GEOLOGY, SEDIMENT PATTERNS, AND WIDESPREAD DEFORMATION ON THE SEA-FLOOR OFF WESTERN-SAMOA REVEALED BY WIDE-SWATH IMAGERY

GLORIA and SeaMARC II sea-floor images of offshore Western Samoa revea l large-scale mass movements, volcanism, and structural modification. These processes are driven by hot-spot mantle diapirism and nearby pla te subduction. Debris avalanche deposits extend from the island slope onto the adjacent abyssal plains, covering at least 20,000 km2. Sedime nt flows occur in sheets up to 30 km wide; slump structures are common on steep slopes. Volcanic cones and lava sheets are evident on lower slopes and abyssal plains. Major volcanic rift zones on the island of Savaii continue offshore. Subduction-induced flexure has produced inte nse tensional fracturing on the outer wall of the Tonga Trench.