Spatial distribution of drumlins: is it really random? Quaternary International 279-280 (2012) 346–461

Drumlins are the most common subglacial bedform and can be observed in all landscapes formerly occupied by ice sheets. Drumlin formation, upon which there is still no agreement, is essential to fully understand the ice-bed coupling in particular and the dynamics of ice sheets in general.Despite a vast literature on drumlins, only a handful of papers focus on their spatial distribution. Do drumlins tend to aggregate in clusters or are they dispersed? Is their distribution completely random? This is a crucial aspect because some theories of their formation link drumlin distribution to the presence of obstacles or nuclei that might be expected to be randomly distributed in the landscape. Other theories (e.g. instability)favour the idea of drumlinisation as a self-organising phenomenon that tends towards the creation of a coherent spatial patterning. Thus far, papers that have analysed drumlin spatial distribution have showed mixed results, but with a preference for random distributions. However, we suggest that a robust conclusion has yet to be reached from previous studies, partly because of the relatively small sample sizes utilised and partly because of the techniques applied. This paper presents the results of a new analysis of drumlin spatial distribution based on an extensive mapping program of drumlin fields in the British Isles, North America andScandinavia, generating a sample size of>50,000 landforms. GIS techniques were applied to a statistical study of the spatial distribution of drumlins in 100s of different drumlin fields. Analysis focused on the nearest neighbour distance between drumlins, decoupled into the two fundamental (along and across) ice flow components. Results reveal a clear spatial patterning, far from the random distribution often advocated in the literature. We further suggest a genetical relationship with ribbed moraine, which supports the concept of a subglacial bedform continuum, and crucially, a unifying theory of bedform formation