Seismic stratigraphy of the Hawaiian flexural moat

Approximately 4,400 km of single-channel seismic reflection data were collected over the northern Hawaiian flexural moat between Hawaii and Kauai. These data include eight cross-moat profiles and three 600-km-long moat-parallel lines. The thick (>2 km) sedimentary section filling the Hawaiian flexural moat is composed primarily of the products of large-scale mass wasting from massive slope failures on the adjacent Hawaiian islands. The observed stratigraphy can be described by four main lithostratigraphic units: (1) a basal unit of relatively constant thickness that we interpret as pelagic sediment predating the formation of the flexural moat; (2) a thick wedge of lens-shaped units onlapping the flexural arch, each with highly chaotic internal reflectivity that we interpret as buried landslide deposits; (3) a sequence of highly reflective, continuous horizons that offlap the flexural arch and are tilted down toward the islands; and (4) a ponded unit confined to the deepest part of the moat representing the youngest sediments transported to the moat. This distinctive stratigraphy--onlap of the flexural arch in the lower moat section (landslide unit), offlap migrating back toward the islands in the upper moat section (offlapping unit), and ponding of the youngest sediments in the deepest parts of the moat (ponded unit)--can be explained in terms of the competing effects of sediment influx to the moat from large-scale mass wasting and distributed subsidence due to the progressive loading of a purely elastic plate by each successive volcano. The role of large-scale mass wasting in the sedimentation history of the Hawaiian flexural moat is expected to characterize the moats of other large subaerial oceanic volcanoes.