喜马拉雅山北坡冰碛湖坝温度特征及其对堤坝稳定的影响

堤坝稳定性是评价冰湖溃决危险性的重要指标, 而堤坝的温度特征与其稳定性密切相关. 基于2012年11月-2013年9月对西藏定结县龙巴萨巴湖冰碛坝的0~150 cm不同深度的温度观测数据, 分析冰碛坝地温变化特征及其影响. 结果显示: 冰碛坝表层(<20 cm)地温与气温变化一致, 温度日变化常出现白天为正温梯度而夜间为负温度梯度的特征, 全年日均梯度一般为负温梯度(上部温度高、下部温度低); 中层(20~100 cm)和深层(>100 cm)表现为冬季下层温度高于上层温度的正温梯度, 夏季下层温度低于上层的负温梯度逐渐加强, 但地温日变幅逐渐减弱; 中间层地温变化不到气温变化幅度的1/5~1/10; 深层地温无明显的日变化. 冰碛坝的消融率约为2.1 cm·d^-1, 夏季消融深度超过250 cm. 现有夏季消融深度对堤坝的稳定影响有限, 但是湖盆区如果持续升温, 冰碛坝冻土的年消融率和消融深度都将增大, 致使堤坝稳定性下降, 溃决风险增大.

Temperature features of a moraine-dam on north slopes of the Himalayas and their effect on the dam stability

The dam stability is an important evaluation index for the outburst of a glacial lake, and the ground temperature features of the moraine dam and their variation are closely related with the dam stability. Based on the ground temperature observation data within the moraine dam from 11th November, 2012 to 5th September, 2013 at different depths (from 0 cm to 150 cm),the annual variation of ground temperatures and temperature gradients at different depths within the moraine dam are used to calculate the moraine dam thawing. The results show that the ground temperatures at different depths within the dam change obviously. In the surface layer (<20 cm in depth) change in ground temperature is consistent with air temperature change, where daily temperature variation is often characterized by a positive temperature gradient by day and a negative temperature gradient by night. In addition, annual mean temperature gradient is generally positive. In the middle layer (20-100 cm in depth)and deep layer(>100 cm in depth)the ground temperature profiles are characterized by the phenomena that in winter the temperature in the lower layer is higher than that in the upper layer, with a positive temperature gradient, in summer the temperature in the lower layer is lower than that in the upper layer, with a negative temperature gradient. Amplitude of ground temperature variation gradually decreases with depth. In the middle layer, amplitude of ground temperature variation is less than 1/5-1/10 of that of air temperature. There is no obvious daily variation in deeper layers. The thawing rate of the moraine dam is about 2.1 cm·d^-1, and thawed depth of the dam in summer exceeds 250 cm. If the ground temperature rising rate at the lake basin continues to maintain at > 0.03 ℃·a^-1 and the maximum negative temperature gradient in summer maintain at 0.036 ℃·cm^-1, it is no doubt that the thawing rate and thawed depth of permafrost within the moraine dam will increase, resulting in decreasing the stability of the dam, and increasing the risk of outburst of the lake.