469 
1973 a. b; Shepard et al. 1974 a. b). But Southard and Stanley (1976) re- 
port that downcanyon velocities are higher and of longer duration than up- 
Canyon. This accounts in part for the net downcurrent transport of fine 
sediments in the form of migrating asymmetrical ripples. 
Worldwide Occurrence of Submarine Canyons 
Another fact that makes submarine canyons likely as special care disposal 
sites for polluted dredged material is their worldwide distribution and the 
fact that their origins are often not unreasonably far offshore. 
European Canyons. Large submarine canyons are found along the Atlan- 
tic coasts of Europe and the north side of the Mediterranean (Shepard and 
Dill, 1966). Some of the best of these are located off the west coasts of 
France, Spain, and Portugal (Figures 11 and 12). 
Other European canyons are found along southern France, the Italian Rivi- 
era, the west side of Corsica, the lower part of Italy, the south side of 
Crete, and along the southern coast from Tunisia to Morocco. 
Japanese Canyons. Canyons occur all along the east coast of Honshu 
from the head of Sagami Bay to the tip of Boso Peninsula. Tokyo Canyon is 
one of the best known because it extends into the outer portion of Tokyo 
and Tateyama Bays (Figure 13). The floor of the canyon, which is 50km 
long, is covered with coarse sand and gravel near its termination at a 
water depth of 1465m. 
American Canyons. There are submarine canyons on all coasts of the 
USA. On the West Coast canyons are found from San Diego to the Strait of 
Juan de Fuca. Some of the best known of these are La Jolla and Scripps 
Submarine Canyons (Figure 14); Monterey Canyon, which is the deepest and 
largest submarine canyon along the east coast, heads at the center of Mon- 
terey Bay; Columbia Canyon off the mouth of the Columbia River; and Juan de 
fuca Canyon, which is the northernmost on this coast. 
