Pyroclastic flows and surges over water: an example from the 1883 Krakatau eruption

Pyroclastic deposits from the 1883 eruption of Krakatau are described from areas northeast of the volcano on the islands of Sebesi, Sebuku, and Lagoendi, and the southeast coast of Sumatra. Massive and poorly stratified units formed predominantly from pyroclastic flows and surges that traveled over the sea for distances up to 80 km. Granulometric and lithologic characteristics of the deposits indicate that they represent the complement of proximal subaerial and submarine pyroclastic flow deposits laid down on and close to the Krakatau islands. The distal deposits exhibit a decrease in sorting coefficient, median grain size, and thickness with increasing distance from Krakatau. Crystal fractionation is consistent with the distal facies being derived from the upper part of gravitationally segregated pyroclastic flows in which the relative amount of crystal enrichment and abundance of dense lithic clasts diminished upwards. The deposits are correlated to a major pyroclastic flow phase that occurred on the morning of 27 August at approximately 10 a.m. Energetic flows spread out away from the volcano at speeds in excess of 100 km/h and traveled up to 80 km from source. The flows retained temperatures high enough to burn victims on the SW coast of Sumatra. Historical accounts from ships in the Sunda Straits constrain the area affected by the flows to a minimum of 4x10³ km². At the distal edge of this area the flows were relatively dilute and turbulent, yet carried enough material to deposit several tens of centimeters of tephra. The great mobility of the Krakatau flows from the 10 a.m. activity may be the result of enhanced runout over the sea. It is proposed that the generation of steam at the flow/seawater interface may have led to a reduction in the sedimentation of particles and consequently a delay in the time before the flows ceased lateral motion and became buoyantly convective. The buoyant distal edge of these ash-and steam-laden clouds lifted off into the atmosphere, leading to cooling, condensation, and mud rain.     

四川龙门山南段东缘泥石流

当地断裂众多，岩体破碎，崩塌滑坡遍布，加之是强震带和川西大暴雨中心区，相对高度３００—３５００ｍ，泥石流形成条件极为充分．泥石流沟汇水面积小，沟床比降陡，主沟长度短．绵竹汉旺后山泥石流综合治理后，可成为一个示例．     

An extreme value analysis of the flow of Burbage Brook

An extreme value analysis of the flow of Burbage Brook is carried out by modelling peaks over a high threshold. The aims are to illustrate recently developed statistical techniques and to report on interesting features of the flow of the brook over a 58-year period. Peak flows are found to show marked seasonal variation and a downward trend. Then-year return level is estimated for various values ofn, and the reliability of the estimates is assessed.     

泥石流监测预警站的组建

泥石流监测预警站利用的是泥石流预警报系统,以便对泥石流进行监测后,作出泥石流预警报。泥石流预警报系统由三个子系统组成,这就是:1.暴雨类泥石流预报子系统;2.泥石流地声报警子系统;3.泥石流规模报警子系统。三个子系统分别用在泥石流监测预警站所属的雨量、地声、泥位三类泥石流监测点上。泥石流预警报系统由中国科学院东川泥石流观测研究站在蒋家沟研制而成,1985年底通过鉴定,获1986年度中国科学院科学技术进步三等奖。     

泥石流颗粒级配倒置浅释

泥石流固体颗粒级配倒置,影响流速垂线分布、流态与冲击力,是一个十分重要的问题。本文根据力学及流变学对泥石流固体颗粒级配倒置进行了解释,对于泥石流运动机理的认识是有裨益的。     

苍山十八溪的水石流及其防治

云南省苍山十八溪发育十分典型的水石流,流动时表面为高含沙洪水,底部为粗相沙砾和巨石,固液两相离析为非均质两相流。流体具有很大的动能和冲击力,对富绕的苍洱平坝区造成危害。为了治灾除害,保护生态环境,本文对防治目的、治理目标、防治方针与方法,以及实施顺序、程序、方案、技术措施等问题作了阐述。     

高位滑坡的运动转化形式

高位滑坡剪出口高于坡脚,它一旦滑离滑坡发生区,运动可能转化成四种形式:1.崩塌:由滑体经分级解体滑过剪出口处依次向前倾倒而成;2.碎屑流动或3.碎屑滑动:由滑动块体经碎屑化而成;4.泥石流:在适当的细粒物质量和水体条件下生成的碎屑流动。     

基于熵值法和突变级数法的泥石流易损度评价

泥石流易损度（危害性）评价是泥石流风险评估的重要组成部分.结合熵值法和突变理论的泥石流易损度评价方法，采用客观的熵值法判断指标间相对重要程度，利用突变级数法计算突变级数值进行评价，方法理论基础牢固且避免了确定指标权重值的弊端.以吉林省和龙市地质灾害调查与区划中的10条泥石流易损度评价实例进行验证，结果表明：数据获取、标准化和评价过程简便，易损度等级以轻度和中度为主的评价结果符合实际情况，该方法经过完善指标体系后可更加合理地应用于实际工作中.因此，基于熵值法和突变理论的泥石流易损度评价方法是可行的、可靠的.     

云南保山金鸡剖面丁家寨组及其古水温问题的讨论

保山金鸡剖面丁家寨组下部含砾层的双层结构特征与不同的地质作用有关:下部砾岩层为滨海相砾岩;上部角砾状灰岩由碎屑流产生。所产遗迹化石指示滨海相环境。根据保山地区丁家寨组的颗粒成分、胶结物及地球化学特征,对丁家寨组冷温水成因的观点提出了质疑     

Assessment of flow–ecology relationships for environmental flow standards: a synthesis focused on the southeast USA

ABSTRACT

Environmental flow standards are a management tool that can help to protect the ecosystem services sustained by rivers. Although environmental flow requirements can be assessed using a variety of methods, most of these methods require establishing relationships between flow and habitat of species of concern. Here, we conducted a synthesis of past flow–ecology studies in the southeast USA. For each state or interstate river basin, we used the published data to determine the flow metrics that resulted in the greatest changes in ecological metrics, and the ecological metrics that were most sensitive to hydrologic alteration. The flow metrics that were most important in preserving ecological metrics were high-flow duration and frequency, 3-day maximum and minimum, and number of reversals. The ecological metrics most sensitive to hydrologic alteration were mostly related to presence or absence of key indicator species.