A streamlined rock knob with symmetrical longitudinal profiles caused by abrasion of both stoss and lee sides. Small whalebacks can form under only a few hundred metres of ice; larger ones under deep ice streams. In theory, whalebacks tend to form in areas of deep ice with rapid flow velocities (James (2003) Geomorph. 55, 1–4). See also Glasser and Harrison (2005) Geograf. Annal. A 87, 3.