On September 5, 2019, the Veslemannen unstable rock slope (54,000 m3) in Romsdalen, Western Norway, failed catastrophically after 5 years of continuous monitoring. During this period, the rock slope weakened while the precursor movements increased progressively, in particular from 2017. Measured displacement prior to the failure was around 19 m in the upper parts of the instability and 4–5 m in the toe area. The pre-failure movements were usually associated with precipitation events, where peak velocities occurred 2–12 h after maximum precipitation. This indicates that the pore-water pressure in the sliding zones had a large influence on the slope stability. The sensitivity to rainfall increased greatly from spring to autumn suggesting a thermal control on the pore-water pressure. Transient modelling of temperatures suggests near permafrost conditions, and deep seasonal frost was certainly present. We propose that a frozen surface layer prevented water percolation to the sliding zone during spring snowmelt and early summer rainfalls. A transition from possible permafrost to a seasonal frost setting of the landslide body after 2000 was modelled, which may have affected the slope stability. Repeated rapid accelerations during late summers and autumns caused a total of 16 events of the red (high) hazard level and evacuation of the hazard zone. Threshold values for velocity were used in the risk management when increasing or decreasing hazard levels. The inverse velocity method was initially of little value. However, in the final phase before the failure, the inverse velocity method was useful for forecasting the time of failure. Risk communication was important for maintaining public trust in early-warning systems, and especially critical is the communication of the difference between issuing the red hazard level and predicting a landslide.

中文翻译：

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挪威西部 Veslemannen 滑坡的运动、破坏和气候控制

2019 年 9 月 5 日，挪威西部 Romsdalen 的 Veslemannen 不稳定岩石边坡（54,000 立方米）在经过 5 年的连续监测后发生灾难性破坏。在此期间，岩石斜坡减弱，而前兆运动逐渐增加，特别是从 2017 年开始。 失稳前测得的位移在失稳上部约为 19 m，在趾部区域约为 4-5 m。故障前的运动通常与降水事件有关，峰值速度出现在最大降水后 2-12 小时。这表明滑动带中的孔隙水压力对边坡稳定性有很大影响。从春季到秋季，对降雨的敏感性大大增加，表明对孔隙水压力的热控制。温度的瞬态模型表明接近永久冻土条件，并且肯定存在严重的季节性霜冻。我们提出，在春季融雪和初夏降雨期间，冻结的表面层可以防止水渗入滑动区。模拟了 2000 年后滑坡体从可能的永久冻土到季节性霜冻环境的过渡，这可能影响了斜坡稳定性。夏末和秋季的反复快速加速共导致红色（高）危险等级和危险区疏散事件 16 起。当增加或减少危险级别时，速度阈值用于风险管理。反速度法最初价值不大。然而，在失败前的最后阶段，反速度法可用于预测故障时间。风险沟通对于保持公众对预警系统的信任很重要，尤其重要的是沟通发布红色灾害级别和预测滑坡之间的差异。