1997 Volume 73 Issue 6 Pages 89-94
Direct observation and sampling by research submersible Shinkai 6500 together with bathymetric and geophysical survey revealed that sequences of serpentinized peridotite, basalt and limestone are exposed on the landward slope of the Palau Trench. A huge block (larger than 3km2 in horizontal dimension) of coral-reef limestone was discovered at depths ranging from 4, 900m to 6, 500m. The result seems to indicate that extensive slope failure is occurring on the landward slope from which great amount of mass is wasted to the trench axis. Nevertheless, greater portion of the Palau Trench axis has V-shaped bottom with little sediment cover, regardless its very slow rates of plate convergence accompanied with no deep-focus earthquakes. Islands of Palau (Belau) are extraordinarily close to the trench axis and appear to be now uplifted. A hypothesis is postulated to explain this unique situation.
