apron—a gentle slope, with a generally smooth surface, particularly found around groups of islands 
and seamounts. 
bank—an elevation, typically located on a shelf, over which the depth of water is relatively shallow 
but sufficient for safe surface navigation. 
basin—a depression more or less equidimensional in plan and of variable extent. 
*bench—a small ferrace. 
borderland—a region adjacent to a continent, normally occupied by or bordering a shelf, that is 
highly irregular with depths well in excess of those typical of a shelf. 
canyon—a relatively narrow, deep depression with steep sides, the bottom of which generally has 
a continuous slope. 
continenial rise—a gentle slope rising from oceanic depths towards the foot of a continental slope. 
cordillera—an entire mountain system including all the subordinate ranges, interior plateaus, and basins. 
escarpment (or scarp)—an elongated and comparatively steep slope separating flat or gently 
sloping areas. 
fan—a relatively smooth feature normally sloping away from the lower termination of a canyon or 
canyon system. 
*flat—a small level or nearly level area. 
*fork—a branch of a canyon or valley. 
fracture zone—an extensive linear zone of irregular topography of the sea floor, characterized by 
steep-sided or asymmetrical ridges, troughs, or escarpments. 
*furrow—a closed, linear, narrow, shallow depression. 
gap—a narrow break in a ridge or rise. 
*gully—a small valley-like feature. 
hill—an elevation rising generally less than 500 meters. 
hole—a small depression of the sea floor. 
knoll—an elevatiou rising generally more than 500 meters and less than 1,000 meters and of 
limited extent across the summit. 
*ledge—a rocky projection or outcrop, commonly linear and near shore. 
levee—an embankment bordering a canyon, valley, or seachannel. 
median valley—the axial depression of the mid-oceanic ridge system. 
moat—an annular depression that may not be continuous, located at the base of many seamounts, 
islands, and other isolated elevations. 
*mound—a low, isolated, rounded hill. 
mountains—a well delineated subdivision of a large and complex positive feature. 
peak—a prominent elevation, part of a larger feature, either pointed or of very limited extent 
across the summit. 
pinnacle—a high tower or spire-shaped pillar of rock or coral, alone or cresting a summit. 
plain—a flat, gently sloping or nearly level region. 
plateau—a comparatively flat-topped feature of considerable extent, dropping off abruptly on one 
or more sides. 
province—a region identifiable by a group of similar physiographic features whose characteristics 
are markedly in contrast with surrounding areas. 
*ramp—a gentle slope connecting areas of different elevations. 
range—a series of associated ridges or seamounts. 
*ravine—a small canyon. 
reef—a hazard to navigation with a depth of 20 meters or less, composed of consolidated 
rock. 
ridge—a long, narrow elevation with steep sides. 
rise—a broad elevation that rises gently and generally smoothly from the sea floor. 
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