Retrogressive thaw slumps (RTSs) are among the most dynamic geomorphic processes in degrading permafrost, posing growing risks to ecosystems and infrastructure. Collapse–subsidence RTSs (CS-RTSs), which develop on gentle slopes often preferred for engineering works, remain poorly characterized. This study examines two CS-RTSs on the northeastern Qinghai–Tibet Plateau (QTP) through combined drilling, field monitoring, geophysical imaging, CT scanning, and thermal analysis. Field evidence shows that slump initiation is controlled by thermo–gravitational coupling, with shallow ice-rich layers acting as critical failure zones. Strong contrasts in ground-ice content near the headwall provide structural conditions for collapse. Although both sites are underlain by ice-rich permafrost, their internal structures differ: Slump A, consisting mainly of fine soils and small ice lenses, remains relatively intact, whereas Slump B, containing coarse–fine mixtures and larger ice lenses, exhibits pronounced thaw and deformation. Microstructural observations reveal that gas inclusions and disrupted ice–soil contacts reduce thermal conductivity and weaken the frozen matrix, whereas gravel–ice frameworks enhance heat transfer and accelerate thaw. These results demonstrate how multi-scale field and laboratory methods can capture the coupled processes driving CS-RTS development, providing a practical framework for hazard evaluation and infrastructure planning in permafrost regions.
Qi et al. (Thu,) studied this question.