We present an analysis of the formation and evolution of the Waiho Loop terminal moraine. Recent work has shown that the Loop comprises mainly rock avalanche material, and suggested its formation was associated with a rock-avalanche-driven glacier advance. New evidence from shallow seismic studies between the range front and the Loop suggests (i) that the presence of a basal trough critically influences glacier behaviour and moraine formation; and (ii) that the volume of the Waiho Loop is significantly greater than previously thought. A one-dimensional dynamic ice flow model is used to test two rock-avalanche-based scenarios for the formation of the Loop: first, that a rock avalanche caused a significant advance of the glacier terminus from a location within the confined mountain valley to the Loop; and second, that the rock avalanche occurred while the glacier was retreating with its terminus close to the position of the Loop. It is shown that this terminal moraine was not the result of a glacier advance.