erode many submarine canyons. Some turbidity currents are quite dense and abrupt in forming. These currents are set into motion when sand and on the continen mud shelf are loosened, perhaps by sudden melting of gas tal hydrates, by collapse of an overly steep slope, or by an earthquake. The sediment mixes with water to form a dense suspension, flowing like an avalanche down-slope eroding and accumulating more sediment. Turbidity currents are likely contributors to submarine canyon growth. As they lose momentum, they deposit sediment as deep-sea fans at the canyon's lower end These deposits, called turbidites, are characterized by decreasing sediment size from the bottom to the top of a flow forming graded bedding. As sediments settle, coarser, heavier particles settle out first, followed by finer sand and then cla Some 78% of the world's ocean sediments are in these three zones of the continental shelf. They are thickest along passive continental margins like the East and Gulf Coasts and less so along active margins such as the western U. S. coastline