Frequently the reservoir region of a cold surge-type glacier has a temperate base, while in a region surrounding the reservoir the base is cold. We analyse the slump process in such a reservoir region— that is, the process whereby material flows toward the lower end of the region and forms a critical wave profile there. The model agrees qualitatively with observations of Trapridge Glacier, Yukon Territory, Canada, which is currently experiencing a critical pre-surge condition. Calculations based on the model give good agreement with the surge cycle time of Rusty Glacier, Yukon Territory. Laboratory experiments show that a large-amplitude slump-induced wave profile forms prior to a surge. Experimental surges were produced with velocity increases of order one hundred.