青藏铁路北麓河地区典型热融湖变化特征及其对冻土热状况的影响

Variation Characteristics of the Thawing Lake in Permafrost Regions of the Tibetan Plateau and Their Influence on the Thermal State of Permafrost

在全球气候变暖、青藏高原平均气温升高的大背景下,多年冻土区热融湖的发育及其对冻土热状况的影响日益显著.以北麓河地区的一典型热融湖为例,通过对湖岸坍塌及年地温变化等进行监测分析.结果表明:目前该热融湖湖岸逐年坍塌,坍塌主要发生在靠近铁路一侧厚层地下冰发育区域,年平均坍塌宽度大约为0.5m,湖心下原约83.0m多年冻土已全部融化.根据210Pb测年,估算该热融湖形成于约890aBP前.在热融湖的影响下,湖心至路基坡脚天然孔之间多年冻土上限深度及多年冻土厚度均发生了很大变化,湖近岸多年冻土上限深度比路基坡脚天然孔多年冻土上限深约0.65m,湖边多年冻土厚度也比路基坡脚天然孔多年冻土厚度薄约60m;湖心至路基坡脚天然孔之间土层在水平方向形成明显的地温差异,在相同深度,湖心下土层地温年平均值比天然孔地温年平均值高5.0℃左右.热融湖作为热量的载体,以二维热传导方式将热量向其周围传递,导致附近多年冻土温度升高,热稳定性降低.

Under a warming climate on the Tibetan Plateau,the development of thermokarst lakes in the permafrost regions and its influence on the thermal state of permafrost has become increasingly important. In this study a representative thermokarst lake at the west side of the railway at DK1141＋015 is taken as an example to monitor the lakeshore collapse and the change in ground temperature. Integrated analysis indicates that the lakeshore retreats at an average velocity of about 0.5 m per year nearby the railway. In addition,the permafrost under the centre of the lake has thawed out completely. A 210Pb determination indicates that formation of the lake was about 890 a BP. Under the influence of the thawing lake,the permafrost table and the permafrost depth from the lake centre to the railway have changed greatly. The permafrost table in lakeshore is about 0.65 m lower than that in the railway,whereas the depth of the permafrost at the lakeside is about 60 m thinner than that under the railway. Ground temperature is obviously different between the lake centre and the railway. The annual mean ground temperature at the lake centre is about 5.0 ℃ higher than that in the railway. The thawing lake,as a heat carrier,conveys heat to its circumambience by two-dimensional heat conduction,resulting in the permafrost temperature increase and the permafrost stability decrease.