The recent retreat of a marginal outlet glacier of Hofsjökull in Iceland exposed a drumlin field with more than 50 drumlins ranging from in length, in width, and in height. These formed through a progression of subglacial depositional and erosional processes, with each horizontal till bed within the drumlin created by an individual surge of the glacier. The above theory for the formation of these Icelandic drumlins best explains one type of drumlin. However, it does not provide a unifying explanation of all drumlins. For example, drumlin fields including drumlins composed entirely of hard bedrock cannot be explained by deposition and erosion of unconsolidated beds. Furthermore, hairpin scours around many drumlins are best explained by the erosive action of horseshoe vortices around obstacles in a turbulent boundary layer.