What are striations, and how do they form?

Striations or striae are scratches or small elongated grooves in bedrock or on clasts that are the product of abrasion . Clasts protruding out of basal sliding ice are dragged along bedrock surfaces producing the marks. The rate of abrasion depends on the effective force with which individual clast fragments are pressed against the bed, the flux of fragments over the bed, and the relative hardness of rocks in the ice and of the bed (Hallet, 1979). Hallet (1979) also noted that where geothermal heat flow or frictional heating are high, or where the ice is extending, the rate of abrasion should be higher. He also noted that glacier thickness has no affect on abrasion, and hence on the nature of striation morphology.

Explanation:The presence of striations is a reflection of the spatial and temporal variations in the stresses exerted by rock fragments entrained in basal ice, as well as a representation of glacier sliding (e.g., Boulton, 1974; Kamb et al., 1976; Hallet, 1979, 1981; Shoemaker, 1988; Iverson, 1991). The greater the stresses exerted, the greater the promotion of crack growth and brittle failure, and the deeper and wider the striae tend to be (Drewry, 1986).