ABSTRACT
The effectiveness of a threshold is closely related to the feedback processes involved in the interactions between the variables and the processes. Positive feedback is particularly important in glacial geomorphology; thus thresholds play a very significant role in glacial geomorphology. The activity of thresholds is particularly important in the cyclic swing from glacial to nonglacial conditions in the areas alternately covered by the expanding Laurentide and Scandinavian ice sheets and deglaciated as they retreat. One of the most important thresholds from the geomorphological point of view of glacier activity is that at which accumulating snow and ice becomes thick enough to flow. Another aspect of glacier flow that is even more closely associated with thresholds is that of glacier surging. Critical conditions are necessary to explain the origin of many glacial features.
