Rapid response survey of the 20th May 2006 Montserrat lahar deposits: a snapshot of lahar system dynamics and associated hazard

2006年5月20日，蒙特塞拉特岛上的苏弗里埃山火山经历了其11年喷发历史上第二大火山圆顶坍塌。一整天的大雨导致了火山碎屑洪水（称为火山泥流），极大地改变了火山四周的山谷。火山泥流对世界各地的许多火山来说都是相当大的危险，在喷发后的几年里继续发生，并造成大量死亡。它们特别危险，因为它们难以预测，移动迅速，可以运送大量沉积物和碎片（包括巨石）。它们可以极大地改变河谷和随后的河流行为，它们有可能削弱和破坏先前存在的结构，并淹没和掩埋它们。这类洪水本身就很难研究;其发生难以预测，其产物会因后续事件和人类活动而迅速改变。5月20日的火山泥流是蒙特塞拉特洪水范围中最具破坏性的极端。最近一次发生类似事件是在2000年3月。这是一个独特的机会，可以研究这一极端事件的沉积物和形态影响，并将新的信息与我们的降雨记录和对较小事件沉积物的研究联合收割机结合起来，以了解蒙特塞拉特火山泥流的全部范围。该项目将有助于分析拉哈尔系统在连续雨季中的长期反应，以及个别主要拉哈尔对河流动态影响的持久性。新的数据加上重新安装我们的水流监测设备，应能使人们更好地了解该系统，减轻蒙特塞拉特的危害，并将大大有助于全球了解这些危险的水流。为实现这一目标，在后续水流进行实质性人为修改或自然改造之前，必须立即调查破坏和沉积物。必须在记忆还新鲜的时候收集目击者的报告。我们将详细绘制和记录5月20日贝尔汉姆山谷事件造成的形态变化，并详细记录其他地点。我们将记录拉哈尔沉积物的范围和特征，并将这些数据与降雨和目击者数据联合收割机结合起来，以解释流动行为在空间和时间上的变化。我们将把这些意见与早期和随后的流动，以提供一个更准确的图片演变拉哈尔危害蒙特塞拉特。为了实现这一目标，将在未来5个月内进行三次调查。在这些实地考察期间，我们还将修复和重新安装5月20日损坏的UEA雨量计网络和流量监测设备，以便能够在2006年雨季及以后对活动进行远程监测。来自声学流量监测器的实时数据将在MVO处可用，以帮助降低风险。

On 20th May 2006 the Soufriere Hills Volcano on Montserrat experienced the second largest volcanic-dome collapse in its 11 year eruptive history. Heavy rain throughout the day resulted in volcanic-debris-charged floods (called lahars) that dramatically changed the valleys on all sides of the volcano. Lahars are a considerable hazard on many volcanoes worldwide, continuing to occur for some years after eruption and accounting for significant numbers of fatalities. They are especially dangerous as they are difficult to predict, move rapidly and can transport lots of sediment and debris (including boulders). They can drastically alter river valleys and subsequent river behaviour and they have the potential to undercut and destroy pre-existing structures as well as inundate and bury them. Such floods are inherently difficult to study; their occurrence is hard to predictable and their products rapidly altered by subsequent events and human activity. The 20th May lahars were at the most devastating extreme of the range of floods on Montserrat. The last occurrence of similar events was in March 2000. This is a unique opportunity to study the deposits and morphological impact of this extreme event and combine the new information with our rainfall records and studies of the deposits of smaller events, to understand the full range of lahars on Montserrat. The project will contribute towards analysis of the longer-term response of the lahar system through successive rainy seasons and the longevity of the influence of individual major lahars on stream behaviour. The new data coupled with the re-installation of our flow monitoring equipment should lead to a better understanding of the system and to hazard mitigation on Montserrat and will be a substantial contribution to the global understanding of these hazardous flows. To achieve this, immediate survey of the devastation and deposits is essential before substantive anthropogenic modification or natural reworking by subsequent flows. Eyewitness reports must be collected while memories are fresh. We will map and document the morphological change resulting from the 20th May events in the Belham Valley in detail and other sites in less detail. We will record the extent and character of the lahar deposits and combine these data with rainfall and eyewitness data to interpret the variation in flow behaviour in space and time. We will relate these observations to those of both earlier and subsequent flows to provide a more accurate picture of evolving lahar hazard on Montserrat. To achieve this there will be three survey periods spread over the next 5 months. During these field visits we will also repair and re install the UEA rain gauge network and flow monitoring equipment damaged on the 20th May to enable remote monitoring of activity during the 2006 rainy season and subsequently. The real-time data from the acoustic flow monitor will then be available at the MVO to aid risk reduction.