Investigation On Deformation Of Thermokarst Terrain In Permafrost Regions Over Heihe River Basin In Qilian Mountains

Climate warming over the Qinghai-Tibet Plateau is accelerating permafrost degradation.Thermokarst landform is a key indicator of permafrost degradation.However,quantitatively analyze thermokarst process over the Qinghai-Tibet Plateau is poorly understood.A thermokarst landform in the permafrost region of northern Qinghai-Tibet Plateau was selected as our study area.Repeat in-situ observations by terrestrial LiDAR?RTK-GPS and UAV(unmanned aerial vehicle)were carried out during 2016.4.11 between 2018.6.16 to get time series point cloud data ?corresponding ground control point respectively and high-resolution Images.We also obtained high-resolution satellite images of the study area in July 2009 and August 2018 to interpretate thermokarst landform.High-resolution triangulated irregular network models' comparison showed that surface deformation was mainly along the edge of the thermokarst landform.During the observation,the thawing period begins in July 2016 and 2017 had more intense surface elevation deformation than the initial thawing period from April to July.The maximum collapse reached-2.822 m in 2016,-2.599 m in 2017,-3.364 m from 2016.4.11 to 2018.6.16.Maximum lateral expansion along the north-south direction reached 9.590 m along the gully from April 2016 to November 2017.Especially,some specific areas in the upper part of the thermokarst landform underwent large deformations which are restricted to colluvium and transported deposits on lower slopes.The UAV images with an intuitive presentation complement the Lidar observations.We showed that the width of the upper gully continued to increase and the widest part of the gully expanded.From 2009 to 2016,the area of the thermokarst landform increased significantly.This study suggests that temperature changes has a significant influence on thermokarst process.Extreme precipitation events have become a key factor in the development of thermokarst.The results also illustrate that LiDAR is effective for studying thermokarst quantitatively.