<p>Debris flows originating in glacier and snow-covered catchments in cold high mountains exhibit distinctive initiation mechanisms and runout dynamics. However, due to limited records and data, their mechanisms and dynamics have been poorly studied, hindering effective monitoring and mitigation efforts. The Tianmo Gully (TMG) in the southeastern Tibetan Plateau has experienced repeated debris flows in recent years, presenting us with a unique opportunity to study their initiation mechanisms and dynamics. This study investigates the characteristics of five glacial debris flow events in TMG by employing a combination of field investigations and remote sensing interpretation and analyzes the spatial–temporal distribution of debris source materials and frozen water that control the initiation of debris flows. The results of this study reveal two distinct mechanisms responsible for the initiation of glacial debris flow in TMG, each exhibiting significant variations in triggering conditions. Specifically, the catastrophic event in 2007 was triggered by a rock collapse, subsequently leading to an ice avalanche. In contrast, the remaining four events were triggered by the deposition of snow avalanches. Notably, the velocity and discharge of glacial debris flow surpass those rainfall type debris flow events, with a 50% increase observed in both parameters. These significant differences are caused by the phase change of ice, which controls the hydrological processes and dynamic characteristics. Additionally, besides the influence of soil materials, the presence of snow avalanche deposits emerges as another key factor impacting the activity of glacial debris flow. The findings of this study provide indispensable insights for enhancing risk assessment and formulating effective mitigation strategies pertaining to glacial debris flow occurrences in alpine mountainous regions.</p>