青藏高原热融湖横向扩张速率对湖下融区发展影响的数值模拟

Numerical simulation of influence of thermokarst lake horizontal expansion rate on talik development beneath thermokarst lakes on Qinghai-Tibet Plateau

热融湖是高纬度和高海拔富冰多年冻土区重要的自然景观。这些湖由于富冰多年冻土或地下冰的融化而形成,由于湖水向周边多年冻土传递热量而持续扩张。以青藏高原北麓河地区一个热融湖的信息和冻土监测资料为基础,运用柱坐标系下伴有相变的热传导模型模拟了以不同的横向扩张速率演化的热融湖湖下融区的发展过程。结果表明:在青藏高原多年冻土厚度为75 m的北麓河盆地,分别以横向扩张速率0.10 m·a^(-1)、0.15 m·a^(-1)、0.20 m·a^(-1)和0.25 m·a^(-1)演化的热融湖,在湖形成分别达760 a、703 a、671 a和652 a时,湖下形成贯通融区,相应的多年冻土从上向下融化的平均速率分别为8.22 cm·a^(-1),8.89 cm·a^(-1),9.31 cm·a^(-1)和9.74 cm·a^(-1)。热融湖的横向扩张速率对湖下的融区发展和土壤热状况有重要的影响,在现场调查资料的基础上选取正确的热融湖横向扩张速率是热融湖对多年冻土热状况作用数值模拟研究的必要前提。

Thermokarst lakes are an important sight of the high-latitude and high-altitude landscapes where icerich permafrost exists.These lakes form as a result of thawing of ice-rich permafrost or thawing of massive ground ice,and expand their basins by conduction of heat from lake water into adjacent permafrost.In this study,the talik development processes beneath thermokarst lakes with different lake horizontal expansion rates are investigated by using a heat transfer model with phase change under a cylindrical coordinate system,on the basis of the thermokarst lake information and the observed permafrost data from a monitoring project in the Beiluhe Basin on the Qinghai-Tibet Plateau.The numerical simulation results indicate that the open taliks form beneath the thermokarst lakes with the horizontal expansion rates of 0.10 m·a^（-1）,0.15 m·a^（-1）,0.20 m·a^（-1）,and 0.25 m·a^（-1） respectively in years 760,703,671,and 652 in the Beiluhe Basin on the Qinghai-Tibet Plateau where permafrost thickness is about 75 m,and the corresponding mean permafrost top thaw rates are 8.22 cm·a^（-1）,8.89 cm·a^（-1）,9.31 cm·a^（-1）,and 9.74 cm·a^（-1）,respectively.The horizontal expansion rates of thermokarst lakes have an important influence on talik development and ground thermal regime.Choosing a correct horizontal expansion rate of a thermokarst lake based on the field measurement data is an essential prerequisite for numerical simulation of the influence of thermokarst lakes on permafrost thermal regime.