What are flutes?
Glacial flutes are elongated, low-relief ridges formed subglacially and orientated in the direction of glacier flow [1,2,3]. Their size can range between several centimetres to a few metres both wide and high, and occur in groups of streamlined ridges known as ‘swarms’ [1].
Flutes are formed subglacially and are found in glacial foregrounds. They are more likely to be found in modern glacier foreground as they can be subjected to erosion because of their till-like composition [1].
Flutes are found in a variety of glaciated regions including Iceland, Sweden, Norway, New Zealand, and Alaska [1,2,3]. Because of their relatively small size, they are often hard to identify whilst at ground level. Therefore high-resolution satellite data or LiDAR methods are used to map them [2].
Flute formation
Flutes can be formed subglacially beneath both polythermal, and warm-based glaciers. There have been several models proposed about the formation of flutes, but the most widely accepted model is the Cavity Infill Model [1,2,4].
This model proposes that a boulder causes an obstruction beneath the actively flowing glacier. The glacier then forces highly saturated sediment into a cavity on the leeside of the boulder obstruction [1,2]. The pressure on the leeside of the boulder drops, allowing the saturated sediment to freeze, and is carried forward by the ice, forming the elongated flute shape [1,3].