caused by the flow events, enabling us to measure their timing, magnitude, speed, and location. Time-lapse and triggered video cameras will record vital information on flow depth and sediment concentration. This combination of data will permit, for the first time, direct correlations between conditions in lahar source zones and the resulting flows. Remote-sensed satellite data, including high-resolution optical and multispectral imagery and Sentinel-1 X radar interferometry data will be used to map the evolution of lahar paths through time and construct high-resolution digital elevation models.