1 1 Triangular-shaped Landforms Reveal Subglacial Drainage Routes in SW 2 Finland 3 Mäkinen, J.a, *, Kajuutti, K.a, Palmu, J.-P.b, Ojala, A.b and Ahokangas, E.a 4 a Department of Geography and geology, University of Turku FI-20014 Turku, Finland. 5 b Geological Survey of Finland, P.O. Box 96 (Betonimiehenkuja 4) FI-02151 Espoo, Finland. 6 * corresponding author (
[email protected]). 7 8 ABSTRACT 9 The aim of this study is to present the first evidence of triangular-shaped till landforms and related erosional 10 features indicative of subglacial drainage within the ice stream bed of the Scandinavian ice sheet in Finland. 11 Previously unidentified grouped patterns of Quaternary deposits with triangular landforms can be recognized from 12 LiDAR-based DEMs. The triangular landforms occur as segments within geomorphologically distinguishable 13 routes that are associated with eskers. The morphological and sedimentological characteristics as well as the 14 distribution of the triangular landforms are interpreted to involve the creep of saturated deforming till, flow and 15 pressure fluctuations of subglacial meltwater associated with meltwater erosion. There are no existing models for 16 the formation of this kind of large-scale drainage systems, but we claim that they represent an efficient drainage 17 system for subglacial meltwater transfer under high pressure conditions. Our hypothesis is that the routed, large- 18 scale subglacial drainage systems described herein form a continuum between channelized (eskers) and more 19 widely spread small-scale distributed subglacial drainage. Moreover, the transition from the conduit dominated 20 drainage to triangular-shaped subglacial landforms takes place about 50-60 km from the ice margin.