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TERMS AND DEFINITIONS 



apron— Si 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 terrace, 

 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 con- 

 tinuous slope. 

 continental 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 for 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 elevation 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. 

 *mesa— an isolated, extensive, flat-topped elevation on the shelf, with relatively steep sides. 

 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. 

 platform— a flat or gently sloping underwater surface extending seaward from the shore. 

 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 surface navigation composed of consolidated material. 

 ridge— a long, narrow elevation with steep sides. 



Vlll 



