A submarine canyon is a steep-sided valley cut into the sea floor of the continental slope, sometimes extending well onto the continental shelf and having relief comparable to even the largest of land canyons. About 3% of submarine canyons are joined to shelf valleys that connect with large rivers; the largest canyons (equal to about 29% by number) incise into the continental shelf but the largest number of canyons (about 69%) terminate on the slope, making so-called “blind” or “headless” canyons. Canyons cutting the continental slopes have been found at depths greater than 2 km below sea level. Many submarine canyons continue as submarine channels across continental rise areas and may extend seawards for hundreds of kilometres onto the abyssal plain. Ancient examples have been found in rocks dating back to the Neoproterozoic. Turbidites are formed in submarine canyons.