Snow stability during rain
Snow stability during rain
复制标题
雨中雪的稳定性
作者：
H. Conway;C. Raymond
摘要在美国华盛顿喀斯喀特山脉中部的两个冬季，观测了积雪对渗透的液态水的机械响应。在降雨开始后，确定了三种雪行为的演化机制：立即雪崩、延迟雪崩和恢复稳定。在降雨开始后的几分钟到一小时内，雪崩立即发生，根据从雪到雨的气象预报，可以预测释放时间，准确度不到一小时。这些雪崩通常在比水或相关热效应渗透的水平深得多的表面上滑动。表面雪的薄皮的变化可能导致深层板破坏的机制尚未确定，但涉及应力重新分布的几种可能性进行了讨论。延迟雪崩在降雨开始后几个小时释放。延迟的变化取决于与额外降水相关的应力增加速率，以及水渗透和削弱潜在滑动层所需的时间。由于雪中液态水的分布很难精确确定，因此很难准确预测雪崩发生的时间。雪沉降速率的深度剖面表明，应变速率增加的波传播到雪中，以响应渗透水。这种类型的测量可以证明是有用的预测时，雪的稳定性达到临界条件。雪崩活动是罕见的持续降雨后15小时或更长时间。这种稳定性的恢复发生在排水结构已经发展并渗透到积雪的整个深度之后。已建立的排水渠道将水从潜在的滑动表面排出，并且也是积雪中相对坚固的结构。
Abstract The mechanical response of snowpacks to penetrating liquid water was observed over two winter seasons in the central Cascade Mountains, Washington, U.S.A. Following the onset of rain, three evolutionary regimes of snow behavior were identified: immediate avalanching, delayed avalanching, and return to stability. Immediate avalanching occurred within minutes to an hour after the onset of rain and the time of release could be predicted with an accuracy of less than an hour from meteorological forecasts of the transition from snow to rain. These avalanches usually slid on surfaces substantially deeper than the level to which water or associated thermal effects had penetrated. The mechanism by which alteration of a thin skin of surface snow can cause deep slab failure has not been identified, but several possibilities involving a redistribution of stress are discussed. Delayed avalanches released several hours after rain started. The delay varied, depending on the rate of increasing stress associated with the additional precipitation, and on the time taken for water to penetrate and weaken a potential sliding layer. It is difficult to define accurately the evolving distribution of liquid water in snow which makes it difficult to predict accurately the time of avalanching. Depth profiles of the rate of snow settlement showed that a wave of increased strain rate propagated into the snow in response to penetrating water. This type of measurement could prove useful for predicting when snow stability is reaching a critical condition. Avalanche activity was rare after continuation of rain for 15 h or more. This return to stability occurred after drainage structures had evolved and penetrated the full depth of the snowpack. Established drain channels route water away from potential sliding surfaces and are also relatively strong structures within a snowpack.