A valley with very steep sides and no floor, such as the Grand Canyon of the Colorado River. A canyon differs from a gorge in that the sides are stepped, reflecting alternating rock resistances. See Spamer (2006) Annal. Imposs. Res. 12, 2, who sounds off about the name ‘Grand Canyon’, but is quite sane in his book of 1984. Submarine canyons are deep troughs in the sea bed, sometimes as prolongations of river valleys on land; see Morais et al. (2007) Marine Ecol. 28, and suppl. 1. Canyons may also form via earth flows, turbidity currents, submarine springs, or the slipping of sediments.