Abstract
The revised chart of the submarine canyon and valley systems around the Japanese Islands, except for the Ryukyu and Izu-Bonin Islands, is mapped on the basis of sea-beam bathymetric charts and J-EGG500 bathymetric data. Most submarine canyons have continuous and winding course apparently. However, the canyon traceable into the ocean floor is only the Tenryu canyon, and meandered courses are distinguishable in some canyons and the deep sea channels. Submarine valleys locate along the axis of flattened depressions, and are discontinuous. Subsequent canyons are grouped into two types. Type 1 strikes parallel to the axis of the Japanese Islands, and Type 2 is distributed in oblique or perpendicular to it. The former may reflect of the boundary faults in accretionary prisms along plate subduction zones, and the latter provides tectonic information on each region, though the faults along the canyons have not recognized in some cases. The consequent type canyons are gully-like ones that are distributed in the upper continental slope along the Pacific side, and the Kurose and Mikura canyons in the northeastern slope of Izu-Bonin Ridge. Longitudinal profiles of all canyons are classified into 7 (A to G) groups, based upon their gradient. These groups may reflect regional tectonic setting and/or sedimentation processes. However, all canyon profiles also have common features; for example, slope is continuous and monoclinal seaward with one or two knick points in spite of various plan views. Submarine canyons show the river-like topographic features that suggest the actions of gravity flows, like turbidity currents, submarine debris flows and bottom currents. Although the submarine canyons undoubtedly have been affected by such flow mechanisms, their formational processes may have been essentially based on the interaction of tectonic movement and sea level change.
