The Origin of Glacially Fluted Surfaces-Observations and Theory

Abstract Studies of fluted surfaces beyond the margins of glaciers in Spitsbergen, Iceland, Norway and the Alps show that almost all emanate from rigid obstructions, commonly boulders in till. Field relations of flutes are described and it is shown that a relationship exists between flute height and the height of the initiating obstruction. Subglacial observations indicate that flutes form when till is intruded into tunnels which tend to open up in the lee of obstacles. The pattern of strain implied by this process is shown to be reflected by micro- and macrofabrics in the till. The commonly found occurrence of an average spacing between flutes does not arise because of some rhythmic or periodic mechanism in the glacier, but is produced by the random seeding of boulders which themselves generate flutes. It is suggested that the term flute be used as a genetic rather than a descriptive term, and be restricted to long parallel-sided ridges which reflect accurately the direction of ice movement and which form when deformable subglacial materials are intruded into tunnels which tend to open up on the lee sides of single rigid obstructions on the glacier bed.