Tunnel channels in southeast Alberta, Canada: evidence for catastrophic channelized drainage

Tunnel channels in southeast Alberta are attributed to erosion by channelized, subglacial meltwater flows. An anabranching tunnel channel network dissects the preglacial drainage divide of the ancestral Milk River. Channel morphology and landform associations are used to evaluate competing hypotheses of tunnel channel formation. Mechanisms that invoke subaerial channel incision, direct glacial erosion or steady state, time-transgressive erosion at the ice margin cannot explain convex-up longitudinal channel profiles, anabranching channel networks or confinement to the preglacial drainage divide. Results conclude that the tunnel channel network in southeast Alberta represents late-stage erosion by a channelised subglacial flow of catastrophic dimensions. Interpretations for this tunnel channel network are in agreement with conclusions obtained for the regional subglacial landform assemblage. (C) 2002 Elsevier Science Ltd and INQUA. All rights reserved.