We collected more than 30 seismic reflection lines across landslide-related features along the flanks of the Hawaiian Islands on board the R/V Maurice Ewing in January and February of 1998. Primary targets included (1) the active Hilina slump, along the south flank of Kilauea volcano, (2) the Puna Ridge extension of Kilauea's east rift zone, (3) Loihi seamount and adjacent slopes, and (4) the north flank of Oahu, thought to have collapsed in a catastrophic debris avalanche 1-1.5 Mya. In addition, we collected hydrosweep bathymetric data across the submarine debris field north of Oahu.
The seismic data provide first peaks into the subsurface character of the deformed volcano flanks, revealing shallow and deep structures and stratigraphy common to many of the areas. A prominent reflection is observed on all lines at approximately 5.5-8 km below sea level; this is interpreted as the top of the Cretaceous oceanic crust, upon which the mobile flanks may have slid. The ocean crust reflector can also be traced beneath the large blocks north of Oahu, confirming their landslide origins. Landward dipping reflections rising from the ocean crust beneath the flanks suggest the presence of back-rotated flank strata within rotational slump blocks (north of Oahu), or possibly the existence of deep compressional faults related to volcanic spreading and seaward sliding of the flanks (e.g., Kilauea and Puna). Thick accumulations of well-bedded sediments drape many of the volcano flanks, particularly along the Hilina slump and the north flank of Oahu. In places these sediments are folded, uplifted, truncated, and overlain by more recent flank parallel strata. The unconformable relationships point to discrete episodes of deposition and deformation along the mobile flanks. Along the south flank of Kilauea, flank parallel reflections beneath the slope sediments may define a shallower slump detachment, possibly related to the on-land Hilina fault system.