Subglacial drainage patterns of Devon Island, Canada: Detailed comparison of river and tunnel valleys

Abstract

Abstract. Tunnel valleys are bedrock incised channels (N-channels) attributed to erosion by meltwater in subglacial conduits.They exert a major control on meltwater accumulation at the base of ice sheets, serving as drainage pathways and modifying ice flow rates. Exposed relict tunnel valleys offer a unique opportunity to study the geomorphologic fingerprint of subglacial erosion and characterize the geometry of individual channels. In this study we present field and remote sensing observations of exposed tunnel valleys on Devon Island (Canadian Arctic Archipelago), including descriptions of tunnel valley cross sec-5 tions and longitudinal profiles, as well as network morphology, to describe the spatial extend and distinctive characteristics of subglacial drainage systems. We use field-based GPS measurements of tunnel valley longitudinal profiles, along with stereo imagery derived Digital Surface Models (DSM), and novel kinematic mobile LiDAR data to establish a quantitative comparison of tunnel and river valleys in our field study area. Tunnel valleys typically cluster in groups of 5-10 channels throughout the island, oriented radially with respect to active or former ice margins. We identify departures in tunnel valley direction from 10 local topographic gradients and undulations in the longitudinal profiles. We also observe that the width of first order tributaries is one to two orders of magnitude larger than in river systems, and remarkably constant downstream. These distinctive aspects of tunnel valley morphology are similar among the different locations characterized in the study. Furthermore, our findings are consistent with expectations of flow driven by gradients in effective water pressure related to variations in ice thickness.Our field and remote sensing observations provide a rigorous way to distinguish tunnel and river valleys in local and regional 15 topography data that revisits well-established field identification guidelines. Distinguishing river and tunnel valleys in topographic data is critical for understanding the emergence, geometry and extent of channelized subglacial drainage systems. The final aim of this study is to facilitate the identification of tunnel valley networks throughout the globe by using remote sensing techniques, which will improve the detection of these systems and help to build understanding of the mechanics of subglacial channelized drainage. 201 The Cryosphere Discuss., https://doi