High-intensity single-beam photorefractive data on LiNbO3 show the occurrence of a well-defined intensity threshold for enhanced deterioration (fanning) of the output beam. That threshold markedly rises with temperature in the range 20–160°C. Below threshold, the beam profile is only slightly modified during propagation and it remains essentially independent of the light intensity. These results offer relevant information on beam degradation in applications involving high light density powers. The data indicate that the thresholding effect is thermally activated with an activation energy of 0.24 eV within the range of values found for the photoconductivity.