Large-scale　landsliding　is　an　extremely　important　geological　process　in　shaping　landscapes　in　the　Tibetan　Plateau.　In　this　research,　an　ancient　river-damming　landslide　with　an　estimated　debris　volume　of　4.9　x　10(7)　m(3),　located　in　the　upper　Jinsha　River,　SE　Tibetan　Plateau,　was　studied.　The　landslide　once　formed　a　dam　over　60　m　high　and　blocked　the　river.　Lacustrine　sediments,　composed　of　silty　clay　with　particle　sizes　of　0.002-0.25　mm,　are　intermittently　distributed　along　both　banks,　extending　about　6.5　km　upstream.　The　OSL　dating　indicates　that　the　lacustrine　sediments　have　an　age　of　2.6　+/-　0.2　ka.　Detailed　field　investigation　and　theoretical　analysis　was　performed　to　investigate　the　characteristics,　potential　cause　and　mechanism　of　the　landslide.　The　results　suggest　that　the　landslide　was　most　likely　triggered　by　buckling　of　planar　rock　slabs　under　gravity.　It　may　start　as　a　translational　sliding　along　the　weak　interlayer　composed　of　mica　schist　at　the　upper　part　of　the　slope　and　then　formed　buckles　by　curving　amphibolite　rock　beds　near　the　slope　toe.　The　hillslope　has　still　been　affected　by　gravitational　deformations,　with　geomorphology　characterized　by　tension　cracks,　buckle　folds,　and　small　landslide　scars　distributed　on　the　slope　surface,　suggesting　that　the　evolution　of　the　river　valley　caused　by　buckling　deformation　has　not　achieved　equilibrium.