Zhouqu, China, disaster - data capture, modelling and preliminary geohazard assessment

8月8日星期天凌晨1点，中国甘肃省西南部的一个县城舟曲发生了一次大规模的泥石流。目前的信息表明，触发因素是一场降雨事件，据报道在不到40分钟的时间内降雨量为97毫米（年平均降水量为400至900毫米）。先前的降雨也可能发挥了作用。这次灾难性的事件造成1000多人死亡（截至8月13日星期五，仅舟曲就有1,144人死亡，至少600人失踪）。在更广泛的地区，泥石流和泥石流继续影响当地人口，陇南（舟曲南部和下游）和天水（东北部）的死亡人数进一步增加。该地区的特点是地震活跃的山区地形，西藏隆起的延伸区，并受到汶川地震（12/5/2008）的影响，产生并重新激活了大量的山体滑坡。在舟曲，白龙江在海拔1300 m左右形成局部侵蚀基底。周围的山峰高度约为3500至3750米。沉积物来源的集水区约为20平方公里，其特点是坡度非常陡。植被稀疏，只剩下少量的高地森林覆盖。灾难发生后，一场激烈的辩论兴起，将责任归咎于该地区的森林砍伐、水电开发和采矿。为了从这类事件中吸取教训，而不是进行猜测，需要采取科学的方法来收集数据，核实数据的可靠性，进行公正的观察，并建立可靠的过程模型，这对于为未来制定适当的缓解战略至关重要。Dijkstra和吉布森于2009年11月访问了该遗址，并与舟曲政府就该地区大规模山体滑坡带来的风险进行了讨论。尽快收集数据至关重要。与所有滑坡事件一样，了解当地地质结构、排水、形态和岩土参数对于建立可靠的滑坡模型至关重要（例如，Geertsma等人，2006年）。该地区的滑坡和滑坡坝的主要特征往往被导致它们的不稳定性迅速消除。滑坡转化为具有复杂和瞬态机械和流变相互作用的灾难性粘性流的可能性本质上是难以绘制的。然而，这是任何可靠的风险评估的一个基本组成部分。这种评估是罕见的，因为可用于这类研究的事件稀缺。在大多数情况下，我们对这些过程的理解来自小规模的实验室实验，需要扩大规模，这可能会影响观察的相关性。在这种情况下，一个独特的现场实验室正在等待探索，以更好地了解地质灾害对该地区人口构成的风险。

At 1am on Sunday the 8th of August a large flow slide took place in Zhouqu, a county town in SW Gansu Province, China. Current information suggests that the trigger was a rainfall event delivering a reported 97mm in less than 40 minutes (annual precipitation averages from 400 to 900mm). Antecedent rainfall may also have played a role. The devastating event caused the deaths of more than 1000 people (1,144 as of Friday 13th of August in Zhouqu alone with at least 600 people still missing). In the wider region, mudslides and debris flows continue to affect the local population with further fatalities in Longnan (south and downstream of Zhouqu) and Tianshui (to the northeast). The region is characterised by a seismically active mountainous terrain, an extension zone of the Tibetan uplift, and was affected by the Wenchuan earthquake (12/5/2008) that generated and re-activated a large number of landslides. At Zhouqu, the local erosion base is formed by the Bailong River at about 1300m asl. The surrounding peaks reach heights of about 3500 to 3750m. The catchment where the sediments originate is approximately 20km2 and is characterised by very steep slopes. Vegetation cover is sparse with only a small remnant of upland forest cover remaining. Following the disaster a lively debate has sprung up apportioning blame to deforestation, hydropower development and mining in the area. In order to learn lessons from this kind of events, instead of speculation, a scientific approach is required to collect data, verify their robustness and make impartial observations and develop reliable process models that will be essential to develop appropriate mitigation strategies for the future. The site was visited in November 2009 by Dijkstra and Gibson and discussions were held with the government of Zhouqu about the risk posed by large landslides in the area. It is vitally important to collect data soon. As with all landslide events, an understanding of local geological structure, drainage, morphology and geotechnical parameters are essential in building a robust model of landsliding (e.g. Geertsma et al. 2006). The key characteristics of landslides and landslide dams in this region are often removed rapidly by the very instability that causes them. It is inherently difficult to map out the potential for landslides to transfer into catastrophic viscous flows with complex and transient mechanical and rheological interactions. However, this is an essential component in any reliable assessment of the risks. These sort of assessments are rare because of the scarcity of events available for this type of research. When these occur we must make the most of it. Mostly, our understanding of these processes is derived from small-scale laboratory experiments, requiring upscaling that may affect the relevance of the observations. In this case, a unique field laboratory is waiting to be explored to gain a better understanding of the risks posed by geohazards to the population in this region.