Glacial flutes, also known as glacial fluting, are low, narrow, elongate, straight, parallel ridges that range between several centimeters to a few meters both in width and height. This glacial landform generally consist of

glacial A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...

till image:Geschiebemergel.JPG, Closeup of glacial till. Note that the larger grains (pebbles and gravel) in the till are completely surrounded by the matrix of finer material (silt and sand), and this characteristic, known as ''matrix support'', is d ...

, but sometimes either

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is usually defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural ...

silt Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension (chemistry), suspension with water. Silt usually ...

and

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...

. They form subglacially and are orientated parallel to the direction of glacier flow. They occur in parallel sets of ridges known as ''swarms''.Bell, T., Cooper, A.K., Solheim, A., Todd, B.J., Dowdeswell, J.A., and others, 2016. ''Glossary of glaciated continental margins and related geoscience methods.'' In: Dowdeswell, J.A., Canals, M., Jakobson, M., Todd, B.J., Dowdeswell, E.K. and Hogan, K.A., eds. ''Atlas of Submarine Glacial Landforms: Modern, Quaternary and Ancient.'' Geological Society, London, Memoirs, 46, 555–574.Boyall, L., 2021
''Flute-formation''''Glacial depositional landforms,''AntarcticGlaciersOrg.
/ref>Benn, D.I., and Evans, D.J.A., 2010. ''Glaciers and Glaciation.'' London, England, Hodder-Arnold. 816 pp. Because of their narrow width and low height, they are often hard to identify during ground or bottom surveys. As a result, they have to be mapped by high-resolution

satellite A satellite or an artificial satellite is an object, typically a spacecraft, placed into orbit around a celestial body. They have a variety of uses, including communication relay, weather forecasting, navigation ( GPS), broadcasting, scient ...

data or

LiDAR Lidar (, also LIDAR, an acronym of "light detection and ranging" or "laser imaging, detection, and ranging") is a method for determining ranging, ranges by targeting an object or a surface with a laser and measuring the time for the reflected li ...

techniques on land and by high-resolution side-scan sonar at sea.Ely, J.C., Graham, C., Barr, I.D., Rea, B.R., Spagnolo, M. and Evans, J., 2017. ''Using UAV acquired photography and structure from motion techniques for studying glacier landforms: application to the glacial flutes at Isfallsglaciären.'' ''Earth Surface Processes and Landforms'', 42(6), pp.877-888.Boulton, G.S., 1976. ''The origin of glacially fluted surfaces-observations and theory''. ''Journal of Glaciology'', 17(76), pp.287-309. A fluted moraine, also called a fluted moraine surface, is a

moraine A moraine is any accumulation of unconsolidated debris (regolith and Rock (geology), rock), sometimes referred to as glacial till, that occurs in both currently and formerly glaciated regions, and that has been previously carried along by a gla ...

whose surface exhibits numerous glacial flutes. The long axes of these flutes are parallel to the flow direction of the glacier. Fluted moraines are typically associated with terrestrial glaciers, but some have been found in glaciomarine settings.Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, eds. (2005) ''Glossary of Geology'' (5th ed.). Alexandria, Virginia, American Geological Institute. 779 pp. {{ISBN, 0-922152-76-4

Occurrence

Flutes are found in a number of actively glaciated regions including the Alps, Antarctica, Alaska, Iceland, New Zealand, Norway, Sweden, and Spitsbergen. Flutes formed subglacially beneath both polythermal, and warm-based glaciers. They are more likely to be found on recently exposed glaciated surfaces as they are readily eroded because of their composition. They have also been found in shallow glacimarine environments. Because of their relatively low relief and narrow width, they are often hard to identify from ground level observations. Therefore high-resolution satellite, drone and LiDAR methods are used to map them.

Origin

Various models about the formation of flutes have been proposed. The most widely accepted model is the Cavity Infill Model.Gordon, J.E., Whalley, W.B., Gellatly, A.F. and Vere, D.M., 1992. ''The formation of glacial flutes: assessment of models with evidence from Lyngsdalen, North Norway.'' ''Quaternary Science Reviews'', 11(7-8), pp.709-731. According this model, the formation of a flute is initiated when basal melting lodges a boulder on the subglacial bed of a glacial. Once the boulder is lodged, the passing glacial ice can no longer move the boulder and must flow around it. The flow of glacial ice around a boulder creates an elongated cavity in the ice downstream and parallel to its flow. The high confining pressures on the glacier bed from the weight of the overlying glacial ice fills the elongate cavity by squeezing water-soaked till into it. As a glacier melts back and recedes, it exposes the till bed of the glacier and the long, low ridges of till that have been molded upon it. The long, low ridges of till impart a ''fluted'' appearance to the exposed bed of the glacier, giving rise to the term ''flute''. Flutes can often be traced back upstream to single large boulders embedded in the glacial till at their head

Fluting

In older publications, fluting is used for smooth, deep, gutterlike channels or furrows cut by glaciers into the stoss side of a rocky hill obstructing its advance. This type of ''fluting'' is wider than glacial grooves and does not extend around the hill to its lee side.Chamberlin, T.C., 1888. ''The Rock-scorings of the Great Ice Invasions'', In J. W, Powell, ''7th Annual Field Report 1885-6''. United States Geological Survey, pp. 155-248.

References

Glaciers Glaciology Glacial landforms

Occurrence

Origin

Fluting

See also

References