Significant changes in freeze and thaw conditions in southeast Tibet Mountains result in frequent propagation of cracks and disintegration of rock masses. Depending on the elevation, the mechanism that drives the fractures may greatly vary. In this work, we employ computational Fracture Mechanics to study three different fracture mechanisms in which ice or water drives the crack propagation. These case studies are corroborated by field observations at low, intermediate and high altitudes. We employ a novel extended finite element method (XFEM) to propagate cracks without remeshing, and study the effect of the driving forces, crack geometry, and characteristics of the perilous rock. It is shown that SIFs induced by freezing of water or thermal expansion of ice are much higher than that induced by hydrostatic pressure, resulting in a smaller critical crack lengths and tinier collapses in intermediate or high elevations. Moreover, the effect of crack inclination and propagation may significantly affect the rock collapse. In particular, longer cracks with a larger outward inclination located near free surfaces of perilous rocks would fracture easily.