Sediment slides and sediment waves in the Bonin Trough, western Pacific

Seismic reflection profiles, 3.5-kHz and 12-kHz echograms reveal a major sediment-slide deposit in the Bonin Trough, western Pacific. On the seismic reflection profiles the deposit appears as an acoustically transparent zone with incoherent reflectors and a slightly rough to hummocky surface. On 3.5- and 12-kHz echograms the surface appears as hyperbolae with varying vertex elevations. This hyperbolated zone and a small area of relatively smooth, transparent sediment (on 3.5-kHz echograms) are elevated with respect to the surrounding undisturbed sea floor. A piston core containing a section of highly disturbed sediment was taken from the hyperbolated zone and confirms our slide deposit interpretation. Poorly defined sediment waves are also observed along the lower margin of the Bonin Trough where they form two bands that parallel the regional bathymetric contours. In the north the sediment waves appear to migrate upslope. These observations suggest a bottom current origin, but nephelometer stations imply only a moderate to weak bottom current at present. The waves may be relict features.