A glacier's debris cover strongly modifies its mass balance in contrast to a clean-ice glacier. A key parameter for calculating sub-debris melt is the thermal diffusivity of the debris layer. Conway and Rasmussen (2000) present a method to estimate this value based on simple heat diffusion principles. Our analysis shows that the selected temporal and spatial sampling intervals affect the estimated value of thermal diffusivity, resulting in glacier melt being systematically underestimated.