Study On Ground Deformation Of Permafrost In MaXian Mountain

Permafrost is an important part of the cryosphere.Recent studies indicated that permafrost degradation has occurred around the world due to climate warming,and hence leading to a series of environmental problems(such as ground deformation).For example,permafrost temperatures have rose abruptly and permafrost area has decreased significantly in circumpolar regions and Tibetan Plateau in recent decades.Permafrost degradation could cause damage to the stability of permafrost,which in turn affecting ecological and hydrological processes.Moreover,to some extent,ground deformation in permafrost region can yield an insight into degradation of permafrost and changing of hydrothermal processes.In addition,ground deformation could also provides some evidence for determination of permafrost zones and construction and maintenance of infrastructures in permafrost area.In the present study,We layouted the cross section and monitored the ground deformation between October 2015 and August 2016 in the permafrost region of Mahan Mountain,Lanzhou City.Furthermore,We analyzed the freezing-thawing processes and the determinants of ground deformation through ground temperature of active layer,non-frozen water and soil moisture.The main results are shown in the following paragraphs.(1)The period of frost heaving in the study area was from mid-October 2015 to late-March 2016,and the maximum depth of frozen was 125 cm.Additionally,it began to melt in late-March 2016.(2)From October 2015 to August 2016,the ground in the permafrost region of Mahan Mountain was deformed,with an average settlement of 1.33 cm.During the period from January to March of 2016,the maximum amount of frost heaving was reached with an average amount of 9.43 cm,and the maximum value was 17.73 cm at the nine point.The permafrost is well developed in the small lake area,and the deformation of the frozen area is small in the marginal area of the small lake.The permafrost development is generally deformed between the central and the marginal area of the small lake.(3)During the period of frost heaving,soil moisture in the active layer migrated to topsoil layer(0-40cm).By contrast,it transported to deep layer(40-60cm)during the intensified forst heaving.Soil moisture content in active layer reached the lowest and highest value in October 2015 and between March and May 2016,respectively.(4)The segregated frost-heaving amounts caused by the migration of soil moisture mainly contributed to frost-heaving amounts in the permafrost region of Mahan Mountain.Slope,vegetation type and soil type as the external factors that affected the difference of ground deformation.However,the changing of ice-water phase and the migration of soil moisture directly caused the ground deformation.Overall,the changing of soil moisture at the depth of 20-30 cm had the greatest influence on the ground deformation in the permafrost region of Mahan Mountain.