Fluting (geology)

Fluting is a process of differential weathering and erosion by which an exposed well-jointed coarse-grained rock such as granite or gneiss, develops a corrugated surface of flutes; especially the formation of small-scale ridges and depressions by wave action.

Fluting in glacial geology:

• flutes are narrow, elongated, straight, parallel ridges generally consisting of till, but sometimes composed of sand or silt/clay. Flutes typically reach a height of only a few meters or less, but some may reach heights of 10 meters (~30 ft.), and may extend up to several kilometers in length. Flutes are oriented parallel to the direction of ice movement, and are formed when boulders become lodged on the subglacial floor by basal melting, and can no longer be moved by the passing glacial ice. The glacial ice must then flow around these boulders, creating elongated cavities in the ice parallel to the ice flow. These cavities in the ice are then filled with water-soaked till, which is squeezed up into the cavities as a result of high confining pressures on the glacier bed from the overlying glacial ice. As a glacier recedes, it exposes these long, low ridges of till. These glacial processes give the topography a "fluted" appearance, giving rise to the name flutes. Flutes can often be traced back to single large boulders embedded in the glacial till.
• the formation by glacial action of smooth deep gutterlike channels or furrows on the stoss side of a rocky hill obstructing the advance of a glacier; the furrows are larger than glacial grooves, and they do not extend around the hill to the lee side. Also, a furrow so formed
• lineations or streamline grooves and ridges parallel to the direction of ice movement, formed in newly deposited till or older drift. They range in height from a few centimetres to 25 metres, and in length from a few metres to more than 20 km.

Fluting with respect to sedimentary action:

• the process of forming a flute by the cutting or scouring action of a current of water flowing over a muddy surface
• scalloped or rippled rock surfaces.
• flute cast