Shelf valleys – Valleys incised more than 10 m into the continental shelf and greater than 10 km in length overall are mapped as shelf valleys. Only features that had a definite elongate shape were included as valleys, nominally more than 4 times greater in length than width. Features that intersected the shelf break and extended both onto the shelf and down-slope (where they become submarine canyons) were also included. Shelf valleys of glacial origin incised >100 m into the shelf are mapped here as glacial troughs.
Shelf valleys are most common in polar areas where valleys have formed by glacial erosion (Hambrey, 1994; Anderson, 1999). Non-glacial shelf valleys were formed mainly during the Pleistocene ice ages by fluvial erosion when rivers flowed across what is now the submerged continental shelf, and also by the erosive effects of tidal and other ocean currents. Other non-glacial shelf valleys have formed in some tropical carbonate provinces, where valleys appear as inter-reef channels formed when sea level changes have left submerged banks (drowned reefs) stranded offshore, delimiting inter-bank channels that are a type of shelf valley (Harris et al., 2005).