Abstract Subduction of seamounts at destructive sedimented plate margins results in spectacular deformation of the overriding plate. High-resolution sidescan sonar imagery from the Costa Rica margin show the tracks of five individual seamounts, of which four are described in this paper. These were subducted at various times during the last 690 ka and each represents a different stage in the subduction process. Each subducted seamount leaves a parallel-sided depression in its wake, that can be traced for up to 55 km landward of the deformation front. This wake is created by deformation and uplift of the continental slope as the seamount passes beneath it, followed by collapse due to landsliding as support for the uplifted area is withdrawn. Areas of uplift above seamounts are characterized by complex normal and strike-slip fault patterns. Collapse of the uplift along the trailing edge of the seamount creates a zone of slope failure (landsliding) that migrates upslope (or landward) with the seamount. Landslide processes are dominated by debris flow, but also include sliding of coherent blocks and debris avalanche. Erosion occurs by repeated landslides, which produce a series of overlapping debris flows. Downslope sediment transport typically extends over limited distances, resulting in partial ‘backfilling’ of the scar as its headwall moves up slope. The amount of margin material disrupted by seamount subduction is four to five times the volume of the subducting seamount, of which about three quarters seems to be recycled downslope, backfilling the scar, and nearly one quarter is subducted with the seamount.

ABSTRACT ODP Leg 105 drilled three sites (645, 646, 647) in Baffin Bay and the Labrador Sea. Paleontologic correlations with regional seismic reflectors established that glacial ice-rafting in the region started about 2.5 Ma (possibly as early as 3.4 Ma in Baffin Bay). Southward directed bottom water circulation in Baffin Bay started in early to mid-Miocene, while major drift sedimentation at Site 646 (Labrador Sea) started in the late Miocene. The opening of Baffin Bay occurred between 55 and 36 Ma. Oceanic crust at Site 647 (Labrador Sea) was dated as early Eocene in age (55-56 Ma, Chron 24).